Effects of the cooling rate on mechanical properties and microstructure of near-α Ti-6Al-3Zr-2Nb-Mo alloy

To quantitatively understand the influence of the cooling rate on the microstructural evolution and mechanical properties of titanium alloy forgings, we investigate the mechanical properties and microstructures of Ti-6Al-3Zr-2Nb-Mo (Ti6321) in different cooling mediums by combining mechanical tests, optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results revealed that with the increase of the cooling rate, the width of the secondary alpha (alpha s/alpha)' phase decreased; therefore, the ultimate tensile and yield strengths increased. Furthermore, the impact property of alloy was decreased, which is attributed to the decreased volume fraction of the primary alpha (alpha(p)) phase. Based on in-depth structural characterizations and mechanical evaluations, the quantitative link between the cooling rate and the width of alpha s/alpha ' phase, and a quantitative description of the relationship between the YS and the width of alpha s/alpha ' phase are established. Our work provides theoretical guidance for the heat treatment of thick forging of Ti6321 for industrial production.