Microstructure and tribological performance of NbC-Ni cermets modified by VC and Mo2C. (August 2017)

• Record Type: Journal Article
• Authors: Huang, S.G.; Vleugels, J.; Mohrbacher, H.; Woydt, M.
• Is Part Of: International journal of refractory metals & hard materials. Volume 66(2017)
• Page Start: 188
• Page End: 197
• Publication Date: 2017-08
• Subjects: Cermet -- Liquid phase sintering -- Grain growth -- Wear -- Niobium carbide; Heat resistant alloys -- Periodicals; Refractory materials -- Periodicals; Metallography -- Periodicals; Alliages réfractaires -- Périodiques; Matériaux réfractaires -- Périodiques; Métallographie -- Périodiques; Heat resistant alloys; Metallography; Refractory materials; Periodicals; Electronic journals; 669.73
• DOI: 10.1016/j.ijrmhm.2017.03.012
• Languages: English
• ISSNs: 0263-4368

Abstract

Abstract: The current study reports on the influence of the addition of 5–15 vol% VC or/and Mo2 C carbide on the microstructure and mechanical properties of nickel bonded NbC cermets, which are compared to cobalt bonded NbC cermets. The NbC, Ni and secondary carbides powder mixtures were liquid phase sintered for 1 h at 1420 °C in vacuum. The fully densified cermets are composed of a cubic NbC grains matrix and an evenly distributed fcc Ni binder. NbC grain growth was significantly inhibited and a homogeneous NbC grain size distribution was obtained in the cermets with VC/Mo2 C additions. The mechanical properties of the NbC-Ni matrix cermets are strongly dependent on the carbide and Ni binder content and are directly compared to their NbC-Co equivalents. The liquid phase sintered NbC-12 vol% Ni cermet had a modest Vickers hardness (HV30 ) of 1077 ± 22 kg/mm 2 and an indentation toughness of 9.1 ± 0.5 MPa·m 1/2 . With the addition of 10–15 vol% VC, the hardness increased to 1359 ± 15 kg/mm 2, whereas the toughness increased to 11.3 ± 0.1 MPa·m 1/2 . Addition of 5 and 10 vol% Mo2 C into a NbC-12 vol% Ni mixtures generated the same values in HV30 and KIC when compared to VC additions. A maximum flexural strength of 1899 ± 77 MPa was obtained in the cermet with 20 vol% Ni binder and 4 vol% VC + 4 vol% Mo2 C addition, exhibiting a high fracture toughness of 15.0 ± 0.5 MPa·m 1/2, but associated with a loss in hardness due to the high Ni content. The dry sliding wear behaviour was established at room temperature and 400 °C from 0.1 to 10 m/s. Highlights: Fully densified NbC-Ni/Co based cermets with secondary carbide VC and Mo2 C additions were prepared by conventional pressureless liquid phase sintering. Replacing Co by Ni binder increases significantly the fracture toughness of the sintered cermet at comparable hardness level. It was found the secondary carbides, Mo2 C and VC exhibited a significant effect on the grain growth of NbC based carbide grains. The sintered NbC-Ni based cermet tribologically compete with WC and Cr3 C2 bearing cemented carbides or cermets. The wear resistance of Co and Ni bonded NbC cermets is highest at room temperature and high sliding velocities (> 1 m/s).