Design of Microwave Sintering Unit for Development of Copper-Chromium Contact Materials

Abstract

In the present work design modification and development of microwave sintering unit has been carried, to make it suitable for its usage at high vacuum, using traditional methodology which is assisted by modern analytical tool. The present work investigates the possibility of consolidating 75Cu-25Cr alloy through microwave sintering technique. An attempt has been made to compare the results of microwave sintered specimens with its conventional counterparts. This study also compares the sintering behaviour of 75Cu-25Cr alloy powder made with mechanical milled Cr powder in both conventional method as well as microwave method. The study also aims to understand the effect of mechanical milling on the sinterability and on different properties of same alloy developed in both conventional and microwave furnace. The phase evolution and morphological changes of the milled samples were carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The consolidation of green compacts was carried out at 1050 ºC with variation of sintering as a function of three peak soaking periods i.e. 30 minutes, 60 minutes and 180 minutes, and also with variation of three relative green density values i.e. 57% , 67% and 78% of theoretical density. The comparative analysis is based on the sintered density, hardness, electrical conductivity and microstructures of samples. The results show that microwave sintering requires about 75% less processing time as compared to conventional sintering for this alloy. The microwave sintered specimens showed superior mechanical properties compared to conventionally sintered counterparts due to better densification. Also, microwave sintered specimens have showed good enhancement in electrical conductivity. Microstructural study revealed that microwave sintering produces well rounded and finer chromium particles which are wellseparated from each other as opposed to the sharp, irregular and wedge shaped chromium particles for the conventionally-sintered samples. Also, microwave sintering resulted in significantly lower Cr grain coarsening.