The Preparation Of WC-8Co Hardmetal By One-step Method And Its Cutting Performance

Along with the development of modern machinery technology towards to dry cutting, high speed cutting and high performance cutting direction, there is an increasing demands for developing excellent cutting tool materials. Owing to excellent hardness and wear resistance even at high temperature, hardmetals is considered as one of the most ideal tool material. However, conventional hardmetals is not good enough to meet the tutting requirements of high efficiency, high cutting accuracy and high reliability. This issue would be solved successfully with the development of nanocrystalline/ultrafine hardmetals, which turns out to be an effective means to achieve high hardness and high transvese rupture strength hardmetals. Therefore in this research, nanocomposite powders were prepared by DBDP assisted high energy ball milling, and subsequently carbonizing and sintering to prepare WC-8Co bulks in a one-step method. In addition, wear behavior and cutting performance were investigated for WC-8Co hardmetals prepared by our method in comparison with the commercial YG8 hardmetal.Firstly, the effect of different DBDP milling process and added carbon on preparation of powder and microstructure were investigated. It has been found that, in contrast to pure high energy ball milling, the finer grain size and the structure of lamellar composite powder was achieved by suitable time of DBDP milling. Besides that, with this DBDP milling powder mixture and an additional 7.5% added carbon, WC-8Co hardmetals were obtained by one-step vacuum sintering at 1390℃ with neither the lack of carbon phase, nor free graphite phase existed.Secondly, the effect of different sintering temperature on the mircostructure and properties of WC-8Co hardmetals were studied. The results show that as the temperature increasing, the migration of liquid Co phase enhanced, which increases the density of the hardmetals. But abnormal grain growth of WC too seriously and the contiguity of WC-WC increased, which leaded to decrease the hardness and TRS. In comparison to those sintered at 1410 ℃, 1430 ℃ and 1450 ℃, the WC-8Co hardmetal sintered at 1390℃ had a relatively optimum combination of hardness and TRS. The hardness and TRS were 91.9HRA and 1849 MPa respectively. What’s more, through controlling the heating rate and holding time, microstructure homogensity was better and WC grain growth was inhibited. Among them, the WC-8Co hardmetal prepared by sintering processⅡgot the best mechanical properties. The hardness and TRS reached 93.1HRA and 2264 MPa respectively.Furthermore, wear measurement showed that WC-8Co hardmetals prepared by the present methods had a lower friction coefficient and wear loss than that of YG8 due to the finer WC grain size and better mechanical performance. Among them, the WC-8Co hardmetal prepared by sintering processⅡgot the best wear properties.Finally, the cutting performance of above hardmetals showed that the WC-8Co hardmetal prepared by sintering processⅡis the best. The durability of it reached to 28 min at the cutting speed of 90m/min and the flank wear mechanism was mainly to abrasive wear. While at the cutting speed of 200m/min, the durability of WC-8Co hardmetal prepared by sintering processⅡ was 33% longer than YG8 and its flank wear mechanism was oxidation wear.