| Molybdenum is a structural material.Because of its high temperature strength,low expansion coefficient,good corrosion resistance and good molding,it is widely used in aerospace,manufacturing and other fields.But the surface hardness of molybdenum alloy is low,leading to low wear resistance.The preparation of ceramic multilayer film on molybdenum surface is an effective way to improve the hardness of molybdenum surface.However,there is a common problem of weak adhesion between layers and between film and matrix.In order to solve this problem,a method of preparing Mo2C/W2C multilayer film on Mo surface by combining magnetron sputtering and carburization was proposed in this paper.Firstly,Mo/W metal multilayer film was prepared on Mo surface by magnetron sputtering,and then transformed into Mo2C/W2C ceramic multilayer film by carburizing.The interdiffusion of Mo and W in the process of high temperature carburization improves the interlayer bonding strength of ceramic multilayers.When the thickness of the carburized layer exceeds the thickness of the Mo/W multilayer film,the surface layer of the molybdenum matrix is also transformed into a Mo2C ceramic layer,and a high strength Mo2C/Mo film/substrate interface can be obtained.In this paper,two methods are used to carburize Mo/W.The results and conclusions are as follows:Interstitial carburization can provide uniaxial pressure to prevent the delamination of the multilayer film at high temperatures,Therefore,in this paper,the Mo/W bilayer film was modified by interstitial carburizing,and Mo2C/W2C/Mo2C three-layer film was prepared on molybdenum surface.The study of microstructure characteristics,microstructure formation process and mechanical properties shows that the growth of ceramic layer is accompanied by the motion of ceramic/metal boundary towards the matrix during carburizing.The obtained ceramic multilayer film has uniform thickness and is dense without pores.The volume fraction of ceramic phase in the multilayer film is close to 100%,in which W2C layer contains a small amount of WC,Mo2C and W2C are mainly columnar grains,and the ceramic phase grains in the surface Mo2C layer and W2C layer are small,while those in the substrate side Mo2C layer are large.There are obvious interdiffusion of W and Mo elements at the interlayer interface,and the degree of interdiffusion increases with the increase of temperature.The hardness of the multilayer film is about 2000HV,and the binding force of the film base is greater than 91N.Solid carburizing is suitable for the workpieces with complex surface.Therefore,in this paper,solid carburizing was used to modify Mo/W multilayers(10-layer),and Mo2C/W2C multilayers(11-layer)were obtained.The microstructure and mechanical properties of the multilayer films are similar to those prepared by interstitial carburization.However,in the carburizing modification of the 10-layer film,Mo2C layer appears below the tungsten layer which has not been completely carbonized.This indicates that the critical carbon concentration required for Mo2C formation is lower than that required for W2C formation.Under the effect of this mechanism,Mo2C/W2C grains are formed through the Mo2C layer and the adjacent W2C layer.Therefore,the Mo2C/W2C 11 film has 6 layers of grains.In this work,Mo2C/W2C multilayer films with diffusional bonding interface were successfully prepared on molybdenum surface by magnetron sputtering and carburizing,and the surface strengthening of molybdenum metal was realized,which provided a new method for the preparation of ceramic/ceramic multilayer films. |
PDF Full Text Request