Influence of Temperatures on Creep Behavior of Pt-Al Coated Third-Generation Low-Cost Single Crystal Superalloy

Abstract:

The influence of applied temperatures on the creep rupture life of the third-generation low-cost single crystal (SX) superalloy with Pt-Al coating was evaluated. The creep damage was observed under the conditions of 1100 °C/137 MPa, 1120 °C/137 MPa, and 1140 °C/137 MPa. Results show that the properties of bare superalloy outperform those of coated superalloy under all test conditions. The most significant reduction in creep life reaches 50% when the test condition is 1100 °C/137 MPa. At higher temperatures (1120 and 1140 °C), the crack propagation rate in Pt-Al coatings to SX superalloy substrate decreases, thereby reducing the degradation degree of mechanical properties. Instead of the penetration into SX substrate, tip oxidation and Al diffusion of the coating cracks cause the formation of oxides, therefore leading to the slow degradation in microstructures of the substrate beneath the coating. At 1100 °C, however, the microstructure of coating/SX superalloy substrate degrades due to the Al internal diffusion. This diffusion mechanism promotes the formation of harmful topologically close packed phases around 1100 °C. At 1120 and 1140 °C, the dislocation of SX superalloy substrate beneath the coating is relatively unchanged, compared to that in the inner superalloy. In contrast, the dislocation network of the substrate beneath the coating becomes sparse, and the number of superdislocations cutting into γ′ phases increases at 1100 °C.

Key words:Pt-Al coating;high-temperature creep;single crystal superalloy;crack oxidation;microstructure evolution