Effect of W on formation and properties of precipitates in Ni-based superalloys

The formation and properties of precipitates in wrought Ni-based superalloys with different W contents during long-term exposure to high temperatures were investigated. The scanning electron microscope, transmission electron microscope, and chemical phase analysis were used to investigate the formation and properties of precipitates. It is found that with increasing W content, the quantity and thermal stability of MC carbide in Ni-based superalloys increased, while the quantity of M23C6 carbides decreased. As the results show, W has a higher partition coefficient in gamma '- and gamma-matrix, and the addition of W promotes the precipitation of gamma ' phase. W content has no significant effect on the morphology, size, crystal structure, and coarsening rate of gamma ' precipitates. The influence of W content on high-temperature tensile and creep properties of the alloys was investigated. The results showed that W content has no obvious influence on the high-temperature yield strength, but the elongation and area reduction decreased significantly when the addition of W was more than 4 wt.%. Because of the similar volume fractions of gamma ' phase, the creep fracture strengths in the tested alloys with lower W concentrations were not significantly different after long-term exposure at 700 degrees C.