The Martensitic Transformation and Mechanical Properties of Ti6Al4V Prepared via Selective Laser Melting.

This article investigated the microstructure of Ti6Al4V that was fabricated via selective laser melting; specifically, the mechanism of martensitic transformation and relationship among parent ß phase, martensite (α') and newly generated ß phase that formed in the present experiments were elucidated. The primary X-ray diffraction (XRD), transmission electron microscopy (TEM) and tensile test were combined to discuss the relationship between α', ß phase and mechanical properties. The average width of each coarse ß columnar grain is 80⁻160 µm, which is in agreement with the width of a laser scanning track. The result revealed a further relationship between ß columnar grain and laser scanning track. Additionally, the high dislocation density, stacking faults and the typical ( 10 1 ¯ 1 ) twinning were identified in the as-built sample. The twinning was filled with many dislocation lines that exhibited apparent slip systems of climbing and cross-slip. Moreover, the α + ß phase with fine dislocation lines and residual twinning were observed in the stress relieving sample. Furthermore, both as-built and stress-relieved samples had a better homogeneous density and finer grains in the center area than in the edge area, displaying good mechanical properties by Feature-Scan. The α' phase resulted in the improvement of tensile strength and hardness and decrease of plasticity, while the newly generated ß phase resulted in a decrease of strength and enhancement of plasticity. The poor plasticity was ascribed to the different print mode, remained support structures and large thermal stresses.