Research On Wear Mechanisms Of Coated Cemented Carbide Tool In Turning Of Titanium Alloy

Titanium alloy is widely used in military industry such as aerospace,weaponry,nuclear industry and warship because of its low density,high strength,good corrosion resistance,excellent thermal stability and short radioactive half-life.As the precision and surface quality requirements of some key military components become higher and higher,the demand for precision machining of titanium alloys is increasing.Due to the low thermal conductivity and strong chemical activity of titanium alloys,the tool wears quickly,the cost is high,and the machining accuracy and surface quality are difficult to guarantee when diamond turning is used.Coated cemented carbide has low cost and good oxidation resistance,and has become an excellent material for replacing diamond tools.However,the unknown wear mechanism of the tool has become a difficult obstacle to the application of coated cemented carbide in the field of precision cutting titanium alloy technology.Revealing the wear mechanism of coated cemented carbide can not only provide a theoretical basis for further research on measures to suppress tool wear,but also provide a basis for the development and manufacture of titanium alloy cutting tools with excellent performance,and promote the wide application of titanium alloy at the same time.In order to study the wear mechanism of coated cemented carbide,a commercial coated tool suitable for precision cutting of titanium alloys was targeted.First,the physical and chemical properties of the tool were tested and analyzed using precision equipment.The results showed that the coating was a TiAlN coating with a high Al content.The molar ratio of Ti and Al?excluding N?was 0.38:0.62.The coating TiAlN was a NaCl face-centered cubic structure with a lattice constant of 0.416138 nm.The hardness and elastic modulus of the coating were 31.58 GPa and 400 GPa respectively.Then thermal analysis experiments of coated carbide tools with/without titanium alloy adhesion were carried out based on these parameters.The experimental results showed that the coating would form an Al₂O₃ protective film without diffusion in the case of a non-adhesive titanium alloy.No diffusion was observed between the adhesive layer and the coating under the condition of adhering the titanium alloy.And the adhesive layer hindered the coating to form an Al₂O₃ protective film which would reduce the wear resistance of the coating at high temperature.Immediately through the friction and wear test of titanium alloy/coated cemented carbide,the combined effect of fatigue wear and adhesion wear on the main wear mechanism of the coating is found.The coating would generate fatigue under the action of continuous periodic shear stress and adhesive stress.The fatigue would cause cohesive forces and coating/substrate bonding forces to decrease.When they were less than adhesive stress and shear stress,the bonding layer would be sheared together with the coating to become abrasive debris.When the substrate lost protection of coating,the tool wear would be accelerated,because it was in direct contact with the titanium alloy.Finally,the first principle calculation method was used to analyze the adhesion mechanism of titanium alloy/coating interface.The results indicated that the Ti atoms of the outermost and second outer layers of the bcc-Ti crystal could be transferred to the outermost layers of Ti,Al and N of the 5Al-3Ti-8N crystal in the Ti/TiAlN interface.They were very easy to form strong covalent bonds which were the root cause of the adhesion stress between titanium alloy and coating.