Parameter Optimization And Cutting Performance Of(Cr,Al)N/AlN Nano Multilayer Coatings

With the rapid development of the manufacturing industry,the application of dry cutting technology has become more and more common.However,in the face of some new difficult-to-machine materials,uncoated tools and traditional coated tools have low machining efficiency and short cutting life,which cannot meet the needs of more increasingly demanding processing conditions,the development of new coated tools is imminent.The nano-multilayer structure coating represented by Cr N/AlN has become a research hotspot due to its superhard effect of abnormally increasing hardness and elastic modulus.However,due to the influence of the modulation cycle on the superhard effect of nano-multilayer coatings,the thickness of the AlN layer in the Cr N/AlN coating can only be high when the thickness of the AlN layer is less than the thickness of the Cr N.This causes the Al content to be limited,and with the Al content increasing,it is easier to form a continuous and dense oxide film on the coating surface and improve the high temperature oxidation resistance of the coating.In view of the above problems,this paper proposes to add Al element(30-75at%)to the Cr N modulation layer of the Cr N/AlN nano-multilayer coating.The Al atoms in this modulation layer replace the Cr atoms in the Cr N phase to maintain the original surface.Centered cubic structure,while the AlN modulation layer is epitaxially grown along the fcc-(Cr,Al)N phase to form a nano-multilayer structure of fcc-(Cr,Al)N and fcc-AlN co-grown,namely(Cr,Al)N/AlN nano multilayer structure.This paper firstly uses DC magnetron sputtering and arc ion plating to prepare Cr N/AlN nano-multilayer coatings,and systematically studies the effect of Al content on its performance.Subsequently,a(Cr,Al)N/AlN nano-multilayer coating was prepared,and the effect of different substrate bias on its performance was studied.Finally,the optimal bias voltage is used to prepare Cr N coating,Cr N/AlN nano multilayer coating and(Cr,Al)N/AlN nano multilayer coating milling cutters.Compare these three kinds of coated milling cutters and uncoated milling cutters and the analysis of the tool failure mechanism.The specific research content is as follows:1.By changing the Al target power,the Al content of Cr N/AlN nano multilayer coating was changed.It was found that with the increase of Al content,the preferred orientation of the coating gradually changed from(111)crystal face of fcc-(Cr,Al)N phase to(100)crystal face of hcp-AlN phase,which also resulted in the gradual decrease of coating hardness.When the Al target power is 2.2kw,the coating has the largest H(30.2GPa),E*(494.3GPa),H/E*(0.063),H~3/E*~2(0.120),and the mechanical properties are the best.Moreover,the cutting life of the turning tool coated with the coating is prolonged by 2 times.2.The effect of substrate bias on the properties of(Cr,Al)N/AlN multilayer coatings was studied.It was found that the phase structure of the coatings under bias voltage of-40V,-80V,-120V and-160V showed a cubic structure of Na Cl type,while the coating under-200V bias showed a mixed cubic wurtzite structure.The preferred orientation of the five coatings was fcc-(Cr,Al)N(111)plane.With the increase of negative bias voltage,the mechanical properties of(Cr,Al)N/AlN nano multilayer coatings increase at first and then increase.When bias voltage is-160V,the hardness and elastic modulus of the coating are 33.1GPa and 548GPa respectively,and the friction and wear resistance of the coating is superior.When the bias voltage is-120V,the H/E*value and H~3/E*~2 value of the coating are the best,which are 0.063 and 0.13,respectively.3.The cutting performance of(Cr,Al)N/AlN nano multilayer coating milling cutter was compared with that of uncoated millin g cutter,Cr N coating milling cutter and Cr N/AlN nano multilayer coating milling cutter by dry cutting method.The cutting life of(Cr,Al)N/AlN nano multilayer coating milling cutter is the longest,reaching 200 min,which is 5.4 times of that of uncoated milling cutter,4.2 times of Cr N coated milling cutter and 2.3 times of Cr N/AlN nano multilayer coating milling cutter,respectively.The cutting performance of(Cr,Al)N/AlN nano multilayer coating milling cutter is the best.By EDS and SEM analysis,the wear mechanism is mainly abrasive wear,adhesive wear,oxidation wear,micro chipping edge and coating peeling off.