Study On Residual Stress Of TiAlN Coating Under Cyclic Thermal Shock Load By Raman Spectroscopy

TiAlN coating is widely used as a protective coating for cutting tools due to its advantage like high hardness,excellent thermal rigidity,strong adhesion,high temperature oxidation resistance,small friction coefficient,and low thermal conductivity.However,due to the difference in thermal expansion coefficients of the coating and the substrate,residual stress is often produced in coating,at same time the residual stress and the service load together lead to premature coating failure.Therefore,it is really important to understand residual stress of TiAlN coating in service environment deeply for getting best tool performance and increase its using life.At first,this paper discusses the key issues of measuring the residual stress of TiAlN coating by Raman spectroscopy,and use infrared thermal imager to measure the chip temperature at different spindle speeds,different feed speeds,and different axial and radial feeds.Have done those work,the set temperature of the thermal shock of the TiAlN coating was conformed.Experiments result show that the chip temperature of TiAlN-coated tools decreases linearly with the increasing of spindle speed during the high-speed milling process,and increases linearly with the increase of feed speed and axial feed;The final confirmation was that maximum thermal shock temperature is around 375?.In this paper,the surface residual stress of TiAlN coating samples on two substrates of stainless steel and high-speed steel after different thermal shocks at375 ? and 700 ? was measured,at the same time the surface residual stress in TiAlN coating with heat was discussed like the changing law of the number of impacts.The experimental results show that there is tensile residual stress in the TiAlN coating deposited on the stainless steel and high-speed steel substrates.The tensile residual stress in the coating increases first and then decreases with the increase of the number of thermal shocks.At times,the 700? Raman frequency shift is greater than 375?,and the residual stress changes more drastically.In this paper,the distribution of the residual stress in the cross section of the TiAlN coating on the stainless steel substrate without thermal shock,10 thermal shocks at 375? and 10 thermal shocks at 700? is further studied.The results show that the tensile residual stress of the TiAlN coating increases with the increase of the coating depth,and the cross-sectional residual stress of the coating after thermal shock is higher than that of the coating without thermal shock.The research results in this paper clarify the change law of residual stress in TiAlN coating with thermal shock load,which is helpful for more scientific prediction of service life of tool coating.