Fabrication of Ti-6Al-4V alloy powder by a novel sintering-deoxygenation process

Abstract

Given the high cost of fabricating the Ti-6Al-4V alloy powder by the traditional hydriding-dehydriding and atomization methods, a novel sintering-deoxygenation process was proposed and studied in this research. With the help of the developed deoxygenation treatment, value-added raw materials such as Ti sponge can be substituted by low-cost and low-grade materials with high oxygen content. In addition, sintering in a solid state saves a significant amount of processing energy compared to alloying above the melting point of Ti in the conventional alloy production process. This paper prepared six sintering precursors with different initial compositions and oxygen contents using the low-valued raw materials of crude titanium, crude vanadium, V2O3, Al powder, and Al2O3 powder. These precursors' sintering performances on shrinkage, phase composition, microstructure, and porosity were investigated. The results show that the sintering shrinkage is positively correlated with the sintering temperature and holding time and is also affected by the raw materials. The pellet made by mixed crude titanium and AlV master alloy showed the largest shrinkage and the densest bulk. The various combinations of the raw materials led to the changes in the oxygen contents in the precursors, the alpha-beta phase ratio, and the shift of the diffraction peaks of the α-phase. The dissolving of the AlV master alloy and the formation of the Ti3Al intermediate phase took place during sintering due to diffusion. Sintering at 900–1000 °C is critical for elemental diffusion and densification, and sintering at higher temperatures is decisive for microstructure homogenization and further densification. Using the hydrogen-assisted Mg deoxygenation method, all the sintered samples could be treated to an oxygen level of around 0.4 wt% regardless of oxygen content in precursors. The contents of Ti, Al, V, and Fe in the obtained Ti-6Al-4V powders met the requirements of GB/T 34486-2017. This research has demonstrated the feasibility of fabricating Ti-6Al-4V alloy powder by the novel sintering-deoxygenation process.