Microstructure evolution and mechanical properties of functionally graded Fe–8Cr-xNi alloys fabricated by spark plasma sintering

Abstract

Novel Fe–8Cr-xNi (x ε 0–9.0 wt%) functionally graded materials (FGMs) with strength gradient characteristics of ductile core and strength surface were fabricated by spark plasma sintering (SPS). Microstructure evolution and strength-toughness matching mechanism of the graded Fe–8Cr-xNi (x ε 0–9.0 wt%) alloys was investigated. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (HR-TEM) reveal two representative areas in the microstructures evolve, i.e., an α-Fe, Ni and an α-Cr enriched white region and a remaining γ-Fe, δ-Fe and Ni enriched black region. The strength-toughness matching mechanism of composition gradient Fe–8Cr-xNi (x ε 0–9.0 wt%) alloy was that the strength of materials increased due to the formation and remain of austenitic FCC γ-Fe phase prometed by increasing Ni content, and the metallurgical bond formed among the particles. The Fe–8Cr-9.0Ni gradient layer on the surface of the SPSed gradient sample shown a highest yield strength of 150 ± 24.1 MPa and a high wear resistance of the gradient sample, and the Fe–8Cr-6.7Ni gradient layer on the middle of the sampe shown a particularly excellent ductility of 15 ± 2.1% and played a role in alleviating crack. The compressive strength of the Fe–8Cr-xNi (x ε 0–9.0 wt%) -C2 FGM alloys reaches up 3385 ± 6 MPa, and the microhardness can reach a gradient distribution of 230 ± 2, 345 ± 2 and 392 ± 1 HV from the bottom layer to the upper layer. This work provides a reliable theoretical and experimental basis for the design and application of composition gradient Fe–8Cr-xNi (x ε 0–9.0 wt%) alloys with ductile core and high strength and wear resistance surface synthesized by SPS technology.