High temperature deformation behaviour and recrystallization mechanism of TiC/Ti6Al4V gradient material fabricated by laser directed energy deposition

Abstract

Metal-ceramic gradient materials are of considerable interest due to their unique capability to integrate the ductility of metals with the mechanical strength and high-temperature resistance of ceramics, thereby reducing the risk of cracking induced by thermal stress. In this article, TiC/Ti6Al4V gradient materials were prepared through the laser directed energy deposition (LDED) process. Subsequently, high-temperature compression tests were performed at various temperatures to investigate the deformation behaviour and recrystallization mechanism of the gradient materials. The Zener-Holomon constitutive equation was then used to calculate the gradient material at 750–900 °C and 0.001–0.1 s−1 to obtain a deformation activation energy of 362.36 KJ·mol−1. The EBSD was used to analyze the microstructural evolution of the gradient material. The results indicate a significant reduction in the average grain size of the specimens after high-temperature compression, and a more random crystal orientation due to the occurrence of dynamic recrystallisation (DRX). The primary softening mechanism of TiC/Ti6Al4V gradient materials is discontinuous dynamic recrystallisation, with TiC primarily affecting the nucleation of discontinuous dynamic recrystallisation (DDRX) and the subsequent grain growth. The nucleation becomes easier with increasing TiC content. However, the TiC hinders the migration of grain boundaries, resulting in a smaller DDRX grain size. After high-temperature compression, the main slip system of the crystal is converted from Pri to Bas. Pyr is difficult to activate due to its high critical resolved shear stress.