Laser powder bed fusion of a Ni3Al-based intermetallic alloy with tailored microstructure and superior mechanical performance

• Published in: Advanced Powder Materials 2024-02, Vol.3 (1), p.100152, Article 100152
• Main Authors: Liu, Mingyu, Wang, Jiang, Hu, Tao, Xu, Songzhe, Shuai, Sansan, Xuan, Weidong, Yin, Shuo, Chen, Chaoyue, Ren, Zhongming
• Format: Article
• Language: English
• Subjects: High-temperature tensile performance; Hot isostatic pressing; Laser powder bed fusion; Ni3Al-Based alloy; Solidification cracking
• ISSN: 2772-834X; 2772-834X
• DOI: 10.1016/j.apmate.2023.100152

Ni3Al-based alloys are excellent candidates for the structural materials used for turbine engines due to their excellent high-temperature properties. This study aims at laser powder bed fusion and post-hot isostatic pressing (HIP) treatment of Ni3Al-based IC-221 ​M alloy with a high γ′ volume fraction. The as-built samples exhibits unavoidable solidification cracking and ductility dip cracking, and the laser parameter optimization can reduce the crack density to 1.34 ​mm/mm2. Transmission electron microscope (TEM) analysis reveals ultra-fine nanoscale γ′ phases in the as-built samples due to the high cooling rate during rapid solidification. After HIP treatment, a fully dense structure without cracking defects is achieved, which exhibits an equiaxed structure with grain size ∼120–180 ​μm and irregularly shaped γ′ precipitates ∼1–3 ​μm with a prominently high fraction of 86%. The room-temperature tensile test of as-built samples shows a high ultimate tensile strength (σUTS) of 1039.7 ​MPa and low fracture elongation of 6.4%. After HIP treatment, a significant improvement in ductility (15.7%) and a slight loss of strength (σUTS of 831.7 ​MPa) are obtained by eliminating the crack defects. Both the as-built and HIP samples exhibit retained high σUTS values of 589.8 ​MPa and 786.2 ​MPa, respectively, at 900 ​°C. The HIP samples exhibita slight decrease in ductility to ∼12.9%, indicating excellent high-temperature mechanical performance. Moreover, the abnormal increase in strength and decrease in ductility suggest the critical role of a high γ′ fraction in cracking formation. The intrinsic heat treatment during repeating thermal cycles can induce brittleness and trigger cracking initiation in the heat-affected zone with notable deteriorating ductility. The results indicate that the combination of LPBF and HIP can effectively reduce the crack density and enhance the mechanical properties of Ni3Al-based alloy, making it a promising material for high-temperature applications. Ni3Al-based IC-221 ​M alloy is fabricated by the LPBF technique for the first time. The high γ′ phase content makes the alloy high strength, while internal cracks seriously affect the plasticity of the alloy. The fully dense and defect-free IC-221 ​M alloy is obtained through HIP post-treatment, thereby improving plasticity. [Display omitted]