| In this paper,the superfine composite powder of YT14 cemented carbide whose average particle size is 0.27μm has been prepared successfully by 72-hour high-energy ball milling,and its raw materials were micron-level WC,(W,Ti) C and Co powder whose average particle size is 2.52μm.The process included drying, riddling,pressing and sintering in a vacuum furnace.The preparation of the powder and pressed shape,the sintering process parameters,the performance and the microstructure were studied,the experimental results were also discussed and analysed,conclusions can be drawed as following:1.The pressed shape of YT14 composite powder was prepared by using 80Mpa common pressure,holding the load 2 minutes,and the green density was 5.42 g/m3.The pressed shape which was pressed by common press mould could improve the green density by applying isostatic cool pressing,however,the process was complex.2.While sintering,firstly the temperature was rised from room temperature to 350℃with the heating rate of 15℃/min,holding that temperature 30min.Secondly from 350℃to 800℃with the heating rate of 10℃/min,holding 30min.Thirdly from 800℃to 1100℃with the heating rate of 10℃/min,keeping 30min.Finally from 1100℃to the sintering temperature with the heating rate of 4℃/min,keeping 40min.Sintering temperature were 1380℃.The whole process was under a vacuum status and controlled the vacuum degree from 1.0×10-1 to 1.0×10-2 Pa. This design of process parameter was appropriate,there was no impact on the quality of the sintered body and the sintered metal bond lose a little in sintering.The sintering temperature of the superfine cemented carbide was lower than that of the normal cemented carbide.3.The density of the YT14 green shape was increased from 11.19g/m3 to 11.47 g/m3 while the conditions were 1380℃sintering temperature,80 Mpa preesure, and the holding temperature time were increased from 20 min to 40 min.This density was close to the theoretical density of 11.49 g/m3.While the sintered time was extended to 50 min and 60 min respectively,the density of the sintering body were decreased to 11.457g/m3 and 11.277g/m3.Therefore the sintered demands could be met with 40-minute holding temperature time.4.While the sintering temperatures were 1300℃,1350℃,1380℃and all of the holding temperature time were 40 min,the sintered density increased with the increasing temperature,from 10.17 g/cm3 to 11.47 g/cm3.While the sintering temperature was rose to 1410℃,the sintered density was reduced to 11.42 g/cm3. As the temperature was rose from 1300℃to 1410℃,the linear shrinkage ratio was increased from 13.2%to 17.5%.5.The hardness of the YT14 green shape was increased from 89.7HRA to 92.7HRA while the conditions were the sintering temperatures from 1300℃to 1380℃,80 Mpa preesure,and the holding temperature time was 40 min.Then while the sintering temperature was increased to 1410℃,the hardness was decreased to 90.4HRA.The hardness of the traditional YT14 cemented carbide was only 90.2HRA while the sintering temperature is 1480℃.Obviously,the hardness of the cemented carbide which is applied by the YT14 superfine powder is higher. While the sintering temperature was increased from 1300℃to 1410℃,the bending strength was increased from 963Mpa to 1390Mpa.6.While the sintering temperature under 1380℃,the WC and(Ti,W) C crystal were relatively small,and they were appeared a multilateral shape.As the sintering temperature was increased to 1410℃,the crystal was grown up obviously. WC+(TiW)C+Co+γand a small amount ofηphase were the metallurgical structure,and a small quantity of aperture gap and dirt were existed.The mechanical properties were led to be reduced by the aperture gap and dirt. Measures should be taken to eliminate the dirt,and theηphase should be eliminated by conquering the phenomenon of carbide's lack while sintering.Then the purpose that improving the performance of the bending strength etc would be achieved. |
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