Effect of the Cubic Phase Distribution on Ultrafine WC–10Co–0.5Cr–xTa Cemented Carbide

Abstract

The (Ta, W)C cubic phase distribution plays a key role in the microstructure and mechanical properties of ultrafine WC-CoCr 3 C 2 -TaC cemented carbides. By integration of thermodynamic calculations and key experiments, the influence of the cubic phase distribution in ultrafine WC-10Co-0.5Cr-xTa cemented carbides was systematically investigated. A series of ultrafine grained cemented carbides were designed and fabricated through ball-milling and vacuum sintering at 1410°C for 1 h. The microstructure was investigated using scanning electron microscopy (SEM). The electron backscattered diffraction (EBSD) was used to measure the orientation and size of cubic phase segregation. The results indicate that the cubic phase in the microstructure distributes more heterogeneously in the range of 0.2 to 0.7 wt% Ta addition, but finally the isolated cubic phase is homogeneously distributed with a Ta content from 0.7 to 1 wt%. Combining the thermodynamic calculation with the experiment, the mechanism for the microstructure evolution has been revealed. The mechanical properties of alloys substantially depend on the cubic phase distribution in the microstructure. A synergetic correlation between the transverse rupture strength (TRS) and Rockwell hardness was observed. The homogeneity of cubic phase can be designed and controlled effectively via the present approach.

Effects of Cr3C2, VC, and TaC on Microstructure, WC Morphology and Mechanical Properties of Ultrafine WC–10 wt. % Co Cemented Carbides

“…This result was in good agreement with Li et al conclusions [23]. Li et al [23] determined these precipitates to be (Ta, W) C phase which was formed as the amount of added TaC exceeded the saturation solubility. The non-uniform distribution of precipitates leads to the heterogeneous microstructure, which has the negative influence on mechanical properties of cemented carbides.…”

“…The EDS analysis result of point B (shown in Figure 4d) indicates that the precipitates are rich in Ta, W, and C but deplete in Co. This result was in good agreement with Li et al conclusions [23]. Li et al [23] determined these precipitates to be (Ta, W) C phase which was formed as the amount of added TaC exceeded the saturation solubility.…”

“…%. Studies have shown that dissolved GGI will precipitate out when the amount of added inhibitors is over the maximum solubility [23,25,27,28]. EDS analysis results indicate the precipitates formed in A3 are rich in V, W, and C, but deplete in Co, which can be deduced to be (V, W) C cubic phase.…”

Investigation of WC–Co alloy properties based on thermodynamic calculation and Weibull distribution

“…A slight change of the carbon activity may lead to the formation of a harmful phase. At lower carbon activity, the two-phase region is limited by the three-phase equilibrium WC–Co–eta(M 6 C), and at higher carbon activity the three-phase region is limited by the three-phase equilibrium WC–Co–graphite [19]. Neither the brittle eta nor the soft graphite phase is desired in the sintered structure.…”