Investigation On Fabrecation,Structures And Properties Of Submicron WCu Alloys

WCu contact,as a core component of circuit breaker,plays an important role in the EHV(330~1000KV)and UHV(above 1000KV)transmission grid.Conventional contacts just can be used only for tens times,but in the new grid environment,the contacts need to be used for 3,000 times,which can be satisfied.Thus improving the arc erosion resistance and wear resistance should be the key to develop a new contact material.In this paper,the effects of temperature and copper content on the microstructure and properties of submicron WCu alloy during the liquid phase sintering process,and the homogenization by refining the precursor powders were studied.Then the properties of the alloy sintered at optimum temperature with suitable copper content under simulate actual conditions were tested.With the analysis of experiment results,the following conclusions can be obtained:The densification rate of submicron WCu alloy increases linearly with sintering temperature during liquid phase sintering process,but the relative density is limited by short-term high temperature sintering.When the alloy is re-sintered under appropriate condition,the relative density can be improved effectively leading to a significant effect on all the performance of the alloy.The densification rate of submicron WCu alloy increases exponentially with copper content during liquid phase sintering process.When the copper content is less than 25 wt.%,it is helpful to contact,neck growth,mergence for submicron tungsten particles with copper content increasing,which can ensure the continuity of the tungsten skeleton making the alloy has high strength.When copper content is more than 25 wt.%,the excess copper will hinder mass transfer between the tungsten particles and inhibit mergence growth.When the copper content is more than 35 wt.%,it will weaken the capillary force during initial liquid-phase sintering process making the excess liquid copper fall and overflow to the bottom of the sample,which will cause a larger deviation to the actual copper content.The high energy ball milling of the mixed powders can effectively improve the uniformity of the WCu alloy.While to the homogenized sample,the tungsten particles has a special stacking form(nearly close-packed stacking),which will lead to a reduction of actual copper content,making the conductivity decline to a certain extent.On the other hand,to the homogenized sample,the tungsten particles have higher tendency to reunite during the high temperatures(900 ℃)thermal fatigue process than the sample without homogenization.The submicron WCu alloy with 25 wt.% copper content sintered at 1300℃ and re-sintered gets high relative density(99.6%).The hardness(220HB)is well matched with the conductivity(50.43% IACS).The electrical breakdown strength is stable and the chopping current is small.Under the simulate actual conditions,compared with the traditional commercial CuW70,the submicron WCu alloy has better resistance to high temperature fatigue and abrasion and the high temperature compressive strength is more excellent as well.