Evaluation of residual stresses of thermal barrier coatings with HVOF thermally sprayed bond coats using the Modified Layer Removal Method (MLRM)

Abstract

The use of thermally sprayed thermal barrier coatings (TBC) has permitted the increase of combustion temperatures of gas turbines and diesel engines in the last decades. In terms of system performance, the possibility of increasing in working temperature is always welcome. It is well known that the residual stresses due to the mismatch between metallic bond coat and ceramic top coat as well as the stresses due to the oxidation of the bond coat generate debonding of the TBC, leading to a collapse of all thermal barrier system. Several attempts have been done to minimize or even to solve this kind of problems. One of the possibilities that have been tried is to apply graded or multilayered coatings, or to induce compressive stresses that can compensate the tensile residual stresses due to spraying process. In this work, two TBC systems were obtained by applying two distinct bond coats and two distinct top coats. The commercial bond coats were applied by High Velocity Oxygen Fuel (HVOF) thermal spraying. Residual stresses were measured by the Modified Layer Removal Test. Results show that the residual stresses are mainly influenced by the thermal history regarding the quenching of individual splats and the plastic deformation of ceramic deposits.