Effect Of Heat Treatment On Microstructures And Properties Of CuWCr Composite

With the development of switch equipments to fit larger capacity,higher voltage and miniaturization,it is required for the contact material,as a central part of the breaker to have an increasingly excellent combined properties.CuWCr composite is a new contact material.It has higher breakdown strength and lower chopping current,but has some flaws such as lower electric conductivity,bigger brittleness and so on.In order to improve combined properties of the composite and apply to higher voltage,bigger current vacuum breaker,in this paper,the heat treatment is used to improve its mierostrueture and enhance its combined properties.The microstructure,hardness and some vacuum breakdown properties of CuWCr composite are researched before and after heat treatment in order to make sure weather high comprehensive properties can be achieved or not by solid solution+aging heat treatment.The effect of heat treatment on microstructures and properties of CuWCr composite is systematically investigated by changing solid solution temperature and time,aging temperature and time.The microstructure is studied and hardness and electric conductivity are measured in different heat treatment process.Under the same heat treatment process,the microstructure, hardness and some vacuum breakdown properties of CuWCr composite with different Cr contents are studied.It can be drown the following conclusions from those investigations:1.Comparison of un-heat treatment,solid solution and solid solution+aging treatment three different states' CuWCr composites,the hardness of the last one is highest,the first one is lowest,the electic conductivity of the two states'composites has not changed significantly and the second one obtains the lowest.After 100 times' vacuum electric breakdown,the CuWCr composite after solid solution +aging has the biggest breakdown strength,the longest arc life and the lowest chopping current.However,those counterpart values have the total opposite results after solid solution treatment. 2.Under the same aging process,the largest quantity and the thinnest Cr grains are precipitated in Cu and W areas of CuWCr composite after 920℃solution,holding 0.5h.The electic conductivity of CuWCr composite decreases with increase of solid solution temperature from 890℃～980℃,the hardness firstly increases and obtains the highest at 920℃,then decreases.In the range of 0.5h～2h solid solution time,the hardness of CuWCr composite decrease with prolong of solid solution time and the electic conductivity reverses.3.Under the confirmed solid solution process,the largest amount of strengthening phases is dispersively precipitated in Cu and W areas of CuWCr composite after 500℃aging,holding 2h.The electic conductivity and hardness of CuWCr composite firstly increase and obtain the highest at 500℃,then decrease with increase of aging temperature from 450℃～600℃.In the range of 1h～4h aging time,the eleetic conductivity and hardness of CuWCr composite firstly increase and obtain the highest at aging 2h,then decrease with prolong of aging time.4.The maximum hardness and electic conductivity of CuWCr composite can be researched at 920℃solution,holding for 0.5h and 500℃aging,holding for 2h under this experiment condition.5.CuWCr composite with different Cr contents after the same solid solution +aging heat treatment process,the strengthening phases quantity decreases,the hardness decreases and the electic conductivity increases with decrease of Cr content.After 100 times' vacuum electric breakdown,with decrease of Cr content,the breakdown strength of CuWCr composite decreases,the chopping current increases and the arc life shortens.