Bolts and nuts are one of most common joining methods since they are simple and low-cost to connect parts. Appropriate clamp force from bolted joint remains resultant joints secured, but higher/lower preload on bolted joint increases risk of the failure of mechanism. Therefore, achieving accurate clamp force in bolted joint is always the aim of tightening process. Torque control tightening tool are the most common tightening tool present in the market. The clamp force obtained from torque control tightening is highly dependent upon friction. Only small part of applied torque is transferred into the effective torque that turns in to clamp forces because most of applied torque is consumed by friction forces under bolt /nut head and in a thread interface. However, friction coefficient does not remain constant during tightening process and it relates to many factors such as tightening speed, speed profile, tightening time, joint’s material, etc. Hence, it changes the distribution ratio and leads to an error in estimation of clamp force between the components. This project aims to develop a tribometer which is capable of operating in different speeds and load conditions corresponding to different tightening process. A new concept of pin-on-disc tribometer is proposed and the speed and load profile are achieved by using closed loop control in the linear actuator and the motor. The test rig was built up and the several validation tests were done. / Skruv och mutter tillhör bland de vanligaste medlen att binda ihop två ytor med varandra då det är ett billigt och enkelt sätt att uppnå det önskade resultatet. Det är viktigt att rätt klämkraft uppnås i skruvförbandet, vid för låg/hög klämkraft är risken för haveri i konstruktionen stor. Därför är att uppnå korrekt klämkraft i ett skruvförband alltid målet i en åtdragningsprocess. Skruvdragare som drar åt med ett förinställt moment (torque control) är för tillfället det vanligaste verktyget på marknaden för att uppnå rätt klämkraft. Klämkraften som uppstår vid åtdragning av ett skruvförband med ett sådant verktyg är i största del beroende på friktionskraften i skruvförbandet för korrekt moment. Endast en liten del av momentet som påverkar skruven övergår till effektivt fasthållande moment i skruvförbandet, det mesta momentet går åt för att övervinna friktionen mellan skruv och mutter. Friktionskoefficitenten håller sig inte konstant vid ett åtdragande moment utan beror på flera faktorer såsom åtdragningshastighet, profilhastighet, åtdragningstid och vilket material skruvförbandet är gjort av bland annat. Eftersom friktionskoeffiecienten ständigt ändrar sig leder detta till ett fel då man ska uppskatta klämkraften mellan två ytor. Detta examensarbete ämnar till att bygga en tribometer som är kapabel till att fungera vid olika hastigheter och kraftförhållanden som korresponderar till olika åtdragningsprocesser. Ett koncept på en ny pin-on-disc tribometer föreslås och hastighets samt kraftprofiler skapas genom ett closed-loop reglertekniksystem i ett linjärt ställdon och motorn. Testriggen konstruerades och flertalet utvärderingstester utfördes.

During tightening of a screw, the variation in friction will affect the force acting on the joint, especially when tightening using torque as a control parameter. So, it is crucial to have a proper understanding of the contact mechanism and friction in the screw head to joint and thread interfaces. This will make it possible to develop tightening strategies that compensate for the friction variation to assure a better quality of the joint. This understating could be achieved through conducting experiments using a pin on disc tribometer. In the present study, the frictional behavior of three different coatings has been investigated using a tribometer. The study comprises both the experimental and numerical procedures. Experimental tests have been conducted to find the required material inputs for numerical modeling, and also, to log the results required for validation of the simulation results. The Central Composite Design (CCD) method has been employed for the design of experiments where the normal pressure and sliding velocity have been selected as the test parameters (design factors). For the numerical part of the study, the localized finite element model of the contact region of the pin and coated disc has been made in ANSYS. The model represents a portion of the test specimen used in the tribometer so that a high level of refinement could be applied. Two different approaches have been implemented in ANSYS to model the friction coefficient as a function of normal pressure and sliding velocity. The both approaches are based on a mathematical model for friction coefficient which has nine constants that could be determined using the experimental tests’ results. Also, a correction scheme for the contact stiffness has been implemented so that the mesh dependency of the model could be reduced significantly. Finally, the results of the numerical modeling have been compared with those obtained from experiments for friction force. The comparison shows a good agreement between them, proving the accuracy of the utilized numerical model and the correction scheme employed. / Vid åtdragning av en skruv kommer variationen i friktion att påverka kraften som verkar på fogen, speciellt vid åtdragning med vridmoment som styrparameter. Så det är avgörande att ha en ordentlig underskattning av kontaktmekanismen och friktionen i skruvhuvudet till skarvar och gänggränssnitt. Detta kommer att göra det möjligt att utveckla åtdragningsstrategier som kompenserar för friktionsvariationen för att säkerställa en bättre kvalitet på fogen. Denna underskattning kan uppnås genom att utföra experiment med en stift på skivtribometer. I föreliggande studie har friktionsbeteendet hos tre olika beläggningar undersökts med hjälp av en tribometer. Studien omfattar både de experimentella och numeriska procedurerna. Experimentella tester har genomförts för att hitta nödvändiga materialingångar för numerisk modellering, och även för att logga de resultat som krävs för validering av simuleringsresultaten. Central Composite Design (CCD) metod har använts för design av experiment där det normala trycket och glidhastigheten har valts som testparametrar (designfaktorer). För den numeriska delen av studien har den lokaliserade finita elementmodellen av kontaktområdet för stiftet och den belagda skivan gjorts i ANSYS. Modellen representerar en del av testexemplaret som används i tribometern så att en hög nivå av förfining kunde tillämpas. Två olika tillvägagångssätt har implementerats i ANSYS för att modellera friktionskoefficienten som en funktion av normalt tryck och glidhastighet. Båda tillvägagångssätten är baserade på en matematisk modell för friktionskoefficient som har nio konstanter som kan bestämmas med hjälp av de experimentella testernas resultat. Dessutom har ett korrigeringsschema för kontaktstyvheten implementerats så att modellens meshberoende kan reduceras avsevärt. Slutligen har resultaten av den numeriska modelleringen jämförts med de som erhållits från experiment för friktionskraft. Jämförelsen visar en god överensstämmelse mellan dem, vilket bevisar noggrannheten hos den använda numeriska modellen och det använda korrigeringsschemat.

Dentre os principais e mais efetivos tratamentos superficiais para a melhora das propriedades da superfície dos aços, encontra-se a nitretação e a nitrocarbonetação. Os benefícios da nitretação nos aços são o aumento da dureza, resistência ao desgaste, resistência à fadiga e resistência à corrosão. Por possuírem elementos como cromo, molibdênio e manganês, os aços ferramenta e aços baixa liga de ultra alta resistência são beneficiados pela nitretação. Neste trabalho, estudou-se o efeito da nitretação nos aços SAE 4140 e SAE H13 através de análises metalográficas, espectroscopia de emissão óptica, difração de raios-x, microdureza e ensaio pino-sobre-disco. Para efeito de comparação, amostras de aço SAE 1045 e ferro puro foram nitretadas juntamente com amostras dos dois materiais anteriores. Foram executados três tratamentos diferentes em cada um dos aços, nitretação com baixo potencial de nitrogênio, nitretação com alto potencial de nitrogênio e nitrocarbonetação. Os dois primeiros tratamentos foram realizados em três tempos diferentes de duas, quatro e seis horas e a nitrocarbonetação foi realizada em seis horas. Os resultados mostraram a formação de uma camada nitretada com de camada branca seguida de uma camada de difusão com gradiente de propriedades. Um aumento significativo de dureza superficial é observado com a aplicação dos tratamentos. A nitrocarbonetação junto com alto potencial de nitretação se mostrou não sendo benéfica para a formação da camada em relação à nitretação com mesmo potencial. Nos testes tribológicos realizados, a camada nitretada se mostrou eficiente em aumentar a resistência ao desgaste nos aços SAE 4140 e SAE H13. / Among the main and most effective surface treatments for improving the surface properties of steels are nitriding and nitrocarburizing. The benefits of nitriding in steels are the increase in hardness, wear resistance, fatigue resistance and corrosion resistance. Because they have elements such as chromium, molybdenum and manganese, tool steels and low alloy steels of ultra high strength are benefited by nitriding. In this work, the effect of nitriding on SAE 4140 and SAE H13 steels was studied through metallographic analysis, optical emission spectroscopy, x-ray diffraction, microhardness and pin-on-disc test. For comparison purposes, samples of SAE 1045 steel and pure iron were nitrided together with samples of the two former materials. Three different treatments were performed in each of the steels, nitriding with low nitrogen potential, nitriding with high nitrogen potential and nitrocarburizing. The first two treatments were performed at three different times of two, four and six hours and nitrocarburizing was performed in six hours. The results showed the formation of a nitrided layer with a white layer followed by a gradient layer of properties. A significant increase in surface hardness is observed with the application of the treatments. Nitrocarburizing together with high nitriding potential proved to be of no benefit to the formation of the layer in relation to nitriding with the same potential. In the tribological tests carried out, the nitrided layer proved efficient in increasing wear resistance in SAE 4140 and SAE H13 steels.

Hot extrusion of aluminum is widely practiced in industries for economic production of structural components. The surface finish and tolerance of the extruded components, both from design and aesthetic requirement, are important parameters. Hot extrusion involves forcing of aluminum in the form of a billet at a predetermined temperature through a shaped opening called die. Attempts, over time, are made to evolve the die profile to produce quality components. The main geometric feature of the die enables it in imparting plastic deformation and subsequent surface generation of the extrudate. The surface of extrudate is generated on the portion of the die called bearing channel or die land. Aluminum metal which moves relative to bearing channel experiences a different state-of-stress as it passes through the bearing channel. At the entry side of the bearing channel, the stress is compressive which is large in magnitude and this magnitude of compressive stress gets diminished as metal moves towards exit side and eventually becomes zero at the exit. Temperature gradients and its distribution along the bearing channel, similar to stress gradient, are reported. Literature reports formation of the transfer layer on the bearing channel. The transfer layer is of two distinctive types, the one near entry side which virtually leads to contact between aluminum and die steel and the other nearer to exit side which isolates aluminum from die steel. The understanding of the mechanism of formation of transfer layer is most important since it is instrumental in determining the surface finish of the extruded component. All of the previous studies were conducted either in an actual extrusion press or using an instrumented extrusion press in the laboratory. The variables during these experiments could be the temperature of billet, extrusion ratio and speed of ram. Conducting these experiments using extrusion press is expensive and time consuming. To do experiments where the condition in a bearing channel can be simulated would be useful in conducting a more comprehensive study. To simulate the condition in the bearing channel a high temperature vacuum based pin-on-disc machine is designed and built. The fact that in a bearing channel there is virtually metal to metal contact with minimal or no chance of any intervening oxide layer, necessitated studies to be conducted under vacuum. A pin-on-disc test conducted under vacuum and high temperature would almost simulate condition on a bearing channel. Using this specially designed and built experimental setup the parameters influencing the transfer layer formation, temperature, sliding speed, load on the specimen, vacuum level and surface characteristics of the die are studied. Another feature of the test rig is that the configuration of pin and disc setup is vertical, which is different from regular pin on disc tribo-system, where pin and disc are held in horizontal configuration. The advantage of holding in vertical configuration is to eliminate the possibility of trapping the debris which alters the existing friction force and conditions. The test rig is constructed using a cylindrical shell and a matching dome shell. The test rig, to facilitate the isolation of the instrumentations used to measure the forces and wear from the heat source is partitioned into two portions. The cylindrical bottom compartment called test chamber and dome shaped top compartment called sensor chambers are separated by a plate. On the plate in the sensor chamber, a load-cell to pickup friction force, a linear variable differential transformer (LVDT) to measure linear wear and loading lever mechanisms for imparting normal load and measuring friction force are fitted. The lever mechanism, in particular the one which magnifies the normal load is designed to conserve the space in the vacuum chamber. Housing the instrumentation inside the vacuum chamber thereby reducing the number of ports required to sense mechanical signals, increases the efficiency of the pumping system. The cylindrical shell of the testing chamber is a double walled structure and water cooled in order to prevent the exposer of sensors to higher testing temperature. Rubber ‘O’ rings are used, wherever it is required to seal the vacuum. The necessary temperature required at the contact interface in the testing chamber is obtained by an electric resistance furnace, which is configured in such a way in the chamber that the heat generated is completely directed to the area where pin and disc are positioned. The interface temperature is monitored using a chromal-alumal thermocouple which is fixed very close to sliding interface on the pin holder. The power input to the furnace is controlled using PID (proportional integral derivative). The required sliding speed is achieved with the help of direct current (DC) servomotor. The shaft on which the disc or ring is fixed is connected to a timer-pulley. The timer-pulley in turn is connected to servomotor through a timer-belt. The diameter ratio of the driving pulley and driven -timer-pulley is selected in such a way that the rpm of driven-pulley is reduced by four times and the torque increased by four times resulting in a more stable mechanical input to the sliding pair. The necessary high vacuum level in the test chamber is created by using rotary pump and diffusion pump combination. Following tests are carried out. 1. Compression test: The strain rate response of aluminum (6060) under compressive state of loading is studied at strain rates 10-3s-1, 10-2s-1, 10-1s-1, 1s-1, 10s-1 and 102sand temperature ranging from 573 to 823K. The compression specimen is machined out of homogenized aluminum alloy (6060) cast ingots. True stress and true strain are estimated from load-displacement data of compression test. The true stress and true strain data are made use of in predicting the friction coefficient and sliding mode during sliding of aluminum relative to die steel at various temperature and other independent variables in vacuum. 2. The tensile test: A series of tensile tests at different temperatures and 10-1s-1 strain rate are conducted. The temperatures employed are from 423K to 723K. True stress, true strain, ultimate tensile strength and total percentage of elongation are estimated using load displacement data. The estimated ultimate tensile strength and total percentage of elongation are used for qualitatively explaining the morphology of transfer layer formed in the sliding experiments under different independent variables like temperature, speed, normal load, and surface texture of steel surface. 3. Adhesion test: The interaction at different temperature between the die steel (H11) and aluminum (6060) pair under static load is studied by conducting test in vacuum. The pin is made of homogenized aluminum and disc is made of die steel whose surface is generated by polishing on diamond paste until the average surface roughness (Sa) is of the order of 0.1 microns. The test temperatures are varied from 423 to 723K. The result is used in qualitatively explaining the morphology of transfer layer formed during sliding of aluminum and die steel pair in vacuum at various temperature, speeds and, normal load. 4. Sliding experiment: Steel pin and aluminum disc Pin on disc experiments are conducted at different temperatures in vacuum of the order of 4X10-4Pa. The experiments are conducted employing factorial design. The temperature, speed and load are the experimental parameters. The pin and disc are respectively made out of die steel and aluminum. Experiments are carried out with normal loads 20N, 40N, 63N, 80N, and 100N and speeds 0.1ms-1, 0.3ms-1, 0.5ms-1, 1.0ms-1, and 1.5ms-1 and with temperature over a range from 423 to 773K. The sliding distance covered is 500 meters. The friction force during sliding is monitored and used for estimating friction coefficient. Scanning electron microscopic study is carried out on surface, subsurface, wear track. The results, specifically, the friction coefficient and morphology of transfer layer are used to evaluate the influence of independent parameters on transfer mechanisms. The data generated from subsurface study and compression tests are used for estimating friction coefficient using Rigney’s plastic deformation model at 0.1ms-1. 5. Sliding experiment: aluminum pin and Steel disc The experiments reported in the previous paragraph where aluminum disc is slid against die steel pin had developed only the stresses of the order 16MPa. The estimated magnitude of stress level on bearing surface of extrusion die by various methods including numerical analysis is found to be more than 16MPa. In order to achieve a higher magnitude of stress and preserve the transfer layer mechanism, sliding an aluminum pin over the part of the textured surface of die steel ring is carried out. The changed boundary condition resulted in a nominal stress of 28 MPa which is comparatively more at 723K. The experiments are conducted employing factorial design. The other advantage of doing these experiments is that the effect of texture on the die surface can be studied by sliding aluminum pin over various surfaces. Thus temperature and surface texture are the experimental parameters for the present test. Different textured die steel surface is generated by machining process like, milling, electro discharge machining (EDM), wire electro discharge machining, silicon carbide slurry polishing, silicon carbide wheel grinding, CNC-milling and diamond paste polishing. Thus surfaces are basically of two types 1) with a lay on the surface and 2) a random surface. The tests are conducted at ambient temperature, 423, 573, 673, and 723K with a normal load of 56N and speed of 0.129ms-1. The morphology of transfer layer on the die steel ring is studied in scanning electron microscope. The friction coefficient is estimated from monitored friction force. The average surface roughness (Sa), results of compression test, and transfer layer are made use of to identify the sliding mode. The sliding of aluminum pin on diamond polished surface showed interesting results. Hence, another series of experiments using only diamond polished surface are conducted. The surface roughness of the steel surface achieved is 0.05 micro-meters. The load is 47N and speed is 0.043ms-1. The morphology of transfer layer and pin surface is studied using a Scanning Electron Microscope. Results of compression and tensile test: The flow stress is found to decrease with increase in compression test temperature. The SEM micrograph indicates large amount of fragmentation of harder phase with increase in strain rate at all temperature except for 423K. The fractured surface under tensile loading shows both intergranular and transgranular failure. Results of adhesion test: The area covered by the material transfer is found to increase with increase in temperature. The test can be used, to study the adhesive tendency between two pair of contacting surfaces. The area covered by the material transfer is found to be maximum at 723K. Results of sliding of die-steel pin on aluminum disc in vacuum: 1. The ANOVA (analysis of variance) results indicate the existence of transition speed of about 0.5ms-1, more than which the friction coefficient was found constant. The extrusion speeds employed in industries are in the range of 0.1ms-1 to 1.7ms-1 and the transition speed found in the present study is within this range. 2. The magnitude of friction, with a few exceptions, is found to be independent of temperature and sliding speed when the sliding speed is 0.5ms-1and above. The invariance of friction coefficient with temperature and sliding speed beyond 0.5ms-1 is beneficial in that it will not lead to any instability like stick-slip or squeal. 3. Though both ambient temperature and speed influence the morphology of transfer layer and friction coefficient, speed is found to be dominant according to statistical analysis. 4. The observed dependency of friction coefficient and morphology of transfer layer on test temperature and normal load is attributed to decrease in flow stress and increase in friction factor ‘m’, a ratio of interfacial shear stress to shear yield stress of the softer material. Though ANOVA shows the significance of speed and not that of temperature, the observed dependence of friction coefficient on temperature is attributed to the enhanced effect of adhesion at elevated temperature observed in the adhesion test. 5. The state of stress at the contacting surface is found to control the morphology of transfer layer. When the normal load exceeded 40N, it gave rise to higher magnitude of stress state at the contacting surface, resulting in formation of continuous transfer layer and hence the higher magnitude of friction coefficient. 6. Plastic deformation model based on Rigney’s approach for estimating friction coefficient can be used. The estimated friction coefficient is on the higher side. Hence, any design of equipments based on the Rigney’s plastic deformation model is a conservative design. 7. There appears to be a close relation between the morphology of wear track and quantity of wear-loss. The formation of debris and rough track, primarily for low temperature sliding indicate larger magnitude of wear-loss. The parameters, which bring about increased ductility of aluminum as observed in the case of higher temperature of sliding, results in reduced wear-loss due to large scale smearing and back transfer of material. The results of sliding of aluminum pin on die-steel ring in vacuum: 1. The mode of sliding changes from adhesive to abrasive mode depending on depth of penetration, tan(θ) where θ is the base angle of the conical asperity and average roughness parameter Sa ,all of them in turn depend on morphology of die steel surface and test temperature. 2. The friction coefficient and morphology of transfer layer are found to depend on the mode of sliding. The sub-surface plastic deformation, which characterizes the friction coefficient and morphology of transfer layer, is dependent on temperature of sliding. 3. The sliding experiment is capable of simulating the stress state on the bearing channel of the die; elucidating evolution of transfer layer, with change in operating parameters. 4. The ANOVA has clearly indicated the significance in friction coefficient at different temperatures and surface textures. In addition, the complex comparison below and above homogenization temperature (573K) has indicated significance in friction coefficient and thereby recognizing the importance of extrusion of aluminum at a temperature where it is in a single phase. Also, ANOVA indicates the dependency of both friction coefficient and transfer layer on the texture, i.e. either a lay or random. The results of sliding aluminum pin on diamond polished die steel ring: 1. Shearing of the cold welded junction is a probable mechanism involved in the formation of transfer layer up to 423K. 2. The transgranular and intergranular mode of fracture are identified to be the two possible modes of fracture of the asperity at temperatures greater than 573K. The large ductility of the aluminum alloy facilitated smearing resulting in a continuous transfer layer at temperatures greater than 573K. 3. The formation of a continuous transfer layer at temperatures greater than 573K is responsible for the observed high friction coefficient at these temperatures. Scanning electron microscopy observations of the fracture surfaces of the tensile test specimen revealed fracture to be a combination of both transgranular and intergranular modes.

The composition of orthopaedic wear testing lubricants used to mimic synovial fluid (SF) is known to significantly affect in vitro polyethylene (PE) wear; however, some wear testing standards may be promoting the use of lubricants that are not clinically relevant. The present thesis evaluated the biochemical composition of human osteoarthritic and periprosthetic SF in order to propose changes to lubricant specifications in current wear testing standards. Using this data, pin-on-disc wear tests were conducted to explore the effects of more clinically relevant lubricants on PE wear. Results showed that wear decreased using a more clinically relevant lubricant. Samples of these lubricants were biochemically evaluated and compared to the SF results previously obtained, which showed that current standards for wear testing lubricants are biochemically different from SF. The findings from the present thesis encourage the modification of standardized lubricant specifications to improve wear testing protocols and guarantee clinically relevant wear testing.

The composition of orthopaedic wear testing lubricants used to mimic synovial fluid (SF) is known to significantly affect in vitro polyethylene (PE) wear; however, some wear testing standards may be promoting the use of lubricants that are not clinically relevant. The present thesis evaluated the biochemical composition of human osteoarthritic and periprosthetic SF in order to propose changes to lubricant specifications in current wear testing standards. Using this data, pin-on-disc wear tests were conducted to explore the effects of more clinically relevant lubricants on PE wear. Results showed that wear decreased using a more clinically relevant lubricant. Samples of these lubricants were biochemically evaluated and compared to the SF results previously obtained, which showed that current standards for wear testing lubricants are biochemically different from SF. The findings from the present thesis encourage the modification of standardized lubricant specifications to improve wear testing protocols and guarantee clinically relevant wear testing.

Dentre os principais e mais efetivos tratamentos superficiais para a melhora das propriedades da superfície dos aços, encontra-se a nitretação e a nitrocarbonetação. Os benefícios da nitretação nos aços são o aumento da dureza, resistência ao desgaste, resistência à fadiga e resistência à corrosão. Por possuírem elementos como cromo, molibdênio e manganês, os aços ferramenta e aços baixa liga de ultra alta resistência são beneficiados pela nitretação. Neste trabalho, estudou-se o efeito da nitretação nos aços SAE 4140 e SAE H13 através de análises metalográficas, espectroscopia de emissão óptica, difração de raios-x, microdureza e ensaio pino-sobre-disco. Para efeito de comparação, amostras de aço SAE 1045 e ferro puro foram nitretadas juntamente com amostras dos dois materiais anteriores. Foram executados três tratamentos diferentes em cada um dos aços, nitretação com baixo potencial de nitrogênio, nitretação com alto potencial de nitrogênio e nitrocarbonetação. Os dois primeiros tratamentos foram realizados em três tempos diferentes de duas, quatro e seis horas e a nitrocarbonetação foi realizada em seis horas. Os resultados mostraram a formação de uma camada nitretada com de camada branca seguida de uma camada de difusão com gradiente de propriedades. Um aumento significativo de dureza superficial é observado com a aplicação dos tratamentos. A nitrocarbonetação junto com alto potencial de nitretação se mostrou não sendo benéfica para a formação da camada em relação à nitretação com mesmo potencial. Nos testes tribológicos realizados, a camada nitretada se mostrou eficiente em aumentar a resistência ao desgaste nos aços SAE 4140 e SAE H13. / Among the main and most effective surface treatments for improving the surface properties of steels are nitriding and nitrocarburizing. The benefits of nitriding in steels are the increase in hardness, wear resistance, fatigue resistance and corrosion resistance. Because they have elements such as chromium, molybdenum and manganese, tool steels and low alloy steels of ultra high strength are benefited by nitriding. In this work, the effect of nitriding on SAE 4140 and SAE H13 steels was studied through metallographic analysis, optical emission spectroscopy, x-ray diffraction, microhardness and pin-on-disc test. For comparison purposes, samples of SAE 1045 steel and pure iron were nitrided together with samples of the two former materials. Three different treatments were performed in each of the steels, nitriding with low nitrogen potential, nitriding with high nitrogen potential and nitrocarburizing. The first two treatments were performed at three different times of two, four and six hours and nitrocarburizing was performed in six hours. The results showed the formation of a nitrided layer with a white layer followed by a gradient layer of properties. A significant increase in surface hardness is observed with the application of the treatments. Nitrocarburizing together with high nitriding potential proved to be of no benefit to the formation of the layer in relation to nitriding with the same potential. In the tribological tests carried out, the nitrided layer proved efficient in increasing wear resistance in SAE 4140 and SAE H13 steels.

Dentre os principais e mais efetivos tratamentos superficiais para a melhora das propriedades da superfície dos aços, encontra-se a nitretação e a nitrocarbonetação. Os benefícios da nitretação nos aços são o aumento da dureza, resistência ao desgaste, resistência à fadiga e resistência à corrosão. Por possuírem elementos como cromo, molibdênio e manganês, os aços ferramenta e aços baixa liga de ultra alta resistência são beneficiados pela nitretação. Neste trabalho, estudou-se o efeito da nitretação nos aços SAE 4140 e SAE H13 através de análises metalográficas, espectroscopia de emissão óptica, difração de raios-x, microdureza e ensaio pino-sobre-disco. Para efeito de comparação, amostras de aço SAE 1045 e ferro puro foram nitretadas juntamente com amostras dos dois materiais anteriores. Foram executados três tratamentos diferentes em cada um dos aços, nitretação com baixo potencial de nitrogênio, nitretação com alto potencial de nitrogênio e nitrocarbonetação. Os dois primeiros tratamentos foram realizados em três tempos diferentes de duas, quatro e seis horas e a nitrocarbonetação foi realizada em seis horas. Os resultados mostraram a formação de uma camada nitretada com de camada branca seguida de uma camada de difusão com gradiente de propriedades. Um aumento significativo de dureza superficial é observado com a aplicação dos tratamentos. A nitrocarbonetação junto com alto potencial de nitretação se mostrou não sendo benéfica para a formação da camada em relação à nitretação com mesmo potencial. Nos testes tribológicos realizados, a camada nitretada se mostrou eficiente em aumentar a resistência ao desgaste nos aços SAE 4140 e SAE H13. / Among the main and most effective surface treatments for improving the surface properties of steels are nitriding and nitrocarburizing. The benefits of nitriding in steels are the increase in hardness, wear resistance, fatigue resistance and corrosion resistance. Because they have elements such as chromium, molybdenum and manganese, tool steels and low alloy steels of ultra high strength are benefited by nitriding. In this work, the effect of nitriding on SAE 4140 and SAE H13 steels was studied through metallographic analysis, optical emission spectroscopy, x-ray diffraction, microhardness and pin-on-disc test. For comparison purposes, samples of SAE 1045 steel and pure iron were nitrided together with samples of the two former materials. Three different treatments were performed in each of the steels, nitriding with low nitrogen potential, nitriding with high nitrogen potential and nitrocarburizing. The first two treatments were performed at three different times of two, four and six hours and nitrocarburizing was performed in six hours. The results showed the formation of a nitrided layer with a white layer followed by a gradient layer of properties. A significant increase in surface hardness is observed with the application of the treatments. Nitrocarburizing together with high nitriding potential proved to be of no benefit to the formation of the layer in relation to nitriding with the same potential. In the tribological tests carried out, the nitrided layer proved efficient in increasing wear resistance in SAE 4140 and SAE H13 steels.

This Paper deals with a design of tribometer for pin-on-disc and disc-on-disc tests. The purpose of these tests is Investigation of friction coefficient during hot forming. The main emphases of this paper are tool heating and quick tool change. The conductive sample heating is analyzed with FEM software Ansys and the results of this snalysis are taken into design consideration. Existing pin mounting design is considered as satisfying. Various disc mounting concepts are compared. The best solution - specimen mounting by an inside clamping cone with integrated specimen ejector was manufactured (heating excluding) and successfully tested.

Wear and biological response to wear debrisof artificial joints remain the major concerns in total hip arthroplasty (THA) [1].Silicon carbide reinforced alumina, Al2O3-SiCw,can be considered as a candidate for hip implants due to its high hardnessand toughness, aswell as chemical inertness. In this study, thewear and friction properties of Al2O3-SiCw areinvestigated by pin-on-disc experiments, with Hank’s Buffered Salt Solution(HBSS) as lubricant. Comparisons with BIOLOX®delta,the most commonly used ceramic in THA, under the same test conditions are made as well.