The effect of γ′ content on the densities of Ni-based superalloys

The γ′ phase increases the mechanical strength of Ni-based superalloys. Equations have been derived to calculate the atomic percent of γ′ phase from the Al content of the alloy. It is shown that increased γ′ phase content results in an increase in density (of the solid) and a decrease in the thermal expansion coefficient. Equations based on the Al content of the alloy have been derived to calculate the magnitude of these effects. The coarsening of the γ′ phase from 800 °C to 1000 °C was found to be accompanied by an increase in the temperature dependence of the thermal expansion coefficient. Densities for the entire temperature range of the solid alloys calculated with the equations are within 2 pct of measured values. The strong bonding between the Ni and Al was maintained in the liquid and resulted in increased densities. Equations were derived to quantify the effect on density (of the liquid) and the calculated density values for Ni-based superalloys were within 2 pct of the measured values. These uncertainties are commensurate with the experimental uncertainty in the measurements.