Effect of carbon content on the microstructure and mechanical properties of NbC-Ni based cermets

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 degrees 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 (HV30) 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

Les bases de données tribologiques

Une base de données tribologiques a été développée avec 15 000 fichiers. Celte base stocke les données dans un format uniforme et permet ainsi de consulter à la fois des données existantes pour rechercher des solutions et/ou des données sur le comportement d'un couple spécifique. La base de données met les utilisateurs dans la position de rechercher d'une manière simple et rapide des matériaux potentiels et d’obtenir des données fiables sur le comportement tribologique de matériaux, revêtements et lubrifiants dans un tribosystème fermé. Elle répond aux besoins des consultants, scientifiques, bureaux d'études, projeteurs et ingénieurs, ainsi qu’à ceux des producteurs de matériaux et revêtements. Tous les paramètres sont normalisés et peuvent être comparés, puisqu'ils sont stockés dans le même format. L'étendue de la base couvre un très grand nombre de tribomètres et bancs d'essais en utilisatio

Influence des conditions d’essais sur les données tribologiques

Plusieurs essais coopératifs multilaboratoires ont été effectués en 1997, 1998, 1999, 2000 et 2001 par le groupe de travail DIN 51834 “Essais tribologiques dans l’appareil translation-oscillation”. Il s’agit d’essais effectués sur des machines différentes et dans différents lieux. Pour simplifier, on les dénomme “essais circulaires”. L’analyse statistique des résultats a examiné l’influence du choix du solvant, du modèle de l’appareil et des paramètres sur les caractéristiques tribologiques des différentes huiles. Le coefficient de frottement et les taux d’usure peuvent être classés selon les dix différents solvants utilisés: l’isopropanol donne des coefficients de frottement plutôt bas et l’isoparaffine des coefficients plutôt élevés. La variation du coefficient de frottement selon le modèle de machine se situe entre 0,2 % et 0,9 % et les taux d’usure ne sont pas non plus affectés par les solvants. Le diamètre de l’empreinte est insuffisant pour caractériser la résistance à l’usure d’une huile. Le critère pour l’adhésion a du être redéfini. La répétabilité et la reproductibilité ont été améliorées

New Methodologies Indicating Adhesive Wear in Load Step Tests on the Translatory Oscillation Tribometer

When looking in detail at analyses of the tribological load-carrying capacity of lubricants, it becomes apparent that an exclusive evaluation of the evolution of the coefficient of friction alone cannot provide any sufficient criteria for determining the occurrence of adhesive failure. For this reason, extending the knowledge base by combining several criteria in order to draw a clearer picture of adhesive wear mechanisms is urgently required. This can be achieved by combining the evolution of coefficient of friction with stroke signals and/or the electrical contact resistance and/or contact temperature and/or acoustic emission and/or stroke zero position, frictional power input and further derived parameters

Friction and wear of binder-less niobium carbide

The tribological profile of alumina (99.7%) mated against binder-less niobium carbide (NbC) rotating disks were determined unidirectional sliding tests (0.1–7.5 m/s; 22 1C and 400 1C) as well as in oscillation tests (f¼20 Hz, Δx¼0.2 mm, 2/50/98% rel. humidity, n¼105 /106 cycles) under un-lubricated (dry) conditions. In addition, the microstructure and mechanical properties of NbC were determined as well. The reason for testing hot-pressed NbC was to avoid side effects generated by sintering additives and/or second phases. The tribological data obtained were benchmarked with different ceramics, cermets and thermally sprayed coatings. NbC exhibited low wear rates under dry sliding associated with high load carrying capacity. The tribological profile established revealed a strong position of NbC under tribological considerations and for closed tribo-systems against traditional references, such as WC, Cr3C2, (Ti,Mo) (C,N), etc.publisher: Elsevier articletitle: Friction and wear of binder-less niobium carbide journaltitle: Wear articlelink: http://dx.doi.org/10.1016/j.wear.2013.07.013 content_type: article copyright: Copyright © 2013 Elsevier B.V. All rights reserved.status: publishe

An Alternative Approach to Simulating an Entire Particle Erosion Experiment

Solid particle erosion affects many areas, such as dust or volcanic ash in areo-engines. The development of protective materials and surface engineering is costly and time consuming. A lot of effort has been placed into the advancement of models to speed up this process. Finite element or discrete element-based models are quite successful in predicting single or multiple impacts. However, they reach their limit if an entire erosion experiment is to be simulated. Therefore, in the present work, an approach is presented which combines various aspects of the former models with probability considerations. It is used to simulate the impact of more than one billion Alumina particles onto a steel substrate. This approach permits the simulation of an entire erosion experiment on an average PC (i5-2520M [email protected] GHz processor, 4 GB main memory) within about six hours. The respective predictions of wear scar and impact-mass/mass-loss curve are compared to the real experiment

The tribological and mechanical properties of niobium carbides (NbC) bonded with cobalt or Fe3Al

The tribological and mechanical properties of niobium carbide bonded with 8 vol.-% (NbC-8Co), 12 vol.-% of cobalt (NbC-12Co) or 12 vol.-% of Fe3Al (NbC-12Fe3Al) are presented. Rotating discs made of metalbonded niobium carbide were mated against alumina (99.7%) under unlubricated (dry) unidirectional sliding tests (0.1 m/s to 12.0 m/s; 22 1C and 400 C) as well as in oscillation tests (f¼20 Hz, Δx¼0.2 mm, 2/50/98% rel. humidity, n¼105 /106 cycles). Microstructure and phase compositions were determined as well. The tribological data obtained were benchmarked with different ceramics, cermets, hard metals and thermally sprayed coatings, where NbC bonded with 8% and 12% Co presented above 7 m/s the lowest wear rates so far in such a benchmark. Binderless NbC (HP-NbC1) and the metal-bonded NbCs exhibited low wear rates under dry sliding associated with P V high load carrying capacities. NbC-based hard metal bonded with 12 vol.-% of Fe3Al resulted in a higher hardness level than for 12 vol.-% cobalt. The tribological profile established revealed a strong position of NbC-bearing materials under tribological considerations and for closed tribosystems against established reference tribo-couples.publisher: Elsevier articletitle: The tribological and mechanical properties of niobium carbides (NbC) bonded with cobalt or Fe3Al journaltitle: Wear articlelink: http://dx.doi.org/10.1016/j.wear.2014.09.007 content_type: article copyright: Copyright © 2014 The Authors. Published by Elsevier B.V.status: publishe

The tribological property profile of hard metals and metal matrix composites based on niobium carbide

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The use of niobium carbide (NbC) as cutting tools and for wear resistant tribosystems

© 2014 Elsevier Ltd. The tribological profile of alumina (99.7%) mated against rotating disks made in binder-less niobium carbide (NbC) and cobalt-bonded NbC were determined under unidirectional sliding tests (0.1 m/s to 8.0 m/s; 22 °C and 400 °C) as well as in oscillation tests (f=20 Hz, Δx=0.2 mm, 2/50/98% rel. humidity, n=105/106 cycles) under unlubricated (dry) conditions. In addition, themicrostructure andmechanical properties of binderless NbC and NbC bonded with 8% cobalt were determined as well. The reason for testing hot-pressed NbC was to avoid side effects generated by sintering additives and/or second phases. The tribological data obtained were benchmarked with different ceramics, cermets and thermally sprayed coatings. NbC and cobalt-bonded NbC exhibited low wear rates under dry sliding associated with high load carrying capacity. The tribological profile established revealed a strong position of NbC bearing materials under tribological considerations and for closed tribo-systems against traditional references, such as WC, Cr3C2 and (Ti,Mo)(C,N).publisher: Elsevier articletitle: The use of niobium carbide (NbC) as cutting tools and for wear resistant tribosystems journaltitle: International Journal of Refractory Metals and Hard Materials articlelink: http://dx.doi.org/10.1016/j.ijrmhm.2014.07.002 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.status: publishe