The influence of corrosion damage on the thermal fatigue resistance of superalloys

The aim of the research is to develop a method for evaluating the effect of high-temperature corrosion damage on the thermal fatigue resistance of samples made of heat-resistant alloys on the nickel bas used for blades and disks of gas turbine units. For preliminary application of corrosion damage, the specimens were exposed to a corrosive environment at high temperatures. The metal microstructure of the samples before thermal fatigue tests (after accumulation of corrosion damage and production of one polished surface) was studied by digital metallography. Thermal fatigue tests were carried out in vacuum on plane corset specimens. Heating of the axially fixed specimens is performed by passing electric current. The specified cyclic heating/cooling program was maintained automatically during the entire test. Test programs with temperature changes within the cycle in the ranges of 100 ↔ 850, 100 ↔ 900, 100 ↔ 1000°C without delay and 100 ↔ 800, 100 ↔ 900, 100 ↔ 1000, 100 ↔ 1100, 500 ↔ 1000, 500 ↔ 1050°C with delay at the maximum temperature from 2 to 15 min were considered. The performed tests of specimens with corrosion damages of different intensity have shown a significant influence of the corrosion layer and separate delay time at the maximum cycle temperature on the thermal fatigue resistance of materials. A method for taking into account the effect of corrosion damage on thermal fatigue resistance has been developed using a four-term deformation criterion of thermal fatigue failure by taking into account the linear dependence of the criterion parameters on the thickness of the corrosion layer. The proposed method was initially tested on two heat-resistant alloys KhN56KVMTYuB and VZhM4-VI with varying degrees of corrosion damage.