The β phase evolution in Ti-6Al-4V additively manufactured by laser metal deposition due to cyclic phase transformations

This paper investigates the evolution of the β phase in laser deposited Ti-6Al-4V via track of the cyclic phase transformation processes by dilatation experiments and characterization of the laser deposited microstructures by transmission electron microscopy (TEM) and an energy dispersive X-ray spectrometer (EDS). The formation temperature of the β phase in as-received mill-annealed Ti-6Al-4V decreased with increasing number of thermal cycles at the heating and cooling rates of 50 °C/s, while the vanadium (V) content in the β phase increased with decreasing β phase formation temperature. The distribution of the V content in the β phase in the laser deposited Ti-6Al-4V showed an increasing gradient from the top layer (i.e., the last deposited) to the fourth layer from the top, which is related to the thermal cycles and the formation temperature of the β phase. The formation mechanism of the β phase was discussed based on the experimental observations.