Microstructure and mechanical properties of hot-rolled ZrB alloys

The microstructure, mechanical property behavior, and fracture characteristics of Zr- chi B alloys ( chi =0, 0.05, 0.3, 0.8wt%) obtained by casting and hot-rolling were investigated. Microstructural observation indicated that the dendritic equiaxed prior- beta grain morphology was slightly elongated after hot-rolling treatment. The widths of the alpha lath of all the hot-rolled Zr- chi B alloys were similar, and the length of the alpha lath decreased with increasing boron concentration. Tensile test results showed that the improved strength of the Zr- chi B alloys can be primarily attributed to grain refinement. Strengthening the Zr- chi B 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 alpha 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- chi B alloys was also discussed.