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

Abstract

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 (α + β) titanium alloy, with the aluminum ratio less than 10%, encapsulated by the (α2 + γ) 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 (α2 + γ) 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 (α + β)/(α2 + α + β)/(α2 + γ) phases, were investigated. Moreover, a customized pattern of the letters “TH” was created using the (α + β) titanium alloy in the (α2 + γ) TiAl alloy to demonstrate the capability of this presented technique to fabricate complex FGM shapes.