Hydrogen induced microstructure evolution of titanium matrix composites

The effect of melt hydrogenation on microstructure evolution of Ti-6Al-4V matrix composites was investigated in this study. Molten alloy was hydrogenated with a mixture of hydrogen and argon, and reinforced at 5% total volume fraction with a 1:1 mol ratio mixture of TiB and TiC particles. Microstructure of as cast composites showed hydrogen induced more TiB whiskers with higher length-diameter ratio (LDR), because hydrogen accelerated atomic diffusion and then increased growth rate of TiB whiskers. Hot compression results indicated hydrogen reduced peak flowing stress. Microstructure of as compressed composites indicated hydrogen encouraged decomposition of residual lamellas. Hydrogen eliminated most cracks and holes along the interface between ceramic particles and matrix. Compared with unhydrogenated composites, the original ceramic particles in hydrogenated composites were fragmented into smaller pieces after compression. Electron back-scattered diffraction and transmission electron microscopy results indicated hydrogen increased volume fraction of dynamic recrystallization (DRX). And hydrogen decreased the density of dislocations nearby the interface.