EXPERIMENTAL STUDY ON DETERMINATION OF RESIDUAL STRESS IN COATINGS OF STEELS

Abstract

Recent advances in science and technology has help us to develop materials which are more resistant to the adverse effect of environment, wear and tear during its use and high temperature protection. One of such technology is the surface engineering, today the use of coating technology for improving material properties is growing day-by-day from decorative items to act as thermal barrier in gas turbine engines. Prediction of residual stress in coatings is necessary as residual stress may be beneficial or detrimental, tensile residual stress can cause delamination of coating while compressive stress can improve the coating fatigue resistance. In present work, Alumina Titania (13%) coating has been deposited by air plasma spray process on mild steel substrate by preheating the substrate to different temperatures. Coating thickness were measured by scanning electron microscope, hardness of coatings was measured and morphology were also checked. The crack compliance technique has been used to determine the residual stress as it is a very simple method and also it is compatible with conventional machining equipment and wire electric discharge machining equipment. Samples were cut by the Diamond cutter up to certain depth in microns and the strain relieved were recorded. For finding out the residual stress these recorded values of strain has been used by doing a Finite Element Analysis (FEA) using the ANSYS 15.0 software. For validation of the model uniaxial tension was applied on sample by using the INSTRON universal testing machine and strain values at both the coating side and the substrate side were recorded and matched with the model under the same value of load. After verifying the model an equation has been developed using the Minitab software and the strain previously recorded were used as an input to the equation obtained and the value of residual stress were calculated.