Microstructure modulation and mechanical property improvement of TiC/Ti–5Al–5Mo–5Zr–6Cr composites by hot rolling

Abstract

Hot rolling has been used to solve the problems of uneven distribution of reinforcing phases in titanium matrix composites and the difference in mechanical properties between the reinforcing phases and the matrix. And the research mainly focuses on the α+β phase region. In this study, TiC/Ti–5Al–5Mo–5Zr–6Cr composites were hot-rolled in 900 °C with deformation levels of 50%, 60%, 70%, and 80%. The microstructure evolution, mechanical properties, the mechanism of dynamic recrystallization, and strengthening mechanisms of the rolled composite sheets were systematically investigated. Hot rolling resulted in a reduction of the grain size of the composites. Specifically, at 80% deformation, the average grain size was 35.65 μm. Textures evolved during rolling, and the primary textures were {110}<110> and {112}<110>. During rolling, the deformation mechanisms transformed with increasing deformation degree, evolving from dislocation slip to dynamic recovery and ultimately to dynamic recrystallization. During rolling, TiC particles facilitated the DRX of TiC/Ti–5Al–5Mo–5Zr–6Cr composites through hindering dislocations, promoting sub-grain boundary growth, and serving as nucleation sites for recrystallization. The DRX mechanism was determined to be the sub-grain boundary nucleation mechanism. Mechanical property tests demonstrated that hot rolling improved both the strength and plasticity of the composites. Specifically, at 80% deformation, the strength reached 943 MPa, while the elongation was 8.2%. Compared to the as-cast sample, the strength increased by 9.2%, and the elongation increased by 90.7%, demonstrating a favorable strength-plasticity balance. The strengthening mechanisms of the composite sheets were attributed to grain refinement, solid solution strengthening, second phase strengthening, and heterogeneous structure strengthening.

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