THE EFFECT OF MICROSTRUCTURE ON MECHANICAL PROPERTIES OF SINGLE CRYSTAL CMSX-4 SUPERALLOY

The effect of size and volume fraction of cuboidal. gamma'(Ni-3(Al,Ti)) precipitates on Vickers hardness and tensile properties at 950 degrees C of a single crystal nickel-based superalloy CMSX-4 was studied. Samples with various size and volume fraction of the cuboidal gamma' precipitates were prepared by heat treatment consisting of solution annealing, quenching and ageing at a temperature of 950 degrees C. Both the Vickers hardness and yield strength linearly decrease with decreasing normalized volume fraction and increasing normalized mean size of the gamma' precipitates. A linear relationship between the yield strength and Vickers hardness is determined which allows high-temperature yield strength to be predicted from simple Vickers hardness measurements at room temperature. Critical resolved shear stress is calculated to increase from 116 to 234 MPa by decreasing a mean width of the gamma (Ni-based solid solution) channels from 71 to 32 nm. The decrease of the yield strength with decreasing normalized volume fraction and increasing normalized size of the gamma' precipitates is controlled by a decrease of order stress resulting from shearing of the gamma'/ gamma precipitates at high tensile stresses.