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<p>The effect of cold isostatic pressing (CIP) of unsintered powder blanks on the formation of the structure and mechanical properties of the hard alloy WC–8Co–0.3VC was studied. Three series of samples of the following compositions were produced: WC–8Co, WC–8Co–0.3VC and WC–8Co– 0.3VC, which before CIP was subjected to sintering. All samples were obtained from the same batch of powders under identical conditions of pressing and sintering. It was established that the alloy with 0.3 wt. % VC contributed to the reduction of the average WC grain size from 0.88 to 0.80 μm, while the combination of VC and CIP addition to 0.68 μm, which in turn was accompanied by a thinning of the thickness of the Co layers. However, in the alloy, which was additionally subjected to isostatic pressing before sintering, the CIP led to the formation of a bimodal distribution of the binding phase with the formation of local clusters (lakes) of cobalt. It is shown that with a decrease in the average WC grain size, the hardness increases (up to 16.3 GPa for the WC-8Co-0.3VC series, which was subjected to CIP). As is characteristic of doped hard alloys with grain growth inhibitors, the introduction of 0.3 wt. % VC to WC-8Co leads to a drop in strength and crack resistance. The strength limit during the three-point bending test decreased from 1770±65 MPa to 1110±85 MPa, which is about 40%, and the crack resistance – from 12.0±0.3 MPa·m<sup>1/2</sup> to 10.1±0.2 MPa·m<sup>1/2</sup> (about 16%). This is due to the thinning of the cobalt layers and the decrease in the coherence of the WC/Co interface due to the formation of complex carbide (W,V)C<sub>x</sub> at the interface. Compared to the WC– 8Co–0.3VC alloy formed only by uniaxial pressing, the series, which was additionally subjected to sintering by CIP, showed an increase in the strength limit to 1340±95 MPa (about 21%) and an increase in crack resistance to 15.4±0.2 MPa·m<sup>1/2</sup> (about 50%). Cold isostatic pressing significantly reduced the average size of WC grains, which was accompanied by an increase in the hardness of the alloy, at the same time partially eliminated the negative effect of GGI on the strength of the alloy and provided a significant increase in the material’s crack resistance.</p>

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Efficiency of Cold Isostatic Pressing For Cobalt Bimodal Structure Formation in Strength and Crack Resistance Enhancement of VC-doped WC–8CO Hard Alloy

  • 期刊论文

  • 发表日期：

    2026年7月4日

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  • V. I. Sheremet,
  • G. Ya. Akimov,
  • I. V. Andreev,
  • S. P. Staryk,
  • I. Yu. Trosnikova,
  • O. V. Stepanov,
  • S. O. Rudenkiy,
  • P. I. Loboda

摘要

The effect of cold isostatic pressing (CIP) of unsintered powder blanks on the formation of the structure and mechanical properties of the hard alloy WC–8Co–0.3VC was studied. Three series of samples of the following compositions were produced: WC–8Co, WC–8Co–0.3VC and WC–8Co– 0.3VC, which before CIP was subjected to sintering. All samples were obtained from the same batch of powders under identical conditions of pressing and sintering. It was established that the alloy with 0.3 wt. % VC contributed to the reduction of the average WC grain size from 0.88 to 0.80 μm, while the combination of VC and CIP addition to 0.68 μm, which in turn was accompanied by a thinning of the thickness of the Co layers. However, in the alloy, which was additionally subjected to isostatic pressing before sintering, the CIP led to the formation of a bimodal distribution of the binding phase with the formation of local clusters (lakes) of cobalt. It is shown that with a decrease in the average WC grain size, the hardness increases (up to 16.3 GPa for the WC-8Co-0.3VC series, which was subjected to CIP). As is characteristic of doped hard alloys with grain growth inhibitors, the introduction of 0.3 wt. % VC to WC-8Co leads to a drop in strength and crack resistance. The strength limit during the three-point bending test decreased from 1770±65 MPa to 1110±85 MPa, which is about 40%, and the crack resistance – from 12.0±0.3 MPa·m1/2 to 10.1±0.2 MPa·m1/2 (about 16%). This is due to the thinning of the cobalt layers and the decrease in the coherence of the WC/Co interface due to the formation of complex carbide (W,V)Cx at the interface. Compared to the WC– 8Co–0.3VC alloy formed only by uniaxial pressing, the series, which was additionally subjected to sintering by CIP, showed an increase in the strength limit to 1340±95 MPa (about 21%) and an increase in crack resistance to 15.4±0.2 MPa·m1/2 (about 50%). Cold isostatic pressing significantly reduced the average size of WC grains, which was accompanied by an increase in the hardness of the alloy, at the same time partially eliminated the negative effect of GGI on the strength of the alloy and provided a significant increase in the material’s crack resistance.