Effect of Carbon on the Microstructures and Mechanical Properties of a Ni-Based Superalloy with High W Content

The microstructures and mechanical properties of experimental Ni-based superalloys K416B with high tungsten (W) content and various carbon (C) contents were studied. The results revealed that C addition led to a decrease in the size and volume fraction of eutectic (γ + γ′) phase. With the increase in C content, the volume fraction and size of MC carbides increased, and an interdendritic network of carbides evolved more prominently. The carbide network occupied most of the interdendritic area and exhibited “dendrite” form. The grain size of the alloy decreased significantly with the increase in C content. The precipitation of α-W is observed in the alloys without C, while M 6 C carbides formed when the C content was raised to 0.27 wt.%. No significant change in tensile properties of the alloy when the carbon content increases from 0 to 0.1 wt.%, when the carbon content is increased to 0.27 wt.% the tensile properties of the alloy decrease significantly. With increasing C content, the stress rupture properties increase. Eutectic and grain boundaries are the weak areas in the stress rupture properties process. As the carbon content increases the eutectic content of the alloy decreases, the grain size increases and grain boundaries decreased. Therefore, the stress rupture properties of the alloy improved. The presence of a large amount of primary M 6 C reduced the tensile properties of the alloy because the brittle phases in primary M 6 C were generated as the carbon content increased, and the primary M 6 C was first fractured during tensile testing.