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 beta 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 beta phase in as-received mill-annealed Ti-6Al-4V decreased with increasing number of thermal cycles at the heating and cooling rates of 50 degrees C/s, while the vanadium (V) content in the beta phase increased with decreasing beta phase formation temperature. The distribution of the V content in the beta 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 beta phase. The formation mechanism of the beta phase was discussed based on the experimental observations.