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

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

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

Combustion synthesis of silicon by magnesiothermic reduction

<p></p> <p>Magnesiothermic reduction of silica is a powerful method for producing silicon owing to its simplicity, low reduction temperature and low production cost. However, the inevitable formation of magnesium silicide (Mg₂Si) limits the use of this method. A new approach was developed in this research to prevent the formation of Mg₂Si by using alumina as a consumer of gaseous magnesium. Utilizing this approach, highly pure silicon was produced by firstly purifying the silica regent by acid-leaching. It was then subjected to magnesiothermic reduction regimes in order to optimize the power input and molar Mg/SiO₂ ratio to minimize Mg₂Si production. Silicon products were analyzed by X-ray powder diffraction (XRD) and quantitative Rietveld refinement. Optimum electrical power and molar ratio were found to be 3.75 kW and 2.25:1, respectively. The silicon product was examined by glow discharge mass spectrometry which indicated that its purity was 99.96%, with 0.10 ppm of B and 0.15 ppm of P, making it an attractive material for solar cell generation.</p