EVALUATION OF THERMOMECHANICAL FATIGUE RESISTANCE OF COATED SUPERALLOYS BY A LASER THERMAL SHOCK SYSTEM

摘要

As the thermomechanical characterization of coated superalloys is very expensive, because the tests are long and complex, an alternative technique was developed, based on the use of a Nd:YAG laser thermal shock system, developed in CESI to locally and automatically apply the thermal cycles chosen by the operator onto the coating surface. During tests the thermal cycling is continued until the first surface cracks appear. FEM methods were used to calculate the stress-strain field around the heated zone and the △ε obtained in several different cycling conditions. From the simulation results, a typical test matrix was established, able to evaluate a △ε range from 1.5 to 0.4, so that the number of cycles to fracture between one hundred and one thousand can be expected. Results are plotted on a fatigue resistance plot (△ε vs Number of cycles to surface cracking). The proposed test method was applied on AMDRY995 coatings sprayed on IN738 superalloy, both with LPPS and with HVOF technique, the last one being almost three times cheaper. Thermal shock test results show that HVOF coatings have a resistance to thermomechanical fatigue comparable to LPPS sprayed coatings.