Shock compression and spallation of TiZrHf refractory multi-principal element alloy

Abstract

The micro-structure, dynamical compression property and spallation behaviour were investigated in TiZrHf refractory multi-principal element alloy (RMPEA) with a single Hexagonal Close-Packed (HCP) phase, considering the spatial heterogeneity between central and peripheral regions. Based on a single-stage gas gun, plate impact experiments were driven with impact velocities ranging from 327 to 710 m·s⁻¹, and results showing the Hugoniot data were c₀ = 3.55 km·s⁻¹ and s = 0.97, while the spall strength σ_spall increased from 1.92 GPa to 2.01 GPa. The shock-response behaviour was accurately predicted using the equation of state derived from a cold-energy mixture model. Microstructural analysis of recovered samples revealed that voids nucleated preferentially at grain boundaries, especially at triple junctions of twin boundaries. As the impact velocity increased, the damage mode shifted from intergranular to a mix of intergranular and intragranular, eventually becoming predominantly intragranular. Additionally, under impact loading, multiple cross-slip and <c+a> type pyramidal dislocations were activated, forming dislocation loops and walls. Moreover, interactions between dislocations and grain boundaries promoted stacking faults (SF) activation, twin formation and HCP-to-Face-Centered Cubic (FCC) phase transformation. Additionally, the self-activated twinning mechanism facilitated the formation of low-energy twins under high strain rates, as stacking fault energy (SFE) became dominant over short-range order (SRO). Comparative data on various MPEAs showed a negative correlation between the yield strength to spall strength ratio (σ_y/σ_spall) and valence electron concentration (VEC).