Influence of gas atmosphere (Ar or He) on the laser powder bed fusion of a Ni-based alloy

Abstract

The gaseous atmosphere plays a major role in the quality of the manufactured parts in Laser Powder Bed Fusion (L-PBF) by protecting the metal from high temperature oxidation. If argon and nitrogen are the most commonly used gases, helium has almost never been considered as a possible candidate as a chemically inert shielding gas. To provide a better understanding of the influence of the gas atmosphere on the process stability, a comparative study of L-PBF manufacturing under argon and helium atmospheres has been carried out, considering a nickelbased alloy Inconel® 625 and a single bead configuration. To this end, in-situ process measurements were carried out on a dedicated experimental setup. The melt pool behaviour, the expansion of the vapour plume and the amount of spatters were evaluated with high-speed imaging for the two gases considered, together with the final L-PBF bead dimensions. Results were also compared to single fusion beads carried out in an industrial L-PBF machine for a comparable range of volume energy densities. The influence of the shielding atmosphere on L-PBF single beads was as follows: (1) dimensions of beads were shown to be constant whatever the gas; (2) fewer and smaller spatters were produced under helium atmosphere, especially for high volume energy densities. Physical mechanisms were then discussed to understand those specific effects.

Theab initiopotential energy curves of atom pairs and transport properties of high-temperature vapors of Cu and Si and their mixtures with He, Ar, and Xe gases

“…The VHS model cannot fit, however, the diffusion coefficient with the same accuracy as the viscosity and thermal conductivity, since eqn (39) does not include any adjustable parameter that can be changed to enforce the agreement between D VHS;ref and D ref , while D and m are defined by different O-integrals in eqn (22) and (23). This well-known deficiency of the VHS model results in relatively large RMS deviations D½D A of diffusivity, which are on the order of 10-30% for all atom pairs (Table 6).…”

“…For pure substances, eqn ( 37)-( 39) with parameters in Tables 5 and 6 provide the first-order power-law approximations of all transport coefficients. For gas mixtures, eqn (37) can be used directly for binary diffusivity, while the power-law approximations in eqn (38) and (39) for single-and cross-species contributions should be used together with eqn (25)- (27). The final algebraic form of eqn ( 25)-( 27) is given, e.g., in ref.…”

“…Copper and silicon are chosen for investigation due to the tremendous practical importance of these materials and, correspondingly, large amounts of experimental and computational studies involving laser-, ion spattering-, and plasma etchinginduced flows of Cu or Si vapor plumes, e.g., ref. 35-38. The simultaneous consideration of light-weight He, medium-weight Ar, and heavy Xe gases is inspired by the results of recent experimental 39 and computational studies 17,19 that report the strong effect of the molecular weight of a noble background gas on the plume or jet expansion processes in material processing technologies. The transport properties of Cu and Si vapors are of practical interest at elevated temperatures, e.g., roughly from 2000 K to 6000 K at atmospheric pressure.…”

Flow field analysis for multilaser powder bed fusion and the influence of gas flow distribution on parts quality

“…There were two main functions of shielding gas flow. First, inert gases such as Ar, N 2 and He were used to avoid the oxidation of metal alloy during laser melting process (Traore et al , 2021). Second, it was also used to remove the by-products during the metal vaporization process.…”

Study of spatter ejections during laser-powder bed fusion process for aluminum alloys

“…Moreover, due to the small build chamber, AM machines are not easily equipped with visualization instruments. For instance, [1], [10]- [12].With X-Ray, Guo et al and Young et al managed to look directly at the melt-pool for analysis of the spatter formation mechanisms [11], [12]. All of these studies are based upon a global observation of spatters, with a qualitative approach distinguishing the spatters according to their size or their ejection mechanism.…”