Mechanical instability and ideal shear strength of transition metal carbides and nitrides - art. no. 075503

The ideal shear strength of transition metal carbides and nitrides is calcu lated with the use of the ab initio pseudopotential density functional meth od. The microscopic mechanism that limits the ideal strength is studied usi ng full atomic and structural relaxation and the results of electronic stru cture calculations. It is shown that plasticity in perfect crystals can be triggered by electronic instabilities at finite strains. Our study explicit ly demonstrates that the ideal strength in these materials is limited by th e elastic instability which is in turn initiated by electronic instabilitie s. The potential application of alloy hardening due to the onset of instabi lities at different strains is also discussed.