Effect of Overheating Treatment on Microstructure and Stress Rupture Properties of a Nickel-Based Single-Crystal Superalloy

The degradation of microstructure and mechanical properties caused by overheating service of nickel-based single-crystal superalloys poses a serious threat to the safe use of turbine blades. In this work, the overheating treatment was conducted for a second-generation Ni-based single-crystal superalloy in the temperature range of 1100-1260 °C for 10 min. The effects of overheating temperature on microstructure and stress rupture properties (760 °C/800 MPa and 1050 °C/190 MPa) were studied. With the increase in the overheating temperature, the primary γ' phase progressively evolves in shape from cuboidal to spherical and then to petal shape. Meanwhile, the rate of precipitation and growth of the secondary γ′ phase increases with the rising temperature. In addition, the number and depth of interfacial grooves of experimental alloy increase with decreasing cooling rate. At 760 °C/800 MPa, the stress rupture life of the alloy after overheating at 1180 °C/10 min is abnormally increased to 228 h, which is higher than that of the standard heat treatment alloy. At 1050 °C/190 MPa, the stress rupture life of the alloy descends tardily with the increase in the overheating temperature.