Study On Microstructure And Tribological Properties Of TiAlMoCuN Hard Coatings

TiAlN coating has high hardness and high thermal stability and is widely used for cutting tools.However,when cutting difficult-to-machine materials at high speed,the cutting edge temperature can reach 1000°C,far exceeding the service temperature of TiAlN coated tools,due to the intense friction between the chip and the tool surface.Therefore,this thesis aims to reduce the cutting temperature by improving the tribological properties of TiAlN coating through alloying method to reduce the cutting heat generation.Firstly,the effects of Cu and Mo elements on the structure and performance of TiAlN coating are compared;Then the self-lubricating properties at high temperature are obtained by Cu and Mo co-doping;Finally,the cutting life and wear efficiency of coated tools are evaluated by dry turning.The research results of this thesis are as follows:1)The Ti_42.5Al₅₀Cu_7.5N and Ti₃₅Al₅₀Cu₁₅N coatings have a multiphase composite structure consisting of two phases of face-centered cubic structure nitride(Ti,Al)N and metallic Cu,and the competing growth of the two phases results in a featureless growth morphology with fine grains.The addition of Cu significantly reduces the hardness of the coating from 33 GPa for TiAlN to 23 GPa.The coefficient of friction of the TiAlCuN coating increased rather than decreased.The lower mechanical properties and higher friction coefficient cause the poor wear resistance of TiAlCuN(1?2 orders of magnitude increase in wear rate).In addition,Cu easily diffuses outward at high temperatures,accelerated oxidation,further deterioration of the wear resistance of the coating.2)Ti_42.5Al₅₀Mo_7.5N,Ti₃₅Al₅₀Mo₁₅N,and Ti₂₅Al₅₀Mo₂₅N coatings have typical columnar crystal growth,The nitride structure is face-centered cubic,and the Mo element is mainly present in the coating in solid solution,while high Mo content of Ti₂₅Al₅₀Mo₂₅N coatings also contains a small amount of Mo metal monolithic phase.The addition of Mo played a certain solid solution strengthening effect,the hardness of TiAlN coatings increased with the increase of Mo content,and all of them were higher than 33 GPa.In tribological properties,due to the hydration at room temperature to promote the generation of Mo O₃ which decreased the friction coefficient to?0.45 and exhibits excellent wear resistance(10^-8 mm~3/N?m).However at high temperature,the outward migration rate of Mo elements is slow,and the friction surface layer cannot form enough Mo O₃,resulting in the friction coefficient and wear resistance of TiAlMoN coating are comparable to TiAlN coating.3)Ti₄₅Al₅₀Mo_2.5Cu_2.5N coatings show typical columnar crystal morphology,but Ti₃₅Al₅₀Mo_7.5Cu_7.5N and Ti₃₀Al₅₀Mo₁₀Cu₁₀N coatings show a featureless growth morphology with fine grains,and the hardness of all three TiAlMoCuN coatings can be maintained at?32GPa.TiAlMoCuN has the same corfficient of friction as TiAlN at room temperature and400°C.However,Mo and Cu co-alloying effectively improves the friction performance of TiAlN coating at 600°C.The TiAlMoCuN coating forms core-shell structure oxide nanorods with copper oxide coated molybdenum oxide at high temperatures,which have lower shear modulus and reduced contact area with the Al₂O₃ ball.Thus,the friction coefficient is reduced to?0.45 and maintained a good wear resistance.4)Through high-speed dry cutting tests on Ti₅₀Al₅₀N,Ti₃₅Al₅₀Mo₁₅N and Ti₃₅Al₅₀Mo_7.5Cu_7.5N coated tools,compared with Ti₅₀Al₅₀N coated tools,Ti₃₅Al₅₀Mo₁₅N and Ti₃₅Al₅₀Mo_7.5Cu_7.5N coated tools showed an increase in tool life,with Ti₃₅Al₅₀Mo₁₅N coated tool life increased by?15%,and it was found that Ti₃₅Al₅₀Mo₁₅N coating showed better tool service life by virtue of better mechanical properties,oxidation resistance and good friction properties.