Microstructure and mechanical performance tailoring of Ti-13Nb-13Zr alloy fabricated by selective laser melting after post heat treatment

Abstract

The poor ductility of the selective laser melting (SLM)-fabricated parts may lead to the limitation of its applications. Therefore, in the present work, four types of post heat treatments of SLM-proceeded Ti-13Nb-13Zr were performed to tailor the microstructure and mechanical performances. In the super-transus heat treatment, the morphologies of grains are transformed from columnar to equiaxed because of the strain-induced grain boundary migration mechanism (SIBM), while in the sub-transus process, the columnar β grains are remained. In the water quenching process, high resolution transmission electron microscopy analysis revealed that the collapse of the partial layers in the (110) planes and [111] direction results in the original stacking sequence from …ABCABC… to a new stacking sequence …AB’AB’… and an w structure is formed, resulting in the highest ultimate (1155 ± 30 MPa), yield strength (874 ± 30 MPa) and unfortunately the lowest ductility (2.3 ± 0.2%). In the air cooling process, as the heat temperature declines from 750 °C to 650 °C, the electron back-scattered diffraction results show that the coarse and irregular α grains with strong {0001} and {211¯0} orientations are gradually transformed into fine acicular α crystals with the dominated {0001} orientation. In this condition, the residual stresses were released and the fine microstructure was largely retained, thus the high yield strength is maintained (799 ± 10 MPa) and the ductility is improved (7.2 ± 0.3%).