Effects of shock stress and microstructure on shock response of Al-Hf reactive materials

Reactive materials are functional structural materials that balance structural strength and reactivity, and their shock response is greatly influenced by the characteristics of reactive components. This article aims at understanding the shock compression and reaction of Al-Hf reactive materials with two values of the Al-Hf particle size ratio alpha (1 mu m:10 mu m and 10 mu m:10 mu m), which were prepared through hot pressing with a compactness (the ratio of density to theoretical maximum density) greater than 96.46%. The free surface velocity of the materials was measured in the impact velocity range of 279-865 m/s. The Hugoniot elastic limit (HEL), spall strength, and Hugoniot relationships under shock stresses of 1.83-14.46 GPa were analyzed on the basis of the microstructure and phase change. Continuous Al phase was formed in the sample with alpha = 0.1, while more Hf-Hf contact and crushed Hf appeared in the sample with alpha = 1. The velocity profiles presented clear signs of the linear growth to the HEL, the slow increase to the peak, and the subsequent pullback, indicating the transition from elastic to plastic and spall behavior. The HEL fluctuated significantly with increasing shock stress, while the spall strength first increased and then decreased. The sample with a continuous Al phase exhibited a lower HEL (0.52-0.97 GPa) and higher spall strength (0.31-0.46 GPa). The microstructure had a significant effect on the shock induced chemical reaction of the materials. Shock velocity was linearly related to particle velocity for the alpha = 0.1 sample, while a notable quadratic growth was observed for the alpha = 1 sample owing to self -reactions under the lower shock stress (5.32 GPa). The intermetallic Hf4Al3 observed in the recovered product by X-ray diffraction further verified the phenomenon.