Descreve-se os principais tipos de desgaste atuantes em rodas ferroviárias tais como desgaste abrasivo e desgaste por deslizamento. No desgaste por deslizamento os principais mecanismos são deformação plástica, fadiga de contato, fadiga termomecânica, oxidação e escorregamento. Avalia-se o efeito de variáveis como dureza, microestrutura, composição química da liga e escorregamento no desgaste e em seus mecanismos. Compara-se os tipos e mecanismos de desgaste verificados em rodas ferroviárias utilizadas em trens para transporte de minérios, com os obtidos em laboratório através de ensaio de desgaste disco-contra-disco de materiais de roda e trilho. No ensaio, o desgaste foi medido por pesagem dos corpos-de-prova verificando após distâncias predeterminadas a perda de massa. Avaliou-se a influência da carga, dureza, composição química e escorregamento no desgaste. Verificou-se que o desgaste aumenta com a carga e diminui com o aumento da dureza. Aços de rodas com adição de Cromo e Vanádio apresentam um melhor desempenho em desgaste se comparados com aços AAR M 107/208 Classe B ou C. Análise microscópica dos corpos-de-prova após ensaio, mostrou que tal como nas rodas em serviço, os tipos de desgaste atuantes foram desgaste abrasivo e por deslizamento com mecanismos diversos como deformação plástica, delaminação e oxidação. Mecanismo semelhante a delaminação é a formação de escamas ou shelling em rodas. Verificou-se também a formação de camada branca na superfície desgastada, característico de transformação martensítica em aço. Mecanismo similar a este é o de formação de \"spalling\" em rodas. Apresenta-se uma metodologia para desenvolvimento de materiais de rodas, compreendendo ensaios de desgaste em laboratório, produção de rodas e acompanhamento de desempenho em campo, onde se confirma o melhor desempenho de materiais AAR M 107/208 classe C com adição de Cromo e Vanádio se comparado com aços convencionais conforme ) conforme normas AAR M 107/208. / The main types of railroad wheels wear, such as abrasive wear and sliding wear are describe. The main mechanisms of sliding wear are the plastic deformation, the contact fatigue, termomechanical fatigue, oxidation and ship wear. The variables such as hardness, microstructure, chemical composition of alloy and effects of the sliding on wear mechanisms are evaluated. The wear types and mechanisms detected on wheels and rail materials from the real railroad cars tracks, from mining company, are compared with those observed at laboratory testing on disc-against-disc wear testing. The wear rate was measured by mass loss after predefined testing distances. The influence of the load, the hardness and the sliding on the wear rate were also evaluated. It was observed that the wear of the Wheel materials increases with the load increasing and decreases with the material hardness increasing. A better performance was observed for steels AAR M 107/208 class C with Chromium and Vanadium additions when compared to AAR M 107/2088 grade B or C steels. The microscopic examination of the test specimens, as well as on the wheels removed from service, showed occurrence of the abrasive wear and sliding wear with various mechanisms such as plastic deformation, delamination and oxidation wear. A similar mechanism to the delamination is the shelling on wheels. It was observed the formation of White layer on worn surface typical to the martensitic transformation of steel. A similar mechanism is the spalling of wheels material, It is also proposed a methodology for Wheel materials development, including laboratory wear tests, the manufacturing of wheels and the use and attendance of the wheels in service. AAR M 208 grade C steels with Chromium and Vanadium additions presented a better performance when compared the standard AAR M 107/208 steels.

This licentiate thesis has the main focus on evaluation of the wear of coated and uncoated polycrystalline cubic boron nitride cutting tool used in cutting operations against hardened steel. And to exam the surface finish and integrity of the work material used. Harder work material, higher cutting speed and cost reductions result in the development of harder and more wear resistance cutting tools. Although PCBN cutting tools have been used in over 30 years, little work have been done on PVD coated PCBN cutting tools. Therefore hard turning and hard milling experiments with PVD coated and uncoated cutting tools have been performed and evaluated. The coatings used in the present study are TiSiN and TiAlN. The wear scar and surface integrity have been examined with help of several different characterization techniques, for example scanning electron microscopy and Auger electron spectroscopy.   The results showed that the PCBN cutting tools used displayed crater wear, flank wear and edge micro chipping. While the influence of the coating on the crater and flank wear was very small and the coating showed a high tendency to spalling. Scratch testing of coated PCBN showed that, the TiAlN coating resulted in major adhesive fractures. This displays the importance of understanding the effect of different types of lapping/grinding processes in the pre-treatment of hard and super hard substrate materials and the amount and type of damage that they can create. For the cutting tools used in turning, patches of a adhered layer, mainly consisting of FexOy were shown at both the crater and flank. And for the cutting tools used in milling a tribofilm consisting of SixOy covered the crater. A combination of tribochemical reactions, adhesive wear and mild abrasive wear is believed to control the flank and crater wear of the PCBN cutting tools. On a microscopic scale the difference phases of the PCBN cutting tool used in turning showed different wear characteristics. The machined surface of the work material showed a smooth surface with a Ra-value in the range of 100-200 nm for the turned surface and 100-150 nm for the milled surface. With increasing crater and flank wear in combination with edge chipping the machined surface becomes rougher and showed a higher Ra-value. For the cutting tools used in milling the tendency to micro edge chipping was significant higher when milling the tools steels showing a higher hard phase content and a lower heat conductivity resulting in higher mechanical and thermal stresses at the cutting edge.

Abrasive wear occurs when a contact associated with stress between a metal surface and a herd particle (frequently of mineral origin) leads to friction between the two. In a very wide range of industrial applications, abrasive wear is the main reason for component and equipment repair or replacement. In most of these applications, especially those of earth moving, construction and mining equipment, digger teeth are used to improve equipment performance. Digger teeth can be produced in different shapes and sizes (mainly by casting) and a wide range of materials are used. This project is concerned with both a field trial of the wear of digger teeth fixed to the front of a bucket used in a gravel pit, and also a laboratory investigation of abrasive wear mechanisms. It was found that the wear of digger teeth increased with increasing working hours, but the wear rate eventually decreased. The dimensions and shape of the front of the tooth changed and gravel removal became more inefficient. Plastic deformation and phase transformation were observed in the worn surfaces of the teeth. In the laboratory study, many parameters were investigated utilising a pin-on disc technique. Wear rate increases linearly with load and decreases with sliding distance. The effect of attack angle on abrasive wear showed that wear volume increases with increasing attack angle up to a certain value (90°) and then decreases. Corrosion increases the initial wear rate, and the amount of material removed in the wet corrosive test was higher than the corresponding dry test. It was difficult to reproduce the same results from the field trial in the laboratory because of the difference in the conditions in the two cases. Optical and scanning electron microscopy were used to study the worn surfaces, abrasive papers and wear debris. Different abrasive wear mechanisms were observed throughout this investigation. A cutting mechanism associated with spiral debris was observed during short pin-on disc tests and with higher attack angles. A ploughing action associated with plate-like debris was observed during longer tests and at lower attack angles. Fragmentation was observed in brittle materials.

No description available.

Titanium alloys are widely utilized in the aerospace, biomedical,marine, petro-chemical and other demanding industries due to theirdurability, high fatigue resistance and ability to sustain elevateoperating temperature. As titanium alloys are difficult to machine, dueto which machining of these alloys ends up with higher environmentalburden. The industry is now embracing the sustainable philosophy inorder to reduce their carbon footprint. This means that the bestsustainable practices have to be used in machining of titanium alloys aswell as in an effort to reduce the carbon footprint and greenhouse gas(GHG) emissions.In this thesis, a better understanding towards the feasibility of shiftingfrom conventional (dry and flood) cooling techniques to the vegetableoil based minimum quantity cooling lubrication (MQCL) wasestablished. Machining performance of MQCL cooling strategies wasencouraging as in most cases the tool life was found close to floodstrategy or sometimes even better. The study revealed that theinfluence of the MQCL (Internal) application method on overallmachining performance was more evident at higher cutting speeds. Inaddition to the experimental machinability investigations, FiniteElement Modeling (FEM) and Computational Fluid Dynamic (CFD)Modeling was also employed to prediction of energy consumed inmachining and cutting temperature distribution on the cutting tool. Allnumerical results were found in close agreement to the experimentaldata. The contribution of the thesis should be of interest to those whowork in the areas of sustainable machining. / <p>QC 20150915</p>

Hard anodising on aluminium and its alloys has been widely practised for many years in order to improve the resistance of the otherwise poor wear characteristics of aluminium. In recent years there has been an increasing interest in other treatments and coatings, on both aluminium and other base metals. The aim of this investigation is to explain the tribological performance and wear mechanism(s) of an uncoated aluminium alloy, four anodic coated alloys, and also an electroless nickel alloy. All of the coatings are produced on three different aluminium alloys. The thickness of the anodic films is 30-35 micron, as this thickness falls within the range commonly used by industry. In an endeavour to explain the role of coating thickness on wear life, electroless nickel alloy has been produced in a range of thicknesses of 10, 20 and 30 micron. To evaluate abrasive and adhesive wear, the samples were rubbed against a single point diamond and steel ball, respectively, in a reciprocating movement at room temperature and 65-75% relative humidity, under a wide range of load and sliding distance. Some tests continued to run until a breakdown of the coatings occurred, whilst other tests were interrupted at intermediate stages. This enabled the initiation and propagation of failure mechanisms to be studied. Abrasive wear was performed under dry conditions, whereas, adhesive wear was evaluated under both dry and lubricated conditions. Wear of these coatings was proportional to the applied load and sliding distance, but there was no direct relationship between wear and hardness. The tribological performance of these coatings appears to be dictated by a) the composition of the substrate, b) the chemical and physical nature of the coatings and c) the test conditions. Under boundary lubricated conditions there was a considerable increase in the wear life of the coatings. A three dimensional surface texture is superior to a machined surface, in controlling contact conditions. There is an approximate linear relationship between coating thickness and wear life for electroless nickel alloys. These coatings predominantly fail by adhesion, plastic deformation and brittle fracture. A microscopic model for fracture of brittle materials, under both static and dynamic conditions for abrasive and adhesive wear correlates very well with the behaviour of these coatings. Analytical interpretation of adhesive wear was made by separately calculating the coefficient of wear "K" of the counterbodies. This information enables an improved understanding of the wear test itself to be added to the model of the wear mechanisms involved.

This licentiate thesis has the main focus on evaluation of the wear of coated and uncoated polycrystalline cubic boron nitride cutting tool used in cutting operations against hardened steel. And to exam the surface finish and integrity of the work material used. Harder work material, higher cutting speed and cost reductions result in the development of harder and more wear resistance cutting tools. Although PCBN cutting tools have been used in over 30 years, little work have been done on PVD coated PCBN cutting tools. Therefore hard turning and hard milling experiments with PVD coated and uncoated cutting tools have been performed and evaluated. The coatings used in the present study are TiSiN and TiAlN. The wear scar and surface integrity have been examined with help of several different characterization techniques, for example scanning electron microscopy and Auger electron spectroscopy.   The results showed that the PCBN cutting tools used displayed crater wear, flank wear and edge micro chipping. While the influence of the coating on the crater and flank wear was very small and the coating showed a high tendency to spalling. Scratch testing of coated PCBN showed that, the TiAlN coating resulted in major adhesive fractures. This displays the importance of understanding the effect of different types of lapping/grinding processes in the pre-treatment of hard and super hard substrate materials and the amount and type of damage that they can create. For the cutting tools used in turning, patches of a adhered layer, mainly consisting of FexOy were shown at both the crater and flank. And for the cutting tools used in milling a tribofilm consisting of SixOy covered the crater. A combination of tribochemical reactions, adhesive wear and mild abrasive wear is believed to control the flank and crater wear of the PCBN cutting tools. On a microscopic scale the difference phases of the PCBN cutting tool used in turning showed different wear characteristics. The machined surface of the work material showed a smooth surface with a Ra-value in the range of 100-200 nm for the turned surface and 100-150 nm for the milled surface. With increasing crater and flank wear in combination with edge chipping the machined surface becomes rougher and showed a higher Ra-value. For the cutting tools used in milling the tendency to micro edge chipping was significant higher when milling the tools steels showing a higher hard phase content and a lower heat conductivity resulting in higher mechanical and thermal stresses at the cutting edge.

In the automotive industry, Al-Si alloy is widely used for manufacturing of various engine parts. Machinability of die-cast Al-12Si alloy is challenging due to severe abrasion and adhesion wear of the tools. Form tapping is a common method for generating internal threads in engine blocks. It is usually a finishing process on a production line. An unexpected tap failure may lead to significant scrap and high rework costs. The objective of this research was to investigate the wear mechanisms of high-speed steel form taps when machining Al-12Si alloy. This research involved replicating the same process conditions as the industry partner to determine a feasible solution without changing the tap geometry or process parameters. A critical region of wear on the crest was identified where the aluminum adhesion was acute. Intense abrasion wear occurred on the crest and flanks due to hard silicon precipitates. In this study, two methods were proposed for measuring linear and volumetric wear on the chamfered threads. The second and third chamfered threads experienced the most significant wear on the tap. To improve wear-resistance of the form tap, PVD surface coatings were deposited on it. The preliminary tests of 12 surface coatings showed coating-delamination mostly on the critical region. A progressive wear study of the TiAlN coating showed an improvement in tap performance over the ZrN coating currently used. By the 4320th hole, the volumetric wear of the TiAlN coated tap was reduced by nearly 200% and 50% when compared against the uncoated and ZrN coated taps, respectively. / Thesis / Master of Applied Science (MASc)

Metal on metal wear at high sliding speeds and high contact pressures results in the melting of one or both of the sliding solid bodies due to heat generated at the contact interface. Understanding the influence of sliding speeds, contact pressures and material properties on wear rates is important in developing predictive models for designing more efficient and effective engineering system components. Typical engineering applications subjected to these extreme conditions include ultrahigh speed machining, rocket sleds, large caliber cannon, and electromagnetic launchers. Sliding speeds on the order of 1,000 m/s and contact pressures in excess of 100 MPa are common in these applications and difficult to replicate in a laboratory environment. A unique wedge experiment using a minor caliber electromagnetic launcher has been developed and implemented to characterize wear deposition of a 6061-T6 aluminum sliding body on several different guider materials of varying mechanical and thermal properties at sliding speeds from 0 – 1,200 m/s and contact pressures from 100 – 225 MPa. Optical microscopy and 3D profilometry were used to characterize and quantify the slider wear. Three distinct wear regions, plasticity dominated, severe plastic deformation and melt lubrication were observed. Test results provided evidence that the aluminum slider contact interface was molten. Modeling of the experimental wear data showed a dependence on pressure and velocity and guider material properties, density and specific heat. A predictive wear model was developed for the melt lubrication region as a tool for designing components subjected to similar operating conditions.

Wear and friction are among the major problems faced in several industries such as mining industry. This creates challenges to select better materials with good wear behavior in order to improve the service life of the components. In the present project, three steel wire grades OH 70, OH 75 and OH 101 have been heat treated by quenching and partitioning heat treatment and tested using three wear testing methods. The wear tests performed were a pin-on-disc test, dry-pot test and slurry pot-test, and the results were compared with the conventional quenched and tempered steel. Tensile tests, hardness, impact Charpy tests, scanning electron microscope, optical microscope, X-ray diffraction and magnetic measurements were applied to characterize mechanical properties and microstructure of the steels before wear tests. The results showed that the quenched and partitioned steels with considerable amount of retained austenite had higher ductility and good impact toughness than the quenched and tempered steels. After the pin on disc tests, OH 75 grade showed the highest wear resistance, while the lowest wear resistance was obtained by OH 70 grade. The damage mechanisms identified after pin-on-disc were abrasion and oxidative wear. During erosive wear, almost no measurable wear was recorded under the dry pot conditions, while the slurry pot test owned significant wear mass loss. The main modes of the worn surfaces after erosive tests were ploughing and cutting. In addition, cracks were also observed.