Residual Lifetime Assessment Model Based on Microstructural Evolution of the Service-Exposed Dz125 Turbine Blades

Abstract

The dependence of distribution of temperature and stress on the geometrical structure of turbine blades makes the fact questionable that the obtained parameters characterizing microstructural degradation of DZ125 superalloy by standard samples at the specific temperature and stress is directly used to evaluate the residual lifetime of the service-exposed DZ125 blades. In this study, DZ125 turbine blades with the film cooling holes (FCHs) are in service on the engine bench for 408h and 661h, respectively. In order to analyze microstructure of DZ125 blades, the volume fraction and the size of precipitates as well as the width of  matrix channels are regarded as the microstructure characteristic parameters to quantitatively describe microstructural degradation of the service-exposed DZ125 blades. These parameters are also applied to analyze the dependence of the microstructural evolution on the geometrical structure of the service-exposed DZ125 blades. Based on these, a residual lifetime assessment model is proposed by introducing the obtained parameters from the service-exposed DZ125 blades to the Larson-Miller creep model, and then used to evaluate the residual creep lifetime of the service-exposed DZ125 blades. According to the assessed lifetime, the location where the blade fracture possibly happens in service is predicted, well coincident with the experimental ones. This model is of significance for the assessment of the residual creep lifetime by means of the obtained microstructure characteristic parameters from the service-exposed blades.

Keywords: Turbine blades, microstructure, characteristic parameters, lifetime assessment, Larson-Miller Parameter