Evolution of microstructure and mechanical properties of Ti-based metal-matrix composites during high-pressure torsion

Abstract

The microstructure and microhardness evolution of a Ti/TiB and Ti-15(wt.%)Mo/TiB metal-matrix composites (MMC) during high-pressure torsion (HPT) at 400 °C was studied. The composites were fabricated by spark plasma sintering of either hcp α-Ti with 10 wt.% of TiB2 or Ti with 13.5 wt.% of Mo (resulted in a bcc β-Ti matrix) and of 10 wt.% TiB2 powders mixtures at 1000 or 1200 °C, respectively. An increase in the dislocation density, a considerable decrease in the grain size in both hcp or bcc Ti matrix, and shortening of TiB whiskers were observed in the microstructures of the composites during HPT. After five revolutions, a nanostructure with a (sub) grain size of ∼30 or ∼55 nm was produced in Ti or Ti-15Mo matrix, respectively. The microhardness increased with strain from 452 HV in the initial state to 520 HV after 5 revolutions for Ti/TiB MMC and from 575 to 730 HV for Ti-15Mo/TiB MMC. The contributions of various hardening mechanisms to the composites were evaluated.