The Formation of $$ \left\{ {10\bar{1}2} \right\} $$ Deformation Twin in Hybrid TiB-TiC Reinforced Titanium Matrix Composites

Abstract

Deformation twins play a significant role in the plastic deformation of titanium matrix composites and improve their ductility. In this work, $$ \left\{ {10\bar{1}2} \right\} $$ deformation twins nucleated in the parent grains with a hard orientation of prismatic slip and changed the local orientation become a soft orientation, resulting in a good balance between high strength (yield strength of 1068 ± 9 MPa and ultimate tensile strength of 1167 ± 1MPa) and high ductility (elongation of 8.7 ± 0.2 pct) at room temperature for hybrid TiB-TiC reinforced Ti-6Al-4V matrix composites. TiB, TiC and grain boundaries worked as a barrier to dislocation mobility, and resulted in different dislocation substructures distributing around the short TiB fibers and TiC particles. The strain incompatibility resulted in a high local stress concentration which promoted twin nucleation and influenced twin propagation. The nonuniform strain caused a stress gradient inside the grains, and the steep stress gradient hindered the twin propagation. Low stress was not enough to drive the dislocation slip of the twins and dislocation decomposition at the twin tips; thus, the growth of the deformation twins stopped in the parent grains.