Compositional and grain size dependence of the mechanical properties of ZrCx: Effect of annealing on ZrC0.45

Abstract Zirconium carbide (ZrC x ) is an important structural material. Its high strength and hardness makes it suitable for application in hard materials and non-oxide type new ceramics. Hence, several researches have been carried out with the aim of understanding its mechanical properties. In this paper, the mechanical properties of ZrC x (0.45 ≤  x  ≤ 0.72) were investigated considering the grain size effect. The bending strength as a function of grain size obeyed the Hall–Petch relation. The composition dependence of the strength linearly decreased with decreasing carbon content, followed by saturation at x  = 0.6, corresponding to the lowest x value of the ZrC x single phase region. The Young's modulus and hardness monotonically decreased with decreasing carbon content, independently of grain size. The annealing of ZrC 0.45 at 1273 K for 18 ks led to the formation of Zr precipitates, which showed an orientation relationship with the ZrC matrix of (0001) Zr //(111) ZrC . These precipitations formed compressive residual stress in the ZrC phase, resulting in an 80% increase in the bending strength after annealing.