Low-cycle and bithermal fatigue of a cobalt-base superalloy

This contribution deals with the evaluation of the high-temperature mechanical strength of FSX 414, a Co-base superalloy, tested under various conditions. This study is closely related to general experimental and life-prediction problems typical of high-temperature applications. Isothermal tests are carried out, such as static, stress rupture, LCF tests; the characterisation has been extended by introducing bithermal fatigue tests, cycling between 450°C and 950°C. Each fatigue cycle is divided into two half-cycles where tension and compression loads are applied at two different constant temperatures, higher and lower (in-phase) or lower and higher (out-of-phase), respectively. The results thus obtained are compared with those obtained in isothermal conditions. Metallographic observations on the specimen fracture and lateral surfaces are also reported and discussed.