Study On High-frequency Fatigue Performance Of Tool Coating At High Temperature

Tool coating technology plays a very important role in modern cutting industry.Coating tool can greatly improve machining efficiency and machining quality.In the cutting process,the tool coating will always be impacted by a certain frequency and bear the cyclic stress.Therefore,the fatigue performance of the tool coating is an important part of the coating performance.The existing tool coating evaluation methods mainly obtain the performance under static and quasi-static conditions.How to develop an appropriate method to evaluate the fatigue performance of tool coating and how to connect the fatigue performance of tool coating with its cutting performance is a problem that needs to be deeply studied.In this paper,based on the study of high-frequency fatigue performance of tool coating,a simple and efficient mechanical performance testing method(impact test)is proposed to detect the fatigue performance of tool coating,and then characterize and evaluate its cutting performance.For this purpose,Ti-6Al-4V cutting test was carried out using bilayer Ti Si N/Ti Al N coating tool and multilayer Ti Si N/Ti Al N nano-coating tool,the stress state and wear mechanism of the tool coating during cutting were investigated.At the same time,a high-temperature and high-frequency impact test platform was built independently to explore the high-frequency fatigue performance and failure mechanism of the coating at high temperature through high-frequency impact test.Finally,based on the two experimental results,the mapping relationship between the fatigue performance of the tool coating and its cutting performance was established.The main research contents and conclusions of this paper are as follows:(1)Ti-6Al-4V cutting experiment was carried out with bilayer Ti Si N/Ti Al N coating tool and multilayer Ti Si N/Ti Al N nano-coating tool.The serration chip morphology under different feed rates was analyzed and observed.The high-frequency fatigue wear failure process of tool coating will also change according to the change of chip serration degree.Through the analysis of the wear morphology of the coating,the cutting performance of the two tools was studied.the multilayer Ti Si N/Ti Al N nano-coating tool showed better cutting performance under the condition of small feed rate,while the bilayer Ti Si N/Ti Al N coating tool showed better cutting performance under the condition of large feed rate.(2)An independent high-temperature and high-frequency impact test platform was built,which was equipped with a high-temperature system,and the preloading depth variable was introduced into the parameter setting.The impact test platform can simulate the stress and temperature of coating in cutting process.High-temperature and high-frequency impact test was carried out on the bilayer Ti Si N/Ti Al N coating and multilayer Ti Si N/Ti Al N nano-coating.Through the observation of the impact surface morphology of the coating,the fatigue performance and fatigue failure mechanism at different temperatures and preloading depths were studied.The increase of temperature would reduce the hardness of the coating and substrate,the failure mode of the coating gradually changed from fracture failure to powdered deformation failure.(3)Comparing the alternating stress spectrum and coating surface morphology of cutting experiment and impact test,the change trend of the alternating stress spectrum and fatigue failure mechanism of tool coating is coincident.It provides an experimental basis for establishing the mapping relationship between fatigue performance and cutting performance of tool coating.The feasibility and methods of testing the fatigue performance of tool coating by impact test are summarized,so as to evaluate its cutting performance.