Impact-resistance mechanism of gradient ceramic/high entropy alloy composite structure

The gradient ceramic/high-entropy alloy (HEA) composite combines the high hardness of ceramics and the high toughness of metal alloys with a gradient spacious distribution. It is designed to improve the penetration resistance as a promising protective material with high specific stiffness and strength. In this work, the equivalent model of gradient ceramic/HEA composite material is established by adopting layered structure design, and the material properties of gradient material with different ceramic volume content are calculated. Combined with stress wave theory and numerical simulation of the separated Hopkinson pressure bar, the stress wave propagation under impact is studied for the gradient ceramic/HEA composite and the ceramic/HEA double-layered material. The anti-penetration mechanism is scrutinized. The interlaminar wave impedance increase gradually in the gradient composite but smaller than in double-layered material. The coefficient of reflected stress wave in the gradient composite is much smaller than that of the double-layered material. With the increment of ceramic volume content, the reflected wave amplitude in the gradient composites gingerly decreases. Opposed to the distinct interlayer interfaces that discontinue stress waves in the double-layered material, the internal interface of the gradient composite is much more tranquil and modulate the stress wave smoothly and synchronically with the gradient of composite. The smoothened internal interface is the key and the mechanism the better impact resistance of the gradient material. Our results might be beneficial in material design of the protective materials for impact resistance.