Effect of annealing on microstructure and tensile property of a novel ZrB alloy

With the aim to develop new Zr-based alloys with excellent mechanical properties, a novel Zr-0.8B (wt%) alloy was manufactured through the following steps: casting, forging, hot-rolling and annealing treatment. The microstructure and mechanical properties of the hot-rolled and annealed Zr-0.8B alloys were investigated. The microstructure of all specimens was comprised by α and ZrB2 phases. The coarse α laths and ZrB2 whiskers were significantly refined by hot rolling. Also, a high volume of dislocations and many subgrains were formed during the hot-rolling process. A high degree of recrystallization of α phase was obtained during the annealing treatment, due to the substantially stored energy in the Zr matrix and the presence of a significant amount of subgrains. The tensile strength of the annealed Zr-0.8B alloys was decreased with the increase of annealing temperature, until 800 °C, and then increased as the heat treatment temperature was further increased to 900 °C. Many factors, such as the volume fraction of ZrB2 whiskers, grain size, dislocation density, the amount of subgrains and solution strengthening, have a significant effect on the strength. However, the elongation-to-failure showed a reverse tendency compared to the tensile strength. The reasons caused fracture of the annealed Zr-0.8B alloys are primarily attributed to dislocation pile-ups and the presence of microvoids.