Annealing Effects on the Microstructure and Properties of Feconicrti0.4 High Entropy Alloy by Selective Laser Melting

Abstract

Additive manufacturing of high-entropy alloys (HEAs) via selective laser melting (SLM) generates unique microstructural characteristics, while post-processing treatments face challenges in balancing strength and ductility due to thermally induced phase transformations. Dense, crack-free FeCoNiCrTi0.4 HEA bulk samples and tensile specimens were fabricated via optimized SLM parameters. Post-fabrication annealing was conducted at 600°C, 800°C, and 1000°C for 4 hours to systematically evaluate the temperature-dependent effects on microstructure, phase constitution, texture evolution, relative density, and mechanical properties of the HEA. The results showed that annealing at 600°C formed nanoscale Co2Ti/NiTi intermetallic compounds (20-50 nm). Through Orowan strengthening and residual stress elimination, hardness, tensile strength, and elongation were synergistically improved, with elongation reaching 8.11%. At 800°C, excessive Cr2Ti/Co2Ti precipitates induced grain boundary segregation and localized stress concentration, leading to intergranular fracture and a reduction in elongation of approximately 3.4%. Nevertheless, this condition achieved a peak tensile strength of 1534.71 MPa and a maximum hardness of 681.26 HV0.5. Annealing at 1000°C triggered interfacial debonding of coarsened acicular precipitates (100-150 nm), which acted as crack nuclei, resulting in a reduction of strength and elongation to 1401.63 MPa and 5.61%, respectively. This study reveals that nanoscale intermetallic compound design at moderate temperatures optimizes strength-ductility synergy, whereas excessive precipitation or coarsening leads to performance degradation, demonstrating the FeCoNiCrTi0.4 alloy's high microstructural stability and superior resistance to temper softening.

Keywords: selective laser melting, Alloy design, Heat treatment, Microstructure, Mechanical properties