1 College of Mechanics and Materials, Hohai University, Nanjing 211100, China 2 College of Civil and Transportation Engineering, Hohai University, Nanjing 210098, China 3 CCCC Tunnel Engineering Company Limited, Beijing 100102, China
Extra-coarse-grained WC-Co cemented carbides are focused by researchers due to the high wear resistance and toughness, whereas the densification and WC grain tailoring are key factors for obtaining excellent performance. Extra-coarse-grained WC-10Co cemented carbides with an average grain size of 8.3-8.8 μm were prepared by a mild-ball-milling and vacuum sintering processes with ultra-fine WC powder obtained by mild-ball-milling method.The effects of sintering time on density, WC grain and mechanical properties were studied. The results show that the relative density first increases and then decreases with sintering time increasing from 30 min to 120 min.Ultra-fine pores also increase by the oxidation and accumulation of Co on the surface, and abnormal grains are formed by the aggregation of some WC grains.Therefore, the elimination of pores is hindered.Furthermore, the average grain size of WC firstly increases and then decreases due to orderly dissolution-precipitation of ultra-fine WC and fragmented fine WC, and finally WC grains are formed with wide distribution.As sintering holding time increases to 60 min, the partial spherical WC grain with curved surface is transformed into performance friendly hexagonal prism grain with rounded edge through faceted steps growth mechanism. Here, the bending strength and impact toughness reach the maximum of 1733 MPa and 28 kJ·m-2, respectively.Furthermore, the primary defects are difficult to be completely eliminated in some grains during sintering.With longer sintering holding time, the increased multiple defects result in the deterioration of properties.
Fig.4 不同烧结保温时间时超粗晶WC-10Co硬质合金的金相形貌 (a)30 min；(b)60 min；(c)90 min；(d)120 min
Fig.5 烧结保温时间对WC晶粒P的影响
Fig.6 不同烧结保温时间时超粗晶WC-10Co硬质合金的WC晶粒形貌 (a)30 min；(b)60 min；(c)120 min
Fig.7 烧结保温时间对硬度、抗弯强度和冲击韧性的影响
Fig.8 烧结过程中WC晶粒的生长演化示意图
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2021, Vol. 49 
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