Relationship between layered crystal structure and mechanical properties of M 3 AlN (M = Zr and Hf): A first-principles
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Jingyang Wanga) Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Fangzhi Li Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China; and Graduate School of Chinese Academy of Sciences, Beijing 100039, China
Yanchun Zhou Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China (Received 8 June 2009; accepted 10 August 2009)
Bonding character, elastic mechanical parameters, ideal strengths, and atomistic shear deformation mechanisms of M3AlN (M = Zr and Hf) were studied by first-principles method. M3AlN exhibits layered chemical bonding character due to the alternately stacking of relatively soft Al–M and strong N–M covalent bonds. The second-order elastic constants and mechanical parameters of M3AlN 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. M3AlN ceramics are predicted to be “quasiductile” layered nitrides based on the low shear-modulus-to-bulk-modulus ratios, positive Cauchy pressure (c12–c44), and lower ideal shear strength compared to ideal tensile strength. Investigation of the atomistic shear deformation mechanism of Hf3AlN 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 M3AlN are similar with those of other “quasi-ductile” ceramics, such as MAX phases, LaPO4 monazite, and g-Y2Si2O7. The results further suggest that M3AlN nitrides should be quasi-ductile and damage tolerant. I. INTRODUCTION
Transition-metal carbides and nitrides (TMCs and TMNs), which normally crystallize in the rock-salt structure are commonly referred to as hard refractory materials. Because of the excellent properties, such as high hardness, high melting point, high strength at elevated temperature, good wear resistance, good thermal shock resistance, good electric conductivity, and chemical inertness, they are widely applied in high-temperature environments or as hard ceramics.1 However, the intrinsic brittleness has greatly hindered their extensive applications. Recently, development of ternary aluminum carbides or nitrides reveals a possible way to solve this a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0437 J. Mater. Res., Vol. 24, No. 12, Dec 2009
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problem. Lots of materials with layered structure were discovered after aluminum was incorporated into binary carbides and nitrides. Many of them exhibit excellent damage tolerance. For example, MAX phases (typically appear in the Mn+1AXn chemical formula, where M is an early transition metal, A is a group-A element, and X is C and/
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