Structure dependence of creep and creep-fatigue deformation and fracture process of single crystal nickel base superalloy

摘要

The effect of different initial microstructures ofsingle crystal nickel base superalloy, frequently used as bladematerial for gas turbines, defined by gamma prime morphology,has been investigated under the creep and creep-fatigue conditionsat 900beg C and 500Mpa. For cyclic loading the wave form ofstress as a function of time was of trapezoidal shape with a holdtime of 10s at the upper stress level. The fracture life-time andcycles to fracture were criteria being considered to evaluatedeformation behaviour of alloy defined by different structurestates under complex creep-fatigue loading. The TEM study of thinfoils cut from fractured specimens was used to analyze thedeformation mechanism in strengthened matrix in dependence oninitial alloy structure. As the results showed, the higher creepstrength was achieved in case of structures with cuboidal gammaprime morphology. However, the introduction of the cyclic stresscomponent onto creep stress resulted in the lifetime reduction incomparison with the simple creep deformation and in modificationof the fracture mode morphology.