Transition mechanism of strain rate sensitivity in B₄C/Al composites at elevated temperatures

Metal/ceramic composites (MCCs) are promising lightweight materials for extreme service conditions involving high temperatures and dynamic loading. However, studies on the mechanical response of MCCs over wide temperature and strain rate ranges are scarce. Furthermore, the failure mechanisms and strain rate sensitivity of MCCs at high temperatures and high strain rates remain unclear. In this work, static and dynamic compression tests were conducted on B₄C/6061Al MCCs with different ceramic volume fractions (40%, 50%, 60%, 75%) at temperatures from 25 °C to 300 °C and strain rates from 10⁻³ s⁻¹ to 600 s⁻¹. The results show that increasing the B₄C content significantly enhances the quasi-static maximum compressive strength, while the quasi-static strength decreases markedly at elevated temperatures, with a reduction of 45–52% at 300 °C. Composites containing 40% and 50% ceramic exhibit positive strain rate sensitivity across the entire temperature range under dynamic loading. Notably, the strain rate sensitivity of composites with 60% and 75% ceramic content undergoes a transition with temperature and ceramic volume fraction. This transition is attributed to the competition between thermal softening and strain rate strengthening, as well as the restriction of matrix flow by the rigid skeleton formed at high ceramic volume fractions. This study provides theoretical support for the engineering application of MCCs in extreme environments.