The reverse transformation mechanism of β phase and its stability of Ti-6Al-4V alloy fabricated via laser powder bed fusion

The laser powder bed fusion manufactured Ti-6Al-4V alloy predominantly consists of alpha' martensite, resulting in excellent strength but limited ductility, hinders widespread application. Therefore, it is crucial to achieve the decomposition of alpha' martensite and improve the ductility. However, the reverse transformation behavior and its mechanism of the beta phase, as well as its stability remain unclear. Our findings demonstrate that the reverse transformation behavior of the beta phase follows a diffusion -controlled process. The decomposition of alpha' martensite into alpha + beta initiates at approximately 550 degrees C, while the transformation from alpha to beta phase occurs around 870 degrees C. Increasing temperature leads to an increase in reverse -transformed beta phase. The retention of these reversetransformed beta phases at room temperature also depends on their stability, which exhibits a significant correlation with V element partitioning. Additionally, this study reveals a critical temperature (840 degrees C) at which the maximum volume fraction (18.6 %) of retained beta phase is obtained, exhibiting exceptional mechanical properties, particularly the uniform elongation surpassing those observed in an as -printed microstructure of LPBF-ed Ti-6Al-4V alloy.