DRY SLIDING FRICTION AND WEAR OF THE WC/TIC-CO IN CONTACT WITH AL2O3 FOR TWO SLIDING SPEEDS

The paper examines the friction and wear behavior of four different WC/TiC-Co cermets, where three of them are composed of 5%, 10% and 15% TiC additions, and a WC-Co grade without TiC, taken as a reference material for comparison purpose. The principal aim is to improve wear resistance to high sliding speeds (hot rolling) of the WC-Co material as a reference by adding previously-listed percentage of TiC. The samples (cermets) were prepared according to the powder metallurgy procedure, which includes the preparation of the powder mixture, its compression shaping and liquid phase sintering. Sintering was carried out at 1460 ° C, for 14 hours, in a reducing medium (H2). The TiC materials are added in order to boost hardness of the WC-15Co cermet and, consequently, its resistance to wear under thermomechanical conditions. The experiments are conducted using a pin-on-disc tribometer in contact with Al2O3 alumina ball at two sliding speeds of 0.5m/s and 0.75m/s, at a high temperature of 450°C, and a 20 N load.  It has been noticed that some recorded friction coefficients are unstable and exhibit many peaks during almost the whole friction test period. The obtained results from the SEM microscope show that the wear behavior of the new proposed material is improved, where it has been shown that, at the sliding speed of 0.75m/s, the greater the TiC percentage is, the lower the average friction coefficient will be. Also, for the speed of 0.5 m/s, the average friction coefficient is relatively more stable with the TiC percentage increase. Moreover, the obtained experimental results show an average wear rate decrease, with respect to reference grades (NA), that amounts to nearly 36% and 41% at the two sliding speeds P1 (0.5m/s) and  P2 (0.75m/s), respectively

A new method to fabricate Fe-TiC composite using conventional sintering and steam hammer

The aim of this research paper is to fabricate a Fe-TiC composite by a novel and simple manufacturing method. The latter is based on two cumulative processes; a conventional sintering (transient liquid phase sintering) and a hot forging with steam hammer respectively. The blinder phase of the studied simples is varied from carbon steel to high alloy steel using alloying additive powders. The obtained outcomes showed that after the sintering process, the relative density of the performed simples is improved from 86% to 95.8% without any densification process. Otherwise, in order to ensure maximum densification and enhance in addition the solubility of the alloying additives the hot forging process is then applied. Indeed, the final obtained composite product is a TiC-strengthened steel with a relative density around 99% (about 6.5 g/cm3 of density) wherein 30% (wt.) of spherical and semi-spherical TiC particles are homogeneously distributed in the metal matrix

Effect of Liquid Salt Bath Nitrocarburizing on Mechanical Properties of Low-Alloy Sintered Steels

The purpose of this study is to produce Fe–2Cu–2Ni–0.7Mo–XC steels by means of the powder metallurgy at different sintering temperatures. The mechanical properties of sintered steels have recently reached a level equivalent to that of steels produced by other processes. The static and dynamic mechanical properties of parts made of sintered steel depend on density and microstructure. Many process parameters such as initial composition, alloying elements, atmosphere, time, sintering temperature, and nitrocarburizing influence the microstructure of steel parts. The compacts’ preparation involves powder mixing, cold pressing at 500 MPa, and sintering at 1250°C within the H2 atmosphere for 2 hours and 25 min. The influence of sintering temperature on both hardness and microstructure of the steel is investigated. In this study, sintered Fe–2Cu–2Ni–0.7Mo–XC-type steels are developed. The impact of nitrocarburizing on this structure is evaluated. Microscopy, SEM, and destructive testing are used for characterization of the sintered steels.Метою даної роботи є одержання сталей типу Fe–2Cu–2Ni–0,7Mo–XC методами порошкової металурґії за різних температур спікання. Механічні властивості спечених сталей нещодавно сягнули рівня, аналогічного рівню сталей, що виробляються іншими методами. Статичні та динамічні механічні властивості деталів із спеченої сталі визначаються густиною та мікроструктурою. При цьому велика кількість характеристик процесу, наприклад, вихідний склад, леґувальні елементи, атмосфера, час, температура спікання та нітроцементація впливають на мікроструктуру сталевих деталів. Виготовлення пресованого матеріялу потребує змішування порошку, холодного пресування при 500 МПа та спікання при температурі у 1250°C в атмосфері Н22 протягом 2 годин 25 хв. Було досліджено вплив температури спікання на твердість і мікроструктуру сталі. В даній роботі було розглянуто сталі типу Fe–2Cu–2Ni–0,7Mo–XC. Було проведено оцінку впливу нітроцементації на такі структури. Для характеризації спечених сталей використовувалися мікроскопія, СЕМ та випробування на руйнування.Целью данной работы является получение сталей типа Fe–2Cu–2Ni–0,7Mo–XC методами порошковой металлургии при различных температурах спекания. Механические свойства спечённых сталей недавно достигли уровня, аналогичного уровню сталей, производимых другими методами. Статические и динамические механические свойства деталей из спечённой стали определяются плотностью и микроструктурой. При этом большое количество характеристик процесса, например, исходный состав, легирующие элементы, атмосфера, время, температура спекания и нитроцементация, влияют на микроструктуру стальных деталей. Изготовление прессованного материала требует смешивания порошка, холодного прессования при 500 МПа и спекания при температуре 1250°C в атмосфере Н22 в течение 2 часов 25 мин. Было исследовано влияние температуры спекания на твёрдость и микроструктуру стали. В данной работе были рассмотрены стали типа Fe–2Cu–2Ni–0,7Mo–XC. Была проведена оценка влияния нитроцементации на такие структуры. Для характеризации спечённых сталей использовались микроскопия, СЭМ и испытания на разрушение

Investigation of the tribological behaviour of WC/TiC based cermets in contact with Al2O3 alumina under high temperature

WC/TiC-based cermets are, generally, considered as potential alloys widely used in hot rolling industry because of their interesting properties, namely high resistance to wear and oxidation. This work was aimed at studying the tribological behaviour, at relatively high temperatur, of WC/TiC-based cermets prepared using the powder metallurgy procedure. Three WC/TiC-Co cermets were prepared with different titanium carbide (TiC) additions namely 5%, 10% and 15% [in weight percentage (wt.%)], and a tungsten carbide-cobalt (WC-Co) grade without TiC which was considered as a reference material, resulting in a total of four samples. Friction tests were carried out, at two different contact temperatures of 450°C and 650°C, using a tribometer and an alumina ball during 2 h 46 min with load and speed of 20 N and 0.5 m/s, respectively. The obtained friction coefficients indicate that WC/TiC-based grades are relatively stable compared to the reference grade which shows an unstable friction coefficient with many peaks. It was also found that wear rates decreased with increasing TiC content, but exhibited a noticeable increase with rising temperature. Moreover, and in order to characterise the tribological degradation, the wear tracks microstructure composed of 80% WC, 15% Co and 5% of TiC, were analysed using a scanning electron microscope (SEM) process. Consequently, an enhancement of the wear resistance at 650°C was observed, and oxides of various types rich in tungsten, cobalt and oxygen were identified through SEM/energy electron spectrometery (EDS) images. © 2018 Walter de Gruyter GmbH, Berlin/Boston

DRY SLIDING FRICTION AND WEAR OF THE WC/TIC-CO IN CONTACT WITH AL2O3 FOR TWO SLIDING SPEEDS

peer reviewedThe paper examines the friction and wear behavior of four different WC/TiC-Co cermets, where three of them are composed of 5%, 10% and 15% TiC additions, and a WC-Co grade without TiC, taken as a reference material for comparison purpose. The principal aim is to improve wear resistance to high sliding speeds (hot rolling) of the WC-Co material as a reference by adding previously-listed percentage of TiC. The samples (cermets) were prepared according to the powder metallurgy procedure, which includes the preparation of the powder mixture, its compression shaping and liquid phase sintering. Sintering was carried out at 1460 ° C, for 14 hours, in a reducing medium (H2). The TiC materials are added in order to boost hardness of the WC-15Co cermet and, consequently, its resistance to wear under thermomechanical conditions. The experiments are conducted using a pin-on-disc tribometer in contact with Al2O3 alumina ball at two sliding speeds of 0.5m/s and 0.75m/s, at a high temperature of 450°C, and a 20 N load. It has been noticed that some recorded friction coefficients are unstable and exhibit many peaks during almost the whole friction test period. The obtained results from the SEM microscope show that the wear behavior of the new proposed material is improved, where it has been shown that, at the sliding speed of 0.75m/s, the greater the TiC percentage is, the lower the average friction coefficient will be. Also, for the speed of 0.5 m/s, the average friction coefficient is relatively more stable with the TiC percentage increase. Moreover, the obtained experimental results show an average wear rate decrease, with respect to reference grades (NA), that amounts to nearly 36% and 41% at the two sliding speeds P1 (0.5m/s) and P2 (0.75m/s), respectively

Influence de la fatigue thermique et des chocs thermiques sur la tenue au frottement et à l'usure d'un revêtement en acier inoxydable austénitique 304L

L’objectif principal de ce travail est de concevoir au sein de notre laboratoire un banc d'essai de fatigue et de chocs thermiques. Il a été mis à profit, dans un premier temps, dans l’étude de l’influence de la fatigue thermique (180 – 550°C) et des chocs thermiques (20 – 600°C) sur la tenue au frottement et à l’usure d’un revêtement en acier inoxydable austénitique AISI 304L. Ce revêtement a été déposé par le procédé de soudage T.I.G sur des éprouvettes en acier ferritique 42CD4. L'étude concerne 3 états différents du dépôt : sensibilisé, sensibilisé écroui en surface et hypertrempé. Les profils de microdureté des dépôts cyclées montrent un adoucissement au niveau de la zone de liaison entre le substrat et le dépôt, par rapport au dépôt de référence "brut de soudage". On a constaté, que l'évolution microstructurale observé sur tous les dépôts analysés au microscope optique, influe considérablement sur la cinétique d'usure et les pertes de masse, surtout en surface. Nous nous sommes intéressé également à l'étude du frottement. On a constaté que son évolution est irrégulière dans le sens de l'épaisseur et qu'il est indépendant des pertes de masse. L'analyse des traces d'usure au MEB a démontré l'influence de l'état de surface sur les pertes de masse, surtout après chocs thermiques; l'usure abrasive est aggravée par un désagrégement de la surface due à la corrosion. L'écrouissage de la surface favorise la formation de fissures transgranulaires et diminue l'effet des chocs thermiques sur les pertes de masse. Dans ce cas, l'usure passe d'une usure douce dite surcontrainte au début vers une usure abrasive plus sévère en fin d’essai.Mots clés: fatigue thermique; choc thermique; acier inoxydable austénitique; frottement; usure; soudage. The main objective of this work is to design an experimental set up for thermal fatigue and shocks analyses. Initially, The influence of thermal fatigue (180-550°C) and of thermal shocks (20-600°C) on both friction and wear of a coating is studied in an AISI 304L austenitic stainless steel. This coating has been deposit by T.I.G welding process on specimens made out of 42CD4 ferritic steel. The study concerns tree different cases of deposits: sensitized, sensitized and strain hardened in surface and hyperquenched (not sensitized). The profiles of cycled microhardness deposits show a softening at the contact zone between the substrat and the deposit, with respect to the reference deposit (welding raw deposit). It is noted, that the microstructural evolution observed in all deposits, as analyzed by optical microscopy, affects considerably the wear kinetics and the rate of weight loss, especially at the surface. It is also observed that friction evolution is irregular in thickness direction and it is independent of the observed weight loss. Wear traces analysis by SEM demonstrated the influence of surface quality on weight loss, especially after thermal shocks and abrasive wear is aggravated by surface disintegration as a result of corrosion. The strain hardening of the surface favors the formation of transgranular cracks and lowers thermal shock effetcs on weight loss. In this case, wear evolves at the beginning, from soft wear called "overstress” towards a severe abrasive wear by the end of the test.Keywords: thermal fatigue; thermal shocks; austenitic stainless steel; friction; wear; welding

Effet des additions sur la microstructure et le comportement tribologique et en fatigue thermique des revêtements à base de NiAl obtenus par projection plasma

L’objectif principal de ce travail est de comprendre l’influence des additions des particules de TiC, SiC, MgO et WC dans le mélange de base NiAl, sur la structure, le comportement en fatigue thermique, à l’usure et par érosion du revêtement obtenu par projection plasma (APS). La microstructure des revêtements a montré une structure lamellaire, caractéristique des revêtements obtenus par projection plasma. Le revêtement NiAl+5%WC a acquis ainsi une dureté plus élevée que les autres revêtements. L'essai de fatigue thermique a été réalisé par un chauffage cyclique par effet joule dans l’intervalle 100 et 800°C . Les résultats expérimentaux ont montré que le revêtement enrichi en WC présente le meilleur comportement en fatigue thermique. Les essais d'érosion ont été effectués à température ambiante avec un angle d'attaque de 90°. Le coefficient de frottement a été déterminé sous une charge normale de 5N, avec une vitesse de 11,31 cm/s et à température ambiante. Le revêtement NiAl accuse le plus bas coefficient de frottement. L'incorporation des autres particules améliore le comportement à l’érosion ainsi que le coefficient de frottement.Mots-clés: Fatigue thermique- érosion- projection plasma-revêtement NiAl- coefficient de frottementEnglish Title: The effect of additions on the microstructure, tribological behavior and thermal fatigue of the NiAl coating, obtained by atmospheric plasma spraying (APS)English AbstractThe main focus of this work is to highlight the influence of the TiC, SiC, MgO and WC particles, as additions on the microstructure, thermal fatigue and tribological tests of the NiAl coating, obtained by atmospheric plasma spraying (APS). It was founded that the NiAl–5%WC microhardness and thermal fatigue behaviour were more improved than the TiC, MgO, and SiC coatings. In addition, the MgO, WC, SiC and TiC coatings showed lower erosion rates compared to NiAl base ones. However, the thermal fatigue and erosion tests were conducted by a cyclic heating Joule effect within the range 100–800 °C degrees and at room temperature with an attack angle of 90° respectively.. Furthermore, the microstructure of all the coatings showed a lamellar morphology, which is typical of the coatings obtained by atmospheric plasma spraying. The friction coefficient was determined under a normal load of 5 N with sliding speed of 11.31 cm/s and at room temperature. The NiAl coating present the lowest coefficient of friction. The incorporation of the particles improves the coefficient of frictionKeywords: Thermal fatigue-erosion-plasma Spray-NiAl coating-friction coefficien

Soudage par explosion thermique sous charge de cermets poreux à base de TiC-Ni sur substrat en acier-comportement tribologique Welding of porous TiC–Ni based cermets on substrate steel by thermal explosion under load-tribological behaviour

Dans ce travail, nous nous intéressons à l'élaboration de cermets à base de TiC-Ni par dispersion de particules de carbures, oxydes ou borures dans une matrice de nickel, grâce à la technique de l'explosion thermique sous une charge de 20 MPa. La combustion de mélanges actifs (Ti-C-Ni-An où An = Al2O3, MgO, SiC, TiB2, WC), basée sur la réaction de synthèse de TiC (ΔHf298K = −184 kJ/mole), génère des cermets complexes. Un court maintien sous charge du cermet à 1373 K, après l'explosion thermique, permet son soudage sur un substrat en acier XC55. Les cermets obtenus dans ces conditions demeurent poreux et conservent une porosité de l'ordre de 25–35 %. La densité relative du cermet, sa dureté et son comportement tribologique, dépendront de la nature de l'addition dans les mélanges de départ. <br> Porous TiC-Ni based cermets were obtained by dispersion of carbides, oxides or borides particles in a nickel matrix thanks to the thermal explosion technique realized under a load of 20 MPa. The combustion of active mixtures (Ti-C-Ni-An where An = Al2O3, MgO, SiC, TiB2 or WC) based on the titanium carbide reaction synthesis (ΔHf = −184 kJ/mol), generates porous complex cermets. After the thermal explosion, a short maintenance under load at 1373 K of the combustion product, allows at the same time the cermets welding on a carbon steel substrate. The obtained cermets under these conditions preserve a porosity of about 25–35%. The relative density, hardness and tribological behaviour of the complex cermets depend on the additions nature (An) in the starting mixtures

Comportement à la corrosion des alliages TiNi et TA6V4 dans la salive artificielle et performance d’usure

Ce travail porte sur l’étude du comportement tribologique sans lubrification et électrochimique dans la salive artificielle des alliages TiNi (50/50) et TA6V4 pour les applications en orthodontie (implants dentaires). L'alliage TiNi (50/50) a été préparé dans un four à induction sous vide alors que l'alliage commercial TA6V4 sera utilisé comme matériau de référence. L’analyse microstructurale et la composition chimique des deux alliages TiNi et TA6V4 a été réalisée par microscopie électronique à balayage (MEB) couplée à l’EDS. Les résultats montrent que l'alliage TiNi présente une meilleure résistance à l'usure par glissement à sec (1,327x10-4 mm3 /Nm) par comparaison avec l'alliage TA6V4 (9,506x10-4 mm3 /Nm). Les mécanismes  d’usure ont été clairement identifiés pour les deux alliages et sont principalement basés sur une usure abrasive et adhésive pour l'alliage TiNi, et une usure abrasive associée à une oxydation, pour l’alliage TA6V4. L'étude électrochimique a révélé que les deux alliages présentent un caractère passif avec une résistance élevée à la corrosion.Mots clés: Alliages de titane- Microstructure- Comportement à l'usure- Résistance à la corrosion- Impédance.Corrosion Behavior of TiNi and TA6V4 Alloys in Artificial Saliva and Wear PerformanceThis work aims to study the tribological performance in dry conditions and electrochemical behavior, in the artificial saliva of TiNi (50/50) alloys in comparison with TA6V4 alloys in the focus to use them for dental applications. The TiNi alloy was prepared in a vacuum induction melting furnace whileTA6V4 commercial alloy should be used as a reference material. The TiNi alloy (50/50) was prepared in a vacuum induction melting furnace while the TA6V4 commercial alloy will be used as a reference material. The microstructural analysis and chemical composition of the two TiNi and TA6V4 alloys was determined by scanning electron microscopy(SEM) coupled to EDS. Results showed that TiNi alloy exhibits a better wear resistance in dry sliding mode (1.327x10-4 mm3 / Nm) when compared to the alloy TA6V4 (9,506x10-4 mm3 / Nm). The wear mechanisms of both alloys have been clearly established. It can be retained that NiTi alloy degradation is governed by an adhesive and abrasive wear mechanism, but for the TA6V4 alloy, abrasive and oxidative wear mechanisms are determined. Electrochemical studies reveal a passive behavior character and higher resistance against corrosion.Key words: Titanium alloys- Microstructure- Wear behavior- Corrosion resistance- Impedance

Performances tribologique et électrochimique de l’alliage TiNi poreux

Ce travail vise l’étude de l’effet de la porosité sur le comportement tribologique et électrochimique de l’alliage TiNi poreux pour des applications biomédicales. L’alliage TiNi poreux a été élaboré par le procédé de frittage en phase solide à la température de 850°C. En effet, l’analyse microstructurale par MEB et EDS confirme bien que lorsque la pression de compactage varie il se produit un changement de la morphologie des pores et des fractions des phases formées. L’étude du glissement à sec de notre matériau a permis de mettre en évidence que la présence de la porosité interconnectée améliore leur comportement tribologique. Cependant l’étude électrochimique a révélé que quelque soit le taux de porosité les échantillons présentent un caractère passif. Les paramètres électrochimiques dépendent dans une large mesure du pourcentage de pore, leur morphologie et leur distribution.Mots-clés: biomatériaux, porosité, tribologie, résistance à la corrosion, impédanceEnglish Title: Tribological and electrochemical performances of porous TiNi alloyEnglish AbstractThis work aims to study the effect of porosity on the tribological and electrochemical behavior of the porous TiNi alloy for biomedical applications. The porous TiNi alloy was developed by the solid phase sintering process at the temperature of 850°C. Indeed, the microstructural analysis by SEM and EDS confirms that when the compaction pressure varies there is a change in the morphology of the pores and fractions of the phases formed. The study of the dry sliding of our material made it possible to highlight that the presence of the interconnected porosity improves their tribological behavior. However, the electrochemical study revealed that whatever the porosity rate, the samples have a passive character. The electrochemical parameters depend to a large extent on the percentage of pore, their morphology and their distribution.Keywords: biomaterials, porosity, tribology, corrosion resistance, impedanc