Investigation Of The Wettability Of Copper Alloys On Tungsten And Molybdenum

Cu-W composites are widely used as materials for high voltage contact,electronic sealing and hotdepositing due to excellent electric and thermal conductivity,low thermal expansion.Because the meltingpoint of W is higher than that of Cu as well as the mutual insolubility,Cu-W composites are generallyfabricated by infiltration.The problem that how to decrease the solution of preform in liquid and meanwhilethe corrosion of metallic liquid on the preform is one of the difficulties necessarily solved in the researchfield.Whether the infiltraion process is available or not is directly related to the wettability between the liquidand the solid.Nowadays,there are few reports in detail about the effect of various factors on the wettabilitybetween Cu and W.From the analysis mentioned above,this paper described the influence of conditions suchas temperature,contents of Cr and Ni,atmosphere and the intensity of electric field on the wettability betweencopper alloys and W using sessile drop method,respectively.The effects of temperature as well as the contentof Cr on the wetting of Cu-Cr alloys and Mo were also investigated.The purpose of the study is to optimizethe infiltration technology and provide the basic theory for its popularity and application.Firstly,the wetting angles of Cu-Cr alloys with different Cr contents on W and Mo in vacuum at 1100℃,1200℃as well as those of Cu-Ni alloys with different Ni contents on W in Ar atmosphere at 1150℃,1250℃,1350℃were examined respectively.The wetting mechanisms of Cr and Ni contents and temperatureon the wetting characteristics were analysed.The results show that the addition of Cr and Ni into Cu reducesthe wetting angle between Cu and W and that the wetting angle can be gradually decreased with theincrement of Cr and Ni contents because of Cr and Ni as active elements.The wetting angles of copper alloyswith the same additive contents on both W and Mo are decreased with the increase of tempearature.Theinterface was analyzed by EDS and EPMA.It is revealed that the improvement of the wettability is related tothe diffusion of elements and that the interfacial diffusion is enhanced by increasing temperature.Themechanism may be diffusion-soluion wetting which decreases the interfacial tension and can be considered asthe combination of reactive wetting and no reactive wetting.Secondly,the effects of different atmosphere conditions on the wetting between Cu and W as well asCu-Cr alloys and W were examined systematically.For Cu-W system,the results show that the wettability invaccum,N2 and Ar is bad because oxygen film is found.The product should be practically manufactured inH2 atmosphere in the point of antioxidation.For Cu-Cr-W system,the best result is gotten in vacuum,next is in Ar.Chromium has high affinity to hydrogen and meanwhile reacts with nitrogen to form ceramic phase whichinhibits the wetting so that the wettability in H2 and N2 is not good.This segment shows that the appropriateprocess atmosphere should be chosen for the preparation for Cu-W-Cr composites.Formation of precursorfilm on the substrate in atmosphere may change the configuration of triple line and to some extent results ingood wettability.Finally,the influence of electrostatic field on the wetting between Cu-Cr alloys and W substrate wasstudied.It is found that the electric field has some positive effects on the wettability between Cu-Cr alloys andW.The research of phenomenological theory shows that increasing the intensity of electric field coulddecrease the interface energy and that facilitate the elements diffusion which leads to the decrease of thewetting angle consequently.By deducing the function relation between the wetting angle andΔG of interfaceenergy,the influence of the reduction of interface energy caused by electric field on the good wetting was setforth further.The mechanism of the effect of electric field on the wetting between metallic liquid and solid isstill well worth investigating.