Power Injection Molding Of A Kovar Alloy

Kovar alloys have a lower thermal expansion coefficient .They can be sealed with materials such as ceramics, glass. And they are widely used in the fields of microelectronics and optical fiber communication. The rheological behaviors of powder feedstocks and debinding rules ofmolded compact are studied on the base of capillary rheometer and TGA. The SEM and thermal expansion analysis are used to investigate the microstructures of the parts of MIM Kovar alloys and the thermal expansion properties respetively.The feedstocks rheology of three wax-based multi-polymer binders were investigated. Through comparison of n value (exponent used to characterize the fluid ) .The feedstock suitable for MIM was abtained:58%PW+20CERESIN+10%EVA+10%HDPE+2%SA. The according optimum MIM process parameters were also acquired: injection temperature is between 135℃ and 140 ℃ ,molding pressure is 80%,holding pressure is 70% and mold temperature is 40 ℃ .Thermal debinding technology and solvent debinding technology were both used. And thermal debinding was under the atmosphere of H2.The ideal process was divided into four stages:(1)the temperature increases from room temperature to 115℃ in 30mins;(2) the temperature increases form 115 ℃ to 350 ℃ in 240mins and thenremains for 60mins; (3) the temperature increases from 350℃to 490℃ in 30mins and then holds 30mins; (4) the temperature increases from 490 ℃ to 650℃ in 30mins and then holds 30mins.The ideal solvent debinding process in that the injection compact is dipped into the mixture of trichlene+ethanol+peanut oil to do debinding for 13 hours. Then the following thermal debinding process is needed: the temperature increases from 350 ℃ to 430 ℃ in 60mins and then holds 60mins;thus the debinding compact cools to room temperature with the oven.The different sintering temperatures and holding times on sintered compact density were also studied. The results show that the sintered compact density was obvious improved with the increase of sintering temperature and holding time. The compacts were sintered at the temperature of 1280℃ for two hours and their densities were increased to 8.13g/cm3.Sintered under the atmosphere of H2,the carbon in the sintered compact was almost eliminated. This has a positive effect on the expansion coefficient of alloys.The thermal expansion coefficients of Kovar alloys meet the requirement of GB.