Fabrication of functionally graded materials from a single material by selective evaporation in electron beam powder bed fusion

Based on electron beam powder bed fusion, a novel process, called selective evaporation, is introduced, which could fabricate FGMs from a single material powder by irradiating different electron beam energy onto different locations in the powder bed to evaporate varying magnitude of aluminum element from a raw Ti47Al2Cr2Nb powder. A three dimensional FGMs of the (alpha + ss) titanium alloy, with the aluminum ratio less than 10%, encapsulated by the (alpha(2) + gamma) TiAl alloy, with the aluminum ratio keeping 45%, were successfully produced by this process. A low energy multiple scan strategy was utilized to facilitate the irradiation of high energy to selected regions without inducing curling of the surface. The aluminum diffusion from the adjacent (alpha(2) + gamma) phases was also considered and required a higher energy input to compensate the aluminum element restoring. The microstructure and micro-hardness of the FGM structure, which consists of (alpha + ss)/(alpha(2) + alpha + ss)/(alpha(2) + gamma) phases, were investigated. Moreover, a customized pattern of the letters TH was created using the (alpha + ss) titanium alloy in the (alpha(2) + gamma) TiAl alloy to demonstrate the capability of this presented technique to fabricate complex FGM shapes.