Preparation Of WC/Fe Alloy Three-Layer Film On Tungsten Surface By Thin Film Deposition Combined With Interstitial Carburizing Modification

Tungsten and its alloys are widely used in aerospace,military chemical industry,machinery manufacturing,mining metallurgy and other fields,known as the ’teeth’ of industry.However,the low surface hardness and toughness of tungsten and its alloys greatly limit its application.The preparation of ceramic metal multilayer film on the surface of metal tungsten can effectively enhance the surface strength and toughness.However,the common preparation methods of multilayer films have problems such as too flat film-substrate interface,low bonding strength,and poor film-substrate bonding strength.Therefore,in this work,WC/Fe-C alloy/WC trilayer film and WC/Fe-Ni alloy/WC trilayer film on tungsten surface were prepared by a combination of thin film preparation technology and interstitial atom carburizing.For the preparation of WC/Fe-C alloy/WC three-layer film,firstly,the Fe layer on the surface of tungsten was prepared by electroplating method,and then the W layer was deposited by magnetron sputtering to obtain the W/Fe double layer film on the surface of metal tungsten,and then the W/Fe double layer film on the surface of tungsten was modified by interstitial atomic carburization method to WC/Fe-C alloy/WC three-layer film.For the preparation of WC/Fe-Ni alloy/WC three-layer film,the W/Ni double-layer film on the surface of tungsten was prepared by magnetron sputtering.The W/Ni double-layer film on the surface of tungsten was carburized by interstitial atom carburizing method.The W/Ni double-layer film on the surface of tungsten was modified to WC/Fe-Ni alloy/WC three-layer film.In this work,the microstructure,phase transformation,hardness,adhesion and fracture toughness of WC/Fe alloy/WC three-layer films were studied.The results show that:(1)WC/Fe alloy/WC three-layer films were successfully prepared by interstitial carburization of W/Fe bilayer films and W/Ni bilayer films on the surface of tungsten metal.The interface has good diffusion bonding(the adhesion of the film to the substrate is greater than 85 N).(2)The WC on the surface of the three-layer film prepared by interstitial atom carburizing of the W/Fe double-layer film on the surface of metal tungsten is mainly composed of columnar crystals and a part of fine equiaxed crystals.The volume fraction of WC ceramic layer is close to 100%.The crystal structure of the intermediate metal layer Fe-C alloy is BCC crystal structure,and its grains are mainly composed of fine equiaxed grains.(3)During the preparation of WC/Fe-Ni alloy/WC three-layer film on the surface of tungsten metal,carbon element diffuses into the double-layer film and reacts with tungsten to form WC,while iron element diffuses into the Ni layer to transform it into Fe-Ni alloy layer with Fe element as the main component.When the total carburizing depth exceeds the thickness of the W/Ni bilayer film,the W/Ni bilayer film on the tungsten surface will eventually transform into a WC/Fe-Ni alloy/WC three-layer film.(4)During the preparation of WC/Fe-Ni alloy/WC three-layer film on the surface of metal tungsten,the crystal structure of the intermediate metal layer was controlled by adjusting the carburizing temperature and holding time.When the content of Ni element in the iron-nickel alloy layer is low(such as less than 25%),the iron-nickel alloy layer has a body-centered cubic crystal structure.When the content of Ni element in the iron-nickel alloy layer is high(such as more than 30%),the crystal structure of the iron-nickel alloy layer is a face-centered cubic crystal structure.(5)The hardness of WC/Fe alloy/WC three-layer films increases gradually with the increase of carburizing temperature and carburizing time.When the final microstructure is formed,the hardness value reaches the maximum,and the maximum hardness value can reach 1400-1500 HV,which is about 3 times of the Vickers hardness(500 HV)of the tungsten matrix.The fracture toughness of WC/Fe alloy/WC three-layer film is about 4.37-4.82 MPa·m1/2 by indentation method.Crack deflection,plastic deformation of ductile layer under pressure and its blocking crack propagation are the main mechanisms of toughening of three-layer film.