Effects of Alloying Elements on Thermal Expansion Behavior of Ni-Fe-Cr-Based Superalloys

The effects of alloying elements on the thermal expansion of Ni-Fe-Cr-based superalloys are investigated by optical microscope, scanning electron microscope, and transmission electron microscope. The results indicate that Fe and Cr increase the thermal expansion coefficient (TEC) of alloys and the effect of Cr on the TEC is significantly enhanced by the presence of Fe. Al and Ti present a minor influence on the TEC owing to their low contents in the alloys. The TEC of alloys rises with the reduction of lattice parameter of gamma matrix in the Fe-containing or non-ferrous alloys; indeed, this is the essential reason why the TEC changes with the modification of the contents of various elements. Finally, it is found that the TEC of alloys is principally determined by the gamma matrix due to its dominant amount. The gamma' phase and grain boundary also contribute to reducing the TEC, but their effects are screened by the matrix due to their negligible volume (or weight) fraction. (C) The Minerals, Metals & Materials Society and ASM International 2018.