Understanding process-microstructure-property relationships in laser powder bed fusion of non-spherical Ti-6Al-4V powder

• Published in: Materials characterization Vol. 198
• Main Authors: Asherloo, Mohammadreza, Hwang, Junghyun, Leroux, Ryan, Wu, Ziheng, Fezzaa, Kamel, Paliwal, Muktesh, Rollett, Anthony D., Mostafaei, Amir
• Format: Journal Article
• Language: English
• Published: United States Elsevier 26-02-2023
• Subjects: Additive manufacturing; Hardness; Hydride-dehydride powder; MATERIALS SCIENCE; Synchrotron X-ray high-speed imaging; Texture analysis; variant selection
• ISSN: 1044-5803; 1873-4189

Powder feedstock is a major cost driver in metal additive manufacturing (AM). Replacing the spherical powder with the cost-efficient non-spherical one can reduce the feedstock cost up to 50% and attract more interest to adopt AM in production and new alloy development. Here, for this paper, a comprehensive study was conducted to understand process-microstructure-property relationships in laser powder bed fusion of hydride-dehydride Ti-6Al-4V powder. We demonstrated that variation of laser scan speed had a significant impact on the grain structure, pore evolution and properties compared to laser power. Dynamic X-ray radiography showed that with decreasing scan speed at a constant laser power, a transition from conduction to keyhole mode laser processing occurred, in which a deeper melt pool at lower scan speed intensified texture. In other words, an increase in laser scan speed resulted in formation of the refined prior β grains with shape factor of ~5, lowering the anisotropy. Furthermore, the degree of variant selection was evaluated based on the analyzed texture as a function of laser power and scan speed. With increasing laser scan speed, the dominant α/α boundary type was altered from type 2 to 4 and the degree of variant selection was noticeably decreased. On the other hand, increasing laser power left the morphology of prior β grains, their size, and the dominant α/α boundary (type 4) unchanged, while the texture and anisotropy were intensified, and the degree of variant selection was slightly decreased. Finally, dependency of surface roughness and microhardness were discussed as a function of laser processing parameters.