Microstructural evolution in laser-deposited multilayer Ti-6Al-4V builds: Part I. Microstructural characterization

The macro and microstructure of laser-deposited Ti-6Al-4V has been investigated to determine the evolution of unique microstructural features in mutilayer builds. The macro and microstructures exhibited in the build include large, columnar prior-beta grains, a gradient in the individual alpha-lath thickness between the deposited layers, and the presence of layer bands within each layer, except for the last three layers deposited. The layer band consists of a colony Widmanstätten alpha morphology, while the nominal microstructure between layer bands exhibits a basketweave morphology. Optical microscopy, hardness, and composition measurements were used to determine that the layer-band and gradient morphologies are resultant from the complex thermal history the build experiences and not a result of segregation or oxidation. The gradient alpha and layer-band morphologies form in layer n after the deposition of layer n+3.