Dans l'industrie du forage pétrolier, les conditions de travail de plus en plus sévères requièrent sans cesse de nouveaux outils plus résistants à l'usure abrasive et à l'impact. Afin de répondre à ce défi, les travaux présentés ici, ont pour but l'élaboration de matériaux en carbure cémenté à gradient de composition par le procédé d'imbibition réactive. Ce procédé peut être décomposé en deux procédés de gradation, à savoir : l'imbibition et le revêtement réactif. L'imbibition a pour rôle d'enrichir graduellement, en phase liante, le coeur d'une pièce en carbure cémenté dense et repose sur le principe de migration de phase liquide dans un corps solide-liquide. Le revêtement réactif est un procédé qui s'applique également sur un carbure cémenté dense sur lequel est déposé un revêtement de nitrure de bore. Après avoir atteint le liquidus de la phase liante du carbure cémenté, une précipitation de borures ternaires prend place à la surface du matériau et s'étend graduellement sur des distances millimétriques. Dans le cas de pièces industrielles (inserts tricône et supports de taillants PDC (Polycrystalline Diamond Compact)), le traitement d'imbibition réactive permet de générer des gradients de dureté pouvant atteindre 450 HV sur 25 mm. L'élaboration de tels gradients a nécessité une meilleure compréhension des cinétiques ainsi que des phénomènes mis en jeu durant l'imbibition et le revêtement réactif. Dans le cas des taillants PDC, l'influence des paramètres du procédé HPHT de synthèse de la plaquette diamantée, sur le gradient de composition présent dans le support WC-Co après imbibition réactive, a été étudiée. Ces travaux se sont également intéressés à l'effet de ces gradients de composition sur les propriétés des plaquettes diamantées ainsi obtenues. A la suite d'essais mécaniques, les inserts WC-Co et taillants PDC gradués montrent une augmentation significative de leur résistance à l'abrasion (de 30 à 100%) et de leur tenue à l'impact (de 20 à 40%). / In oil drilling industry, harsher working conditions require ever new and more abrasive wear and impact resistant tools. To meet this challenge, the work presented here, is to develop graded cemented carbide materials by reactive imbibition process. This method can be divided into two gradation processes, namely, reactive coating and imbibition. Imbibition gradually enriches the core of dense cemented carbide with binder phase and is based on the principle of liquid phase migration in a solid-liquid body. Reactive coating also takes place in dense cemented carbide on which a boron nitride coating is deposited. After reaction with the WC-Co liquid binder, some ternary boride precipitations take place from surface to several millimeters deep. For industrial parts (inserts for roller cone bits and PDC (Polycrystalline Diamond Compact) cutters substrates), hardness gradients obtained can reach 450 HV on 25 mm. Such gradients development is passed through a better understanding of kinetics and phenomena occurring during imbibition and reactive coating. In case of PDC cutters, influence of HPHT process parameters, allowing diamond table synthesis, on the WC-Co substrate gradient, generated by reactive imbibition, was studied. This work was also interested in gradient effect on the obtained diamond tables properties. After mechanical tests, graded WC-Co inserts and graded PDC cutters show a significant increase of both wear resistance (from 30 to 100%) and impact resistance (from 20 to 40%).

The development of alternative binder systems for tungsten carbide (WC) based cemented carbides has again become of relevance due to possible changes in EU regulations regarding the use of Cobalt (Co). A framework for the ICME (Integrated Computational Materials Engineering) based Materials Design is presented to accelerate the development of alternative binder systems. Part one of this work deals with the design of the cemented carbide composite hardness. It has been shown that the intrinsic binder hardness is comparable to a bulk metal alloy and that based on the binder solubilities a solid solution strengthening model developed in this work can be employed. Using a method presented in this work the non-equilibrium, frozen-in binder solubilities can be obtained. Both the design of the binder phase and composite hardness is presented based on a general Materials Design approach. Part two deals with a multiscale approach to model the surface gradient formation. The experimentally missing data on liquid binder diffusion has been calculated using AIMD (Ab initio Molecular Dynamics). The diffusion through the liquid cemented carbide binder has to be reduced to an effective diffusion value due to the solid carbides acting as obstacles that increase the diffusion path. The geometrical reduction of the diffusion has been investigated experimentally using the SIMS (secondary ion mass spectroscopy) technique in WC-Nickel-58Nickel diffusion couples. The geometrical contribution of the so-called labyrinth factor has been proven by the combination of the experiments and in conjunction with DICTRA simulations using the precise liquid AIMD diffusivities. Unfortunately, despite the improved kinetic database and the geometrical diffusion reduction, the surface gradient formation cannot be explained satisfactory in complex cemented carbide grades. Additional, but so far unidentified, contributions have to be considered to predict the surface gradient thickness. / <p>QC 20170919</p>

This diploma thesis deals with increasing the service life of parts intended for soil cultivation. The work evaluates the current possibilities of increasing the utility value of spare parts. Practical tests will provide recommendations for the most appropriate method to increase durability. The work examines uncharted methods of testing soldered joint. The results are evaluated in terms of quality and economic profitability. All results from this work are based on the basis of practical tests of plowing machine in rocky soil.

This eleborate study is aimed at analysis of complete methods machining. There are characterized particular methods and their effect on the surface´s quality of machined area in this study. Concluding part of the study includes practical demonstration of machining by using cemented carbide-tipped tool and polycrystalline diamond and evaluation of this demonstration.

This diploma thesis is aimed on methods of the coating cutting material (cemented carbide, cermets, cutting ceramic, super hard materials) and evalutation individual method regarding technological posibilities of deposition of hard coatings a their mechanical, thermal and che-mical properties. The task of the work is full elaboration obtained technical knowledges and mainly evalutation a comparison of the work conditions (kind of the cutting materials, cutting conditions) that selected producers recomended for effective turning aplications of the coa-tings cutting materials.

Thema dieser Arbeit ist eine experimentelle Untersuchung zur Verbesserung der tribologischen Eigenschaften von Hartmetallen auf der Basis von Wolframkarbid– Kobalt unter Benutzung von Ionen–Implantation in Kombination mit den hierbei auftretenden Struktur– und Phasen–Änderungen. Die vorliegende Arbeit unterscheidet sich von allen anderen bisherigen Arbeiten besonders durch (1.) die detaillierte Analyse der mikroskopischen Veränderungen und durch (2.) deren Verknüpfung mit der Änderung der tribologischen Eigenschaften des Materials.

In this master thesis, performed at Sandvik Coromant Västberga (Stockholm), a comprehensive study has been made to investigate the wear on textured alumina (Inveio™) coated cutting tools when turning low-alloy steels. Specifically, wear studies have been made on tools’ rake faces when turning two separate batches of SS2541, after an initial turning time of 4 min. A particular focus has been given to elucidate what particular role the inclusions might have for the wear of the alumina coating onthe tools. Evaluation of tool wear has been made by employing several different analytical techniques, such as LOM, SEM, Wyko, Auger-spectrometry (AES), EPMA and XRD. The results shows that the arisen wear marks on both tested tool types may be divided into three separate and highly distinguishable wear zones, denoted here in thiswork as “wear bands”. Largest amount of wear tended to occur initially at the topmost part of the 3rd wear band. This was true for both tested tool types. This area demonstrated a characteristic 'lamellar' wear pattern, composed of narrow andstructured ridges. All the tools tested demonstrated the adhesion of workpiece materials of various composition that formed into smeared layers in these formed ridges. Depth-profiling Auger-spectrometry revealed that a significant amount of calcium was present in the machined alumina coating layers. This suggests that a reaction between the calcium-containing inclusions found in the steel and the aluminacoating layer had occurred during the performed turning tests.These results arecontradictory to the general belief that alumina is chemical inert during machiningand has previously, to the authors knowledge, not yet been published. Based on the results from this thesis and from a literature review concerning thebehavior of α-alumina during deformation, a new theoretical wear model has been developed. In this model, it is emphasised that the sliding of hard inclusions from the steel may activate pyramidal slip systems in the textured alumina coating. This causes a nano-crystallisation and/or amorphisation in the topmost part of the coating, which facilitates the further wear of these coated tools. / I detta examensarbete, som har utförts vid Sandvik Coromant i Västberga (Stockholm), har en omfattande studie gjorts i syfte att undersöka slitaget på texturerad aluminiumoxid-belagda skärverktyg (Inveio™) vid svarvningen av låglegerade stålsorter. Förslitningsstudier har framförallt gjorts på verktygens spånsidor vid svarvningen av två separata batcher av stålsorten SS2541 efter en inledande ingreppstid på 4 min. Ett särskilt fokus har även ägnats åt att belysa vilken roll stålets inneslutningar kan ha för slitaget av aluminiumoxidbeläggningen. Utvärderingen av verktygsslitaget har gjorts med hjälp av flera olika analytiska tekniker, däribland LOM, SEM, Wyko, Auger-spektrometri (AES), EPMA samt XRD. Resultaten från detta examensarbete visar på att det uppkomna slitaget på de verktyg som har testats kan uppdelas till tre separata och mycket distinkta ”slitagezoner”. Dessa zoner har för detta arbete benämnts som ”nötningsband”. Störst förslitning framträdde initialt i den översta delen av det 3:e nötningsbandet på de testade skärverktygen. Detta område uppvisade ett karaktäristiskt ”lamell”-liknande utseende, bestående av smala och strukturerade åsar och skåror. Vidare uppvisade samtliga undersökta verktyg på förekomsten av påsmetat arbetsmaterial av varierande sammansättning i dessa bildade åsar. När de slitna verktygen undersöktes med djuprofilerande Auger-spektrometri påvisades det att en signifikant mängd kalcium fanns inuti aluminiumoxidbeläggningen. Detta tyder på att en reaktion mellan de kalciuminnehållande inneslutningarna (som finns inuti stålet) och aluminiumoxidbeläggningen har reagerat med varandra under bearbetningsförloppet. Dessa resultat är motsägande till den allmänna uppfattningen om att aluminiumoxid är kemiskt inert vid bearbetningen av stål. Därutöver har dessa resultat även, till författarens kännedom, aldrig tidigare publicerats. Baserat på de resultat som har erhållits från detta examensarbete, och från en omfattande litteraturstudie gällande deformationen av α-aluminiumoxid, har en ny teoretisk förslitningsmodell utarbetats. I denna modell betonas det särskilt att glidningen av hårda inneslutningar från stålet kan aktivera s.k. pyramidala glidsystem i den texturerade aluminiumoxidbeläggningen. Detta orsaker en nano-kristallisering och/eller amorfisering av den översta delen av aluminiumoxidbeläggningen.  Denna omvandling tros kunna underlätta den fortsatta förslitningen av dessa belagda skärverktyg.

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>

<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>

<p>Cemented carbides (WC-Co) are powder metallurgical products produced by liquid phase sintering. WC-Co is widely used for making a large variety of cutting tools, such as drills and inserts turning applications, due to its great mechanical properties, where the hardness of the WC grains is combined with the toughness of the of the Co binder. WC grain size and grain size distribution are the two most important factors to control the mechanical properties of the products.</p><p>This study examined the grain growth dependence of different milling and sintering times. The resulting grain size and grain size distribution were measured using image analysis on scanning electron microscopy images (SEM) and by using electron backscatter diffraction (EBSD). In addition, the correlation between hardness and coercivity, the most common indirect measures of grain size, and different methods of calculating average grain radius were investigated. An attempt was also made to study the contribution of defects to grain growth. This work also includes an overview of various grain growth equations and a numerical implementation of these.</p><p>Experimental results show that for shorter sintering times, powders milled for short times (15 min and 1 h) have larger average grain radii. There is a crossover after 6 to 8 h of sintering, where the powders milled for a long time (40 h and 200 h), have larger average radii. The measured hardness values correlate well with the average grain radius calculated from the grain surface area and the coercivity correlates with the established equations. EBSD measurements detected boundaries that could not be detected by image analysis, and that were not Sigma 2 boundaries. It is likely that these boundaries are either low energy boundaries or boundaries between grains that are very closely oriented. Comparing heat-treated powder with the untreated resulted in a lower average grain size after sintering for the heat-treated powder. None of the growth equations investigated in this work could fully describe the experimental grain growth.</p><p>Through increased understanding of the grain growth, the growth can be controlled and the end product can have the desired tool properties. The occurrence of abnormal grains in cutting tool applications can cause breakage, which is especially important to avoid in applications such as PCB drills. A correlation between hardness and grain size provides further means for cheap and fast indirect measures of the grain size in production.</p> / <p>Hårdmetall är ett pulvermetallurgiskt material som tillverkas genom smältfassintring och som kännetecknas av hårdhet, styvhet och god slitstyrka. Volframkarbidens (WC) kornstorlek och kornstorleksfördelning är två viktiga faktorer för att kontrollera de mekaniska egenskaperna i hårdmetall.</p><p>I den här studien har korntillväxtens beroende på malning och sintring undersökts. WC-Co maldes och sintrades fyra olika tider och kornstorleksfördelningen mättes med bildanalys på svepelektronmikroskopbilder samt med ``electron backscatter diffraction'' (EBSD). I arbetet har även korrelationen mellan hårdhet, koercivitet och olika sätt att beräkna medelkornstorleken undersökts. Ett försök har också genomförts för att studera hur defekterna i det malda pulvret påverkar korntillväxten. I arbetet har även ett flertal olika tillväxtekvationer modellerats numeriskt och för och nackdelar med de olika tillväxtekvationerna har vägts mot varandra.</p><p>En lång maltid (40 h och 200 h) visade sig ge liten kornstorlek för sintring kortare än 6 h, men för sintringar längre än 8 h gav istället kort malning (15 min och 1 h) den mindre kornstorleken. Det visade sig att uppmätt hårdhet korrelerar bäst med den medelkornstorleksradie som räknats fram från kornytan. I EBSD mätningarna kunde man observera ett flertal korngränser, utöver Sigma 2 korngränser, som inte hade detekterats med bildanalys. Värmebehandlingen av det malda pulvret minskade korntillväxten under efterföljande sintring. Ingen av de undersökta tillväxtekvationerna kunde beskriva de experimentella resultaten fullt ut.</p><p>Genom ökad förståelse för korntillväxt kan man kontrollera tillväxten och slutprodukten kan få önskade egenskaper. Förekomsten av abnorm korntillväxt i skärverktyg i hårdmetall är en av de vanligaste kritiska defekterna och det är speciellt viktigt är undvika korntillväxt i tillverkning av små verktyg, som till exempel kretskortsborrar. Hårdhet och koercivitet är de vanligaste indirekta mätmetoderna för att mäta kornstorlek i produktion. En bra korrelation mellan kornstorlek och indirekta mätmetoder ger utökade verktyg för snabba och billiga mätningar.</p>