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Influence Of VC And Mo2C On The Microstructure And Mechanical Properties Of Ni Bonded NbC- Cermets

  • : Shuigen Huang1, Jozef Vleugels1, Hardy Mohrbacher2, Mathias Woydt3
  • : 1KU Leuven, 2NiobelCon bvba, 3BAM Federal Institute for Materials Research and Testing
  • : PDF Download
  • : 2016

Abstract

WC-Co cemented carbides are the most widely used hard materials for wear applications, combining an excellent hardness, toughness and strength. Pure niobium carbide (NbC) has a high hardness (1960 kg/mm2), low density (7.79 g/cm3) and high melting temperature (3600 °C). Moreover, the hardness of cubic structure NbC can be tailored by the Nb/C ratio. However, NbC on the other hand has been hardly explored as a major hard phase for cemented carbides and cermets. The current study reports on the effect of 0-15 vol% VC and Mo2C carbides on the microstructure and mechanical properties of Ni (8-20 vol%) bonded NbC cermets. Powder mixtures were pressurelessly sintered for 1 h at 1420°C in vacuum. Microstructural and elemental mapping of the sintered cermets were performed by electron probe microanalysis (EPMA) to reveal the effect of the secondary carbides on the NbC grain morphology, grain growth as well as mechanical properties. A two-phases cermets, including cubic NbC and fcc Ni binder were obtained in the sintered cermets, regardless of the VC and Ni content. Results indicated that NbC grain growth was significantly inhibited and a homogeneous NbC grain size distribution was obtained in the cermets with the individual carbide addition or the combination of the two carbides. Mechanical properties of the NbC-Ni matrix cermets are dependent on the Ni binder content and the carbide additions. The liquid phase sintered NbC-12 vol% Ni cermet had a Vickers hardness (HV10) of 1130 ± 22 kg/mm2 and indentation toughness of 11.8 ± 0.4 MPa m1/2. With the addition of 5-10 vol% VC, the hardness increased to 1364 ± 18 kg/mm2, whereas the corresponding toughness on the other hand increased further to 14.2 ± 0.5 MPa m1/2. Addition of 8 vol% Mo2C into NbC-12 vol% Ni mixture increased the hardness to 1420 ± 8 kg/mm2 in combination with a fracture toughness of 8.6 ± 0.3 MPa m1/2. The influence of Ni binder content and the carbide additions on flexural strength were also investigated. It was found that the flexural strength was closely related to the fracture toughness of the NbC cermets.  

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