材料期刊网

Bonding character, elastic mechanical parameters, ideal strengths, and atomistic shear deformation mechanisms of M(3)AlN (M = Zr and Hf) were studied by first-principles method. M(3)AlN exhibits layered chemical bonding character due to the alternately stacking of relatively soft AI-M and strong N-M covalent bonds. The second-order elastic constants and mechanical parameters of M(3)AlN were reported for the first time. The stress-strain relationships for different deformation modes were studied and the ideal shear and tensile strength were obtained. M(3)AlN ceramics are predicted to be "quasi-ductile" layered nitrides based on the low shear-modulus-to-bulk-modulus ratios, positive Cauchy pressure (c(12)-c(44)), and lower ideal shear strength compared to ideal tensile strength. Investigation of the atomistic shear deformation mechanism of M(3)AlN shows that stretching of soft Al-Hf bonds and relatively weak bridge N-Hf1 bonds dominate the shear deformation; while the rigid N-Hf2 bonds resist against the applied shear strain. Chemical bonding characteristics and shear deformation mechanism of M(3)AlN are similar with those of other "quasi-ductile" ceramics, such as MAX phases, LaPO(4) monazite, and gamma-Y(2)Si(2)O(7). The results further suggest that M(3)AlN nitrides should be quasi-ductile and damage tolerant.