SiC p/Ti6Al4V functionally graded materials produced by laser melt injection

Abstract

With a well-controlled laser melt injection (LMI) process, for the first time the feasibility is demonstrated to produce SiC particles (SiC p) reinforced Ti6Al4V functionally graded materials (FGMs). SiC p are injected just behind the laser beam into the extended part of the laser melt pool that is formed at relatively high beam scanning velocities. The process allows for the minimization of the decomposition reaction between SiC p and Ti6Al4V melt, and also leads to FGMs of SiC p/Ti6Al4V instead of a homogeneous composite layer on Ti6Al4V substrates. An injection model is designed based on the temperature/viscosity field of the laser pool for a deeper understanding of the mechanism of formation of the FGMs with LMI. The model is based on finite element calculations of the temperature field in the melt pool, physical considerations of the LMI process and it is supported by experimental observations. Three types of reaction layers are observed around SiC p, namely a thin monocrystalline TiC layer, a cellular polycrystalline TiC layer and a thick mixed layer of TiC with Ti 5Si 3. Among them, only the monocrystalline TiC layer exhibits particular orientation relationships (ORs) to the SiC p lattice, i.e. (111) TiC∥(0001) SiC and 〈110〉 TiC ∥〈1 1 ̄ 00〉 SiC or (111 ) TiC ∥(10 1 ̄ 2 ) SiC and 〈1 1 ̄ 0〉 TiC ∥〈1 2 ̄ 10〉 SiC . These two kinds of TiC reaction layers act as a barrier against the interfacial reaction and its swift formation during rapid cooling hinders the dissolution of SiC p in the Ti-melt.