Fine grained microstructure crystallographic feature and its effect on mechanical behavior in Ni-Cr-W superalloy

The microstructure, texture and microsegregation in conventional and fine grained ingots of Ni-Cr-W superalloy were experimentally charactered by metallography, field emission scanning electron microscope equipped with an Electron Backscatter Diffraction and electron probe microanalysis, respectively. Distribution of misorientation angles results indicates that the proportion of low-angle grain boundaries and high-angle grain boundaries is about 15% and 85%, respectively, demonstrating that the particles are genuinely separate grains with mostly high-angle boundaries. Further, inverse pole figure results supply evidence for elucidating the mechanism of grain refinement due to a high effective nucleation rate which is attributed to extremely uniform temperature and composition fields in the bulk liquid at early stages of solidification. Element segregation at the grain boundary of equiaxed fine grain microstructure is smaller than that of the conventional dendrite grain microstructure. The effect of different morphologies of microstructure on yield strength was investigated. The effect of different average grain sizes on micro-hardness and yield strength was also analyzed. Relationship between yield strength and the grain size of this alloy followed the Hall-Petch relationship: σs=700+422d−1/2.