# Development and application of high-purity Ti-O reference alloys for oxygen quantification using high resolution micro laser induced breakdown spectroscopy (HR-μLIBS)

Kevin Gautier, Antoine Casadebaigt, Emilie Fourcade, Enrica Epifano, Tripti Gaur, Aurélie Vande Put, Daniel Monceau

## ► To cite this version:

Kevin Gautier, Antoine Casadebaigt, Emilie Fourcade, Enrica Epifano, Tripti Gaur, et al., Development and application of high-purity Ti-O reference alloys for oxygen quantification using high resolution micro laser induced breakdown spectroscopy (HR-μLIBS). Materialia, 2025, 44, pp.102545. 10.1016/J.MTLA.2025.102545. hal-05359990

HAL Id: hal-05359990

https://hal.science/hal-05359990v1

Submitted on 26 Nov 2025

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published 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>
# Development and application of high-purity Ti-O reference alloys for oxygen quantification using high resolution micro laser induced breakdown spectroscopy (HR-μLIBS)

Kevin Gautier<sup>a,b</sup>, Antoine Casadebaigt<sup>c</sup>, Emilie Fourcade<sup>a</sup>, Enrica Epifano<sup>a,b</sup>, Tripti Gaur<sup>a</sup>, Aurélie Vande Put<sup>a</sup>, Daniel Monceau<sup>a,*</sup>

## ARTICLE INFO

**Keywords:**

Titanium
High temperature oxidation
Oxygen embrittlement
Spark plasma sintering (SPS)
Laser induced breakdown spectroscopy (LIBS)

## ABSTRACT

The precise quantification of oxygen concentration in titanium is crucial for various high-performance applications. In this study, we developed reference samples to calibrate high-resolution micro laser-induced breakdown spectroscopy (HR-μLIBS) for oxygen analysis in titanium. Two fabrication methods were employed: (i) oxidation of titanium powder at high temperature in a controlled atmosphere with oxygen, followed by spark plasma sintering (SPS), and (ii) blending titanium powder with TiO₂ powder before sintering by SPS. Homogenized samples were then used to establish a calibration line correlating HR-μLIBS intensity with known oxygen concentrations. To evaluate the HR-μLIBS method, a titanium sample oxidized 500 h at 650 °C in Ar-20 %O₂ was analyzed using both HR-μLIBS and electron probe microanalysis (EPMA). The results demonstrate a strong agreement between the two methods, with HR-μLIBS offering superior speed and improved accuracy at low oxygen concentrations (< 3 at. %).

## Main body

Titanium and its alloys are widely used in aerospace, biomedical, and industrial applications due to their excellent strength-to-weight ratio, corrosion resistance, and biocompatibility. Oxygen plays a critical role in determining their mechanical properties, increasing yield stress but causing embrittlement when excessive [1]. Therefore, accurate measurement of oxygen concentration is essential for quality control and research applications. Traditional methods such as electron probe microanalysis (EPMA) and inert gas fusion analysis (IGA) provide valuable insights but suffer from surface contamination (EPMA) and lack of spatial resolution (IGA). In contrast, high resolution micro laser induced breakdown spectroscopy (HR-μLIBS) offers a rapid alternative for oxygen quantification. A review on LIBS applications in materials was recently provided [2].

For HR-μLIBS application to oxygen quantification in our titanium alloys, we first calibrated the method using samples of known composition. To measure oxygen diffusion profiles in titanium oxidized at high temperature, high spatial resolution LIBS was required. This study

presents two methods for fabricating Ti–O reference alloys with known oxygen levels, then using them to build a calibration curve for HR-μLIBS. We also compare HR-μLIBS with EPMA through analysis of an oxidized titanium sample.

The first method to prepare reference samples is depicted in Fig. 1. It consists in oxidizing a pure titanium powder in an Ar-O₂ atmosphere and to sinter this powder. Similar method was applied in [3]. Gas atomized Grade 1 Ti powder (maximum diameter Dmax = 45 µm) from Goodfellow (France) was used. The initial oxygen, carbon and nitrogen contents in the powder were measured by IGA (EAG Eurofins Toulouse) and were resp. 770±30, 145±2 and 180±30 wt.ppm. About 5 g of powder was poured into an alumina crucible (75 × 11 mm²). The powder alone and the crucible with the powder were weighed using a SARTORIUS LA75 3200D balance with a precision of ±20 µg, before being placed in the furnace for oxidation. The furnace chamber was initially evacuated to a secondary vacuum (<10⁻⁵ mbar). It was then filled with an Ar-20 vol % O₂ gas mixture, with a continuous flow of 51 mL.min⁻¹. The temperature/duration of the oxidation were chosen to obtain the target oxygen concentration (Table 1). After oxidation, the crucible containing the

<footnote><sup>a</sup> CIRIMAT laboratory, Toulouse-INP, CNRS-INPT-UT, Toulouse Cedex 31030, France</footnote>

<footnote><sup>b</sup> Department of Engineering Physics, University of Wisconsin-Madison, Madison, WI 53706, USA</footnote>

<footnote><sup>c</sup> LASALYS, 1 Avenue du Champ de Mars, CS 30019, Orleans Cedex45074, France</footnote>

<footnote>* Corresponding author.
E-mail address: daniel.monceau@toulouse-inp.fr (D. Monceau).</footnote>
All HR-µLIBS measurements in this study were performed using a “L-HMA-pro” LIBS system (LASALYS, France; www.lasalys.com), equipped with a 266 nm nanosecond pulsed Nd:YAG laser at 20 Hz. The system includes an optical microscope for surface imaging and a 266 nm laser objective. The stages are step-and-settle driven, and the sample is moved perpendicular to the laser beam. Spatial resolution (crater diameters) ranges from 1.5 to 5 µm, with power densities from 1 to 35 GW/cm². HR-µLIBS is highly sensitive to light elements such as C, H, O, N, and Li. In this work, we used the 777.2 nm oxygen line. The analytical resolution was set at 4 µm, with a power density of ~25 GW/cm². The analyses were performed in laboratory air at atmospheric pressure, but the plasma was shielded by a helium gas flow near the surface. This shielding atmosphere prevents signals from being obtained from gas-phase molecules, as demonstrated using argon on steels for carbon analysis [10].

Quantitative HR-µLIBS measurements were obtained using a calibration curve linking intensity to known oxygen concentrations. The Ti-O calibration line was built using five low-oxygen certified standards (450, 1300, 1790, 2460, and 3650 wt. ppm, provided by TECHLAB, France) and five oxygen-rich sintered samples (0.266, 1.95, 4.04, 4.70, and 8.12 wt. %, Table 1). For each sample, five 2D maps with 100 laser shots were performed, each shot corresponding to a local measurement, spaced 4 µm apart. Each map covers 40 × 40 µm². Fig. 2 shows the calibration line with mean intensity values vs. oxygen content. All data from the certified and sintered samples align along the same linear regression. The 95 % confidence interval (Student's law) gives increasing uncertainty with oxygen content: ±1 at. % for 20 at. % O and ±0.08 at. % for 0.20 at. % O. This curve served as a reference for future HR-µLIBS analyses.

In order to test the use of HR-µLIBS to perform oxygen diffusion profiles measurements, we used a Ti-50 grade titanium alloy oxidized for 500 h at 650 °C in Ar-20 %O₂, from a previous study [11]. This atmosphere was used to prevent nitrogen uptake [12]. The sample was prepared in cross-section. 10 cartographies of 100 columns x 100 lines with 4 µm step between each laser shots were performed giving cartography dimensions of 400 µm wide and deep. Each line corresponds to a depth increment of 4 µm going from the resin to the bulk of the sample. For each line, 100 laser shots were performed to accumulate signal and create the oxygen intensity profile. The abscissa of the analyzed points of the profiles were readjusted to realign them and calculate the mean of the 10 profiles. However, the oxide/metal interface of the sample was damaged because of fast oxidation [11], lowering the mean signal of oxygen measured close to the interface. Only data obtained on undamaged titanium matrix was kept to draw the final oxygen diffusion profile and perform the profile modeling.

The oxygen diffusion profiles were compared with previously published EPMA measurements [11]. Notably, the HR-µLIBS profiles were obtained from the exact same sample as the one analyzed by EPMA. EPMA measurements details can be found in [11]. As EPMA measurements are strongly affected by the native oxide layer and potential

spectral interferences (Ti Lβ and O Kα lines) which can lead to an overestimated oxygen concentration of 3 to 5 at. % in materials, a correction procedure was applied. Oxygen concentration was measured five times in the unoxidized bulk alloy, and the average background intensity was subtracted from each point along the EPMA profile to account for this artifact.

A comparison of the oxygen concentration profiles obtained by HR-µLIBS and EPMA is presented in Fig. 3. Both profiles were fitted using the analytical solution of Fick's second law (error function), assuming a constant surface concentration Cₛ and a constant oxygen diffusion coefficient D. For the HR-µLIBS profile, the best-fit parameters were Cₛ = 21 at. %, D = 1.8 × 10⁻¹⁶ m²/s, and a bulk oxygen concentration C₀ = 0.35 at. %. In contrast, the EPMA analysis yielded Cₛ = 27 at. %, D = 1.1 × 10⁻¹⁶ m²/s, and C₀ = 0 at. % due to the correction applied during EPMA data processing. The two values of oxygen diffusion coefficients are close to the ones gathered by Vaché et al. for pure Ti and near α-Ti alloys [13].

While the results from both techniques are in reasonable agreement, some differences are evident. Firstly, the oxygen concentration just beneath the oxide layer is higher in the EPMA profile. Secondly, although the diffusion coefficients are of the same order of magnitude, HR-µLIBS suggests a slightly higher value. Thirdly, HR-µLIBS allows the measurement of the bulk oxygen content, which EPMA cannot provide due to the background subtraction necessary to account for surface contamination. The bulk concentration measured by HR-µLIBS (0.35 at. %) is consistent with independent measurements performed on unoxidized Ti-50 using IGA that yielded 0.269 at. %. This confirms the reliability of HR-µLIBS for quantifying low oxygen concentrations.

One limitation of HR-µLIBS in this context was its spatial resolution. While EPMA could provide measurements within 1–2 µm of the metal/oxygen interface, HR-µLIBS was constrained by the crater size and spacing, preventing such fine resolution near the interface. However this resulted from a choice of 4 µm done with HR-µLIBS in the present study in order to favor low concentration measurements. On its side, EPMA faces challenges in concentration accuracy due to surface contamination by native oxide layer, which require subtracting an intensity equivalent to 3–5 at. % O. This correction assumes uniform surface contamination on the micrometer scale, which may not be always valid. EPMA struggles to measure low oxygen concentrations with precision. At low levels, where concentrations are inferred by subtracting two intensity signals corresponding to about 4 at. %, even small noise can introduce significant errors—as seen in the noisy EPMA signal for low concentrations in Fig. 3. While this is acceptable when extracting diffusion coefficients, it becomes problematic when precise quantification of oxygen for low concentrations is required. In industrial titanium-based alloys, the typical oxygen content is around 0.3 at. %, and even small variations can significantly impact properties such as yield strength. Furthermore, when oxygen diffuses into the material during oxidation, embrittlement occurs at concentrations around 1 at. % (e.g. [14]).

While HR-µLIBS is also affected by the native oxide layer, the impact

<caption>**Table 1**</caption>

Samples prepared by SPS sintering with two methods (powder oxidation or powder blending).

<table><thead><tr><th colspan="8">1st method (powder oxidation)</th></tr><tr><th>Sample name (at%)</th><th>wt. % O</th><th>at. % O</th><th>Oxidation temperature (°C)</th><th>Oxidation time (min)</th><th>SPS conditions</th><th>Annealing (under secondary vacuum)</th></tr></thead><tbody><tr><td>Ti-0.80</td><td>0.266</td><td>0.792</td><td>400</td><td>132</td><td></td><td>N.A.</td></tr><tr><td>Ti-5.60</td><td>1.953</td><td>5.62</td><td>500</td><td>1260</td><td>850 °C, 2 h</td><td>N.A.</td></tr><tr><td>Ti-12.90</td><td>4.698</td><td>12.85</td><td>550</td><td>870</td><td>25MPa<br>1 atm Ar</td><td>5 h at 870 °C<br>+ 12 h at 890 °C</td></tr></tbody></table><table><thead><tr><th colspan="8">2nd method (TiO<sub>2</sub>+Ti blending)</th></tr><tr><th>Sample name (at. %)</th><th>wt. % O</th><th>at. %O</th><th>TiO<sub>2</sub> (g)</th><th>Ti (g)</th><th>SPS conditions</th><th></th></tr></thead><tbody><tr><td>Ti-110</td><td>4.04</td><td>11.2</td><td>0.6256</td><td>6.4508</td><td>1050 °C, 1 h</td><td></td></tr><tr><td>Ti-210</td><td>8.12</td><td>20.9</td><td>1.3471</td><td>5.7201</td><td>25MPa<br>1 atm Ar</td><td></td></tr></tbody></table>
<figure><img src="image_2.png" /><figcaption>**Fig. 2.** Calibration line (blue line) obtained for the measurement of oxygen concentration using the HR-µLIBS method (red lines indicate 95 % confidence interval using the Student's law).</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>**Fig. 3.** Oxygen concentration profiles measured under the oxide scale of a Ti-50 sample oxidized 500 h at 650 °C in Ar-20 %O₂. Comparison of analyses performed with EPMA and with HR-µLIBS.</figcaption></figure>

is reduced. The laser ablates material to a depth of ~3 µm, mixing the thin surface oxide (a few nanometers thick, e.g. 8 nm in [15]) into a much larger volume of bulk material. The resulting oxygen contribution from surface contamination is effectively incorporated into the calibration curve (Fig. 2) in the intercept at the origin. For future analyses, it will be important to verify whether different industrial titanium-based alloys follow the same calibration curve as pure Ti-50, as variations in native oxide composition could influence results.

This study demonstrates the successful fabrication of Ti–O reference alloys with oxygen contents ranging from 0.79 to 20.9 at. % using two distinct methods, and their effective application in calibrating HR-µLIBS. The HR-µLIBS technique proved to be a highly effective method for measuring oxygen concentrations in titanium, offering key advantages over EPMA. These include faster analysis and greater accuracy at low oxygen levels due to reduced sensitivity to surface contamination. Improved precision at low concentrations is particularly relevant, as even small amounts of oxygen — below 1 at. % — can significantly

influence titanium's mechanical behavior at room temperature. Given these advantages, HR-µLIBS presents a promising alternative for oxygen quantification in titanium alloys, especially when rapid, accurate measurements are required and a spatial resolution of ~2–5 µm is sufficient for the application.

CRediT authorship contribution statement

**Kevin Gautier:** Writing – review & editing, Visualization, Validation, Methodology, Investigation. **Antoine Casadebaigt:** Writing – review & editing, Writing – original draft, Visualization, Software, Resources, Methodology, Formal analysis, Data curation, Conceptualization. **Emilie Fourcade:** Visualization, Methodology, Investigation. **Enrica Epifano:** Writing – review & editing, Visualization, Validation, Supervision, Resources, Project administration, Methodology, Investigation. **Tripti Gaur:** Writing – review & editing, Investigation. **Aurélie Vande Put:** Writing – review & editing, Validation, Supervision,
Resources, Project administration, Methodology, Investigation. **Daniel Monceau:** Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Resources, Project administration, Methodology, Investigation, Formal analysis, Conceptualization.

**Declaration of competing interest**

The authors have no competing interests to declare.

**Funding sources**

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

**References**

[1] H.R. Ogden, R.I. Jaffee, The effects of carbon, oxygen, and nitrogen on the mechanical properties of titanium and titanium alloys, TML Report n°20 (1955).

[2] V. Palleschi, S. Legnaioli, F. Poggialini, F.O. Bredice, I.A. Urbina, N. Lellouche, S. M. Aberkane, Laser-induced breakdown spectroscopy, Nat. Rev. Methods. Primers. 5 (2025) 17.

[3] Y.S. Zhang, W. Zhang, W.T. Huo, J.J. Hu, L.C. Zhang, Microstructure, mechanical and wear properties of core-shell structural particle reinforced Ti-O alloys, Vacuum 139 (2017) 44–50.

[4] Z. Cai, J. Chen, P. Du, T. Xiang, J. Chen, G. Xie, Mechanical behavior and microstructure control of the low-cost titanium-oxygen alloy prepared by ball milling and spark plasma sintering, J. Alloys. Compd. 887 (2021) 161349.

[5] X. Shi, X. Wang, B. Chen, J. Umeda, A. Bahador, K. Kondoh, J. Shen, Precision control of oxygen content in CP-Ti for ultra-high strength through titanium oxide decomposition: an in-situ study, Mater. Des. 227 (2023) 111797.

[6] H. Okamoto, O-Ti (Oxygen-Titanium), J. Ph. Equilib. Diffus. 22 (2001) 515.

[7] C.J. Rosa, Oxygen diffusion in alpha and beta titanium in temperature range of 932 degrees to 1142 degrees C, Metall. Trans. 1 (9) (1970) 2517.-.

[8] D.A Cremers, L.J. Radziemski, Handbook of laser-induced breakdown spectroscopy. A useful guide by the authors who contributed to the early development of LIBS, Wiley (2013).

[9] P.F.D. Menut, J.L. Lacour, A. Rivoallan, P. Mauchien, Micro-laser-induced breakdown spectroscopy technique: a powerful method for performing quantitative surface mapping on conductive and nonconductive samples, Appl. Opt. 42 (30) (2003) 6063–6071.

[10] J.A. Aguilera, C. Aragon, J. Campos, Determination of carbon content in steel using laser-Induced breakdown spectroscopy, Appl. Spectrosc. 46 (9) (1992) 1382–1387.

[11] K. Gautier, E. Epifano, T. Gheno, D. Connétable, D. Monceau, Effects of Al and refractory alloying elements (W, Ta and Hf) on oxidation kinetics, oxygen dissolution and diffusion in titanium alloys, Corros. Sci. (2024) 112330.

[12] A.M. Chaze, C. Coddet, The role of nitrogen in the oxidation behaviour of titanium and some binary alloys, J. Less Common Met. 124 (1986) 73–84.

[13] N. Vaché, Y. Cadoret, B. Dod, D. Monceau, Modeling the oxidation kinetics of titanium alloys: review, method and application to Ti-64 and Ti-6242s alloys, Corros. Sci. 178 (2021) 109041.

[14] A. Casadebaigt, D. Monceau, J. Hugues, High temperature oxidation of Ti-6Al-4V alloy fabricated by additive manufacturing, in: Proceedings of the Influence on Mechanical Properties. The 14th World Conference on Titanium, Nantes (France), 2019.

[15] E. McCafferty, J.P. Wightman, An X-ray photoelectron spectroscopy sputter profile study of the native air-formed oxide film on titanium, Appl. Surf. Sci. 14 (1999) 92–100.