MICROSTRUCTURAL ANALYSIS AND NANOINDENTATION CHARACTERIZATION OF TI-6AL-4V PARTS FROM ELECTRON BEAM ADDITIVE MANUFACTURING

In this study, the microstructure analysis and nanoindentation characterization from electron beam additive manufacturing (EBAM) were experimentally investigated. Specimens with different build heights of an EBAM built part were tested for microstructure observations by optical microscopy and scanning electron microscopy. The correspondent Young's modulus and hardness were measured by nanoindentation. Columnar prior 13 structure is found along the build direction from the X-plane, while the Z-plane is characterized by equiaxed grains and fine Widmanstatten (alpha+beta) structure. The microstructure varies along the build height: the top layers present finer columnar prior beta grains and inside Widmanstatten (alpha+beta) structure, while the bottom layers show bigger percentage of alpha' martensitic phase owing to the very high cooling rate. Nanoindentation tests identify the highest Young's modulus of 127.9 GPa and hardness of 6.5 GPa from the top layers of Z-plane. The Young's modulus and hardness of the middle layers are lower because of the repeated heating. The Z-plane shows higher mechanical properties compared to that of the X-plane. The enhancement of modulus and hardness of the Ti-6Al-4V alloy could be attributed to the strengthening phase of a' and fine microstructure.