Effect of layer band and heterogeneity of microstructure on electrochemical dissolution of laser solid formed Ti-6Al-4V alloy Available to Purchase

Laser solid forming (LSF) is a newly advanced additive manufacturing technique which offers a big potential in efficiency and cost-savings for fabricating aerospace titanium alloys components with high performance. In this research, the macro-/micro-structure and electrochemical dissolution features of Ti-6Al-4V alloy produced by LSF and forging were investigated. The LSFed Ti-6Al-4V that included as-deposited and annealing heat treatment (HT) conditions contains three periodically distributed microstructural morphology, including fine microstructure zone (FMZ), coarse microstructure zone (CMZ), and layer band. All zones of the microstructural morphology in entire deposit is constituent of α-laths and small amount of remained β phase. An alternating structure of coarse and fine microstructures were observed along the deposition direction in the deposit. Layer bands generally spaced above the CMZ. The CMZ is constituent of slightly coarser basket weave structure than the FMZ. However, the layer bands present the microstructure of colony α. Additionally, the α-laths are slightly coarsened by HT, and simultaneously results in a more homogeneous microstructure comparing with the as-deposited microstructure. Moreover, the forged Ti-6Al-4V possesses the most homogeneous microstructure and largest size of α phase. Simultaneously, a variety of dissolved morphology features were observed in the three types of samples after potentiodynamic polarization tests. The order of surface macro-smooth level of these samples is forged>HT>as-deposited. For LSFed Ti-6Al-4V, the FMZs and layer bands present a faster electrochemical dissolution rate than that the CMZs. Consequently, the uneven surface is revealed by the distinct dissolution rate of different microstructural zones at the same LSFed sample. The forged Ti-6Al-4V alloys present uniformly dissolved behavior attributed to their homogeneity of microstructure. The elimination of layer bands and homogenization of the microstructure of the LSFed Ti-6Al-4V are of great significance for improving the surface quality during electrochemical machining (ECM).