Effect of multiple alloying additions on microstructural features and creep performance at 950 °C and 400 MPa in Ru-containing single crystal superalloys

Abstract

Microstructural features, including γ channel width, γ' size, γ' volume fraction, γ-γ' lattice misfit, TCP phase as well as dislocation substructures had influence on the creep performance in Ni-base single crystal superalloys. However, relatively limited work has been conducted to investigate the effect of microstructural features based on various alloying additions on creep properties in Ru-containing single crystal superalloys. In this study, the creep tests were conducted at 950°C and 400MPa in experimental alloys with different levels Co (7.0wt% and 15.0wt%), Cr (3.5wt% and 6.0wt%), Mo (1.0wt% and 2.5wt%) and Ru (2.5wt% and 4.0wt%) additions, and the microstructures during creep were characterized in detail. Co and Ru were found to decrease the γ channel width, respectively. The high level of Cr addition decreased the γ' volume fraction and promote the TCP phase formation during creep. The addition of Mo decreased the γ channel width and also acted as a TCP former. The γ-γ' lattice misfit was increased to more negative by the individual additions of Co, Ru, Cr, and Mo, respectively. The joint addition of microstructural stabilizers Co and Ru inhibited the TCP phase formation during creep. The precipitation of TCP phases served as one of the main factor to decrease the creep property in alloys with high level of Cr and Mo additions, respectively. The synergistic effect of Mo and Ru additions in the alloy with high level of Co content was found to increase the γ-γ' lattice misfit and the amount of stacking faults in γ matrix during creep process, which improved the creep resistance at 950°C and 400MPa. This study is helpful to understand the effect of alloying elements additions and microstructures on creep performance and to get better improvement of physical metallurgy knowledge and alloy design in Ru-containing single crystal superalloys.