# Comparison between modulated-pulsed and continuous wave laser powder bed fusion on an Inconel 625 alloy

Patrice Peyre, Pierre Hébrard, Frédéric Coste, Eglantine Vignal, J. Laurent, P. Aubry, Morgan Dal

► To cite this version:

Patrice Peyre, Pierre Hébrard, Frédéric Coste, Eglantine Vignal, J. Laurent, et al. Comparison between modulated-pulsed and continuous wave laser powder bed fusion on an Inconel 625 alloy. Progress in Additive Manufacturing, 2025, 10.1007/s40964-025-01050-3. hal-05138890

HAL Id: hal-05138890

https://cnrs.hal.science/hal-05138890v1

Submitted on 2 Jul 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Comparison between modulated-pulsed and continuous wave laser powder bed fusion on an Inconel 625 alloy

P. Peyre<fnref n="1" /> · P. Hébrard<fnref n="1" /> · F. Coste<fnref n="1" /> · E. Vignal<fnref n="2" /> · J. Laurent<fnref n="3" /> · P. Aubry<fnref n="2" /> · M. Dal<fnref n="1" />

Received: 10 December 2024 / Accepted: 1 March 2025

© The Author(s) 2025

## Abstract

Using pulsed or modulated laser irradiation for laser powder bed fusion (L-PBF) manufacturing can be an attractive solution for better controlling heat input, mastering geometry, and tuning microstructures of built samples. A comparison was made between a continuous wave (CW) and a modulated pulsed wave (PW) L-PBF process, considering high pulse frequencies (50 kHz), various duty cycles, and an Inconel 625 powder. In the first step, considering the precise shape of laser pulses, the peak powers were adjusted to provide similar mean powers between PW and CW and analyze the specific effect of the pulse regime at constant mean power. In the second step, single L-PBF beads were considered. The PW regime was shown to reduce the process window on (P, V) maps, increase powder-denudated widths around scan tracks, and slightly reduce the dimensions (depth, width and area) of fusion beads. In the third step, 3D samples were manufactured with PW (with duty cycles of 0.9 and 0.7) and CW regimes. The PW regime was shown to slightly increase the porosity rate, reduce the mean grain size by 30–40%, and modify the crystallographic texture.

**Keywords** Powder bed · Laser · Fusion · Pulsed · Modulated · Inconel 625

## 1 Introduction

The main physical processes involved during the laser powder bed fusion (L-PBF) additive manufacturing process are now rather well understood, thanks to the use of dedicated and instrumented L-PBF prototypes. Such set-ups, combined with numerical modeling have allowed a precise description of complex physical phenomena occurring at the melt-pool range, especially considering single tracks. This includes the origin of spatters and denudation phenomena, mainly attributed to melt-pool vaporization [1, 2], the description of balling and humping melt-pool instabilities or the experimental validation of theoretical models of welding for predicting fusion beads’ geometries [3, 4]. The origin of defects (lack of fusion, keyhole pores and solidification cracks) is also rather well documented on a large range of materials.

However, there is still a demand for new L-PBF procedures to stabilize the process, increase productivity, or tune microstructures. For instance, the combination of small spots (for the contours) and large spots (for the hatching areas) has been addressed recently [5, 6] with productivity increases and a reduction of spatters. Modifications of the laser spot geometry (from round to elliptic) have also shown significant benefits, with the formation of more equiaxed

<figure><img src="image_2.png" /></figure>

P. Peyre
patrice.peyre@ensam.eu

P. Hébrard
pierre.hebrard@ensam.eu

F. Coste
frederic coste@ensam.eu

E. Vignal
eglantine.vignal@cea.fr

J. Laurent
jerome.laurent2@cea.fr

P. Aubry
pascal.aubry@cea.fr

M. Dal
morgan.dal@ensam.eu

<footnote n="1">1 PIMM Laboratory, UMR 8006 CNRS, Arts et Métiers
Science & Technology, Paris, France</footnote>

<footnote n="2">2 Université Paris-Saclay, CEA, SRMA, 91191 Gif-sur-Yvette,
France</footnote>

<footnote n="3">3 Université Paris-Saclay, CEA, LIST, 91191 Gif-sur-Yvette,
France</footnote>
microstructures [7]. Similarly, new wavelengths (in the visible spectrum: green, blue), more adapted to highly reflective materials (Aluminum, Copper, Gold ...) have been marketed in the past two years, and publications are now available on this topic [8–10].

Using a PW laser irradiation instead of a CW for modifying and possibly improving the stability of the laser powder bed fusion (L-PBF) process is an interesting scientific and industrial challenge. It has been recently addressed only by a few authors:

- either to understand the underlying physics by checking the process efficiency and comparing the dimensions of single tracks with those obtained in CW mode

- or to investigate possible benefits of the PW regime on microstructures and parts geometries.

For instance, Caprio et al. [11, 12], have investigated the effect of duty cycles dc (= ratio between the time-on of the laser and the inverse of the modulation frequency) on single tracks carried out on 316L powder beds, and compared them with CW tracks, for similar power densities. They concluded that the melting efficiency was better in CW mode, but that a better spatial resolution could come for the PW regime, due to a narrowing of melt pools. However, the used frequencies—in the 5–10 kHz regime—were a bit too low to provide a wide range of pulsed irradiations, including quasi-continuous regimes (with a very high duty cycle), at classical scan speeds for L-PBF. Moreover, they did not carry out 3D parts to confirm the single-track results.

Nearly similar experimental conditions were used on single 316L tracks by Laitinen et al. [13] but with an even lower modulation frequency of 2 kHz. Just like Caprio et al. [12], the authors logically evidenced narrower tracks with the PW regime at constant peak power/scan speeds, due to a reduction of mean power.

Biffi et al. [14] have compared the influence of CW and PW regimes on the microstructures and mechanical properties of an Al10SiMg cast aluminum alloy. They concluded with a significantly stronger crystallographic texture (more columnar and oriented grains) with PW irradiation. However, due to the different power densities considered in the PW and CW regimes, and the different laser diameters, the specific influence of the PW regime was complex to establish. Moreover, they did not consider pulsed laser irradiation constantly applied during scanning, but a sequence of static laser irradiations during a constant time exposure (pulse duration = 110 µs), each irradiated zone being distant from its neighbor zone by a constant distance = laser diameter. They also evidenced lower Mg₂Si precipitation, correlated to a larger activation enthalpy due to faster cooling rates in PW regimes. The effect was a reduction of precipitation

hardening and lower compressive resistance in the PW regime. Other authors like Chou et al. [15] have also tested a pulsed L-PBF procedure to modify the microstructural properties of A356 aluminum alloy. However, no comparison was proposed with the new regime.

Karami et al. [13] have recently considered both CW and PW regimes (with a pulse duration of 550 µs) on Ti6Al4V lattice structures, with a more homogeneous microstructure and more isotropic behavior in PW. At the same time, the CW strategy allowed a higher fatigue resistance because of fewer defects. Guo et al. [16] have also shown that a 5-kHz PW irradiation could limit cracking issues in Inconel 738 L-PBF, by forming smaller grains than the CW regime, despite a larger number of pores.

Other AM laser processes have tested PW irradiations. Xiao et al. [17] used quasi-continuous wave laser irradiation (at a low frequency of 10 Hz) to limit segregation and deleterious Laves phase formation in an Inconel 718 superalloy during DED fabrication. The one-order of magnitude higher cooling rate during solidification was the main reason for the improved metallurgical behavior observed by the authors.

Chou et al. also observed a significant refinement of solidification cells on Al10SiMg [18] and A356 [15] aluminum alloys with a PW regime compared with those obtained with classical CW irradiation. According to the authors, such refinements traduce one order of magnitude higher local cooling rates in PW conditions. However, the precise PW conditions are not mentioned in the papers.

A potential benefit of the PW regime was also shown earlier by Gharbi et al. [19] on direct energy deposited (DED) Ti6Al4V samples. Using a quasi-continuous regime (with duty cycles comprised between 0.75 and 0.9) at a frequency of 200 Hz, significant improvements of surface finish were obtained (smaller lateral menisci), attributed to an interruption of Marangoni flow and the oscillation of melt-pools.

Caprio et al. [20] also mentioned that especially when using near keyhole fusion modes, a sharp increase of laser irradiance with time (squared or ramp-down pulses with a steep rise time) could promote significant instability by promoting large gradients of recoil pressure applied on the melt pool. Therefore, triangular or ramp-up pulses were recommended for stabilizing the process.

Last, Grünewald et al. [21] demonstrated that a pulsed laser exposure regime could limit supports in overhang areas of Ti6Al4V L-PBF parts and improve surface finish. Similarly, Demir et al. [22] indicated that a 3-kHz PW regime could reduce energy input, stabilize melt pools, and allow better control of narrow parts geometries.

Finally, considering all these works, possible effects of the PW mode could be (1) a modification of the (P, V) process windows resulting in more stable tracks on a larger P/V range, (2) an improvement of surface finish, (3) a modification (refinement, texture and precipitation state) of
solidification microstructures due to higher cooling rates. Such modifications could overcome some of the limitations of the CW regime in terms of part accuracy, process stability, and microstructural control which are not easy to obtain with a standard CW irradiation.

However, most of the existing works [14, 23] have used a so-called point laser-based (PLB) L-PBF with a succession of static laser irradiations (exposure times usually between 100 and 500 µs) separated by pre-programmed inter-spot distances (Fig. 1a). For such conditions, the induced melt-pools are relatively round and the material solidifies between subsequent laser pulses, which is fundamentally different from usual CW regime where a moving laser generating an elongated melt-pool forms a continuous track on the powder bed.

The present work aims to address the influence of a pulsed laser regime during powder bed fusion using a fully experimental approach and combining single-track analysis with 3D L-PBF building of representative parts. An Inconel 625 alloy was selected for this work because of its ease of L-PBF manufacturing in the CW regime [24, 25] and because it has a large range of applications, including heat-exchangers [26] and reactors built with materials, for which a deep control of heat input through a PW irradiation could be a significant benefit.

Different aspects are addressed in the current paper:

(1) a detailed and compared analysis of single tracks obtained in CW and PW regimes,

(2) a comparison of porosity rates for the two regimes,

(3) a metallurgical analysis of PW and CW microstructures.

The main differences with published works concern the applied PW regime, which uses a high maximum frequency of $f=50$ kHz (instead of a few kHz for most of the existing publications) and pulse durations $\tau_{las}$ of 10, 14, and 18 µs, with a maximum peak power of 1 kW. The 50 kHz frequency is in the same order of magnitude as ultra-sound assistance frequencies used for microstructure refinement in a recent work [27]. With such conditions, melt-pools are continuous but laser irradiates intermittently the surface with duty cycles between 50 and 90%. Compared with previous works, this fundamentally different approach aims more at interrupting a CW L-PBF process to stabilize it than really using an overlap of round and already solidified melt-pools (Fig. 1), with an increase in cooling rates.

## 2 Materials and experimental conditions

A gas-atomized Inconel 625 powder (Ni—22.2 Cr—9.2 Mo—3.7 Nb+Ta—0.3 Fe—0.3 Al+Ti) supplied by SLM Solutions Group AG was used in this study. A Cilas Particle Size 920 L analyzer determined the particle size distribution the following values were obtained: $D_{10}=11$ µm, $D_{50}=25$ µm, and $D_{90}=42$ µm (with $D_{50}$ = median diameter of the particle distribution).

CW and PW experiments were carried out in an L-PBF prototype chamber already described by Sow et al. [6], under Argon shielding (less than 800 ppm), using a 1-kW (Red Power) SPI laser, and a 420 f-theta lens, which allowed obtaining a $D_{laser}=55$ µm laser diameter at $1/e^2$ with a Gaussian power distribution. For all the tests, a uniform laser spot displacement was used, thanks to the scan head (Fig. 1b), contrary to interrupted point-based irradiation

<figure><img src="image_3.png" /><figcaption>**Fig. 1** Comparison between a point laser-based (PLB) regime [14, 23], b quasi-continuous PW regime, and c CW regime (the current work)</figcaption></figure>
where the scan head positions the laser spot to predefined locations with programmed inter-spot distances (Fig. 1a). The resulting configuration is a quasi-continuous PW regime.

Three stages were considered for the experimental work:

(1) First, a photodiode analysis of pulsed laser irradiation was carried out for a large range of peak powers (100–800 W) and pulse durations (in-between 10 and 20 µs) at a constant modulation frequency of 50 kHz (period T=20 µs). The objective was to estimate precisely the real duty cycles, suspected to be different from the theoretical one (Eq. 1), to compare CW and PW trials at similar mean powers.

$$dc_{theor} = \frac{\tau_{las}}{T} \qquad (1)$$

$T = 1/f$ = period of the modulation frequency (= 1/f), $\tau_{las}$ = programmed pulse duration (µs)

(2) Second, single tracks of 10 mm length were made on a ~ 80 µm-thick powder bed hand-deposited on 50 mm × 80 mm Inconel 625 substrates. The objective was to estimate the range of process conditions allowing a stable L-PBF manufacturing regime, with laser powers of 100 W, 200 W, 300 W, and 400 W for the CW regimes, and four scan speeds of 0.5 m/s, 0.75 m/s, 1 m/s, and 1.25 m/s. For the PW tests, similar scan speeds were used but the real mean powers were calculated with estimated duty cycles ($P_{mean} = dc \times P_{peak}$). The stability of tracks (balling, stable, humping, unstable keyhole) was also checked with the use of a top-view optical microscope analysis. Then, the dimensions of the tracks (width, depth, height) were measured on cross-sections.

(3) Third, using a selection of optimum (P, V) conditions, cubic samples of 10 mm × 10 mm × 10 mm were built with PW and CW conditions, and a 50 µm layer height, corresponding nearly to the 80–90 µm powder layer height used for single tracks. PW and CW tests were compared at constant mean powers to estimate the specific influence of a PW regime on the densification of

L-PBF parts for similar ($P_{mean}$, V) conditions. The corresponding microstructures were also analyzed using optical microscopy and electron back scattered diffraction (EBSD).

(4) Additional LPBF tests were performed in CW and PW regimes on a homemade open-architecture mini LPBF machine already detailed in [28], with a slightly larger spot diameter (65 µm vs 55 µm) and parallelepiped 3D samples (10 mm × 10 mm × 2 mm).

Last, a high-frequency (50 kHz) camera analysis (SA2 Photron, with Halogen light) of single bead-on-plate tracks carried out in PW or CW regime was also carried out to provide a complementary understanding to observed results.

# 3 Results

## 3.1 Analysis of PW irradiation

In the current work, the main interest of a high-frequency modulation is to provide a small inter-spot distance and large overlap for typical L-PBF scan speeds (~0.5–1 m/s). For instance, at 1 m/s and 50 kHz, the inter-spot distance is $T \times V = 20$ µm, and the spot overlap is 67%. This makes a quasi-constant fusion depth along x and y during scanning, whereas lower frequencies would promote an oscillating melt-pool depth, much more complex to consider to densify parts.

Making a comparison between CW and PW regimes at a similar mean energy input requires precise calibration of PW irradiation depending on programmed peak power and duty cycle. More explicitly, due to the rise and fall times of the laser pulses (approximately 6–7 µs), laser pulses at 50 kHz do not exhibit a perfect squared shape like programmed (Fig. 2), and duty cycles are smaller than theoretical values. Therefore, to provide a realistic comparison of PW and CW regimes at similar input energies, an estimation of real duty cycles $dc_{real}$ is mandatory. This was made considering a time integration of photodiode (=peak power) signals on a range of pulse durations (Eq. 2, Fig. 3), at a constant frequency of

<figure><img src="image_4.png" /><figcaption>Fig. 2 Programmed PW cycles with: a $dc_{theor} = 0.5$, b $dc_{theor} = 0.75$</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Fig. 3 Example of photodiode analysis of PW regime for f=50 kHz and a 300 W and b 600 W peak power for 10 µs, 14 µs, and 18 µs pulse durations. In orange: the ratio of peak integrals (yellow) over two periods of time T provides the real duty cycle for (τ<sub>las</sub>=10 µs, P<sub>peak</sub>=600 W), equal to 0.46</figcaption></figure>

50 kHz (T=20 µs) and for various (P<sub>peak</sub>, τ<sub>las</sub>) values. The laser pulses were analyzed for five peak powers of 100 W, 200 W, 300 W, 400 W, and 600 W, and for three pulse durations of 10 µs, 15 µs, and 18 µs. Each photodiode analysis was carried out twice to provide statistical reliability.

Figure 4 shows that the difference between theoretical dc (dc<sub>theor</sub>) and real dc (dc<sub>real</sub>) varies with both P<sub>peak</sub> and τ<sub>las</sub>. On the one hand, the difference between dc<sub>theor</sub> and dc<sub>real</sub> is important for low peak powers and short pulses (0.25 versus 0.5 for 100 W-10 µs, and 0.4 versus 0.5 for 200 W-10 µs) because laser pulses are far from squared pulses. On the other hand, dc<sub>real</sub>-dc<sub>theor</sub> for higher peak powers and longer pulses (0.88 versus 0.9 for 300 W-18 µs and 0.895 versus 0.9 for 600-18 µs).

Finally, the estimation of dc<sub>real</sub> allows calculating the real mean power P<sub>mean</sub> (Eq. 3) that will be used to compare the pulsed regime with CW one at a similar energy input. For instance, to compare a PW regime with a CW single track carried out at 300 W, we will select peak powers of respectively 340 W (18 µs), 460 W (14 µs), and 660 W (10 µs), all conditions corresponding to the same mean power of 300 W (Fig. 5). An important point to mention is that, for τ<sub>las</sub> = 18 µs, the peak power laser irradiation (=maximum photodiode voltage U<sub>max</sub>) is not fully interrupted, contrary to τ<sub>las</sub> = 10 and 14 µs pulses (Fig. 2), but only divided by a factor 2 in the inter-pulses. The resulting irradiation can be considered quasi-continuous, with slight temporal oscillations of the power density.

$$dc_{\text{real}} = \frac{\int_{t_0}^{t_0+nT} U dt}{nU_{\text{max}} T} \qquad (2)$$

with n = number of pulses considered to estimate dc, t<sub>0</sub> (s) = initial time considered, U<sub>max</sub> (V) = maximum photodiode signal, T = time period = 1/f

$$P_{\text{average}} = dc_{\text{real}} \cdot P_{\text{peak}} \qquad (3)$$

<figure><img src="image_6.png" /><figcaption>Fig. 4 Estimation of real duty cycles dc<sub>real</sub> versus peak power and laser pulse duration (f=50 kHz) using Eq. 2</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**Fig. 5** Calibration curves indicating the mean power versus peak power and laser pulse duration dependence. For instance, to obtain a mean power of 300 W with a 10 µs pulse, one needs to apply a 660 W peak power $P_{peak}$</figcaption></figure>

## 3.2 Analysis of single tracks

### 3.2.1 Experimental conditions

All the experimental conditions carried out for single L-PBF tracks are shown in Annex 1. Four scanning speeds were used (0.5, 0.75, 1, and 1.25 m/s), with one CW regime, and three PW regimes (10 µs, 14 µs, and 18 µs) corresponding to three theoretical duty cycles of 0.5, 0.7 and 0.9. The CW regime used laser powers of 100 W, 200 W, 300 W, and 400 W. In PW, peak powers $P_{peak}$ were adjusted considering theoretical duty cycles, to provide nearly similar mean

powers than in the CW regime. Therefore, peak powers approximately comprised between $1.1 \times P_{mean}$ (with 18 µs pulse) and $2.5 \times P_{mean}$ (with 10 µs pulse) were used. The objective was to address the real effect of the PW regime for constant mean powers.

### 3.2.2 Top view analysis of tracks' stability and denudation widths.

Without removing the powder bed, an estimation of powder denudation width around fusion tracks was made using top-view optical micrographs (Fig. 6). Rather large

<figure><img src="image_8.png" /><figcaption>**Fig. 6** Top view optical microscopy analysis of powder denudation widths around single LPBF tracks obtained in CW and PW (10 µs and 18 µs) regimes (similar mean power ~ 300 W, scan speeds = 0.75 m/s—left column, and 1 m/s right column)</figcaption></figure>

<figure><img src="image_9.png" /></figure>
<figure><img src="image_10.png" /><figcaption>**Fig. 7** Top view optical microscopy analysis of single LPBF track widths obtained in CW (left) and PW (right) regimes (mean power = 300 W, $t_{las}$ = 14 µs) after powder removal. At 1.25 m/s, the PW track is less stable than the PW</figcaption></figure>

denudation widths were obtained (comprised between 340 and 560 µm), to be compared with much smaller tracks' widths (90–120 µm: Fig. 7). No clear influence of the fusion regime (CW or PW) or the scan speed was shown, except in the case of quasi-continuous PW regime ($\tau_{las}$ = 18 µs, $dc$ ~ 0.85), for which a reduction of denudation phenomena was evidenced (lower widths + less efficient denudation rate with a lot of retained powder grains, Fig. 6). On the other hand, PW tests with a low dc ($\tau_{las}$ = 10 µs, $dc$ ~ 0.45) exhibit larger denudation areas than the CW regime and similar denudation efficiency. This last result is believed to come from two times larger peak powers tending to promote a more energetic laser-powder bed interaction and stronger recirculation flow that drags powder grains toward the melt pool [2].

Depending on (P, V) conditions, single L-PBF tracks can be destabilized either by surface tensions and by a balling effect at a low dilution rate (low P/V), or by an acceleration of liquid backward flow that tend to generate valleys and humps at high P and high V (Fig. 8).

($P_{mean}$, V) stability diagrams are reported in Fig. 9 for the four analyzed conditions. The main conclusion is that the PW regime tends to reduce the stability domain, even for high-duty cycles for which laser irradiation is quasi-continuous. For instance, the humping mode is only detectable for $\tau_{las}$ = 10 µs and $dc$ ~ 0.5.

This destabilizing effect could be explained by the transient nature of the pulsed keyhole regime in terms of hydrodynamic melt-pool flow. When the time-off (Fig. 2) of the laser pulse increases (at low dc), the keyhole front wall is not irradiated anymore which induces a vertical and periodic oscillation of the melt pool. This effect is also promoted using higher peak power, especially for low dc, but is not detected on bead-on-plate tracks without powder. Caprio et al. [20] reported the same effect on 316 L stainless steel for lower frequencies of 2–8 kHz and attributed it to sharp variations of recoil pressures on the melt pool in the PW regime. This will be discussed further in Sect. 4.

<figure><img src="image_11.png" /><figcaption>**Fig. 8** Various tracks' morphologies: a stable, b discontinuous, c Balling, d humping</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Fig. 9** (P<sub>mean</sub>, V) stability diagrams for a CW regime, b PW regime with τ<sub>las</sub>=18 µs, c PW regime with τ<sub>las</sub>=14 µs, d PW regime with τ<sub>las</sub>=10 µs. Using a PW regime with low duty cycles reduces the stability domain</figcaption></figure>

3.2.3 Cross-sectional analysis of single L-PBF tracks in PW
and CW regimes.

A comparative analysis was made between single L-PBF
tracks built with CW and PW regimes (Fig. 9) on metallo-
graphic cross-sections. For each condition, to simplify the
comparison, mean powers in PW regime were calculated
considering real duty cycles whatever the pulse duration,
as shown in Sect. 2.1 (Figs. 4,5).

The single tracks were analyzed as follows: (1) top view
optical analysis of tracks without removing powder, (2)
top view analysis after powder removal, (3) cross-section
analysis after cutting, resin mounting, polishing, and
chemical etching.

The dimensional analysis of single tracks (Figs. 10, 11)
indicates that:

- A little smaller (– 3% to – 5%) tracks’ dimensions (built areas and penetration depths) were obtained in PW modes when compared with CW mode at nearly

similar mean power and mean volume energy densi-
ties (VED), which combines laser power, scan speed,
and spot diameter in a volumetric energy formulation
(Eq. 4).

- Despite the tiny differences in tracks' dimensions between PW and CW at similar VED, results confirm that mean *P* and VED are prone to describe laser-material coupling and resulting track dimensions and fused areas (Fig. 10) either in CW or in the PW regime.

- In agreement with recent welding models [3, 4], a linear dependency is found between penetration depths and volume energy densities defined by Eq. (4), for similar beam diameters (Fig. 11b).

- Considering a D<sub>laser</sub>=55 µm diameter, penetration depths up to 400 µm i.e. nearly 8 times higher than the spot diameter and the layer height can be achieved at high VED (Fig. 11b).

- The PW tests carried out with 18 µs laser pulses (83–88% real duty cycles: see annex 1) indicate lower height/width ratios (lower heights, higher widths) than in CW regime:

<figure><img src="image_13.png" /></figure>
<figure><img src="image_14.png" /><figcaption>**Fig. 10** Cross sections of single tracks obtained with L-PBF in: **a** CW (P=300 W), **b** PW—τ<sub>las</sub> = 18 µs, **c** PW—τ<sub>las</sub> = 14 µs, **d** PW—τ<sub>las</sub> = 10 µs regimes. Due to a lower mean power than initially predicted, PW dimensions are slightly lower than CW ones</figcaption></figure>

around 0.9–1 in the PW regime versus 1.2–1.4 in CW regime in the 100–140 J/mm³ VED range.

$$ VED = \frac{4P_{\text{mean}}}{\pi D_{\text{laser}}^2 V} \qquad (4) $$

with VED = Volume energy density (J/m³), P<sub>mean</sub> = mean laser power (W), V = scan speed (m/s), D<sub>laser</sub> = laser spot diameter.

For similar (P<sub>mean</sub>, V) conditions, results not only indicate a small reduction of built volumes and penetration depths with the PW regime but also a larger scatter on built heights, which traduces more fluctuations of the built tracks. This result can be partly explained by the small differences in real mean powers, which are systematically 3–5 J/mm³ superior in CW mode (see annex 1). However, such small differences between CW and PW conditions are not sufficient to explain smaller dimensions in PW

mode. This is confirmed by the (P<sub>mean</sub>, V) stability diagrams where the stable domain is wider for the CW regime (Fig. 9), due to larger molten volumes and higher dilutions at high scan speeds.

## 3.3 Analysis of 3D samples built with CW and PW L-PBF

3D cubic samples (10 mm × 10 mm × 10 mm) were built using (1) either a CW regime or (2) a PW regime with a ~0.86 to 0.88 duty cycle (for a pulse duration = 18 µs, see Tavle A4). Corresponding conditions are presented here below (Table 1) and have been mostly selected to provide similar mean powers and mean VED to consider the specific effect of a pulsed regime. For instance, (CW1, CW2, CW3, and CW4) conditions are similar to (PW1, PW2, PW3 and PW4) conditions carried out with a 10% increase of peak power. Only one pulse duration (18 µs) was used for these tests because it provokes a clear reduction of melt-pool
<figure><img src="image_15.png" /><figcaption>**Fig. 11** Melt pool area (a), total height (b), and width (c) versus mean volume energy density for single tracks obtained with L-PBF in CW and PW regimes with corresponding linear regression (a, b) and logarithmic regression (b)</figcaption></figure>

aspect ratios ($h/w$) with the PW regime and attenuation of denudation phenomena. In this condition, the laser

interaction regime is quasi-continuous, with a 10% irradiation time off.

In the first step, a preliminary analysis of build surfaces indicated a small increase in $S_a$ average roughness with the use of a pulsed regime (PW2 versus CW2 in Fig. 12), which can be compared with the small destabilization observed on single PW tracks (Fig. 9).

In the second step, the analysis of porosity provides the following information:

- first CW and PW samples exhibit lower porosity rates for high scan speeds (1000–1200 mm/s) at nearly similar VED (105–120 J/mm³),

- second, experimental data (Table 1, Figs. 13 and 14) indicate a tiny but systematic increase in porosity in PW samples. Last, a lower porosity rate (near 0.1%) is obtained for samples manufactured with $P_{mean} \sim 300$ W (CW2, CW3, PW2, PW3) than for those (CW1, CW4, PW1, PW4) built with $P_{mean} \sim 192–200$ W. The analysis of porosities obtained with the lower power (200 W) mainly reveals lack-of-fusion (Fig. 13c, d), possibly due to an insufficient laser power (192–200 W) at 0.7 m/s.

Additional tests (CW5, CW6, PW5 and PW6) were carried out with a slightly modified pulse diameter (65 µm instead of 55 µm) on a homemade open-architecture mini-LPBF system [6]. In this second configuration, samples of 10 mm × 10 mm × 2 mm in height were built to analyze porosity and microstructures.

Two samples (PW7 and PW8) were also built with a $dc=0.7$ value and a 290 W mean power to provide a preliminary insight into the influence of a larger laser time-off of 6 µs. Larger porosity rates (around 0.4%) were measured than those obtained in CW or PW-$dc=0.9$ conditions (Table 1) at similar $P_{mean}$ and scan speeds (CW2, CW5, PW2 and PW5).

EBSD analyses were also carried out on denser samples (CW2, CW3, CW5, PW2, PW3, PW6) to estimate a possible influence of the PW regime on as-built microstructures.

The use of a modulated regime modifies the grain shapes and morphological texture analyzed by EBSD, with the formation of several random small (<20 µm) and equiaxed grains within the columnar structure (Fig. 15) or higher aspect ratios evidenced in PW regime (Fig. 16). Pole figures (PF) also indicate slightly rotated <001> cube textures, and a small modification of <001> crystal orientation with PW regime, with a moderate texture intensity decrease (Fig. 15) or increase (Fig. 16), depending on the hatch distances. In Fig. 16 with a short hatch distance of 50 µm, the PW regime seems to reduce lateral epitaxy grain growth and promote a more vertical epitaxy. Therefore, PW-induced modifications

<figure><img src="image_16.png" /></figure>
<table><caption>**Table 1** L-PBF conditions for 3D cubic samples in the CW and PW regimes (pulse width = 18 µs)</caption><thead><tr><th>Reference</th><th><i>P</i><sub>peak</sub> (W)</th><th><i>P</i><sub>mean</sub> (W)</th><th><i>V</i> (mm/s)</th><th>Hatch (µm)</th><th>Mean VED (J/mm<sup>3</sup>)</th><th>Sample dimension (mm × mm × mm)</th><th>Porosity (%)</th></tr></thead><tbody><tr><td>CW1</td><td>200</td><td>200</td><td>700</td><td>70</td><td>120</td><td>10 × 10 × 10</td><td>0.8</td></tr><tr><td>CW2</td><td>300</td><td>300</td><td>1000</td><td>70</td><td>126</td><td>10 × 10 × 10</td><td>0.13</td></tr><tr><td>CW3</td><td>300</td><td>300</td><td>1200</td><td>70</td><td>105</td><td>10 × 10 × 10</td><td>0.07</td></tr><tr><td>CW4</td><td>200</td><td>200</td><td>700</td><td>50</td><td>120</td><td>10 × 10 × 10</td><td>0.7</td></tr><tr><td>CW5*</td><td>300</td><td>300</td><td>800</td><td>80</td><td>113</td><td>10 × 10 × 2</td><td>0.15</td></tr><tr><td>CW6*</td><td>250</td><td>250</td><td>800</td><td>80</td><td>94</td><td>10 × 10 × 2</td><td>0.2</td></tr><tr><td>PW1</td><td>222</td><td>192</td><td>700</td><td>70</td><td>115</td><td>10 × 10 × 10</td><td>1.25</td></tr><tr><td>PW2</td><td>333</td><td>290</td><td>1000</td><td>70</td><td>122</td><td>10 × 10 × 10</td><td>0.2</td></tr><tr><td>PW3</td><td>333</td><td>290</td><td>1200</td><td>70</td><td>102</td><td>10 × 10 × 10</td><td>0.17</td></tr><tr><td>PW4</td><td>222</td><td>192</td><td>700</td><td>50</td><td>115</td><td>10 × 10 × 10</td><td>1.05</td></tr><tr><td>PW5*</td><td>340</td><td>300</td><td>800</td><td>80</td><td>113</td><td>10 × 10 × 2</td><td>0.22</td></tr><tr><td>PW6*</td><td>290</td><td>250</td><td>800</td><td>80</td><td>94</td><td>10 × 10 × 2</td><td>0.25</td></tr><tr><td>PW7**</td><td>410</td><td>290</td><td>800</td><td>80</td><td>109</td><td>10 × 10 × 2</td><td>0.35</td></tr><tr><td>PW8**</td><td>410</td><td>290</td><td>1000</td><td>80</td><td>87</td><td>10 × 10 × 2</td><td>0.45</td></tr></tbody></table>

The VED is calculated using the mean laser power $P_{mean} = P_{peak} \times dc$ (* with $D_{laser}=65 \ \mu\text{m}$ and $dc=0.9$ ($t_{las}=18 \ \mu\text{s}$), ** with $D_{laser}=65 \ \mu\text{m}$ and $dc=0.7$ ($t_{las}=14 \ \mu\text{s}$))

<figure><img src="image_17.png" /><figcaption>**Fig. 12** A comparative analysis of build surfaces for a similar average VED = 126 J/mm³ (3D optical profilometer)</figcaption></figure>

are stronger for the higher mean VED (CW3/PW3 at ≈ 120 J.mm⁻³) inducing larger melt-pools.

For this condition, the microstructural modification is particularly obvious when considering the last built layers on top of the samples (Fig. 17), which clearly evidences the PW modulated regime's destructuring effect. Additionally, built surfaces are less regular in PW than in the CW regime, as shown in Fig. 17. Most of all, the analysis of equivalent diameter grain distribution evidences a 40–50% reduction of grain size with the use of a pulsed regime (Fig. 18), for very close melt-pool shapes and dimensions. This refinement occurs mainly thanks to the formation of equiaxed grains smaller than 20 µm (Fig. 18) in PW regime.

On the CW4/PW4 samples, the increase of porosity rate (0.7–1.05%) in PW regime also can play a role in forming locally finer microstructures near the pores, due to higher local cooling rates.

An SEM analysis of solidification cells was carried out on cross-sections after chemical etching (92% HCl, 5% HNO₃, 3% H₂SO₄) to estimate a possible modification of local cooling rates. This analysis only considered cells oriented parallel to the build direction, i.e. included in (001)//BD grains. This experimental procedure allowed estimating the minimum equivalent cell diameter, whatever the process condition. A mean value of 0.6±0.2 µm was obtained on sample CW1 (200–700 mm.s⁻¹) versus a slightly lower value of 0.55 µm±0.2 µm for sample PW1 (Fig. 19). However, the
<figure><img src="image_18.png" /><figcaption>**Fig. 13** Binarized cross-sections of samples obtained with a sample CW2, b sample PW2 ($\tau_{las}$=18 µs), c sample CW1, d sample PW1 (hatch distance = 70 µm)</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>**Fig. 14** Comparison of porosity rates induced by PW—dc0.9 (PW1, PW2, PW3, PW4, PW5 and PW6) and CW (CW1, CW2, CW3, CW4, CW5 and CW6) regimes</figcaption></figure>

observed difference was not pronounced enough to traduce a modification of cooling rates with the PW regime.

In the last step, Vickers hardness tests were also performed on as-built PW and CW samples but did not evidence a significant modification with the change of laser irradiation, despite a grain and cell refinement. The hardness values are near $210 \pm 10$ HV$_{0.2}$ whatever the L-PBF conditions.

## 4 Discussion

A pulsed wave (PW) regime at 50 kHz frequency was evaluated as a possible way to improve the quality and efficiency of the L-PBF process.

First, considering single L-PBF tracks, the comparisons were made with the CW regime using nearly similar mean laser powers, i.e. by increasing peak powers proportionally

<figure><img src="image_20.png" /></figure>
<figure><img src="image_21.png" /><figcaption>**Fig. 15** EBSD analysis of CW a and PW b samples for similar mean VED (CW3 and PW3 samples, 105 J/mm³ and 102 J/mm³, respectively, hatch distance = 70 µm)—inverse pole figures (IPF) maps and corresponding pole figures (with A3 parallel to BD)</figcaption></figure>

to the expected duty cycles (0.5, 0.7 and 0.9), with the use
of dedicated calibration curves (Figs. 4, 5). The analysis
of tracks' dimensions was validated using a mean power
to adequately describe the evolution of penetration depths,
fusion widths, and total molten areas for a 50 kHz modu-
lated regime. This result is not obvious because it mostly
depends on the oscillation period of the melt pool formed
in a pulsed regime. Indeed, for a ten times lower frequency
(5 kHz instead of 50 kHz), the penetration depth oscillates
between a maximum and a minimum level, coinciding
with the peak power. The distance between two succes-
sive maximum penetrations is calculated with T<sub>5kHz</sub> x V,
with T<sub>5kHz</sub> = 200 µs. For instance, with a 1 m/s scan speed,
this gives a 200 µm distance between peak penetrations.
At 50 kHz, T<sub>50kHz</sub> = 20 µs, and this distance is reduced by
a factor of ten, i.e. 20 µm for V = 1 m/s.

To understand further this effect we can consider the clas-
sical drilling velocity from the “Piston model” [29] describ-
ing the keyhole formation (5). With this model (Fig. 20),
considering a 1 m/s scan speed, Vd values between 1 and
1.2 m.s⁻¹ are obtained for 20° (deep keyhole) < a < 45°
(=keyhole threshold). For a = 45°, the penetration depth is
equal to the beam diameter (~60 µm in the current work),
and Vd = 1 m/s. In that case, the drilling time td can be calcu-
lated (Eq. 6) considering the vertical drilling velocity Vd vert = V
cos a = 0.7 m/s. Therefore, it takes 55.10⁻⁶/0.7 = 78 µs for the
keyhole to reach its maximum penetration. For the deeper
penetrations (100–300 µm) obtained in the current work,
the order of magnitude of this drilling time easily reaches
or exceeds 150–200 µs. Such drilling times are much larger
than the “time-on” at 50 kHz (10–18 µs). This means that at
50 kHz (T = 20 µs), and considering a single pulse, whatever
the scan speeds and laser intensity, the keyhole should never
<figure><img src="image_22.png" /><figcaption>Fig. 16 EBSD analysis of CW (a) and PW (b) samples for similar mean VED (CW4 and PW4 samples, 120 J/mm³ and 115 J/mm³ respectively, hatch distance = 50 µm)—inverse pole figures (IPF-z) maps and corresponding pole figures (with A3 axis parallel to BD)</figcaption></figure>

be maintained for a sufficiently long time to reach its maximum penetration at the peak power. This also at least partially explains why the mean power can be considered the most pertinent parameter instead of the peak power to describe the average penetration depth (Fig. 21).

$$V_d = \frac{V}{\tan \alpha} \qquad (5)$$

with $V_d$=drilling velocity (m.s⁻¹), $α$=angle of inclination of the keyhole front wall relative to the vertical, $V$=scan speed (m.s⁻¹)

$$t_d = \frac{d}{V_d^{\text{vert}}} = \frac{d}{V_d \cos(90 - \alpha)} = \frac{d}{V_d \sin\alpha} = \frac{d}{V \cos\alpha} \qquad (6)$$

A ~ 10% reduction of molten areas and heights was obtained between CW tracks and PW tracks (Fig. 11). This was explained partially by a small difference in mean laser power and VED (3–4% smaller for PW trials) but this could not explain the occurrence of more pronounced process instabilities for single tracks carried out at high scan speed in the PW regime (Fig. 9). The pulsed nature of laser irradiation, with or without full extinction of the laser in between two subsequent pulses, is supposed to be detrimental to a stable L-PBF fusion at elevated scan speed. Finally, no clear physical explanation could be found yet, especially because such modifications of the stable building windows (Fig. 9) are also detectable with high duty cycles dc (around 85–88% with $τ_{las}$ = 18 µs) for which laser irradiation can be considered as quasi-continuous or as a combination of a CW and
<figure><img src="image_23.png" /><figcaption>**Fig. 17** EBSD analysis (IPF-z) of the last L-PBF layers of CW (a) and PW (b) samples for similar mean VED (CW4 and PW4 samples, 105 J/mm³ and 102 J/mm³, respectively) with A3 axis parallel to BD</figcaption></figure>

<figure><img src="image_24.png" /><figcaption>**Fig. 18** EBSD analysis. Comparison of grain distributions obtained in CW or PW regimes: a CW3 vs PW3 samples, b CW4 vs PW4 samples</figcaption></figure>
<figure><img src="image_25.png" /><figcaption>(b)</figcaption></figure>

<figure><img src="image_26.png" /><figcaption>**Fig. 19** SEM analysis of solidification cells at similar average VED: a CW4 sample and b PW4 sample</figcaption></figure>

<figure><img src="image_27.png" /><figcaption>**Fig. 20** Schematic of the keyhole wall at the keyhole threshold ($a=45°$) at stationary equilibrium (Fabbro et al. [29])</figcaption></figure>

a PW regime. In that case (Fig. 3), the resulting laser irradiation is not fully interrupted but oscillates with a factor 2 decrease during the inter-pulse.

To understand further this phenomenon, microstructures obtained on 3D parts were investigated, with the latter PW conditions ($\tau_{las} = 18$ µs, $dc \sim 85–88\%$), and compared with nearly equivalent CW conditions in terms of mean power and VED (3–4% difference between mean powers and VED: Table 1).

Once again, comparing CW samples with PW samples shows a small deterioration of porosity rate in the PW regime, for scan speed comprised between 0.7 and 1.2 m/s. This can be correlated with the slightly smaller and more unstable PW single tracks discussed earlier: more unstable tracks induce variable overlaps and can promote local lack-of-fusion porosities. Most of the porosity observed on the PW microstructures is lack-of-fusion (Fig. 13). This could be explained by: (1) the slight reduction in built areas (Fig. 11a) combined with less continuous tracks (Fig. 9) which reduces overlaps between adjacent tracks, (2) rougher as-built surfaces (Fig. 12) promoting larger fluctuations of powder bed heights and reduced dilution between subsequent layers. The transient nature of PW melt pools and more turbulent hydrodynamic flow could promote these two aspects. Oncoming thermo-hydrodynamic simulations, incorporating key-hole dynamics in PW and CW regimes should provide a deeper understanding.

The EBSD analysis of microstructures indicates (1) a decrease in mean grain diameter, due to the formation of small ($<20$ µm) equiaxed grains rather randomly distributed, (2) a tiny modification of crystallographic textures, (3) a tendency to slightly rougher built surfaces (Fig. 13). Such a microstructural change can be explained by the following factors:

(1) Due to the small modifications of melt-pool dimensions and corresponding overlaps, PW samples exhibit more porosities. Locally, in the area surrounding pores, there is a loss of epitaxy which promotes the formation of more equiaxed grains. This could explain the observed results. However, the morphological changes observed between PW and CW microstructures in Figs. 15 and 16 seem too important to be due to a larger porosity rate. Moreover, the increase in porosity rate with the PW regime (Figs. 13, 14) is rather moderate.

(2) Another explanation could come from the oscillation of the melt-pool contours at 50 kHz with an amplitude of $20–30$ µm ~ $T \times V_d$. This could act as a self-induced ultrasound (US) wave assistance, generate an induced fluid flow following the melt-pool contour, and promote grain fragmentation during solidification as shown by Todaro et al. [27] with an external US source. This effect is schematized in Fig. 22 and will require further investigation. It could also modify the build surface roughness, as shown in Figs. 11 and 17b.
<figure><img src="image_28.png" /><figcaption>**Fig. 22** Schematic of the oscillation of the melt-pool contour in a pulsed regime</figcaption></figure>

<figure><img src="image_29.png" /><figcaption>**Fig. 23** High-speed imaging of melt-pools in a CW regime, b PW regime (dc0.9, 50 kHz)</figcaption></figure>

<figure><img src="image_30.png" /></figure>

To address this last aspect, a finite element thermal modeling of laser melting in CW and PW regime was carried out using COMSOL Multiphysics, using a Goldak volumetric equivalent source with a similar simplified approach to one of our recent works [28], combined with a high-frequency (50 kHz) analysis of induced melt-pools. Due to a limited contrast between the melt-pool and the surrounding solid (Fig. 23), automatic analysis of melt-pool areas versus time was not possible, but the experiments globally validated

numerical simulations of melt-pool average areas. Thus, it was possible to track numerically the heat-dissipation-assisted variation of melt-pool areas with time for both PW and CW (Fig. 24) and estimate the width fluctuations. Such calculated fluctuations of melt-pool areas displayed a maximum surface oscillation of $6.10^{-4}$ mm$^2$ (0.2% of the total area) for $dc=0.5$. This roughly corresponds to 0.1% maximum periodic oscillation of the MP length and width during melting, i.e., less than 1 µm.
<figure><img src="image_31.png" /><figcaption>**Fig. 24** FE calculation of melt-pool fluctuations in PW regime (5 kHz), a top view of a calculated melt-pool (50 kHz, dc0.5, $P_{peak}=570$ W, $1 \text{ m.s}^{-1}$), b calculated melt surface vs scanning time for CW and PW regimes ($dc=0.5$ and $dc=0.7$), zoomed view of the dc0.5</figcaption></figure>

Finally, the current work has presented preliminary and original work on the possible use of high-frequency modulation L-PBF on process stability and microstructures. A unique frequency (50 kHz = maximum available with the fiber laser), and a squared pulse shaping (Fig. 2) were used and have induced detectable modifications. However, the a priori selection of PW conditions does not allow a generalization of our conclusions.

In the next step, a deeper focus could be put on the use of lower duty cycles (<50%) combined with lower pulse frequencies of less than 10 kHz (=longer pulse periods) to provide a more pronounced pulsed wave configuration increase solidification rate and generate finer microstructures. To combine such effects with better process stabilization in the PW regime, trapezoidal or ramp-up programmed pulses [20] could also be used to limit sharp recoil pressure transients. Last, using the 50 kHz PW regime a material with a higher diffusivity (like an aluminum alloy), promoting less elongated melt pools will also be an interesting point to address. Preliminary tests on Al10SiMg alloy have confirmed a microstructural change and a reduction of melt-pool width/depth ratio in PW regimes at 5 kHz and 50 kHz [30].

More widely, considering possible applications or such work, an interrupted L-PBF regime such as a 50 kHz

irradiation with high dc could allow better control of heat input and geometries of built parts. For instance, using PW for the contours and reserving CW for the hatching areas could be an attractive strategy to address in further work.

## 5 Conclusion

This work tested the ability of a 50 kHz pulsed laser irradiation to provide stable L-PBF manufacturing, and modified microstructures on Inconel 625 compared to a CW regime. The following conclusions were drawn:

- First, the comparison of single L-PBF tracks obtained in PW or CW regimes at nearly similar mean powers validated the use of $P_{mean}$ to adequately define variations in tracks' dimensions.

- Second, a smaller ($P_{mean}$, V) stability window was obtained for PW samples, whatever the duty cycle and the dimensions of fusion tracks were slightly reduced in PW, even for high dc values (near 0.9).

- Third, a moderate increase in porosity rate was shown on 3D PW samples compared with the classical CW regime.

These three results can be correlated to the transient recoil pressures obtained with a keyhole PW regime, promoting higher melt-pool instability.

- Fourth, the PW regime induces grain fragmentation and refinement, combined to a textural change. At a lower scale, it also slightly refines solidification cells.

Possible explanations could come from tiny melt-pool oscillations inducing self-induced ultrasonic waves and affecting the solidification structure.

On the one hand, for the selected process conditions, and considering the obtained results, this work does not fully qualify a quasi-continuous PW regime as a possible way of stabilizing L-PBF and/or widening the processing window. On the other hand, high-frequency PW modulation affects microstructural development, which opens up interesting physical questions related to melt pool/solid interactions.

Future development of the current work will require multiphysics numerical simulations and complementary experimental investigations for instance on a larger frequency range, and with modified pulse shaping to stabilize the PW process.

## Annex 1: Single L-PBF tracks on an 80 µm thick powder layer. Experimental L-PBF conditions and single track dimensions measured on cross-sections.

See Tables 2, 3, 4, 5.
<table><caption>**Table 2** single tracks carried out in CW mode (3 cross-sections were analyzed on each track)</caption><thead><tr><th>τ<sub>las</sub> (μs)</th><th>dc<sub>real</sub></th><th>P<sub>peak</sub> (W)</th><th>V (mm/s)</th><th>VED (J/mm<sup>3</sup>)</th><th>Width w (μm)</th><th>Height h (μm)</th><th>Depth d (μm)</th><th>Area A (mm<sup>2</sup>)</th></tr></thead><tbody><tr><td>20</td><td>1</td><td>100</td><td>500</td><td>84.18</td><td>86</td><td>86</td><td>26</td><td>5.81E-03</td></tr><tr><td>20</td><td>1</td><td>100</td><td>500</td><td>84.18</td><td>73</td><td>64</td><td>30</td><td>3.67E-03</td></tr><tr><td>20</td><td>1</td><td>100</td><td>500</td><td>84.18</td><td>72</td><td>46</td><td>24</td><td>2.60E-03</td></tr><tr><td>20</td><td>1</td><td>100</td><td>750</td><td>56.12</td><td>72</td><td>46</td><td>14</td><td>2.60E-03</td></tr><tr><td>20</td><td>1</td><td>100</td><td>750</td><td>56.12</td><td>65</td><td>46</td><td>14</td><td>2.35E-03</td></tr><tr><td>20</td><td>1</td><td>100</td><td>750</td><td>56.12</td><td>62</td><td>65</td><td>11</td><td>3.17E-03</td></tr><tr><td>20</td><td>1</td><td>100</td><td>1000</td><td>42.09</td><td></td><td></td><td></td><td></td></tr><tr><td>20</td><td>1</td><td>100</td><td>1000</td><td>42.09</td><td>62</td><td>45</td><td>18</td><td>2.19E-03</td></tr><tr><td>20</td><td>1</td><td>100</td><td>1000</td><td>42.09</td><td>70</td><td>80</td><td>14</td><td>4.40E-03</td></tr><tr><td>20</td><td>1</td><td>100</td><td>1250</td><td>33.67</td><td></td><td></td><td></td><td></td></tr><tr><td>20</td><td>1</td><td>100</td><td>1250</td><td>33.67</td><td></td><td></td><td></td><td></td></tr><tr><td>20</td><td>1</td><td>100</td><td>1250</td><td>33.67</td><td>49</td><td>64</td><td>15</td><td>2.46E-03</td></tr><tr><td>20</td><td>1</td><td>200</td><td>500</td><td>168.36</td><td>125</td><td>190</td><td>128</td><td>1.87E-02</td></tr><tr><td>20</td><td>1</td><td>200</td><td>500</td><td>168.36</td><td>127</td><td>195</td><td>146</td><td>1.95E-02</td></tr><tr><td>20</td><td>1</td><td>200</td><td>500</td><td>168.36</td><td>127</td><td>203</td><td>152</td><td>2.02E-02</td></tr><tr><td>20</td><td>1</td><td>200</td><td>750</td><td>112.24</td><td>113</td><td>123</td><td>78</td><td>1.09E-02</td></tr><tr><td>20</td><td>1</td><td>200</td><td>750</td><td>112.24</td><td>108</td><td>136</td><td>81</td><td>1.15E-02</td></tr><tr><td>20</td><td>1</td><td>200</td><td>750</td><td>112.24</td><td>107</td><td>132</td><td>75</td><td>1.11E-02</td></tr><tr><td>20</td><td>1</td><td>200</td><td>1000</td><td>84.18</td><td>96</td><td>111</td><td>60</td><td>8.37E-03</td></tr><tr><td>20</td><td>1</td><td>200</td><td>1000</td><td>84.18</td><td>104</td><td>104</td><td>60</td><td>8.49E-03</td></tr><tr><td>20</td><td>1</td><td>200</td><td>1000</td><td>84.18</td><td>120</td><td>91</td><td>48</td><td>8.58E-03</td></tr><tr><td>20</td><td>1</td><td>200</td><td>1250</td><td>67.34</td><td>98</td><td>91</td><td>45</td><td>7.00E-03</td></tr><tr><td>20</td><td>1</td><td>200</td><td>1250</td><td>67.34</td><td>90</td><td>73</td><td>40</td><td>5.16E-03</td></tr><tr><td>20</td><td>1</td><td>200</td><td>1250</td><td>67.34</td><td>83</td><td>87</td><td>33</td><td>5.67E-03</td></tr><tr><td>20</td><td>1</td><td>300</td><td>500</td><td>252.54</td><td>134</td><td>330</td><td>260</td><td>3.47E-02</td></tr><tr><td>20</td><td>1</td><td>300</td><td>500</td><td>252.54</td><td>126</td><td>315</td><td>256</td><td>3.12E-02</td></tr><tr><td>20</td><td>1</td><td>300</td><td>500</td><td>252.54</td><td>121</td><td>291</td><td>234</td><td>2.77E-02</td></tr><tr><td>20</td><td>1</td><td>300</td><td>750</td><td>168.36</td><td>121</td><td>189</td><td>146</td><td>1.80E-02</td></tr><tr><td>20</td><td>1</td><td>300</td><td>750</td><td>168.36</td><td>117</td><td>211</td><td>159</td><td>1.94E-02</td></tr><tr><td>20</td><td>1</td><td>300</td><td>750</td><td>168.36</td><td>114</td><td>218</td><td>154</td><td>1.95E-02</td></tr><tr><td>20</td><td>1</td><td>300</td><td>1000</td><td>126.27</td><td>113</td><td>162</td><td>116</td><td>1.44E-02</td></tr><tr><td>20</td><td>1</td><td>300</td><td>1000</td><td>126.27</td><td>121</td><td>158</td><td>106</td><td>1.50E-02</td></tr><tr><td>20</td><td>1</td><td>300</td><td>1000</td><td>126.27</td><td>111</td><td>165</td><td>115</td><td>1.44E-02</td></tr><tr><td>20</td><td>1</td><td>300</td><td>1250</td><td>101.02</td><td>96</td><td>131</td><td>86</td><td>9.88E-03</td></tr><tr><td>20</td><td>1</td><td>300</td><td>1250</td><td>101.02</td><td>105</td><td>134</td><td>93</td><td>1.11E-02</td></tr><tr><td>20</td><td>1</td><td>300</td><td>1250</td><td>101.02</td><td>104</td><td>126</td><td>90</td><td>1.03E-02</td></tr><tr><td>20</td><td>1</td><td>400</td><td>500</td><td>336.72</td><td>136</td><td>434</td><td>364</td><td>4.64E-02</td></tr><tr><td>20</td><td>1</td><td>400</td><td>500</td><td>336.72</td><td>162</td><td>396</td><td>318</td><td>5.04E-02</td></tr><tr><td>20</td><td>1</td><td>400</td><td>500</td><td>336.72</td><td>153</td><td>397</td><td>319</td><td>4.77E-02</td></tr><tr><td>20</td><td>1</td><td>400</td><td>750</td><td>224.48</td><td></td><td></td><td></td><td></td></tr><tr><td>20</td><td>1</td><td>400</td><td>750</td><td>224.48</td><td>126</td><td>281</td><td>224</td><td>2.78E-02</td></tr><tr><td>20</td><td>1</td><td>400</td><td>750</td><td>224.48</td><td>126</td><td>302</td><td>241</td><td>2.99E-02</td></tr><tr><td>20</td><td>1</td><td>400</td><td>1000</td><td>168.36</td><td></td><td></td><td></td><td></td></tr><tr><td>20</td><td>1</td><td>400</td><td>1000</td><td>168.36</td><td>121</td><td>210</td><td>156</td><td>2.00E-02</td></tr><tr><td>20</td><td>1</td><td>400</td><td>1000</td><td>168.36</td><td>115</td><td>232</td><td>172</td><td>2.10E-02</td></tr><tr><td>20</td><td>1</td><td>400</td><td>1250</td><td>134.69</td><td>98</td><td>162</td><td>122</td><td>1.25E-02</td></tr><tr><td>20</td><td>1</td><td>400</td><td>1250</td><td>134.69</td><td>92</td><td>158</td><td>125</td><td>1.14E-02</td></tr><tr><td>20</td><td>1</td><td>400</td><td>1250</td><td>134.69</td><td>110</td><td>178</td><td>125</td><td>1.54E-02</td></tr></tbody></table>
<table><caption>**Table 3** Single tracks carried out in PW mode with a 10 µs pulse duration corresponding to 0.4–0.46 duty cycles (3 cross-sections were analyzed on each track)</caption><thead><tr><th>τ<sub>las</sub> (μs)</th><th>dc<sub>real</sub></th><th>P<sub>peak</sub> (W)</th><th>V (mm/s)</th><th>VED (J/mm<sup>3</sup>)</th><th>Width w (μm)</th><th>Height h (μm)</th><th>Depth d (μm)</th><th>Area A (mm<sup>2</sup>)</th></tr></thead><tbody><tr><td>10</td><td>0.4</td><td>200</td><td>500</td><td>67.34</td><td>62</td><td>42</td><td>22</td><td>2.05E-03</td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>500</td><td>67.34</td><td>69</td><td>30</td><td>19</td><td>1.63E-03</td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>500</td><td>67.34</td><td>74</td><td>41</td><td>19</td><td>2.38E-03</td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>750</td><td>44.90</td><td>52</td><td>31</td><td>15</td><td>1.27E-03</td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>750</td><td>44.90</td><td>59</td><td>47</td><td>18</td><td>2.18E-03</td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>750</td><td>44.90</td><td>60</td><td>51</td><td>13</td><td>2.40E-03</td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>1000</td><td>33.67</td><td></td><td></td><td></td><td></td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>1000</td><td>33.67</td><td></td><td></td><td></td><td></td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>1000</td><td>33.67</td><td></td><td>90</td><td></td><td></td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>1250</td><td>26.94</td><td></td><td></td><td></td><td></td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>1250</td><td>26.94</td><td></td><td></td><td></td><td></td></tr><tr><td>10</td><td>0.4</td><td>200</td><td>1250</td><td>26.94</td><td>36</td><td>22</td><td>7</td><td>6.22E-04</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>500</td><td>144.79</td><td>112</td><td>156</td><td>108</td><td>1.37E-02</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>500</td><td>144.79</td><td>113</td><td>179</td><td>124</td><td>1.59E-02</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>500</td><td>144.79</td><td>114</td><td>134</td><td>92</td><td>1.20E-02</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>750</td><td>96.53</td><td>98</td><td>102</td><td>58</td><td>7.85E-03</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>750</td><td>96.53</td><td>94</td><td>77</td><td>47</td><td>5.68E-03</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>750</td><td>96.53</td><td>98</td><td>73</td><td>42</td><td>5.62E-03</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>1000</td><td>72.40</td><td>76</td><td>81</td><td>21</td><td>4.83E-03</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>1000</td><td>72.40</td><td>82</td><td>67</td><td>32</td><td>4.31E-03</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>1000</td><td>72.40</td><td></td><td></td><td></td><td></td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>1250</td><td>57.92</td><td>77</td><td>42</td><td>22</td><td>2.54E-03</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>1250</td><td>57.92</td><td>98</td><td>63</td><td>15</td><td>4.85E-03</td></tr><tr><td>10</td><td>0.43</td><td>400</td><td>1250</td><td>57.92</td><td>78</td><td>44</td><td>23</td><td>2.70E-03</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>500</td><td>227.29</td><td>114</td><td>233</td><td>185</td><td>2.09E-02</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>500</td><td>227.29</td><td>120</td><td>228</td><td>190</td><td>2.15E-02</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>500</td><td>227.29</td><td>118</td><td>238</td><td>186</td><td>2.21E-02</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>750</td><td>151.53</td><td>98</td><td>175</td><td>132</td><td>1.35E-02</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>750</td><td>151.53</td><td>109</td><td>159</td><td>126</td><td>1.36E-02</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>750</td><td>151.53</td><td>103</td><td>166</td><td>127</td><td>1.34E-02</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>1000</td><td>113.64</td><td>95</td><td>116</td><td>97</td><td>8.66E-03</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>1000</td><td>113.64</td><td>102</td><td>140</td><td>91</td><td>1.12E-02</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>1000</td><td>113.64</td><td>105</td><td>147</td><td>93</td><td>1.21E-02</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>1250</td><td>90.92</td><td>92</td><td>106</td><td>72</td><td>7.66E-03</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>1250</td><td>90.92</td><td>101</td><td>103</td><td>72</td><td>8.17E-03</td></tr><tr><td>10</td><td>0.45</td><td>600</td><td>1250</td><td>90.92</td><td>104</td><td>97</td><td>60</td><td>7.92E-03</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>500</td><td>309.79</td><td>109</td><td>341</td><td>311</td><td>2.92E-02</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>500</td><td>309.79</td><td>111</td><td>344</td><td>293</td><td>3.00E-02</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>500</td><td>309.79</td><td>119</td><td>352</td><td>285</td><td>3.29E-02</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>750</td><td>206.52</td><td>111</td><td>257</td><td>188</td><td>2.24E-02</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>750</td><td>206.52</td><td>101</td><td>218</td><td>203</td><td>1.73E-02</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>750</td><td>206.52</td><td>94</td><td>184</td><td>184</td><td>1.36E-02</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>1000</td><td>154.89</td><td>114</td><td>213</td><td>133</td><td>1.91E-02</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>1000</td><td>154.89</td><td>106</td><td>216</td><td>124</td><td>1.80E-02</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>1000</td><td>154.89</td><td>111</td><td>136</td><td>126</td><td>1.19E-02</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>1250</td><td>123.91</td><td>87</td><td>140</td><td>119</td><td>9.57E-03</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>1250</td><td>123.91</td><td>109</td><td>143</td><td>121</td><td>1.22E-02</td></tr><tr><td>10</td><td>0.46</td><td>800</td><td>1250</td><td>123.91</td><td>102</td><td>153</td><td>101</td><td>1.23E-02</td></tr></tbody></table>

<figure><img src="image_32.png" /></figure>
<table><caption>**Table 4** Single tracks carried out in PW mode with a 14 µs pulse duration corresponding to 0.56–0.65 duty cycles (3 cross-sections were analyzed on each track)</caption><thead><tr><th>τ<sub>las</sub> (μs)</th><th>dc<sub>real</sub></th><th>P<sub>peak</sub> (W)</th><th>V (mm/s)</th><th>VED (J/mm<sup>3</sup>)</th><th>Width w (μm)</th><th>Height h (μm)</th><th>Depth d (μm)</th><th>Area A (mm<sup>2</sup>)</th></tr></thead><tbody><tr><td>14</td><td>0.56</td><td>142</td><td>500</td><td>66.94</td><td>50</td><td>64</td><td>17</td><td>2.51E-03</td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>500</td><td>66.94</td><td>57</td><td>64</td><td>24</td><td>2.87E-03</td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>500</td><td>66.94</td><td>66</td><td>65</td><td>14</td><td>3.37E-03</td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>750</td><td>44.63</td><td>54</td><td>30</td><td>15</td><td>1.27E-03</td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>750</td><td>44.63</td><td>35</td><td>103</td><td>8</td><td>2.83E-03</td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>750</td><td>44.63</td><td>48</td><td>25</td><td></td><td>9.42E-04</td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>1000</td><td>33.47</td><td></td><td></td><td></td><td></td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>1000</td><td>33.47</td><td></td><td></td><td></td><td></td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>1000</td><td>33.47</td><td></td><td></td><td></td><td></td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>1250</td><td>26.78</td><td></td><td></td><td></td><td></td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>1250</td><td>26.78</td><td></td><td></td><td></td><td></td></tr><tr><td>14</td><td>0.56</td><td>142</td><td>1250</td><td>26.78</td><td></td><td></td><td></td><td></td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>500</td><td>146.35</td><td>126</td><td>140</td><td>79</td><td>1.39E-02</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>500</td><td>146.35</td><td>127</td><td>165</td><td>92</td><td>1.65E-02</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>500</td><td>146.35</td><td>125</td><td>148</td><td>95</td><td>1.45E-02</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>750</td><td>97.57</td><td>100</td><td>110</td><td>50</td><td>8.64E-03</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>750</td><td>97.57</td><td>91</td><td>85</td><td>47</td><td>6.08E-03</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>750</td><td>97.57</td><td>102</td><td>86</td><td>47</td><td>6.89E-03</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>1000</td><td>73.17</td><td>98</td><td>76</td><td>27</td><td>5.85E-03</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>1000</td><td>73.17</td><td>86</td><td>83</td><td>32</td><td>5.61E-03</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>1000</td><td>73.17</td><td>80</td><td>60</td><td>21</td><td>3.77E-03</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>1250</td><td>58.54</td><td>77</td><td>85</td><td>23</td><td>5.14E-03</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>1250</td><td>58.54</td><td>77</td><td>90</td><td>32</td><td>5.44E-03</td></tr><tr><td>14</td><td>0.61</td><td>285</td><td>1250</td><td>58.54</td><td>55</td><td>78</td><td>12</td><td>3.37E-03</td></tr><tr><td>14</td><td>0.635</td><td>430</td><td>500</td><td>229.86</td><td>129</td><td>282</td><td>210</td><td>2.86E-02</td></tr><tr><td>14</td><td>0.635</td><td>430</td><td>500</td><td>229.86</td><td>121</td><td>261</td><td>189</td><td>2.48E-02</td></tr><tr><td>14</td><td>0.635</td><td>430</td><td>750</td><td>153.24</td><td>125</td><td>187</td><td>129</td><td>1.84E-02</td></tr><tr><td>14</td><td>0.635</td><td>430</td><td>750</td><td>153.24</td><td>117</td><td>168</td><td>124</td><td>1.54E-02</td></tr><tr><td>14</td><td>0.635</td><td>430</td><td>1000</td><td>114.93</td><td>107</td><td>131</td><td>95</td><td>1.10E-02</td></tr><tr><td>14</td><td>0.635</td><td>430</td><td>1000</td><td>114.93</td><td>100</td><td>135</td><td>98</td><td>1.06E-02</td></tr><tr><td>14</td><td>0.635</td><td>430</td><td>1250</td><td>91.94</td><td>99</td><td>120</td><td>56</td><td>9.33E-03</td></tr><tr><td>14</td><td>0.635</td><td>430</td><td>1250</td><td>91.94</td><td>96</td><td>145</td><td>66</td><td>1.09E-02</td></tr><tr><td>14</td><td>0.65</td><td>570</td><td>500</td><td>311.89</td><td>139</td><td>368</td><td>304</td><td>4.02E-02</td></tr><tr><td>14</td><td>0.65</td><td>570</td><td>500</td><td>311.89</td><td>138</td><td>375</td><td>304</td><td>4.06E-02</td></tr><tr><td>14</td><td>0.65</td><td>570</td><td>750</td><td>207.93</td><td>131</td><td>227</td><td>188</td><td>2.34E-02</td></tr><tr><td>14</td><td>0.65</td><td>570</td><td>750</td><td>207.93</td><td>124</td><td>223</td><td>172</td><td>2.17E-02</td></tr><tr><td>14</td><td>0.65</td><td>570</td><td>1000</td><td>155.95</td><td>105</td><td>159</td><td>127</td><td>1.31E-02</td></tr><tr><td>14</td><td>0.65</td><td>570</td><td>1000</td><td>155.95</td><td>109</td><td>199</td><td>142</td><td>1.70E-02</td></tr><tr><td>14</td><td>0.65</td><td>570</td><td>1250</td><td>124.76</td><td>101</td><td>121</td><td>94</td><td>9.60E-03</td></tr><tr><td>14</td><td>0.65</td><td>570</td><td>1250</td><td>124.76</td><td>95</td><td>114</td><td>95</td><td>8.51E-03</td></tr></tbody></table>
<table><caption>**Table 5** Single tracks carried out in PW mode with an 18 µs pulse duration corresponding to 0.83–0.88 duty cycles (3 cross-sections were analyzed on each track)</caption><thead><tr><th>τ<sub>las</sub> (μs)</th><th>dc<sub>real</sub></th><th>P<sub>peak</sub> (W)</th><th>V (mm/s)</th><th>VED (J/mm<sup>3</sup>)</th><th>Width w (μm)</th><th>Height h (μm)</th><th>Depth d (μm)</th><th>Area A (mm<sup>2</sup>)</th></tr></thead><tbody><tr><td>18</td><td>0.83</td><td>111</td><td>500</td><td>77.56</td><td>58</td><td>66</td><td>18</td><td>3.01E-03</td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>500</td><td>77.56</td><td>67</td><td>70</td><td>19</td><td>3.68E-03</td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>500</td><td>77.56</td><td>78</td><td>81</td><td>17</td><td>4.96E-03</td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>750</td><td>51.70</td><td></td><td></td><td></td><td></td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>750</td><td>51.70</td><td>57</td><td>93</td><td>16</td><td>4.16E-03</td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>750</td><td>51.70</td><td></td><td></td><td></td><td></td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>1000</td><td>38.78</td><td>51</td><td>58</td><td>8</td><td>2.32E-03</td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>1000</td><td>38.78</td><td></td><td></td><td></td><td></td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>1000</td><td>38.78</td><td>44</td><td></td><td></td><td></td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>1250</td><td>31.02</td><td></td><td></td><td></td><td></td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>1250</td><td>31.02</td><td></td><td></td><td></td><td></td></tr><tr><td>18</td><td>0.83</td><td>111</td><td>1250</td><td>31.02</td><td></td><td></td><td></td><td></td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>500</td><td>160.72</td><td>127</td><td>175</td><td>103</td><td>1.75E-02</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>500</td><td>160.72</td><td>130</td><td>132</td><td>77</td><td>1.35E-02</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>500</td><td>160.72</td><td>129</td><td>168</td><td>101</td><td>1.70E-02</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>750</td><td>107.15</td><td>105</td><td>109</td><td>68</td><td>8.99E-03</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>750</td><td>107.15</td><td>101</td><td>108</td><td>46</td><td>8.57E-03</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>750</td><td>107.15</td><td>100</td><td>107</td><td>56</td><td>8.40E-03</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>1000</td><td>80.36</td><td>76</td><td>69</td><td>21</td><td>4.12E-03</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>1000</td><td>80.36</td><td>41</td><td>94</td><td>10</td><td>3.03E-03</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>1000</td><td>80.36</td><td>69</td><td>23</td><td>16</td><td>1.25E-03</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>1250</td><td>64.29</td><td>71</td><td>72</td><td>25</td><td>4.01E-03</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>1250</td><td>64.29</td><td>61</td><td>84</td><td>16</td><td>4.02E-03</td></tr><tr><td>18</td><td>0.86</td><td>222</td><td>1250</td><td>64.29</td><td>57</td><td>88</td><td>17</td><td>3.94E-03</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>500</td><td>243.88</td><td>133</td><td>282</td><td>222</td><td>2.95E-02</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>500</td><td>243.88</td><td>136</td><td>250</td><td>193</td><td>2.67E-02</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>500</td><td>243.88</td><td>132</td><td>266</td><td>192</td><td>2.76E-02</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>750</td><td>162.59</td><td>134</td><td>175</td><td>114</td><td>1.84E-02</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>750</td><td>162.59</td><td>129</td><td>125</td><td>70</td><td>1.27E-02</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>750</td><td>162.59</td><td>127</td><td>136</td><td>86</td><td>1.36E-02</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>1000</td><td>121.94</td><td>101</td><td>126</td><td>86</td><td>9.99E-03</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>1000</td><td>121.94</td><td>111</td><td>120</td><td>84</td><td>1.05E-02</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>1000</td><td>121.94</td><td>117</td><td>112</td><td>66</td><td>1.03E-02</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>1250</td><td>97.55</td><td>93</td><td>91</td><td>45</td><td>6.65E-03</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>1250</td><td>97.55</td><td>98</td><td>112</td><td>63</td><td>8.62E-03</td></tr><tr><td>18</td><td>0.87</td><td>333</td><td>1250</td><td>97.55</td><td>108</td><td>146</td><td>73</td><td>1.24E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>500</td><td>328.91</td><td>150</td><td>362</td><td>289</td><td>4.26E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>500</td><td>328.91</td><td>175</td><td>373</td><td>305</td><td>5.13E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>500</td><td>328.91</td><td>143</td><td>383</td><td>298</td><td>4.30E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>750</td><td>219.27</td><td>140</td><td>259</td><td>193</td><td>2.85E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>750</td><td>219.27</td><td>159</td><td>241</td><td>179</td><td>3.01E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>750</td><td>219.27</td><td>144</td><td>244</td><td>190</td><td>2.76E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>1000</td><td>164.46</td><td>127</td><td>157</td><td>114</td><td>1.57E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>1000</td><td>164.46</td><td>146</td><td>153</td><td>105</td><td>1.75E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>1000</td><td>164.46</td><td>132</td><td>148</td><td>94</td><td>1.53E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>1250</td><td>131.56</td><td>102</td><td>116</td><td>89</td><td>9.29E-03</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>1250</td><td>131.56</td><td>115</td><td>125</td><td>73</td><td>1.13E-02</td></tr><tr><td>18</td><td>0.88</td><td>444</td><td>1250</td><td>131.56</td><td>120</td><td>112</td><td>79</td><td>1.06E-02</td></tr></tbody></table>

<figure><img src="image_33.png" /></figure>
**Author contribution** All authors contributed to the study's conception and design. LPBF tests, Material preparation, data collection, and materials' analysis were performed by P. Peyre, P. Hébrard, F. Coste. P. Peyre and M. Dal carried out modeling tasks. E. Vignal, J. Laurent and P. Aubry participated to the discussion section. P. Peyre wrote the first draft of the manuscript. All authors commented read, commented and finally approved the final manuscript.

**Funding** Open access funding provided by Arts et Metiers Institute of Technology. Open access funding provided by Hong Kong University of Science and Technology.

**Data availability** No datasets were generated or analysed during the current study.

## Declarations

**Conflict of interest** The authors declare no competing interests.

**Open Access** This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

## References

1. Matthews MJ, Guss G, Khairallah SA et al (2016) Denudation of metal powder layers in laser powder bed fusion processes. Acta Mater 114:33–42. https://doi.org/10.1016/j.actamat.2016.05.017

2. Mayi YA, Dal M, Peyre P et al (2020) Laser-induced plume investigated by finite element modelling and scaling of particle entrainment in laser powder bed fusion. J Phys D: Appl Phys 53:075306. https://doi.org/10.1088/1361-6463/ab5900

3. Rubenchik AM, King WE, Wu SS (2018) Scaling laws for the additive manufacturing. J Mater Process Technol 257:234–243. https://doi.org/10.1016/j.jmatprotec.2018.02.034

4. Fabbro R (2019) Scaling laws for the laser welding process in keyhole mode. J Mater Process Technol 264:346–351. https://doi.org/10.1016/j.jmatprotec.2018.09.027

5. Metelkova J, Kinds Y, Kempen K et al (2018) On the influence of laser defocusing in Selective Laser Melting of 316L. Addit Manuf 23:161–169. https://doi.org/10.1016/j.addma.2018.08.006

6. Sow MC, De Terris T, Castelnau O et al (2020) Influence of beam diameter on Laser Powder Bed Fusion (L-PBF) process. Addit Manuf 36:101532. https://doi.org/10.1016/j.addma.2020.101532

7. Roehling TT, Shi R, Khairallah SA et al (2020) Controlling grain nucleation and morphology by laser beam shaping in metal additive manufacturing. Mater Des 195:109071. https://doi.org/10.1016/j.matdes.2020.109071

8. Wagenblast P, Myrell A, Thielmann M et al (2020) Additive manufacturing with green disk lasers. In: Helvajian H, Gu B, Chen H

(eds) Laser 3D Manufacturing VII. SPIE, San Francisco, United States, p 18

9. Wang A, Wei Q, Luo S et al (2023) Blue laser directed energy deposition of aluminum with synchronously enhanced efficiency and quality. Additive Manufacturing Letters 5:100127. https://doi.org/10.1016/j.addlet.2023.100127

10. Kang S-G, Gainov R, Heußen D et al (2023) Green laser powder bed fusion based fabrication and rate-dependent mechanical properties of copper lattices. Mater Des 231:112023. https://doi.org/10.1016/j.matdes.2023.112023

11. Caprio L, Demir AG, Previtali B (2018) Comparative study between CW and PW emissions in selective laser melting. J Laser Appl 30:032305. https://doi.org/10.2351/1.5040631

12. Caprio L, Demir AG, Previtali B (2019) Influence of pulsed and continuous wave emission on melting efficiency in selective laser melting. J Mater Process Technol 266:429–441. https://doi.org/10.1016/j.jmatprotec.2018.11.019

13. Laitinen V, Piili H, Nyamekye P et al (2019) Effect of process parameters on the formation of single track in pulsed laser powder bed fusion. Procedia Manufacturing 36:176–183. https://doi.org/10.1016/j.promfg.2019.08.023

14. Biffi CA, Fiocchi J, Bassani P, Tuissi A (2018) Continuous wave vs pulsed wave laser emission in selective laser melting of AlSi10Mg parts with industrial optimized process parameters: Microstructure and mechanical behaviour. Addit Manuf 24:639–646. https://doi.org/10.1016/j.addma.2018.10.021

15. Chou SC, Trask M, Danovitch J et al (2018) Pulsed laser powder bed fusion additive manufacturing of A356. Mater Charact 143:27–33. https://doi.org/10.1016/j.matchar.2018.02.004

16. Guo C, Zhou Y, Li X et al (2021) A comparing study of defect generation in IN738LC superalloy fabricated by laser powder bed fusion: Continuous-wave mode versus pulsed-wave mode. J Mater Sci Technol 90:45–57. https://doi.org/10.1016/j.jmst.2021.03.006

17. Xiao H, Li S, Han X et al (2017) Laves phase control of Inconel 718 alloy using quasi-continuous-wave laser additive manufacturing. Mater Des 122:330–339. https://doi.org/10.1016/j.matdes.2017.03.004

18. Chou R, Ghosh A, Chou SC et al (2017) Microstructure and mechanical properties of Al10SiMg fabricated by pulsed laser powder bed fusion. Mater Sci Eng, A 689:53–62. https://doi.org/10.1016/j.msea.2017.02.023

19. Gharbi M, Peyre P, Gorny C et al (2014) Influence of a pulsed laser regime on surface finish induced by the direct metal deposition process on a Ti64 alloy. J Mater Process Technol 214:485–495. https://doi.org/10.1016/j.jmatprotec.2013.10.004

20. Caprio L, Demir AG, Previtali B (2022) Understanding the effects of temporal waveform modulation of laser emission power in laser powder bed fusion: Part II - Experimental investigation. J Phys D: Appl Phys 55:495110. https://doi.org/10.1088/1361-6463/ac98d1

21. Grünewald J, Reinelt J, Sedlak H, Wudy K (2023) Support-free laser-based powder bed fusion of metals using pulsed exposure strategies. Prog Addit Manuf 8:1631–1640. https://doi.org/10.1007/s40964-023-00429-4

22. Demir AG, Mazzoleni L, Caprio L et al (2019) Complementary use of pulsed and continuous wave emission modes to stabilize melt pool geometry in laser powder bed fusion. Opt Laser Technol 113:15–26. https://doi.org/10.1016/j.optlastec.2018.12.005

23. Karami K, Blok A, Weber L et al (2020) Continuous and pulsed selective laser melting of Ti6Al4V lattice structures: Effect of post-processing on microstructural anisotropy and fatigue
behaviour. Addit Manuf 36:101433. https://doi.org/10.1016/j.addma.2020.101433

24. Kreitcberg A, Brailovski V, Turenne S (2017) Effect of heat treatment and hot isostatic pressing on the microstructure and mechanical properties of Inconel 625 alloy processed by laser powder bed fusion. Mater Sci Eng, A 689:1–10. https://doi.org/10.1016/j.msea.2017.02.038

25. Li S, Wei Q, Shi Y et al (2015) Microstructure Characteristics of Inconel 625 Superalloy Manufactured by Selective Laser Melting. J Mater Sci Technol 31:946–952. https://doi.org/10.1016/j.jmst.2014.09.020

26. Allahkaram SR, Zakersaee P, Haghgoo SAM (2011) Failure analysis of heat exchanger tubes of four gas coolers. Eng Fail Anal 18:1108–1114. https://doi.org/10.1016/j.engfailanal.2010.11.015

27. Todaro CJ, Easton MA, Qiu D et al (2021) Grain refinement of stainless steel in ultrasound-assisted additive manufacturing. Addit Manuf 37:101632. https://doi.org/10.1016/j.addma.2020.101632

28. Peyre P, Da Silva JR, Hamouche Z et al (2024) Size and build strategy effects for the L-PBF process applied to Inconel 625 vertical struts: a combined numerical and experimental approach. Int J Adv Manuf Technol 132:5063–5086. https://doi.org/10.1007/s00170-024-13634-4

29. Fabbro R (2010) Physical mechanisms controlling keyhole and melt pool dynamics during laser welding. In: Advances in Laser Materials Processing. Elsevier, pp 211–241

30. Hébrard P (2023) Comparative study of pulsed and continuous wave laser powder bed fusion of AlSi10Mg alloy. Madrid

**Publisher's Note** Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

<figure><img src="image_34.png" /></figure>