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In order to reduce the difficulty of preparing binder-less cemented carbide and further broaden its application prospects, tungsten carbide toughened by in situ elongated β-Sialon grains was developed via sintering ball-milled WC and α-Si 3 N 4 powders using Al 2 O 3 –ZrO 2 as a sintering aid and transformation additive. The two-step spark plasma sintering of the mixture at 1650 °C with dwelling at 1500 °C for 10 min was conducted under 30 MPa uniaxial pressure, and the densification behaviors, phase transformations, mechanical properties, and microstructures of the produced composites were investigated. The addition of Al 2 O 3 –ZrO 2 reduced the initial temperature of the densification process by approximately 100 °C and its final temperature by 200 °C (compared with the densification temperatures of pure WC and Si 3 N 4 materials) and fully transformed α-Si 3 N 4 to Sialon (Si–Al–O–N) phases. Microstructural characterization data showed that the WC matrix contained homogeneously distributed equiaxed and elongated β-Si 5 AlON 7 grains. The WC composites containing in situ elongated β-Sialon grains exhibited an optimal hardness of 18.93 ± 0.03 GPa and enhanced fracture toughness of 10.43 ± 0.27 MPa m1/2. The toughening mechanism of the β-Sialon phase involved the pull-out of elongated grains and crack bridging. [ABSTRACT FROM AUTHOR]

In this work, a novel way was developed to facilitate the sintering of a binderless cemented carbide with Al 2 O 3 contain while improving its toughness. WC- 1.87 wt % Al 2 O 3 - 4.13 wt %ZrO 2 cemented carbides with 1 wt % B 2 O 3 as additives were consolidated by high energy ball-milling and spark plasma sintering the as-milled composite powders. The effects of 1 wt % B 2 O 3 content on the sintering behaviour, microstructure and mechanical properties of the obtained cemented carbides were investigated. The presence of B 2 O 3 significantly lowers the sintering temperature by forming liquid phase and react with Al 2 O 3 which contributed to obtaining fully dense specimens at 1350 °C and maintains fine grain sizes of WC until the temperature exceeding 1450 °C. The sintering temperature of the specimens with optimum mechanical properties has been also reduced comparing that of the original WC- 1.87 wt % Al 2 O 3 - 4.13 wt %ZrO 2 cemented carbides. Furthermore, the addition of B 2 O 3 triggered the reaction between B 2 O 3 and Al 2 O 3 resulting in forming in-situ elongated aluminium borate grains (A 4 B 2 O 9 and A 18 B 4 O 33 whiskers), which promoted the toughness. The specimens sintered at 1450 °C exhibited optimal mechanical properties: the Vickers hardness and fracture toughness were 19.26 GPa and 11.49 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

In order to prepare cobalt-free cemented carbide by liquid phase sintering, various contents of Al 2 O 3 –ZrO 2 by eutectic ratio were utilized as binders for tungsten carbides. The effects of Al 2 O 3 –ZrO 2 content on the densification, microstructure, mechanical properties, and interfacial characteristics of these binderless tungsten carbides were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high–resolution transmission electron microscopy, and mechanical properties tests. The fully dense WC toughened by Al 2 O 3 –ZrO 2 composite powders could be consolidated through spark plasma sintering at 1600 °C. The results indicated that a small amount of eutectic Al 2 O 3 –ZrO 2 binder phase (up to 3 wt%) would aggregate, increasing the contact chance of WC particles and eventually leading to abnormal growth of WC grains. When the Al 2 O 3 –ZrO 2 content increases to 6.0 wt%, the abnormal growth of WC particles was inhibited by the pinning effect of the well-distributed second phase. The mean grain size of WC decreased with the increasing amount of Al 2 O 3 –ZrO 2 content, while the mean grain size of Al 2 O 3 –ZrO 2 colony increased. The temperature corresponding to the maximum shrinkage rate of densification process decreased with increasing Al 2 O 3 –ZrO 2 content. In general, with the increase of the eutectic ceramic content, the hardness of the composite decreased and the indentation fracture toughness increased. The toughening mechanisms include crack deflection, crack bridging and t– to m–ZrO 2 phase transformation toughening. The WC–Al 2 O 3 –ZrO 2 composites show maximum toughness of approximately 10.5 MPa m1/2 and hardness value of 22.29 GPa, respectively. [Display omitted] • WC–Al 2 O 3 –ZrO 2 composites were fabricated with different contents of Al 2 O 3 –ZrO 2. •FESEM & TEM confirmed the microstructural features of WC–Al 2 O 3 –ZrO 2 composites. •Al 2 O 3 –ZrO 2 content exceeds 3 wt% can refine WC grain size and improve toughness. •Toughening mechanisms include crack deflection, bridging and ZrO 2 phase transformation. [ABSTRACT FROM AUTHOR]

Ultrafine grain WC-1.0 wt% carbon nanotube (CNT) composites were prepared using spark plasma sintering and the influence of sintering temperature on the properties of the composites was investigated. The specimen tested in this study achieved an optimum hardness of 22.81±0.81 GPa and fracture toughness of 8.95±0.38 MPa m 1/2 after sintering at 1700 °C. On applying a sintering temperature of 1900 °C, the mechanical properties of the specimens deteriorated. Raman spectroscopic analysis results indicated that the structure of the CNTs changed and the graphite phase occurred at 1900 °C, which was responsible for the deteriorating hardness, elastic modulus, and fracture toughness. This study provides details of the transformation of the CNTs in the tungsten carbide matrix, indicating that the WC-CNT composites should be sintered at moderate temperatures. [ABSTRACT FROM AUTHOR]

WC-Al 2 O 3 and WC-ZrO 2 composites in previous research suffered a trade-off between hardness and fracture toughness. Herein, it is found that combining 2.8 wt% Al 2 O 3 and 6.8 wt% ZrO 2 together in a WC composite, via spark plasma sintering, can produce both high hardness and high fracture toughness. The new composite was sintered at temperatures ranging from 1350 to 1600 °C, and the densification, phase constitution, microstructure, and mechanical properties of it were investigated. Surprisingly, the WC-2.8 wt% Al 2 O 3 -6.8 wt% ZrO 2 composite achieved full densification at a low sintering temperature of 1400 °C. With a sintering temperature of 1450 °C, the optima hardness and fracture toughness were produced, 21.0 GPa and 8.5 MPa m 1/2 , respectively. The mechanisms driving the low sintering temperature and well-combined mechanical properties of the composite were identified and explored. [ABSTRACT FROM AUTHOR]