MICROSTRUCTURAL CRITERIA FOR DETERMINING THERMO-MECHANICAL CONDITIONS OF OPERATIONAL VULNERABILITY OF THE WORKING BLADES OF HIGH-TEMPERATURE GAS TURBINE AVIATION ENGINES

Abstract

The necessity of studying the structure of the blade material and corresponding in-service structural changes is attributed, on the one hand, to the fact that the structural changes may impair the performance of the material thus promoting the blade fracture. On the other hand, the structural changes can serve as diagnostic signs in determination of thermo-mechanical conditions of the blade destruction. Moreover, the structural changes in the blade material often determine the service life of the blades: aside of creep mechanism, in-service depletion of the blade lifetime in high temperature gas turbine engines of maneuvering aircrafts is attributed to complex thermo-mechanical loading of the blades which, in turn activates the mechanisms of fatigue and thermo-mechanical fatigue. Monitoring of the structural state of the blade material with equiaxed crystallization (ZhS6U, VZhL12U), directed and monocrystallization (ZhS26, ZhS32) and studying the features of structural changes attributed to the operational vulnerability of the turbine blade material are the main goals of the study. The features of changes in the morphology of the strengthening γ’-phase and carbide transformation in the blade material that occur in-service are considered. The results of monitoring the structural state of the blade material are compared with the results of testing the same samples under laboratory conditions simulating thermo-mechanical loading. Microstructural criteria are recommended for more accurate evaluation of thermo-mechanical conditions of operating vulnerability of the turbine blades of high-temperature aircraft engines.