Evaluating strength of thermally sprayed Al 2O 3 on aluminum

Abstract

We evaluated the strength of thermally sprayed Al 2O 3 on aluminum. The thermally sprayed Al 2O 3 films were processed using low-pressure plasma spraying. The thickness of the thermally sprayed Al 2O 3 was 0.3 mm and 0.7 mm. We arranged a 4-point bending test and a heating test to evaluate the strength of the thermally sprayed Al 2O 3. We also investigated the effect of residual stress on the strength by measuring deformation of the thermally sprayed Al 2O 3 after removing the aluminum substrates. The bending strength was 120 MPa, regardless of thickness. We assumed that the bending strength would be equal to the tensile strength because the thermally sprayed Al 2O 3 films were very thin. A crack was generated at 433 K, regardless of thickness. The thermal stress was 160 MPa when the crack was generated. It was 40 MPa higher than we estimated. We found that the residual stress was compression stress that measured 40 MPa, which contributed to the prevention of the crack generation. We presume that the tensile strength was lower than the thermal stress because the residual stress was reduced by stress-relaxing of the aluminum near the interface in the bending test. The influence of heat-resisting strength is dominant over residual stress. Therefore, strength design should take into account residual stress.