First Principles Calculations of the Equilibrium Mechanical Properties of Simple Metals and Ordered Intermetallic Alloys

High-strength, light-weight intermetallic compounds which are ductile at high temperatures are of great technological interest. Purely experimental searches for improved intermetallic materials are time consuming and expensive. Theoretical studies can shorten the experimental work by focusing on candidate compounds which have several of the desired properties. Although current abinitio density functional calculations are not adequate to calculate material properties at high temperatures, it is possible to compute the equation of state and elastic moduli of ordered compounds with several atoms in a unit cell. Known correlations between equilibrium and high temperature properties can then be used to point the way for experiments. We have demonstrated the power of this approach by applying the linearized augmented plane wave (LAPW) method to calculate the equation of state and elastic moduli for several simple metals (Al, Ca, and Ir), binary cubic intermetallics (SbY, AlCo, AlNi, AlRu, and RuZr), and binary L1 o intermetallics (AlTi and IrNb). Most of the calculated equilibrium lattice constants are within 3% of the experimentally observed lattice constants. Although the available experimental information about the elastic moduli is limited by the lack of single crystal data for most of these materials, we are in excellent agreement (within 10%) with the available experimental data, except for the shear modulus of IrNb. We also use known correlations between the elastic moduli and the melting temperature to predict melting temperatures of the intermetallics. In general the agreement there is good agreement between theory and experiment, indicating that we can qualitatively predict melting temperatures.