The role of planar fault energy in the yield anomaly in L1(2) intermetallics

摘要

We have used ab initio quantum mechanics to calculate planar fault energies in a number of L1(2) intermetallic compounds. Used in conjunction with a diagram of Saada and Veyssiere showing elastic and antiphase-boundary anisotropies we show that such calculations may be used to predict the occurrence of the yield strength anomaly. The less common 'normal' yield behaviour of Pt-3 Al is shown to have a different origin from what was previously thought. We are able to make predicted estimates of the size of the dissociated core of screw superdislocations. The nature of the activated process is also discussed. Microscopic factors determining fault energy are described, and we separate faults into those whose energy is chemical and those whose energy is structural in origin. Use is made of the axial Ising model to analyse structural fault energies. We find a marked difference between the properties of Ni3Si and Ni3Ge and show that this arises because the bonding is more ionic in Ni3Si and more covalent in Ni3Ge. In spite of these wide differences, both show a strong yield anomaly. [References: 41]