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Effect of ZrO₂ Doping on Strength and Toughness of Mo₂NiB₂-Based Cermets

W. Li, Z. Fan, T. Ai, H. Dong, P. Jiang, X. Zou

Journal of Ceramic Science and Technology, Vol. 12, No. 2 (2021), pp. 115-124

DOI: 10.4416/JCST2021-00012

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Abstract

Mo2NiB2-based cermets possess superior strength and excellent corrosion resistance, however, they usually exhibit poor toughness at room temperature. An improvement in toughness without reducing their strength is critical for the practical application of cermets. In this study, four series of Mo2NiB2-based cermets doped with ZrO2 particles (0 wt%, 1.0 wt%, 1.5 wt% and 2.0 wt%) were fabricated based on the boronizing sintering reaction of a mixture of ball-milled Mo-Ni-B-ZrO2 powders. The effect of the ZrO2 content on the microstructure and crystalline phases was investigated by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD). The flexural strength and fracture toughness of the developed materials were also evaluated. At a ZrO2 mass fraction of 1.0 wt%, the sintered cermet exhibited an optimal microstructure consisting of a continuous Ni phase with embedded Mo2NiB2 (∼ 0.5 μm) particles. The Mo2NiB2-based cermet doped with 1.0 wt% ZrO2 particles displayed the highest flexural strength (1 397.33 MPa), along with significantly enhanced fracture toughness (24.08 MPa m1/2). The enhanced strength could be attributed to the increased dislocation density as well as the obstruction to grain boundary slip caused by the ZrO2 particles. Further, the improved toughness might be attributed to crack deflection, crack bridging, transgranular cracks and ZrO2 phase transformation. This study provides the experimental and theoretical basis for the development of the Mo2NiB2-based cermets.

Keywords

Mo2NiB2-based cermets, flexural strength, fracture toughness, strengthening and toughening mechanism

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