Microstructural Behaviour of Protective AlSi Coating under Thermal Load

Abstract

Aircraft engine turbine blades are exposed to high temperatures, high static, variable stresses and strong cyclic thermal loads during their operation. The investigated blades originate from the engine DV2 which is appointed for light training combat aeroplane, where sudden changes of engine transition state are in progress mostly during flight manoeuvring. Under these conditions the engine is liable to suffer from unstable running as surging or failure of the fuel system for a several seconds. These undesirable features of engine cause that the critical value of the output gas temperature T4,C is exceeded and damage of the turbine blades is extensive owing to degradation or total loss of protective coating. A short-time (5 to 20 s) exceeding of the operating temperature T4C by up to several tens of degrees degrades the surface layers of the blades and reduces their service life compared to the planned service life of 1500 flight hours. This work deals with degradation of protective coating on rotor blade of the high pressure turbine (HPT) under condition that the temperature of blades would reach the temperature of outgoing gases. The blades were heated in the laboratory, the temperature of blades were admeasured by platinum-rhodium thermocouple. Degradation of coating was analysed by scanning electron microscope. The aim of the work was get new attainments of AlSi coating behaviour at high temperatures without corroding medium.