Effects of shock pressure and grain size on spall behavior of a HfNbZrVTi body-centered-cubic high-entropy alloy

Under shock-wave loading, spall failure induced by release stress is a dominant damage mode in metallic materials. Elucidating the spall behavior of high-entropy alloys (HEAs) under shock-wave loading is crucial for its potential application in extreme dynamic environments. Here we conduct plate impact experiments under different shock pressures on a HfNbZrVTi body-centered-cubic (BCC) HEA with two different grain sizes. We find that spall strength increases with elevated shock pressure and larger grain size, whereas the degree of damage diminishes with increasing grain size. Under shock pressures of approximately 5 GPa and 10 GPa, the 165 μm-grained alloy exhibits spall strengths of 3.3 GPa and 4.0 GPa, and degree of damage of 2.0% and 13.5%, respectively. By comparison, the 313 μm-grained alloy shows higher spall strengths of 3.6 GPa and 4.3 GPa and lower degree of damage of 0.6% and 6.5%. The increase in shock pressure accelerates micro-crack propagation to main crack, and facilitates the development of kink bands. As an important deformation mode, kink banding can promote crack branching, suppress local spall damage and improve the spall strength. In addition, larger grain size reduces growth rate of micro-voids, yet also shifts damage mode from micro-void coalescence-dominated to micro-void growth-dominated, which therefore reduces spall damage and enhances spall strength.