Superior hot workability of (TiB+TiC)/Ti-6Al-4V composites fabricated by melt hydrogenation

Abstract

In order to improve the poor hot workability of titanium matrix composites (TMCs), an advanced melt hydrogenation method was introduced in this study. The (TiB+TiC)/Ti-6Al-4 V composites were fabricated by melt hydrogenation which was directly melting alloys in gas mixture of H2 and Ar. Microstructure of as-cast TMCs indicated that melt hydrogenation increased the length of TiB whiskers and aggravated the clustering of reinforcements at primary β grain boundaries, which was due to the increased overheat on melt surface. Hot compression results indicated melt hydrogenation improved the hot workability of TMCs in (α + β) phase region, and the peak stress was reduced from 371 to 271 MPa at 800 °C/1 s−1 and from 119 to 60 MPa at 900 °C/0.01 s−1, respectively, which expanded the optimal hot processing window. Microstructure after hot deformation showed that the proportion of DRX grains was increased from ∼56% to ∼81%, which was mainly attributed to the accelerated migration of DRX grain boundary and the decreased density of dislocations, which was due to the dislocation consumption by DRX formation and the improved mobility of dislocations. Therefore, the improvement of hot workability resulted from the formation of more DRX grains and enhanced mobility of dislocations.