Evaluation of thermomechanical performance for thermal barrier type of sintered functionally graded materials

Thermomechanical properties of metal/ceramic functionally graded materials were evaluated by a burner heating test using a H₂/O₂ combustion flame, which simulated the real environment of the heated inner wall of a rocket combustor. Disk-shaped graded samples of a material combination of partially stabilized zirconia and stainless steel were used for the test, in which the ceramic surface of the sample was heated with a burner flame and the back surface was cooled with flowing water. The critical temperature of the first crack formation, which was always observed on the ceramic surface during cooling, was determined in the test. The stress distributions in the sample during heating and cooling cycles, calculated by the finite element method, show the generation of large compressive and tensile stresses during heating and cooling, respectively, which are attributed to the non-elastic deformation of the heated sample surface due to an excess compressive stress. The fracture mechanism in terms of crack formation and spalling in the FGMs is discussed on the basis of the stress distributions in addition to a fracture mechanics approach.