Superplastic deformation behavior of 5 vol% (TiB_w+TiC_p)/Ti matrix composite sheets with lamellar microstructure

Superplastic forming is considered a highly efficient technique for shaping intricate components from titanium matrix composites (TMCs). In this work, high-temperature TMCs with 5 vol% (TiB_w + TiC_p) reinforcements underwent superplastic tensile tests at various temperatures and strain rates. The results demonstrated that at all deformation temperatures (900 °C–1050 °C) and strain rates (5 × 10⁻³ s⁻¹ to 10⁻⁴ s⁻¹), the elongation of composite sheets surpassed 100%. The strain rate of 10⁻³ s⁻¹ and a temperature of 1000 °C were found to yield the maximum elongation of 328.1%. At 900 °C, the matrix grains maintain a lamellar morphology during the main stage of deformation, and dynamic recovery (DRV) is the primary mechanism of matrix softening. At 1000 °C, wide-range dynamic recrystallization (DRX) takes place, and grain boundary slip coordinated by grain rotation is the main mechanism of deformation. At 1050 °C, the matrix grains undergo DRX and grow rapidly by migration, and the number of grain boundaries decreases dramatically, resulting in poor superplastic qualities. In the early stages of superplastic deformation, micropores sprout at the triple grain boundaries and at the interfaces between the reinforcements and the matrix. As the deformation proceeds, the micropores extend along the tensile direction and connect with each other to form cavity stringers (CS). The distance between the CS rapidly narrows as the stretching process continues, and eventually the CS links horizontally to form cavity coalescence (CC). Micropore dilatation around the reinforcements causes debonding and cavitation, leading to material failure.