Influence of Chemistry on the Tensile Yield Strength of Nickel-Based Single Crystal Superalloys

The tensile yield strength of AM1 and MC-NG single crystal superalloys with a gamma' precipitate size close to 300 nm were compared within the 20-1050 degrees C temperature range. The room temperature yield strength of the fourth generation MC-NG superalloy is about 200 MPa less than that of the AM1 first generation one. Inversely, at higher temperatures (T > 800 degrees C), the tensile strength of MC-NG is higher than that of AM1. These results are discussed by taking into account the elementary deformation mechanisms and the respective strengths of the gamma and gamma' phases. Experiments on a modified MC-NG alloy show that reinforcing the gamma' phase by increasing the contents of Ti and Ta is an efficient way to recover a higher tensile strength at low temperatures. Rhenium addition and increase of the gamma' solvus temperature are suggested to be beneficial for the high temperature tensile strength. Data published on various other single crystals are in agreement with these hypotheses.