Los carburos cementados son materiales atractivos para muchas aplicaciones industriales debido a una combinación de propiedades mecánicas y físicas, estabilidad química y a su excelente resistencia al desgaste. Los carburos cementados ultrafinos y nanocristalinos están recibiendo una atención especial debido a su aplicación en el desarrollo de materiales para la industria electrónica y automotriz. La resistencia al desgaste de estos materiales experimenta un notable incremento cuando se reduce el tamaño de grano. La reducción en el tamaño de grano puede obtenerse por la adición de pequeñas cantidades de inhibidores de crecimiento de grano (especialmente Cr3C2 y/o VC), la selección del proceso y las condiciones de sinterización. En esta tesis se evalúa el comportamiento a fricción y desgaste por deslizamiento en seco de carburos cementados obtenidos de mezclas ultrafinas y nanocristalinas de WC-12%pesoCo con adición de VC y Cr3C2 como inhibidores de crecimiento de grano. Estas mezclas fueron consolidadas mediante sinterización convencional en vacío y sinterización por chispa de plasma. Los ensayos de desgaste por deslizamiento en seco se desarrollaron en un tribómetro con configuración bola sobre disco utilizando bolas de WC-6Co y AISI 5210 como contramateriales. Para los ensayos se utilizó como carga de contacto 40N y 60N, distancia de deslizamiento de 2000m y 10000m, velocidad de deslizamiento de 0.1m/s, condiciones medioambientales controladas. Los resultados obtenidos han mostrado que los carburos cementados nanoestructurados presentan una mayor resistencia al desgaste por deslizamiento en seco que los grados ultrafinos o submicrométricos. La adición de inhibidores de crecimiento de grano a la mezcla comercial se ha confirmado como una vía efectiva para incrementar la resistencia al desgaste, especialmente cuando las proporciones son hasta un 1% peso y se utiliza VC como afinador. La naturaleza elástica o plástica de las asperezas en contacto se ha manifestado en las diferencias encontradas en el coeficiente de fricción entre los materiales obtenidos de polvos ultrafinos y nanométricos. La sinterización por chispa de plasma, SPS, (y las condiciones de sinterización) resultó ser el método de sinterización con el que se obtienen las mejores propiedades tribológicas en condiciones de desgaste severo. Los parámetros de sinterización empleados para el método tradicional, Vacío, no resultaron adecuados cuando las proporciones de inhibidores exceden el 1%peso. El estudio de las micrografías de las huellas de desgaste por medio de MEB, EC MEB, EDX, reveló la coexistencia de varios mecanismos de desgaste que contribuyen al deterioro del material. Esto se ha relacionado con las propiedades microestructurales y mecánicas de los carburos cementados, con la naturaleza del contramaterial y con el método de procesado. Finalmente, se ha demostrado que ejerce más influencia en la resistencia al desgaste de los carburos cementados finos un buen control microestructural que solo el incremento de la dureza o reducción en el tamaño de grano. / Espinosa Fernández, L. (2013). Influencia de inhibidores de crecimiento de grano en el comportamiento tribológico de carburos cementados WC-Co a partir de polvos nanométricos [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29534 / TESIS

Les matrices en carbure de Tungstène et Cobalt (WC‐Co) sont utilisées dans les procédés de frappe à froid de l’acier pour leur exceptionnelle capacité à résister aux phénomènes d’usure. Ces travaux ont pour objectif de mieux comprendre les mécanismes complexes qui entrainent finalement la dérive des matrices vers l’état usé. Cette complexité vient des liens étroits entre la microstructure et les propriétés mécaniques macroscopiques de ces matériaux. Pour la compréhension des mécanismes de dérive vers l’usure, une stratégie de travail en quatre étapes est établie. La première étape est le prélèvement de matrices de frappe, avec différentes durées de vie, directement sur la chaîne de production. La deuxième étape est l’identification de la rhéologie. Elle s’accompagne de la modélisation numérique du procédé de frappe pour calculer le champ des contraintes et des déformations plastiques. La troisième étape est la caractérisation localisée de l’évolution de la surface selon trois axes : les propriétés tribologiques, morphologiques, et mécaniques. On quantifie ainsi la dégradation progressive des conditions de contact corrélée avec une fragilisation des surfaces et la décohésion de grains de carbures WC. Pour comprendre les mécanismes qui conduisent à la décohésion de grains, une stratégie de modélisation numérique à l'échelle mésomécaniques 2D est mise en place. L’énergie de rupture entre un grain et le reste du matériau est modélisée par des éléments cohésifs. Ces modèles montrent que la sensibilité de chaque grain à l’arrachement dépend non seulement des conditions de contact et de la ténacité du matériau, mais également de la taille et de la configuration du grain au voisinage de la surface. / Tungsten carbide and Cobalt (WC‐Co) dies are used for cold forming processes of steel because of their exceptional performances in resisting wear phenomena. This work aims to a better understanding of the complex damage mechanisms that eventually cause wear. This complexity comes from the existing relationships between their microstructure and their macroscopic mechanical properties. For a better understanding of the damage mechanisms leading towards wear, a four‐step strategy is presented. The first step is the cold heading dies sampling directly on the production line. They are collected at different lifetimes. The second step is the identification of the die rheology. It is followed by numerical modeling of the forging process to calculate the stress field and plastic strain magnitude. The third step is to characterize the local evolution of the surface properties along three axes: the tribological, the morphological and mechanical aspects. These analyses quantify the progressive decrease of contact conditions correlated with surface embrittlement and WC carbide grains debonding. To understand the mechanisms that lead to the grains debonding, a set of 2D mesoscale contact models are performed. The fracture energy between a WC grain and the rest of the material is computed using cohesive elements. These models show that the sensitivity to debonding depends not only on the contact conditions and the material fracture toughness, but also on the grain size and grain configuration in the vicinity of the surface.

This thesis aims to compare the relationship of physical-mechanical properties of tool materials made of WC-Co sintered carbides with their resistance to initiation and propagation of thermal cracks. The paper presents the results of testing the basic physical-mechanical properties of the three samples sintered carbides with different percentage of Co binder. Next, this thesis describes the progress and results of quench experiment and cutting tests using, which was described resistance of the tested samples to thermal and mechanical shock, depending on the values of physical-mechanical properties.

The object of this work is to obtain a fundamentalunderstanding of the principal issues concerning the handlingof an aqueous WC-Co powder suspension. The WO3 surface layer on the oxidised tungsten carbidepowder dissolves at pH&gt;3 with the tungsten concentrationincreasing linearly with time. Adding cobalt powder to thetungsten carbide suspension resulted in a significant reductionof the dissolution rate at pH&lt;10. Electrokinetic studiesindicated that the reduced dissolution rate may be related tothe formation of surface complexes; the experiments showed thatCo species in solution adsorb on the oxidised tungsten carbidepowder. The surface forces of oxidised tungsten and cobalt surfaceswere investigated using the atomic force microscope (AFM)colloidal probe technique. The interactions at various ionicstrengths and pH values are well described by DLVO theory. Theadsorption of cobalt ions to tungsten oxide surfaces resultedin an additional non-DLVO force and a reduced absolute value ofthe surface potential. It was shown that the adsorption ofpoly(ethylene imine) (PEI) to the WO3 surfaces induces anelectrosteric repulsion. The properties of spray-dried WC-Co granules were related tothe WC primary particle size, and the poly(ethylene glycol)(PEG) binder and PEI dispersant content in aqueous WC-Cosuspensions. The granule characterisation includes a new methodfor measuring the density of single granules. The increase inthe fracture strength of granules produced from suspensionsthat were stabilised with PEI was related to a more densepacking of the WC-Co particles. The AFM was used to study the friction and adhesion ofsingle spray-dried WC-Co granules containing various amounts ofPEG binder. The adhesion and friction force between two singlegranules (intergranular friction) and between a granule and ahard metal substrate (die-wall friction) have been determinedas a function of relative humidity. The granule-wall frictionincreases with binder content and relative humidity, whereasthe granule-granule friction is essentially independent of therelative humidity and substantially lower than the granule-wallfriction at all PEG contents. Key words:Hard Metal, Cemented Carbide, WC-Co, TungstenCarbide, Cobalt, Oxidation, Dissolution, Surface Complexation,XPS, AFM, Colloidal Probe, Hamaker Constant, Cauchy, WO3,CoOOH, ESCA, Zeta-Potential, Surface Potential, Poly(ethyleneimine), PEI, Suspension, van der Waals, Steric, Spray-Dried,Poly(ethylene glycol), Strength, Density, Friction, Adhesion,Granule, PEG, Pressing, FFM. / <p>QC 20161027</p>

Dans ce travail, de nouveaux traitements de protection, à base de couches minces dures, de type nitrures des métaux de transition, ont été développés en vue d'améliorer la tenue de service d'outils destinés à l'usinage de MDF (Medium Density Fiberboard). En raison des sollicitations sévères auxquelles l'arête est soumise, ces revêtements doivent avoir de bonnes propriétés physicochimiques, mécaniques et tribologiques. Compte tenu des travaux précédents où des résultats prometteurs avaient été obtenus en utilisant des films de CrN, nous avons voulu améliorer les principales caractéristiques de ce système binaire en lui ajoutant des éléments métalliques tels que l'Al et le V. De ce fait, des couches de CrAlN et CrVN ont été réalisées par pulvérisation dual magnétron RF. Nous nous sommes intéressés en particulier à l'effet du pourcentage d'Al et de V respectivement sur les propriétés de CrAlN et CrVN. Dans un deuxième temps, les revêtements optimaux ont été par la suite, réalisés sur des plaquettes en carbure de tungstène utilisées en usinage de trois types de MDF (Standard, Hydrofuge et Ignifugé) et en tenant compte de l'épaisseur et du profil de densité de chaque panneau. Une procédure de pré-rodage des plaquettes carbure a été mise au point et les revêtements ont été effectués à la fois sur des plaquettes pré-rodées ou non. Les résultats indiquent que l'utilisation des films minces pouvait apporter des améliorations significatives en termes de résistance à l'usure et qu'une préparation préalable par pré-rodage était fortement conseillée pour permettre une meilleure adhérence de la couche

<p>The object of this work is to obtain a fundamentalunderstanding of the principal issues concerning the handlingof an aqueous WC-Co powder suspension.</p><p>The WO3 surface layer on the oxidised tungsten carbidepowder dissolves at pH>3 with the tungsten concentrationincreasing linearly with time. Adding cobalt powder to thetungsten carbide suspension resulted in a significant reductionof the dissolution rate at pH<10. Electrokinetic studiesindicated that the reduced dissolution rate may be related tothe formation of surface complexes; the experiments showed thatCo species in solution adsorb on the oxidised tungsten carbidepowder.</p><p>The surface forces of oxidised tungsten and cobalt surfaceswere investigated using the atomic force microscope (AFM)colloidal probe technique. The interactions at various ionicstrengths and pH values are well described by DLVO theory. Theadsorption of cobalt ions to tungsten oxide surfaces resultedin an additional non-DLVO force and a reduced absolute value ofthe surface potential. It was shown that the adsorption ofpoly(ethylene imine) (PEI) to the WO3 surfaces induces anelectrosteric repulsion.</p><p>The properties of spray-dried WC-Co granules were related tothe WC primary particle size, and the poly(ethylene glycol)(PEG) binder and PEI dispersant content in aqueous WC-Cosuspensions. The granule characterisation includes a new methodfor measuring the density of single granules. The increase inthe fracture strength of granules produced from suspensionsthat were stabilised with PEI was related to a more densepacking of the WC-Co particles.</p><p>The AFM was used to study the friction and adhesion ofsingle spray-dried WC-Co granules containing various amounts ofPEG binder. The adhesion and friction force between two singlegranules (intergranular friction) and between a granule and ahard metal substrate (die-wall friction) have been determinedas a function of relative humidity. The granule-wall frictionincreases with binder content and relative humidity, whereasthe granule-granule friction is essentially independent of therelative humidity and substantially lower than the granule-wallfriction at all PEG contents.</p><p><b>Key words:</b>Hard Metal, Cemented Carbide, WC-Co, TungstenCarbide, Cobalt, Oxidation, Dissolution, Surface Complexation,XPS, AFM, Colloidal Probe, Hamaker Constant, Cauchy, WO3,CoOOH, ESCA, Zeta-Potential, Surface Potential, Poly(ethyleneimine), PEI, Suspension, van der Waals, Steric, Spray-Dried,Poly(ethylene glycol), Strength, Density, Friction, Adhesion,Granule, PEG, Pressing, FFM.</p>

In the present work further modifications are implemented to an existing test setup for the evaluation of the wear of cemented carbide drill buttons in rock drilling applications. The test setup has been evaluated in previous diploma works, which has shown that the test successfully mimics the wear seen in rock drilling applications. The new modifications include friction and normal force measurements together with the collection of rock debris. This has been made possible by redesigning the sample holder and by manufacturing equipment making rock debris collection possible. The new modifications to the test setup were evaluated by comparing the wear of three different cemented carbide grades tested against sandstone and granite with two different loads. The data collected from the new modifications were found to be robust with lower than expected spread of data. The coefficient of friction when testing against sandstone was higher than when testing against granite. More adhered material was observed on the wear surface when testing against granite than against sandstone. Load dependence on the wear of the cemented carbide buttons is only seen for the softer cemented carbide grades when testing against sandstone. The wear of the buttons indicates a high dependence on the hardness of the different grades as shouldbe expected. This diploma work has been performed for Sandvik Mining, Rock Tools,a world leading supplier of rock drill equipment.

High-performance materials such as stainless steels and nickel based super alloys are widely used in demanding applications where high mechanical and thermal properties are required. The applications of super alloys are mainly found in jet engines, power plants and gas turbines demanding high fatigue strength, corrosion and oxidation resistance as well as wear resistant properties. In order to use them, they go through various machining processes such as milling, turning, cutting, polishing etc. until the final product is achieved. Modern manufacturing industries employs various machining tools and technologies to improve the machining process of heat resistant super alloys. However, there are still challenges which needs to be addressed. Among them, adhesive wear of the machining tools is one of the main wear mechanism during the tribological interaction of tool and workpiece, preventing them to achieve the desired quality and surface finish of the end product. Moreover, it damages the tool reducing its lifecycle and in return, increasing the production cost. Among the cutting tools tungsten carbide (WC/Co) tools coated with TiAlN coating due to their good high temperature performance are extensively used. Nonetheless, these coatings still face issue like adhesive wear, abrasion, oxidation at higher temperature damaging the tools and subsequent machining. Therefore, it is imperative to understand the initiation mechanism of adhesive wear during the tribological interaction of super alloys and coated cutting tool material. In this research work, the tribological response of two coatings deposited by physical vapour deposition (PVD), having the composition Ti60Al40N and Ti40Al60N have been studied against two super alloys material, i.e. Inconel 718 and stainless steel 316L. A high temperature SRV (Schwingung (Oscillating), Reibung (Friction), Verschleiß (Wear)) reciprocation friction and wear test set up was employed to investigate the friction behaviour, wear rate and dominant wear mechanisms.  For Ti60Al40N coating, the experimental results revealed that generally, friction increases in case of sliding against Inconel 718 up to 400 °C and drops at 760 °C. A high wear volume at room temperature and a decrease to a minimum at 760 °C has been observed for Inconel 718. On the other side, Stainless steel 316L (SS 316L) faces a continuous rise in friction coefficient with highest value at 760 °C during sliding against Ti60Al40N coating. Wear is highest at 400 °C for SS 316L pin. The worn surfaces shows that both workpiece materials experience increase in material transfer due to adhesive wear with rise in temperature. At 400 °C, adhesion is the primary wear mechanism for both workpiece materials. A further rise in temperature to 760 °C promotes the adhesive wear through oxides formation on both material surfaces.  Similarly, Ti40Al60N coating shows the same friction behaviour with change in average steady state friction values for both material of Inconel 718 and SS 316L. Both workpiece materials responds in a similar way to wear volume loss, i.e. lowest at room temperature and highest at 760 °C. For Inconel 718, transfer of coating constituents on to the Inconel 718 pin surface was detected and associated with coating rupture and peeling, exacerbating with rise in temperature. Adhesion, abrasion, and oxidation are primary wear mechanisms at 400 °C and 760 °C. For SS 316L, coating transfer only happen at 400 °C. No damage of coating at 40 °C, a complete damage at 400 °C, and formation of dense porous oxides layers at 760 °C have been noticed. At 400 °C, adhesion, abrasion, and chipping while at 760 °C, adhesion, three body abrasion, ploughing and oxidation are the main wear mechanisms.