High throughput in-situ synthesis of Fe-Cr-Ni alloys via laser powder bed fusion: Exploring the microstructure and property evolution

Pure Fe, Cr, and Ni powders was used as raw materials, a high-throughput in-situ alloying technique based on Laser powder bed fusion (LPBF) was employed to synthesize 80 Fe-Cr-Ni alloys. A comprehensive assessment of the chemical composition, phase structure, microstructure, and mechanical properties of the samples was conducted using methods such as μ-XRF and μ-XRD. The 80 samples were categorized into three microstructural types: equiaxed-ferrite, columnar-ferrite, and lath-martensite. A mapping relationship between microstructure and phase diagram was established, revealing a strong correlation between the formation of equiaxed grains and the complete FCC phase region in the phase diagram. Four samples with typical microstructure features were selected for in-depth analysis: 2Cr with randomly oriented equiaxed grains (∼ 10.9 µm), 12Cr with coarse columnar grains and strong <001> texture, 12Cr6Ni with ultra-fine equiaxed grains (∼1.6 µm), and 20Cr7Ni with martensite and a small amount of residual austenite. The evolution mechanisms of these four microstructures were analyzed from the perspectives of phase transformation and cyclic thermal impact. The formation of ultra-fine equiaxed grains in 12Cr6Ni is associated with martensitic transformation and austenitic recrystallization, resulting in excellent overall mechanical properties: microhardness 319 HV, the highest among all samples, ultimate tensile strength 918 MPa, yield strength 884 MPa, and elongation 17.0%.