Papers by Keyword: Niobium Carbide

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Authors: Yao Ning Sun, Ding Fan, Yu Feng Zheng, Min Zheng, Jian Bin Zhang
Abstract: Laser cladding technique was used to form Ni3Si intermetallic composite coating reinforced by in-situ formation NbC particles on Ni-based superalloy substrate. The process parameters were optimized to obtain cladding. The effect of Nb-C addition to the microstructure of the coating was investigated. The morphology of reinforcement particles was discussed. The experimental results showed that an excellent bonding between the coating and the substrate was ensured by a strong metallurgical interface. The clad coating was very good and free from cracks and pores. The microstructure of the coating was mainly composed of Ni(Si), Ni3(Si, Nb) and NbC. The NbC particles were formed by in-situ reaction between Nb and C during laser cladding process. NbC particles were homogeneously distributed in the composite material. Moreover, the maximum size of NbC particles was more than 4 μm.
Authors: Uilame Umbelino Gomes, C. de Souza, Francisca de Fatima P. Medeiros, A.G.P. Silva, C. Ciaravino, M. Roubin
Authors: Céline Hin, Frédéric Soisson, Philippe Maugis
Abstract: The precipitation of niobium carbides in industrial steels is commonly used to control the recrystallization process or the amount of interstitial atoms in solid solution. It is then important to understand the precipitation kinetics and especially the competition between homogeneous and heterogeneous precipitation, since both of them have been observed experimentally, depending on the alloy composition, microstructure and thermal treatments. We propose Monte Carlo simulations of NbC precipitation in α-iron, based on a simple atomic description of the main parameters which control the kinetic pathway : - realistic diffusion properties, with a rapid diffusion of C atoms by interstitial jumps and a slower diffusion of Fe and Nb atoms by vacancy jumps - a simple model of grain boundaries which reproduces the equilibrium segregation properties of Nb and C - a point defect source which drives the vacancy concentration towards its equilibrium value. Depending on the precipitation conditions, MC simulations predict different kinetic behaviours, including homogeneous and heterogeneous NbC precipitation, early segregation of C atoms and its importance as a first stage for NbC precipitation, wetting phenomena on grain boundaries and transient precipitation of metastable carbides.
Authors: S.G. Huang, J. Vleugels, H. Mohrbacher, M. Woydt
Abstract: NbC-xTi (C0.7N0.3)-10Ni-7.5VC (vol%) based cermets with 0, 5, 10, 15 or 25 vol% Ti (C0.7N0.3) were prepared by conventional pressureles liquid phase sintering at 1420°C in vacuum. Detailed microstructural investigation was performed by SEM, EPMA and XRD analysis. Sintering results indicated that the partial replacement of NbC by Ti (C0.7N0.3) had a significant effect on the carbide grain growth, microstructure, hardness as well as fracture toughness of the fully densified NbC-based cermets. The Ti (C0.7N0.3)-free NbC cermet was composed of homogeneous cubic (Nb,V)C solid solution grains, whereas core-rim structured NbC grains were observed in cermets with Ti (C0.7N0.3) addition. All sintered cermets with  15 vol% Ti (C0.7N0.3) were composed of a fcc solid solution Ni binder and a cubic core-rim solid solution (Nb,V,Ti)C phase with a Nb-rich core and a Ti-rich rim. 3.8 vol% of residual pristine Ti (C0.7N0.3) was present in the cermets with 25 vol% Ti (C0.7N0.3) addition. The 15 vol% Ti (C0.7N0.3) starting powder based cermet exhibited the finest average NbC grain size of 1.48 μm, with a core-rim structure and an interesting combination of hardness (1486 kg/mm2) and fracture toughness (8.7 MPa.m1/2).
Authors: Akihiro Nino, Kaori Morimura, Shigeaki Sugiyama, Hitoshi Taimatsu
Abstract: Powder mixtures of WC–(0–2 mol%) NbC and WC–1.5 mol% NbC–(0–5 mol%) C were sintered at 1800°C using a resistance-heated hot-pressing machine; dense WC–NbC and WC–1.5 mol% NbC–C ceramics were obtained. The relative X-ray diffraction (XRD) peak intensity of W2Css decreased with increasing C amount and disappeared at 5 mol% C. Small amounts of C remained after sintering at 5 mol% C. The WC–1.5 mol% NbC ceramics with 0–3 mol% of added C were composed of equiaxed small granular grains. Large WC grains formed in WC–1.5 mol% NbC ceramics above 4 mol% C. The hardness of WC–NbC ceramics decreased from 25.7 GPa for WC to 23.6 GPa for 2 mol% NbC obtained by NbC addition. The hardness change for WC–1.5 mol% NbC ceramics with up to 3 mol% of added C was small, around 24 GPa. The Vickers hardness of WC–1.5 mol% NbC ceramics above 4 mol% C decreased markedly from 23 to 13 GPa with increasing added C, due to extensive WC grain growth.
Authors: A.S. Silva, H. Scatena, Antonio Eduardo Martinelli, Clodomiro Alves Jr.
Authors: Wilson Acchar, Harim Revoredo de Macedo
Abstract: Cemented carbides have been intensively used as cutting tool through their high hardness, high fracture toughness and high wear resistance. A considerable amount of works has been developed in order to improve the mechanical properties of alternate cemented carbide systems. This work has the purpose to reports the first results obtained to WC-Co reinforced with 5 wt.% NbC. The mixture of powders was hot-pressed at 1250 °C in a inert atmosphere. Hardness and fracture toughness were carried out in a Vickers hardness testing machine. The results have showed that the addition of niobium carbide improves the hardness of tungsten carbide and inhibits the WCgrain growth.
Authors: A.H. Rumbao, José Carlos Bressiani, Ana Helena A. Bressiani
Authors: Wilson Acchar, Marcus Diniz, Carlos Alberto Alves Cairo
Authors: A. Rubio, Elena Gordo, Francisco Velasco, N. Candela, José M. Torralba
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