Study On Structure And Performances Of MoS₂-Ti And CrTiAlN+MoS₂-Ti Coatings

Closed field unbalanced magnetron sputtering ion plating is characterized by low treatment temperature,low deformation of work piece and operation simplicity.The composition and structure of coatings can be controlled by this technology.Moreover,by taking advantage of high binding force of the ion plating,this process is able to produce the innovative gradient coating with suitable structure and remarkable property to satisfy the complex working requirements of cutting tool coatings.In conclusion,closed field unbalanced magnetron sputtering ion plating can be used as the final process for the coatings of high speed steel cutting tools.CrTiAlN coatings,MoS₂-Ti coatings and CrTiAlN+MoS₂-Ti composite coatings have been prepared on domestic high speed steel W₆Mo₅Cr₄V₂ using closed field unbalanced magnetron sputtering ion plating.Interlayers and transition layers was introduced to improve the adhesion strength of the coatings. Meanwhile,the surface morphologies,composition,microstructure and the thermal stability of the coatings were investigated by electron probe microanalysis(EPMA),X-ray diffraction(XRD),transmission electron microscope(TEM),differential thermal analysis(DTA).The results show that the CrTiAIN coatings are nano-crystalline structure and their grain size ranges from 10 to 30 nm.Their microhardness is about 2450 HV0.025.The CrTiAlN coatings are composed of(Cr,Ti,Al)N solid solution phase with face-centered cubic structure,whose(111)crystal face oft he solid solution has very strong preferential growth tendency.The components of TiN, AlN and CrN formed during the reaction between titanium and aluminum with nitrogen in sputtering to have the same lattice structure and similar lattice constant.Therefore they may form coherent interface and improve the combine strength of the coating and substrate.The underlayer of chromium and the gradual composition variation of Al,Ti,Cr contribute to the sufficient cohesion strength and hardness for the top layer of the coatings.Moreover,by isolating the nitrogen element with the substrate,the embrittlement of the coatings has been prevented.The titanium and the aluminum atoms that distort the lattice of the solid solution would cause the substitution solid solution strengthening and eventually increase hardness of the coatings.Besides,the chromium and the aluminum could form Al₂O₃,Cr₂O₃ protecting film on the surface layer of the coating to prevent further oxidation and enhance the thermo stability of the coatings.The MoS₂-Ti coatings consist of nano-crystalline and amorphous phase. Microhardness of the MoS₂-Ti coatings is about 980HV0.025.Through X-ray diffraction,it is shown that the slip plane(002)crystal plane is preferential,so the coatings have a low friction coefficient.The oxidization temperature of the MoS₂-Ti coatings is about 503.8℃,far higher than that of the pure MoS₂(315℃). The titanium could reduce the oxygen impurity content,as well as cavity and holes of the MoS₂-Ti coatings,so that the compactness of the coatings would be enhanced.Meanwhile,titanium can also result in solid solution strengthening and elevates the strength and hardness of the coatings.Titanium could form protecting film on the surface layer of the coating to inhibit the oxidation of molybdenum and improve the thermo stability of the coating.The CrTiAlN+MoS₂-Ti coatings are composed of nano-crystalline and amorphous phase and the CrTiAlN+MoS₂-Ti coating oxidizes at about 507.3℃. Microhardness of the CrTiAIN+MoS₂-Ti coatings is about 980HV0.025.The high hardness of CrTiAlM make it the protecting skeleton of the coating which can delay the premature tear and flaking caused by the plastic deformation, thereby increase the strength and hardness of the coating.The MoS₂-Ti coatings can play a role in self-lubricating to reduce the friction coefficient.Besides,the interface effect of the multilayer structure could improve the hardness,toughness and the resistance against crack growth.Likewise,the toughness of the coatings can also be increased by the existence of the amorphous phase in the coatings.