Characterization of interfacial transition zone of functionally graded materials with graded composition from a single material in electron beam powder bed fusion

Abstract Electron beam selective melting (EBSM), is powder bed fusion additive manufacturing (AM) technique by adding materials layer upon layer. The capacity of EBSM to fabricate complex and multi-functional parts has made it a realm of great interest for researchers in the domain of science. However, during the fabrication of functionally graded materials (FGMs) with graded composition by EBSM using at least two different materials, it is difficult to separate and reuse these materials after the fabrication. Additionally, it is difficult to vary the powder composition within a layer to fabricate a horizontal graded structure. In this research, an element evaporation concept based on electron beam powder bed fusion, is presented for fabricating one-dimensional (1D) FGMs of (α2 + γ) TiAl alloy/(α + β) titanium alloy from a single material powder. By irradiating different sub-regions of the powder bed with electron beam energy input of different magnitude to greatly reduce the relative atomic ratio of aluminum from 47% to less than 10%, the 1D FGMs structures with (α2 + α + β) phases in the interfacial transition zone (ITZ) were successfully produced. Since the microstructure of the ITZ has a significant effect on mechanical properties for the 1D FGMs, three different overlap scan distances (0.5, 1.0 and 2.0 mm), which result in different ITZs, were utilized for evaluating the microstructure of the ITZ and resulting mechanical properties. The results showed that no defects were found in the specimens of any overlap distance. Moreover, the width of the ITZ increases as the overlap scan distance, and the tensile strength decreases with the overlap scan distance.