Effect of alloy elements on iridium shear modulus by Ab initio analysis

The effect of the addition of rhodium (Rh), rhenium (Re), tungsten (W), gold (Au), and platinum (Pt) on the shear modulus of face-centered cubic iridium (Ir) was investigated using an ab initio method. The shear modulus was calculated using the second derivative of the strain energy with respect to strain. It was found that both the bulk modulus (G) and the ratio (G/B) between bulk and shear modulus decreased with the addition of elements to the Ir, which meant that all five of these alloy elements lowered the brittleness of the bulk Ir. The decreased shear modulus was the main factor for the lowered brittleness. And the decreasing order of shear modulus in the [112] and [100] crystalline directions was Ir > Rh > Pt > W = Au > Re and Ir > W > Rh > Pt > Au > Re respectively. The reason for the order was both the atomic distance and the bond strength between alloy atoms and Ir atoms. The larger bond strength meant the larger shear modulus, and the smaller atomic distance meant the smaller shear modulus.