Effect of Carbon Content on the Microstructure and Mechanical Properties of NbC-Ni Based Cermets

Abstract

Abstract:The aim of this work was to correlate the overall carbon content in NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo starting powders with the resulting microstructure, hardness, and fracture toughness of Ni-bonded NbC cermets. A series of NbC-Ni, NbC-Ni-VC and NbC-Ni-Mo cermets with different carbon content were prepared by conventional liquid phase sintering for 1 h at 1420 • C in vacuum. Microstructural analysis of the fully densified cermets was performed by electron probe microanalysis (EPMA) to assess the effect of carbon and VC or Mo additions on the NbC grain growth and morphology. A decreased carbon content in the starting powder mixtures resulted in increased dissolution of Nb, V, and Mo in the Ni binder and a decreased C/Nb ratio in the NbC based carbide phase. The Vickers hardness (HV 30 ) and Palmqvist indentation toughness were found to decrease significantly with an increasing carbon content in the Mo-free cermets, whereas an antagonistic correlation between hardness and toughness was obtained as a function of the Mo-content in Mo-modified NbC cermets. To obtain optimized mechanical properties, methods to control the total carbon content of NbC-Ni mixtures were proposed and the prepared cermets were investigated in detail.

Sintering behavior and microstructural evolution of NbC-Ni cemented carbides with Mo2C additions

“…In order to limit this phenomenon, secondary carbides can be added. Several carbides were previously considered with NbC based materials such as WC [11] [13], or a combination of these carbides plus TiC [9][10] [14]. Carbide additions efficiently inhibit grain growth, thus obtaining a finer microstructure and a better hardness.…”

Cermets and Hardmetals

“…Even though a lower elastic modulus phase was incorporated, the increased densification resulted in both improved hardness and wear resistance. In contrast, Mo additions to a carbon-rich NbC system actually increased hardness while reducing the fracture resistance, as the Mo was able to react with free-C to form alloyed (Nb,Mo)C [6], thereby removing the softer C phase from the cermet.…”

“…The current special issue, with a focus on cermets and hardmetals, brings together seven scientific research papers [1][2][3][4][5][6][7] that investigate various aspects of these materials. The papers are broadly divided between WC-based hardmetal systems [1][2][3][4], lower density carbides including TiC [5] and NbC [6], and mixed oxide-carbide systems [7]. In two examples, the hardmetal is present as a thin coating on Cr-Ni-Mo based steel substrates [3,4].…”

“…In two examples, the hardmetal is present as a thin coating on Cr-Ni-Mo based steel substrates [3,4]. There is a strong emphasis among these articles on the evaluation of the material's corrosion behavior [2][3][4][5], highlighting the importance of corrosion resistance in a great many applications, along with their tribological responses [3,7], mechanical behavior [1,4,6,7], and the influence of grain size for near-nano variants [1,2].…”

As Matérias-Primas Críticas Em Ferramentas De Corte Para Aplicações De Usinagem - Uma Revisão

“…No entanto, pesquisas recentes mostraram que o carboneto de nióbio tem importantes propriedades tribológicas, físicas e mecânicas para aplicações de materiais para ferramentas de corte. Na verdade, NbC pode ser usado em substituição ao carboneto de tungstênio, que tem sido usado por muito tempo nesta aplicação (WOYDT et al, 2016;WOYDT et al, 2014;ZHAI, 2011;HUANG et al, 2017). Outro ponto importante refere-se à toxicidade no processo de produção de ferramentas a base de WC-Co. Vários estudos realizados pelo REACH, que é o regulamento europeu relativo ao registro, à avaliação, autorização e restrição das substâncias e misturas químicas, mostram que as composições usadas para obter pó WC-Co por processo de redução, como trióxido de tungstênio (WO3) e tetróxido de tricobalto (Co3O4), receberam várias classificações e rótulos relatados devido à sua relação com toxicidade mutagênica e carcinogênica (WOYDT; MOHRBACHER, 2014;FRANCO et al, 2015;TOLLER, 2017).…”