Chemical bonding and mechanical properties of M 2 A C ( M = Ti, V, Cr, A = Al, Si, P, S) ceramics from first-principles
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Jingyang Wanga) Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016; and International Centre for Materials Physics, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Yanchun Zhou Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China (Received 3 September 2008; accepted 12 November 2008)
MAX-phase carbides (M is an early transition metal, A is an A-group element) exhibit an interesting bonding characteristic of alternative stacking of strong M–C bonds and relatively weak M–A bonds in one direction. In the present first-principles total energy calculations, we establish the relationship between mechanical properties and electronic structure for ternary M2AC (M = Ti, V, Cr, A = Al, Si, P, S) carbides. By systematically tuning elements on the M and A sites, pronounced enhancements of bulk modulus, elastic stiffness, and ideal shear strength are achieved in V-containing V2AC (A = Al, Si, P, and S) carbides. It is suggested that tailoring on the A site is more efficient than on the M site in strengthening the mechanical properties of studied serial carbides. The results highlight a general trend for tailor-made mechanical properties of ternary M2AC carbides by control of chemical bonding. I. INTRODUCTION
Binary transition metal carbides (MC) contain strong covalent bonding between transition metal M and C atoms, and display high hardness and modulus, high melting point, and good wear resistance. However, MC carbides usually suffer intrinsic brittleness because of low dislocation mobility. Interestingly, the mechanical properties of MC carbides significantly change when A-group element atoms are incorporated; and thereafter, compounds crystallize in the so-called layered ternary MAX-phase carbides. Ternary carbides/nitrides with the crystal structures of MAX phases show a unique combination of the merits of mechanical properties of both ceramics and metals, such as high modulus, microscale “ductility,” and damage tolerance.1 These mechanical properties are rarely simultaneously exhibited by carbides/nitrides. Previous firstprinciples calculations demonstrated that these unique mechanical properties of MAX phases could be attributed to the bonding characteristics of alternative stacking of strongly directional M–C bonds and relatively weak M–A bonds along one direction.2 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0066
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http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 2, Feb 2009 Downloaded: 27 Apr 2015
Many efforts have been made to understand the influence of M–A bond on the mechanical properties of MAX phases. We reported that the mechanical properties of M2AC ceramics are dominated by the weak coupling between transition metal carbide slabs and the interleaved A-element atomic planes.3,4 Optimization of the mechanical properties of M2AC was first concentrated on streng
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