Effect of in-situ cooling during pressure and frictional deformation on mechanical and metallurgical properties of Ni-based functionally graded material developed by wire arc additive manufacturing

In this article, Ni-Cr-Mo-based functionally graded material with a designed composition is successfully fabricated using the wire arc additive manufacturing process. The effect of the gradual variation of Ni, Cr and Mo concentration and the effect of high-temperature high-pressure deformation (HTHPD) in the different cooling environments on the morphology, microstructure, and mechanical properties along the gradient direction of the manufactured functionally graded materials (FGMs) have been investigated. With increasing Cr and Mo content from the bottom to the top, the FGM exhibits a gradual increase in tensile strength and microhardness. The hardness varies from 114 to 230, 130 to 205 and 164 to 256 HV for as-deposited, HTHPD with air-cooled (HTHPD-A) and HTHPD with water-cooled (HTHPD-W) samples, respectively, from bottom to top. Similarly, the average tensile strength is achieved at 793, 715 and 875 MPa in as-deposited, HTHPD-A and HTHPD-W samples, respectively. The microstructural examination of fabricated samples shows the columnar grain produced in as-deposited samples, deformed during the HTHPD process and recrystallized grains with orientation along the deformation direction has been formed.