The industrial use of laser powder-bed fusion (L-PBF) in turbomachinery is gaining momentum ren- dering the inspection and quali/uniFB01cation of certain post-processing steps necessary. This includes fusion techniques that allow to print multiple parts separately to take advantage of e.g. various print orienta- tions and join them subsequently. The main motivation of this study is to validate the tungsten inert gas (TIG) welding process of L-PBF manufactured parts using industrial speci/uniFB01cations relevant for gas turbines to pave the way for the industrial production of modular build setups. For this, two commonly used nickel-based super alloys for high-temperature applications, Inconel /seven.pnum/one.pnum/eight.pnum and Inconel /six.pnum/two.pnum/five.pnum are chosen. Since their defect-free printability has been established widely, we focus on the suitability to be joined us- ing TIG welding. The process is evaluated performing microstructural examination and mechanical tests in as-built as well as heat-treated samples. The welds are assessed by applying a general weld quali/uniFB01ca- tion approach used at Siemens Gas and Power. It was found that both materials can be joined via TIG welding using standard weld parameters causing minimal defects. A solution annealing heat treatment before welding is not necessary for a positive outcome, but still recommended for Inconel /seven.pnum/one.pnum/eight.pnum. /one.pnum Introduction L-PBF is an Additive Manufacturing (AM) technology which, due to the achievable feature resolution and processability of high-performance materials, is suited for gas turbine applications (/one.pnum; /two.pnum). It is possible to produce L-PBF parts with similar mechanical and physical properties to those produced by conventional technologies such as casting (/three.pnum). In addition, the technology allows for the manufacturing of highly complex and individualized components without the cost-intensive production of casting or forging molds for every design iteration (/four.pnum). While the L-PBF technology comes with a lot of technical promises and opportunities, it still struggles to compete on an economical basis with already established production methods. Market studies have found that a drop in part production costs by a factor of ten is needed for the technology to become widely accepted in the industry (/five.pnum). Aside from e/uniFB00orts to reduce production costs, it needs to be proven that the L-PBF technology can be integrated into a larger process chain for a widespread industrial adoption by various companies (/six.pnum). Many L-PBF applications for gas turbines today focus on the hot-gas path (/nine.pnum), where complex internal cool- ing features are employed, to utilize the design freedom of the technology (/one.pnum/zero.pnum). The use of L-PBF in rotating parts is still limited due to insu/uniFB03cient creep resistance of the materials available (/one.pnum/one.pnum; /one.pnum/two.pnum; /one.pnum/three.pnum). While a com- mon design approach in AM is to integrate multiple parts into one, subsequent joining is sometimes still required. The main reasons for using non-monolithic build-setups may be limitations of the build chamber size or avoiding support-structures, e.g. for internal structures, which may require speci/uniFB01c build orienta- tions for di/uniFB00erent features of a part. In both cases a modular build strategy can be bene/uniFB01cial. However, this creates the need for an adequate joining process in the subsequent assembly. In turbomachinery, as in all quality-conscious industries, both the material properties and the post-processing technologies, such as welding and joining, need to be quali/uniFB01ed according to speci/uniFB01cations. *Corresponding author: o.fergani@gmail.com 1 Nickel superalloys Inconel /six.pnum/two.pnum/five.pnum (IN/six.pnum/two.pnum/five.pnum) and Inconel /seven.pnum/one.pnum/eight.pnum (IN/seven.pnum/one.pnum/eight.pnum) are commonly used in a wide variety of applications in turbomachinery and aerospace due to their relatively good corrosion resistance, excellent mechanical properties at elevated temperatures and weldability (/one.pnum/six.pnum; /one.pnum/seven.pnum). It has been well established that these materials can be manufactured by L-PBF without defects (/two.pnum/eight.pnum). In general, most L-PBF parts require a post-processing heat treatment to reduce residual stresses or to obtain the required structural perfor- mance, for example via recrystallization (IN/six.pnum/two.pnum/five.pnum) or precipitation hardening (IN/seven.pnum/one.pnum/eight.pnum). Although the chemical composition of IN/six.pnum/two.pnum/five.pnum and IN/seven.pnum/one.pnum/eight.pnum powders for L-PBF is the same as that corresponding to cast ingots, the di/uniFB00erent boundary conditions in the production process, such as the extreme cooling rates of the melt pools, give rise to di/uniFB00erent microstructures and properties (/one.pnum/four.pnum). Analyses on relevant techniques such as TIG welding of conventionally manufactured parts out of these materials are well established and avail- able (/seven.pnum). Additionally, the feasibility of laser welding of L-PBF manufactured parts was proven by Jokisch et al. (/eight.pnum). However, no studies on TIG-welding of L-PBF components using industrial speci/uniFB01cations relevant for gas turbines have been published to date. Thus, investigating whether the metallurgical di/uniFB00erences associated to L-PBF production methods have an in/uniFB02uence on the quality of TIG-welds is timely. The aim of this work is to investigate the applicability of TIG welding to Ni-superalloy components fabricated by L-PBF methods. Two scenarios of interest for gas turbine use cases are investigated and compared in this study, namely welding in the as-built condition or following a post-processing heat treatment. The /uniFB01rst scenario has the potential to reduce the process chain complexity and is therefore interesting for industrialization. For both scenarios, the development of microstructure and the associated hardness were investigated on the cross-section areas of the weld seam. /two.pnum Materials and Methods Table /one.pnum: Chemical composition of Inconel /seven.pnum/one.pnum/eight.pnum (/one.pnum/eight.pnum) Chemical composition of IN/seven.pnum/one.pnum/eight.pnum in percent by weight Ni Cr Nb Mo Ti Al Co /five.pnum/zero.pnum./zero.pnum- /one.pnum/seven.pnum./zero.pnum- /four.pnum./seven.pnum/five.pnum- /two.pnum./eight.pnum- /zero.pnum./six.pnum/five.pnum- /zero.pnum./two.pnum- /five.pnum/five.pnum./zero.pnum /two.pnum/one.pnum./zero.pnum /five.pnum./five.pnum /three.pnum./three.pnum /one.pnum./one.pnum/five.pnum /zero.pnum./eight.pnum/one.pnum./zero.pnum Cu C Si, Mn P, S B Fe[g=cm3] /zero.pnum./three.pnum/zero.pnum./zero.pnum/eight.pnum /zero.pnum./three.pnum/five.pnum /zero.pnum./zero.pnum/one.pnum/five.pnum /zero.pnum./zero.pnum/zero.pnum/six.pnum /one.pnum/one.pnum./five.pnum /eight.pnum./one.pnum/five.pnumTable /two.pnum: Chemical composition of Inconel /six.pnum/two.pnum/five.pnum (/one.pnum/nine.pnum) Chemical composition of IN/six.pnum/two.pnum/five.pnum in percent by weight Ni Cr Nb+Ta Mo O Ti, Al Co /five.pnum/eight.pnum./zero.pnum/two.pnum/zero.pnum./zero.pnum- /three.pnum./one.pnum/five.pnum- /eight.pnum.-0:030:4/one.pnum./zero.pnum/two.pnum/three.pnum./zero.pnum /four.pnum./one.pnum/five.pnum /one.pnum/zero.pnum./zero.pnum Cu C Si, Mn P, S N Fe[g=cm3] /zero.pnum./five.pnum/zero.pnum /zero.pnum./one.pnum/zero.pnum /zero.pnum./five.pnum/zero.pnum /zero.pnum./zero.pnum/one.pnum/five.pnum /zero.pnum./zero.pnum/two.pnum /five.pnum./zero.pnum /eight.pnum./four.pnum In this study, commercial IN/seven.pnum/one.pnum/eight.pnum powder from EOS GmbH (EOS Nickel Alloy IN/seven.pnum/one.pnum/eight.pnum) and IN/six.pnum/two.pnum/five.pnum powder from LPW Technology Limited (LPW-/six.pnum/two.pnum/five.pnum-AACP), both produced by gas atomization, were used. The chemical compositions are shown in Table /one.pnum and Table /two.pnum, respectively. Both powder alloys contain /uniFB01ne-grained, spherical metal particles with properties suitable for L-PBF (/one.pnum/five.pnum). The corresponding gaussian particle size distributions have a d100= 1545m. Table /three.pnum: Chemical composition of Thermanit /six.pnum/two.pnum/five.pnum (/two.pnum/zero.pnum) Chemical composition of Thermanit /six.pnum/two.pnum/five.pnum in percent by weight C Si Cr Mo Ni Nb Fe /zero.pnum./zero.pnum/two.pnum /zero.pnum./zero.pnum/two.pnum /two.pnum/two.pnum./zero.pnum /nine.pnum./zero.pnum Rest /three.pnum./five.pnum /one.pnum L-PBF manufacturing was carried out in an EOS M/two.pnum/nine.pnum/zero.pnum machine, with a build envelope of /two.pnum/five.pnum/zero.pnumx/two.pnum/five.pnum/zero.pnumx/three.pnum/two.pnum/five.pnum mm3. The manufactured parts were pipes with a length of /one.pnum/zero.pnum/zero.pnum mm, an outer diameter of /three.pnum/three.pnum./two.pnum mm and a wall thickness of /one.pnum./six.pnum mm. These dimensions were derived from Siemens speci/uniFB01cations for weld quali/uniFB01cation. All specimens were printed with EOS’ standard parameters for IN/seven.pnum/one.pnum/eight.pnum at a layer thickness of 40musing argon as inert gas. The tubes were built vertically in multiple build jobs, as shown in Figure /one.pnum. Some L- PBF parts thus manufactured were additionally solid solution treated in order to investigate the e/uniFB00ect of annealing on the weldability. A detailed list of the heat treatment conditions is speci/uniFB01ed for IN/seven.pnum/one.pnum/eight.pnum in Table /four.pnum and for IN/six.pnum/two.pnum/five.pnum in Table /five.pnum. As-built and heat treated samples were then TIG welded in the following way. A turning operation was /uniFB01rst carried out to produce a V-seam weld preparation with an opening angle of /six.pnum/zero.pnum. TIG-welding of the pipes was then conducted manually in two layers in a PA (horizontal), PC (cross) and PH (vertically rising pipe) position (as per DIN EN ISO /six.pnum/nine.pnum/four.pnum/seven.pnum) while a gap of approximately /two.pnum mm was left between the specimens. /two.pnum Figure /one.pnum: Welding procedure according to DIN EN ISO /nine.pnum/six.pnum/zero.pnum/six.pnum-/zero.pnum/four.pnum and welding posi- tions according to DIN EN ISO /six.pnum/nine.pnum/four.pnum/seven.pnum. Figure /two.pnum: L-PBF build job setup of welding test specimens The welding procedure including the welding positions is shown in Figure /two.pnum. Thermanit /six.pnum/two.pnum/five.pnum (or UTP A /six.pnum/two.pnum/two.pnum/two.pnum Mo) was used as /uniFB01ller metal for all specimens. It is designed for weld joints of similar high-strength and corrosion-resistant nickel-based alloys. The chemical composition is listed in Table /three.pnum. Table /four.pnum: Parameters for solution annealing heat treatment of IN/seven.pnum/one.pnum/eight.pnum Process Heating/ Atmosphere Program time Temperature cooling rate section [s] [C] [C/min] /one.pnum start /zero.pnum /two.pnum/five.pnum high vacuum /two.pnum heating /six.pnum/nine.pnum/zero.pnum/zero.pnum /one.pnum/one.pnum/seven.pnum/five.pnum /one.pnum/zero.pnum high vacuum /three.pnum storing /one.pnum/zero.pnum/five.pnum/zero.pnum/zero.pnum /one.pnum/one.pnum/seven.pnum/five.pnum high vacuum /four.pnumrapid/one.pnum/one.pnum/three.pnum/one.pnum/zero.pnum /five.pnum/zero.pnum/zero.pnum /five.pnum/zero.pnum Argoncooling free/five.pnumcooling/two.pnum/zero.pnum/eight.pnum/eight.pnum/zero.pnum /two.pnum/five.pnum ArgonTable /five.pnum: Parameters for solution annealing heat treatment of IN/six.pnum/two.pnum/five.pnum Process Heating/ Atmosphere Program time Temperature cooling rate section [s] [C] [C/min] /one.pnum start /zero.pnum /two.pnum/five.pnum high vacuum /two.pnum heating /four.pnum/seven.pnum/seven.pnum/six.pnum /nine.pnum/eight.pnum/zero.pnum /one.pnum/two.pnum high vacuum /three.pnum storing /eight.pnum/three.pnum/seven.pnum/six.pnum /nine.pnum/eight.pnum/zero.pnum high vacuum /four.pnumrapid/eight.pnum/nine.pnum/five.pnum/two.pnum /five.pnum/zero.pnum/zero.pnum /five.pnum/zero.pnum Argoncooling free/five.pnumcooling/one.pnum/seven.pnum/six.pnum/four.pnum/zero.pnum /two.pnum/five.pnum Argon The weld joints were /uniFB01rst inspected visually and by light microscopy. Figure /three.pnum shows an image of the welded tubes obtained using a digital camera (Fig. /three.pnuma) as well as optical macrographs of two welds performed in as-built (Fig. /three.pnumb) and heat-treated (Fig. /three.pnumb) IN/seven.pnum/one.pnum/eight.pnum. The cross sections were prepared with Kalling’s /two.pnum reagent to enhance the visibility of features under the bright /uniFB01eld light microscopy. No major defects can be appre- ciated at this low magni/uniFB01cation examination in any of the two materials investigated. The microstructure of the weld joints was also imaged by electron backscattered di/uniFB00raction (EBSD) using a scanning electron microscope (SEM) equipped with an EBSD system, a CCD camera and the Channel /five.pnum./zero.pnum data acquisition and analysis software package. The presence of microstructural gradients in welds may lead to local variations of the hardness, which might reach levels that are detrimental for a component’s life. According to the DIN EN ISO /one.pnum/five.pnum/six.pnum/one.pnum/four.pnum-/one.pnum norm the maximum permissible values for Ni-based alloys are /four.pnum/five.pnum/zero.pnum HV for non-heat-treated samples and /three.pnum/five.pnum/zero.pnum HV for heat-treated parts (/two.pnum/one.pnum). However, according to internal speci/uniFB01cations, an HV value above /three.pnum/seven.pnum/five.pnum is not permissible for the purpose of this test. In this study, the Vickers hardness (/two.pnum/two.pnum) was mea- sured on a cross section of the welds according to DIN EN ISO /nine.pnum/zero.pnum/one.pnum/five.pnum-/one.pnum (/two.pnum/three.pnum). Instead of the ten indentations required by the norm, /two.pnum/one.pnum measurements were performed for a more detailed analysis. The measurements were carried out using a test load of /one.pnum kgf (HV) and a holding time of /one.pnum/zero.pnum s (/two.pnum/four.pnum). /three.pnum Results and discussion Figure /four.pnum illustrates an Inconel /seven.pnum/one.pnum/eight.pnum cut weld seam in the as-built condition. The structural di/uniFB00erences be- tween the base material (BM), the heat-a/uniFB00ected zone (HAZ) and the weld zone (WZ) can be noted visually. As shown in /four.pnumb, melt pools can be clearly distinguished in the BM of the L-PBF manufactured pipes. Some pores can be seen close to the surface in the BM. However, melt pool boundaries are no longer visible in /three.pnum Figure /three.pnum: Two pipes TIG-welded together (a), Light microscopy photo (/one.pnum/zero.pnumx) of a weld seam of non-heat treated (b) and heat-treated IN/seven.pnum/one.pnum/eight.pnum (c). the HAZ, revealing the occurrence of microstructural changes as a consequence of welding (Fig./three.pnumc). Pores can also be found in the HAZ, close to the weld seam. The IN/six.pnum/two.pnum/five.pnum welds in the as-built condition exhibit a similar appearance at this magni/uniFB01cation. Figures /five.pnum and /six.pnum show the microstructure of the IN/seven.pnum/one.pnum/eight.pnum and IN/six.pnum/two.pnum/five.pnum welds, respectively, in the as-built condi- tion. In both cases, EBSD inverse pole /uniFB01gure maps in three perpendicular directions are given. The horizon- tal direction in the map (X) is parallel to the building direction. The corresponding inverse pole /uniFB01gures are also included in these /uniFB01gures. The latter were determined for the entire area of the EBSD maps and accord- ingly indicate the crystallographic preferential orientations for all zones (BM, HAZ, WZ). It must be noted here that, since the grains in the WZ, especially those in the root layer, occupy a relatively large volume, they have a large in/uniFB02uence on the inverse pole /uniFB01gure. In both materials, the BM and HAZ are populated with grains that are elongated along the building direction, and possess a typical crystallographic texture, in which the building direction is mostly parallel to a </zero.pnum/zero.pnum/one.pnum> direction, as is usually observed in L-PBF man- ufactured Ni superalloys (/two.pnum/eight.pnum; /two.pnum/nine.pnum). Overall, the grain size within the WZ is signi/uniFB01cantly larger than that of the BM and HAZ. The WZ is formed by two layers. The root layer consists mostly of equiaxed grains, while the grains at the top layer are elongated along the direction of thermal /uniFB02ow. Within the WZ, in the IN/seven.pnum/one.pnum/eight.pnum weld, the large grains at the root layer have a tendency to orient with a [/zero.pnum/zero.pnum/one.pnum] direction parallel to all three perpendicular axes examined. In the IN/six.pnum/two.pnum/five.pnum alloy the grains at the root layer are, however, more randomly oriented and slightly smaller in size. Figure /seven.pnum depicts an IN/seven.pnum/one.pnum/eight.pnum cut weld seam in the heat-treated condition. At least visually, the di/uniFB00erence be- tween the BM (Fig./seven.pnumb) and the HAZ (Fig./seven.pnumc)) is much less pronounced for the heat-treated compared to the non-heat-treated pipes. The heat treatment of the BM caused a visible change in the components’ tex- ture. As shown in Fig. /seven.pnumb, the scale-like surface-structure is no longer visible. Instead, a more homogenous structure can be seen. Some pores can still be found in the BM, in regions located near the surface. The IN/six.pnum/two.pnum/five.pnum welds in the heat treated condition exhibit a similar appearance at this magni/uniFB01cation. Figures /eight.pnum and /nine.pnum illustrate the microstructure of the IN/seven.pnum/one.pnum/eight.pnum and IN/six.pnum/two.pnum/five.pnum welds, respectively, in the heat treated condition. In both cases, again, EBSD inverse pole /uniFB01gure maps in three perpendicular directions, as well as the corresponding inverse pole /uniFB01gures, are given. Here, also, the building direction is parallel to the horizontal direction. The inverse pole /uniFB01gures were also determined for the entire area of the EBSD maps and, accordingly, indicate the crystallographic preferential orientations for all zones (BM, HAZ, WZ). The heat treatment is observed to have a clear e/uniFB00ect in the microstructure of the BM and the HAZ, whose textures become clearly weaker, especially in the case of the IN/six.pnum/two.pnum/five.pnum material, where, simultaneously, elon- gated grains are replaced by more equiaxed and irregularly shaped crystallites. The grain size within the /four.pnum Figure /four.pnum: Light microscope images of cross sections of the IN/seven.pnum/one.pnum/eight.pnum specimen without heat treatment a) Overview b) Base material with typical /uniFB02ake structure c) Heat-a/uniFB00ected zone with pores d) Weld seam with inclusion. WZ remains signi/uniFB01cantly larger than that of the HAZ and BM. Within the WZ the main di/uniFB00erence observed is the partial replacement of the elongated grains at the uppermost layer of the IN/seven.pnum/one.pnum/eight.pnum weld by smaller and more equiaxed crystallites, endowed with random orientations. The mentioned elongated shape is, however, retained in the IN/six.pnum/two.pnum/five.pnum WZ. In summary, our data reveal that the heat treatment seems to a/uniFB00ect signi/uniFB01cantly the microstructure and the texture of the BM and HAZ zones and that its e/uniFB00ect on the WZ is less noticeable. The observed weakening of the texture of the BM and HAZ zones, which is more pronounced in the IN/six.pnum/two.pnum/five.pnum alloy, may be attributed to the occurrence of discontinuous recrystallization. This process consists on the long-range migration of high angle boundaries, thus facilitating the nucleation and growth of strain free grains with orientations that are di/uniFB00erent from those present in the as-built material (/three.pnum/zero.pnum). Partial discontin- uous recrystallization is likely also the micromechanism that leads to the appearance of randomly oriented grains at the uppermost layer of the IN/seven.pnum/one.pnum/eight.pnum weld. The feasibility of recrystallization during post-processing heat treatments in SLM processed materials is highly dependent on the amount of strain energy stored during fabrication, which varies with process parameters and material types. Earlier works have demon- strated the occurrence of recrystallization in IN/seven.pnum/one.pnum/eight.pnum and IN/six.pnum/two.pnum/five.pnum samples fabricated by L-PBF processes follow- ing a solution treatment at similar temperature and holding time as those utilized in the present study e.g. (/three.pnum/one.pnum; /three.pnum/two.pnum; /three.pnum/three.pnum). Amato et al.(/three.pnum/one.pnum),in particular, reported a degree of recrystallization of about /five.pnum/zero.pnum percent. Luo et al. (/three.pnum/two.pnum) con/uniFB01rm the presence of recrystallized grains when the solution treatment temperature exceeds /nine.pnum/four.pnum/zero.pnumC. Furthermore, they report that when the solution annealing temperature is increased to /nine.pnum/eight.pnum/zero.pnumC, a large number of recrystallized grains appear at the boundaries of laser scanning tracks and, consequently, the latter become faintly visible. This is consistent with the absence of melt pool traces in the BM and HAZ of the heat treated samples of the present study (Fig. /seven.pnum), in which the solution temperatures were /one.pnum/one.pnum/seven.pnum/five.pnumC for IN/seven.pnum/one.pnum/eight.pnum and /nine.pnum/eight.pnum/zero.pnumC for IN/six.pnum/two.pnum/five.pnum. Additionally, Li et al. (/three.pnum/three.pnum) report that recrystallized grains in L-PBF processed and solution treated IN/six.pnum/two.pnum/five.pnum have random orientations. The microstructural evolution of the BM and HAZ of the Ni superalloys investigated here are fully consistent with earlier works. The absence of signi/uniFB01cant microstructural evolution upon heat treatment within the WZ of the investigated materials is consistent with the presence in these zones of lower levels of stored energy as a consequence of grain growth during welding, resulting in a smaller driving force for recrystallization. The observed lack of signi/uniFB01cant microstructural change reveals, instead, that only recovery processes, which are not detectable in the EBSD maps provided here as they involved only dislocation rearrangement processes. The local variation of the Vickers hardness was evaluated in the Ni-superalloy welds, both in the as-built /five.pnum Figure /five.pnum: EBSD measurements of cross section of IN/seven.pnum/one.pnum/eight.pnum specimen without solution annealing heat treatment; a) IPFX map with inverse pole /uniFB01gure of X direction b) IPFY map with inverse pole /uniFB01gure of Y direction c) IPFZ Map with inverse pole /uniFB01gure of Z direction. Figure /six.pnum: EBSD measurements of cross section of IN/six.pnum/two.pnum/five.pnum specimen without solution annealing heat treatment; a) IPFX map with inverse pole /uniFB01gure of X direction b) IPFY map with inverse pole /uniFB01gure of Y direction c) IPFZ Map with inverse pole /uniFB01gure of Z direction. and heat treated conditions. The cross area of the welds was segmented for hardness evaluation as indi- cated in the upper part of Fig. /one.pnum/zero.pnum. The corresponding HV-values are given also in the same /uniFB01gure. Several observations can be made here. First, as expected, in the as-built condition the hardness is lower in the WZ than in the HAZ and BM due to the presence of signi/uniFB01cantly larger grains. Indeed, the U-shape of the hardness curves corresponding to the as-built materials indicates a negative correlation between grain size and measured hardness, in agreement with the well-known Hall-Petch relationship. The di/uniFB00erence between the three measurement planes (D/one.pnum, D/two.pnum, D/three.pnum) is only marginal. Following solution annealing, how- ever, the hardness values decrease noticeably in the BM and HAZ regions in both materials, while they remain relatively constant in the WZ. In particular, in IN/seven.pnum/one.pnum/eight.pnum the hardness decreases in the BM by approx- imately /seven.pnum/zero.pnum HV while in the same region of IN/six.pnum/two.pnum/five.pnum it decreases by approximately /one.pnum/zero.pnum/zero.pnum HV. The hardness of all WZ areas ranges between /two.pnum/one.pnum/zero.pnum and /two.pnum/four.pnum/zero.pnum HV. These di/uniFB00erences can be explained by the variability of the manual welding process. Investigations by Ramkumar et al. concerning the weldability of conventionally manufactured IN/six.pnum/two.pnum/five.pnum sheets with AISI /three.pnum/zero.pnum/four.pnum sheets using the TIG method, with the same /uniFB01ller material used in this study, measured hardness values around /two.pnum/one.pnum/zero.pnum and /two.pnum/five.pnum/zero.pnum HV in the WZ (/two.pnum/seven.pnum). Thus, there appears to be no signi/uniFB01cant di/uniFB00erence in the measured hardness of the weld metal when comparing conventionally and L-PBF manufactured parts. The observed changes in the hardness values following annealing are fully consistent with the microstruc- tural evolution reported above. Discontinuous recrystallization is usually accompanied by a signi/uniFB01cant de- crease in the hardness, as strain hardened grains are replaced by growing strain free crystallites. Recovery processes, instead, lead only to minor changes in the materials properties (/three.pnum/zero.pnum). Thus, the signi/uniFB01cant de- crease in the hardness observed in the BM and HAZ areas can be rationalized by the occurrence of recrys- tallization in those regions. On the other hand, the negligible change in the hardness of the WZ that follows the solution treatment may be attributed to the occurrence of recovery processes and to the absence of recrystallization. In summary, this study demonstrates the weldability of both Ni superalloys using the TIG method. A weld parameter variation outside of the standard parameters is thus not needed. Both, IN/seven.pnum/one.pnum/eight.pnum and IN/six.pnum/two.pnum/five.pnum, can be TIG-welded using the same welding parameters and materials. Visually no major defects could be seen on any weld seam, regardless of the material and heat treatment. Although no local hardness peaks were found in any of the specimens, the as-built IN/seven.pnum/one.pnum/eight.pnum exhibits hardness values close to the permissible limit of /three.pnum/seven.pnum/five.pnum HV in the BM. Hence, a heat treatment before or after welding is not necessary, but still recommended. This is consistent with the fact, that the IN/seven.pnum/one.pnum/eight.pnum is used in its 00hardened form in most cases, meaning that the production setup without any heat treatment has no relevance in the industry today. The near-surface porosity in all specimens is thought to be caused by a suboptimal contour scanning strategy, which has been addressed in new parameter developments thereafter. /six.pnum Figure /seven.pnum: Light microscopic images of the cross sections etched with Kalling’s /two.pnum in bright/uniFB01eld for IN/seven.pnum/one.pnum/eight.pnum with heat treatment a) Overview; b) Base material c) Heat-a/uniFB00ected zone with pore d) Weld seam with pore Figure /eight.pnum: EBSD measurements on cross section IN/seven.pnum/one.pnum/eight.pnum with solution annealing heat treatment; a) IPFX Map with inverse pole /uniFB01gure of X direction; b) IPFY Map with inverse pole /uniFB01gure of Y direction; c) IPFZ Map with inverse pole /uniFB01gure of Z direction. Figure /nine.pnum: EBSD measurements on cross section IN/six.pnum/two.pnum/five.pnum with solution annealing heat treatment; a) IPFX Map with inverse pole /uniFB01gure of X direction; b) IPFY Map with inverse pole /uniFB01gure of Y direction; c) IPFZ Map with inverse pole /uniFB01gure of Z direction. /four.pnum Conclusions The weldability of L-PBF manufactured pipes made of IN/seven.pnum/one.pnum/eight.pnum and IN/six.pnum/two.pnum/five.pnum using TIG welding has been demon- strated in this study. No defects or weak points, which would preclude a process quali/uniFB01cation according to industry standards, have been discovered. Both materials are applicable for production by laser powder- bed fusion and subsequent tungsten inert gas welding. The results show that heat treatment is not neces- sary for a positive welding result. However, heat treatment is recommended for IN/seven.pnum/one.pnum/eight.pnum. Based on the results of this study, a full quali/uniFB01cation of a process chain involving TIG welding of L-PBF manufactured parts into bigger assemblies is to be expected. This study is an early step toward integrating the L-PBF technology into mass production chain process. Further research is required in order to fully industrialize the technology. For future studies, we recommend investigations on the mechanical properties of TIG-welded tensile test bars produced by L-PBF. Additionally, welding tests combining L-PBF with wrought or cast materials can be /seven.pnum Figure /one.pnum/zero.pnum: Top: Hardness measurement locations, Bottom: Vickers Hardness at the cross sections of IN/six.pnum/two.pnum/five.pnum and IN/seven.pnum/one.pnum/eight.pnum with and without heat treatment. interesting for certain use cases and should be carried out as described in this study. Acknowledgment We would like to thank Carsten Geisler for the contributions during his time with Siemens. Abbreviations The following abbreviations are used in this manuscript: AM Additive Manufacturing L-PBF Laser Powder-Bed Fusion IN/seven.pnum/one.pnum/eight.pnum Inconel /seven.pnum/one.pnum/eight.pnum IN/six.pnum/two.pnum/five.pnum Inconel /six.pnum/two.pnum/five.pnum TIG Tungsten Inert Gas HAZ Heat A/uniFB00ected Zone BM Base Material WZ Weld Zone EBSD Electron Backscatter Di/uniFB00raction IPF Inverse Pole Figure HV Vickers Hardness NDT Non-Destructive Testing