Effect of helium as process gas on laser powder bed fusion of Ti-6Al-4V studied with operando diffraction and radiography

The utilisation of helium as process gas in laser powder bed fusion limits the generation of Ti-6Al-4V hot and incandescent spatters and enhances their cooling rate. In the present study, operando X-ray diffraction using synchrotron X-rays permits to verify that the cooling rates experienced by the deposited material are not significantly affected by the process gas unlike spatters. Topography measurements of the top printed surface reveal lower roughness of He-produced samples, attributed to the previously observed reduction of spatters with He and thus a reduction of redepositions on the powder bed and printed surfaces. Operando radiography provides with insights on the spatter formation mechanisms namely particle entrainment, agglomeration, melting and spheroidization.HighlightsThe top surface average roughness of samples produced with He is lower than that of Ar equivalentDeposited Ti-6Al-4V cooling rates during LPBF are not significantly affected by the use of HeGrain size and orientation of Ti-6Al-4V is similar when processing under Ar, He, and a mixture of bothOperando radiography permits to identify the mechanisms of Ti-6Al-4V spatter formation The top surface average roughness of samples produced with He is lower than that of Ar equivalent Deposited Ti-6Al-4V cooling rates during LPBF are not significantly affected by the use of He Grain size and orientation of Ti-6Al-4V is similar when processing under Ar, He, and a mixture of both Operando radiography permits to identify the mechanisms of Ti-6Al-4V spatter formation

在激光粉末床熔融（Laser Powder Bed Fusion, LPBF）工艺中，以氦气（Helium, He）作为工艺气体，可抑制Ti-6Al-4V合金炽热飞溅的产生，并提升其冷却速率。本研究采用同步辐射X射线开展原位X射线衍射（operando X-ray diffraction）测试，证实沉积材料所经历的冷却速率并不像飞溅那样受工艺气体的显著影响。对打印试样顶面的形貌表征结果显示，氦气制备的试样表面粗糙度更低，这可归因于前文观察到的氦气可减少飞溅产生，进而降低了粉末床与打印表面的再沉积现象。原位放射成像（operando radiography）技术可揭示飞溅形成的具体机制，包括颗粒夹带、团聚、熔化与球化。
研究亮点：
1. 氦气制备的Ti-6Al-4V试样顶面平均粗糙度低于氩气（Argon, Ar）制备的等效试样
2. 激光粉末床熔融过程中，Ti-6Al-4V沉积材料的冷却速率不受氦气使用的显著影响
3. 在氩气、氦气以及二者混合气体环境下制备的Ti-6Al-4V合金，其晶粒尺寸与取向均无显著差异
4. 原位放射成像技术可明确识别Ti-6Al-4V的飞溅形成机制