Effect of Technological Parameters of Selective Electron Beam Melting on Chemical Composition, Microstructure, and Porosity of a TiAl-Alloy of Ti-Al-V-Nb-Cr-Gd System.

The effect of the linear energy input (EL), varied from 120 to 300 J/m due to a change in the electron beam current (I) from 4 to 20 mA and the scanning speed (v) from 2 to 8 m/s, on residual porosity, aluminum content and local distribution, and microstructure has been studied on as-built samples of a new six-component intermetallic beta-solidifying TiAl alloy Ti–44.5Al–2V–1Nb–2Cr–0.1Gd, at.% (Ti–31.0Al–2.5V–2.5Nb–2.5Cr–0.4Gd, wt.%) produced by selective electron beam melting (SEBM). It has been established that layer-by-layer processing at EL ≥ 250 J/m allows producing dense material with a residual porosity of less than 1 vol.%. It has been revealed that an increase in EL results in the average aluminum content reduction by ΔAl = 1.7 at.% at EL = 300 J/m and distribution inhomogeneity thereof in the vertical cross-section of the samples (building direction Z), with the formation of layered structure consisting of Al-enriched and Al-depleted alternating layers. It has been shown that a fine-grained equiaxed microstructure is formed after processing at EL < 200 J/m and I < 8 mA; an increase in EL and I results in the formation of columnar grains, predominantly located in Al-depleted layers, as well as an increase in their size and volume fraction. After all studied SEBM modes, both columnar and equiaxed grains exhibit lamellar intragranular ( γ + α 2 ) colonies with γ and β0/B2 phases at grain boundaries, which corresponds to the sequence of phase transformations predicted by thermodynamic simulation. [ABSTRACT FROM AUTHOR]