Monotonic and Cyclic Stress–Strain Behavior of Uncoated and Coated Superalloy Rene®80 at Elevated Temperature

• Published in: Physics of metals and metallography 2021-12, Vol.122 (14), p.1621-1633
• Main Authors: Barjesteh, M. M., Abbasi, S. M., Madar, K. Zangeneh, Shirvani, K.
• Format: Article
• Language: English
• Subjects: Aluminides; Aluminum coatings; Chemistry and Materials Science; Corrosion resistance; Corrosion tests; Crack propagation; Cyclic loads; Declination; Diffusion layers; Ductile fracture; Ductile-brittle transition; Failure mechanisms; Fatigue failure; Fatigue strength; Fatigue tests; Heat treating; High temperature; Low cycle fatigue; Low temperature; Materials Science; Metallic Materials; Nickel; Oxidation resistance; Shutdowns; Strain rate; Strength and Plasticity; Surface layers; Tensile tests; Turbine blades; Turbojet engines
• ISSN: 0031-918X; 1555-6190
• DOI: 10.1134/S0031918X21140040

Polycrystalline cast superalloy Rene ® 80 is extensively used for manufacturing turbine blades of aero-turbojet engines. Therefore it is under cyclic stress–strain loads such as operation and shutdown. Turbine blades are usually coated to increase their high temperature oxidation/corrosion resistance. In this study, influence of a low temperature-high activity (LTHA) platinum–aluminide (Pt–Al) coating with an initial layer of 6µm platinum, on the tensile (monotonic stress–strain) and low cycle fatigue (cyclic stress–strain) properties of Rene ® 80, at 800°C, has been evaluated. The coating microstructure consisted of an outer bi-phase (PtAl 2 in a matrix of (Ni,Pt)–Al) layer, an intermediate (Ni,Pt)–Al layer (single phase) and an inter-diffusion zone (IDZ). The results of hot tensile tests at 800°C showed a decrease in ultimate and yield strength properties of the coated specimens about 5–6% compared to the uncoated ones. Also results of low cycle fatigue tests under strain-controlled condition at 800°C for R = 0 and strain rate of 2 × 10 –3 s –1 , at a total strain range of 0.8% indicated a declination in fatigue strength of Rene ® 80 after applying Pt–Al coating at 800°C. Results of fractographic studies on coated and uncoated specimens revealed a combination of ductile and brittle failure mechanisms at both states. Although the fatigue crack was nucleated on the oxidized surface layer in the uncoated specimens, it started from the coating in the coated specimens at 800°C.