Microstructure and mechanical properties of hot-rolled ZrB alloys

The microstructure, mechanical property behavior, and fracture characteristics of Zr-χB alloys (χ=0, 0.05, 0.3, 0.8 wt%) obtained by casting and hot-rolling were investigated. Microstructural observation indicated that the dendritic equiaxed prior-β grain morphology was slightly elongated after hot-rolling treatment. The widths of the α lath of all the hot-rolled Zr-χB alloys were similar, and the length of the α lath decreased with increasing boron concentration. Tensile test results showed that the improved strength of the Zr-χB alloys can be primarily attributed to grain refinement. Strengthening the Zr-χB alloys could also be achieved by a shear-lag model mechanism because of the high strength and modulus of the ZrB2 whiskers. The refinement of the α lath and the presence of the ZrB2 whiskers were responsible for the reduced elongation-to-failure. Fractography indicated that fracture behavior strongly depends on the orientation of the ZrB2 whiskers. The effect of this orientation on the fracture mechanisms of the ZrB2 whiskers and the Zr-χB alloys was also discussed.