Microstructure and mechanical properties of additively manufactured Ti6Al4VxCryNi alloy

Abstract

This paper describes development of multi-layer deposition of Ti6Al4V added with 5 at% of Cr, 5 at% of Ni, and 2.5 at% of each Cr and Ni by μ-plasma powder arc additive manufacturing process. It presents findings on their microstructure, porosity, evolution of phases, microhardness, tensile strength, ductility, fracture morphology, fracture toughness, and abrasion resistance. Phase evolution found that α/α’-Ti and β-Ti phases are formed in all the alloys, intermetallic phase Cr₂Ti evolved in Ti6Al4V5Cr and Ti6Al4V2.5Cr2.5Ni alloys whereas intermetallic phase Ti₂Ni is formed in Ti6Al4V5Ni alloy. Their microstructure revealed that addition of chromium and nickel refined grains of their α-Ti and β-Ti phases. Elemental composition of the evolved phases found that at% of chromium, nickel, and vanadium in β-Ti phase is more than the α-Ti phase of the developed alloys. It enhanced their ultimate tensile and yield strength, and microhardness but reduced ductility. It changed the fracture mode from ductile to a combination of ductile and brittle mode possessing large size dimples, micropores, and cleavage facets. It is due to solid solution strengthening, evolution of intermetallic phases Cr₂Ti and Ti₂Ni, and grain refinement of β-Ti and α-Ti phases. Enhanced microhardness and presence of intermetallic phases improved fracture toughness and abrasion resistance of the developed alloys thus imparting them higher resistance to propagation of cracks and abrasive wear.