Abstract The effect of the gas thermal properties and density on the laser powder bed fusion (L-PBF) process was investigated by using inert argon, characterized by high density, and helium, characterized by high thermal conductivity and heat capacity, and their gas mixtures. The results highlighted that for L-PBF of Ti-6Al-4V, the effect of residual impurities such as oxygen and nitrogen on the process stability and defect generation is prevailing the type of the process gas. However, by monitoring the residual oxygen level in the process atmosphere, the results showed that using the argon-helium mixtures allows to increase the produced material density upon higher build rates. High density, greater than 99.98 % is indeed achieved using a mixture of 50 % argon and 50 % helium, allowing for a build rate increase of 44 % in comparison to the standard build rate. The analysis of the produced material revealed the presence of thermal residual stresses attributed to an enhanced energy input when using the gas mixtures. The latter offer a positive balance of density and thermal properties, and in turn, probably reduce the accumulation of process by-products at the melt pool that interfere with and attenuate the laser radiation. The possible detrimental effect of the introduced residual stresses is efficiently eliminated by the conventional stress relieving treatment leading to the decomposition of α´martensite into a fine (α + β) microstructure. This study opens the perspective on the development of the gas recipes for improved process stability and increased productivity of L-PBF process.

中文翻译：

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氩氦混合物作为激光-粉末床聚变气氛：提高 Ti-6Al-4V 的构建速度

摘要 以高密度惰性氩气、高热导率和热容氦气及其混合气体为研究对象，研究了气体热性质和密度对激光粉末床聚变（L-PBF）工艺的影响。 . 结果表明，对于 Ti-6Al-4V 的 L-PBF，氧和氮等残留杂质对工艺稳定性和缺陷产生的影响主要取决于工艺气体的类型。然而，通过监测工艺气氛中的残余氧含量，结果表明，使用氩氦混合物可以在更高的构建速率下增加生产的材料密度。使用 50 % 氩气和 50 % 氦气的混合物确实实现了高密度，大于 99.98 %，与标准构建速率相比，允许构建速率增加 44%。对生产材料的分析表明，当使用气体混合物时，由于能量输入的增加，存在热残余应力。后者提供了密度和热性能的正平衡，反过来，可能会减少熔池中工艺副产品的积累，这些副产品会干扰和衰减激光辐射。引入残余应力的可能有害影响通过传统的应力消除处理有效地消除，导致 α´马氏体分解为精细的 (α + β) 显微组织。这项研究为开发气体配方以提高工艺稳定性和提高 L-PBF 工艺的生产率开辟了前景。对生产材料的分析表明，当使用气体混合物时，由于能量输入的增加，存在热残余应力。后者提供了密度和热性能的正平衡，反过来，可能会减少熔池中工艺副产品的积累，这些副产品会干扰和衰减激光辐射。引入残余应力的可能有害影响通过传统的应力消除处理有效地消除，导致 α´马氏体分解为精细的 (α + β) 显微组织。这项研究为开发气体配方以提高工艺稳定性和提高 L-PBF 工艺的生产率开辟了前景。对生产材料的分析表明，当使用气体混合物时，由于能量输入的增加，存在热残余应力。后者提供了密度和热性能的正平衡，反过来，可能会减少熔池中工艺副产品的积累，这些副产品会干扰和衰减激光辐射。引入残余应力的可能有害影响通过传统的应力消除处理有效地消除，导致 α´马氏体分解为精细的 (α + β) 显微组织。这项研究为开发气体配方以提高工艺稳定性和提高 L-PBF 工艺的生产率开辟了前景。