Liste des publications
Pressureless sintering and tribological properties of in-situ TiC-Ni3(Al,Ti)/Ni(Al,Ti) composites
In this study, we report on the microstructure and tribological characterization of in-situ TiC and γ’-Ni3(Al,Ti)reinforced γ-Ni(Al,Ti) matrix composites, synthesized by in-situ reaction of Maxthal211 (Ti2AlC-Ti3AlC2, MAX phase) and Ni precursors. Three composites were elaborated from 10, 20 and 30 wt % of the MAX phase precursor which fully reacted with Ni-matrix at 1080 °C sintering temperature for 4 h; the MAX phase decomposed into TiC, and the released Al and Ti atoms diffused in Ni matrix forming γ-Ni(Al,Ti) solid solution and γ’-Ni3(Al,Ti)intermetallic. Scanning Electron Microscopy (SEM), X-Rays Diffraction (XRD) and Raman spectroscopy were used to study the different microstructures and worn surface characteristics. Dry sliding properties of the composites under different normal loads were studied using a ball-on-disc tribometer. Addition of 10 wt % MAX phase procured the highest hardness (1.35 GPa) which is two times higher than that of pure Ni. Whereas all there inforced composites exhibited better wear resistance. The formation of a lubricious layer during sliding and the good in-situ bonding between Ni/reinforcement phases, were the main cause to the enhanced wear resistance. Voir les détails
Mots clés : Metal matrix composites, Pressureless sintering, MAX phase, diffusion, In-situ composites, wear
Effect of Heat Treatment on the Structure, Wear and Corrosionof AISI L6 Tool Steel
This work is a contribution in analyzing structure, tribological behavior and corrosion ofAISI L6 hardened tool steel. Structural characterization and tribological behavior of steel wereinvestigated using Optical Microscopy (OM), Scanning electron microscopy (SEM), wear testing byfriction on a pin-on-disc Tribometer and corrosion by potentiodynamic polarization. Comparing tothe as-received steel, hardening has generated a fine martensitic microstructure causing a 1.5 timeshardness increase. Hardening has contributed to improvement of wear resistance as the coefficient offriction has decreased from 0.86 to 0.67μ. An increase in corrosion resistance was observed afterhardening treatment. Voir les détails
Mots clés : tool steel, AISI L6, friction, hardening, corrosion, heat treatment, wear
Study of The Structure and Corrosion Behavior of Al-15%MoAlloy
The influence of the addition of molybdenum on the structure and corrosion behaviour of aluminium was studied using optical microscopy, scanning electron microscope (SEM),potentiodynamic polarization and electrochemical impedance spectroscopy. The results showthat the addition of 15%wt molybdenum causes the precipitation of the Al12Mo intermetallic phase which appears in plate form on the αAl matrix. The results of the electrochemical tests show that the addition of molybdenum displaces the corrosion potential of aluminium towards positive values from -699 mV/ECS to -633 mV/ECS and increases the charge transfer resistance from to 4752 Ω.cm2 to 6608 Ω.cm2. Voir les détails
Mots clés : corrosion, Al-15%MoAlloy, Electrochemical behavior
Reliability Estimation of Cracked API 5L X70 Pipeline Steel
The aim of this paper is to estimate the reliability of cracked pipeline steel grade API5L X70 used for hydrocarbon transportation, by coupling a developed mechanical model, basedin one hand on the simulation of cracked specimen, and an experimental result of tensile and Charpy test, and in the other hand, based on a reliability model by using a first-order reliability method (FORM). These pipes are produced by the Algerian company of manufacture of welded pipes (ALFAPIPE Annaba). The experimental task such as resilience and tensile test were carried out on specimens taken from a pipe in the longitudinal and the transversal directions. The resilience tests are carried out at different temperatures in order to estimate the fracture toughness of the material, basing on a global correlation. Besides, tensile tests are performed to bring out the mechanical characteristics of the material. After, the stress intensity factor is assessed using the analytical model of IRWIN. In the reliability analysis, the limit state function is attributed to the moment when the stress intensity factor estimated by Irwin mechanical model, is equal tothe fracture toughness of the steel pipe. The basic random variables within the limit state function are assumed to follow a normal distribution in order to simplify the assessment. Then, the evaluation of the reliability index and the parameters sensitivities of the cracked pipelines steel are assessed. Voir les détails
Mots clés : Reliability, Cracked API 5L X70, Pipeline Steel
Effect of Environmental Media on the ElectrochemicalBehavior of API X70 Pipeline Steel
This work investigates the corrosion behavior of X70 steel in different environments: sea sand, desert sand, mud, and seawater. The principle of extracting solutions from these media consisted of mixing a soil material with distilled water, and the mixture was agitated using an automatic agitator, which resulted in the extraction of the solution. Potentiodynamic polarization and electrochemical impedance tests are used to characterize the samples in both media. The results show that the pipeline steel X70 has an excellent corrosion resistance in the sea sand solution, resulting in a low corrosion current density compared to other media. The impedance diagrams for both media are characterized by two capacitive loops, the first loop is attributed to charge transfer processes and the second loop is related to diffusion phenomena. The observation of corroded surfaces shows that the corrosion mechanism in different media is by pitting. Voir les détails
Mots clés : pitting, sea sand, seawater, corrosion
Tribological behavior and microstructural characterization ofaustenitic stainless steel stabilized with Nb and V
This study deals with the influence of the addition of vanadium and niobium with concentrations of 1.2% and 0.14%, respectively, on the variation of the microstructure, and the tribological behavior of an AISI309 austenitic stainless steel. The studied specimens were structurally characterized by optical microscopy, scanning electron microscopy (SEM) X-ray diffraction and differential scanning calorimetry (DSC). These samples were also subjected to a tribological study using the friction wear test. The results show that the addition of vanadium and niobium causes precipitation of stable carbides (VC, NbC) which in turn causes a decrease of the chromium carbide precipitation rate. Tribological test results have also shown that the addition of these two elements improves the wear resistance of AISI309 austenitic stainless steel by decreasing the coefficient of friction from 0.824 to 0.554. Voir les détails
Mots clés : Vanadium, niobium, tribological, wear, friction, AISI309
Heat Treatment Effect on the Microstructural, Hardness and TribologicalBehavior of A105 Medium Carbon Steel
The present work is a contribution in investigating the effect of heat treatment on microstructure, hardness, and friction wear of A105N steel. Samples of 25x25 mm² cross-section and15mm thickness have been prepared from the as-received material and then heat-treated. The samples were austenitized at 1050°C for 60 minutes followed by water quenching, then tempered at 500 and700°C for 120 minutes. Microstructural changes and their effect on the wear resistance and hardness were investigated according to the applied heat treatments. The main results show that after quenching the structure is mostly composed of quenched martensite, which confers high hardness and friction resistance to the steel. While the tempered structure is composed of tempered martensite and ferrite.As the temperature rises to 700°C, the tempered martensite decreases and is fully transformed to ferrite and cementite. A good wear resistance is expressed by a low friction coefficient and a low wear rate is achieved by tempering at 500°C. Voir les détails
Mots clés : tempering, Quenching, friction, A105, hardness, heat treatment, wear
Effect of ball burnishing process on mechanical propertiesand impact behavior of S355JR steel
Often, surface mechanical treatment (SMT) or heat (quenching, tempering) is used to improve the surface condition andmechanical characteristics such as impact resistance and tensile strength. Hence the objective of this experimental work, whereball burnishing (BB) as well as quenching and tempering were applied on S355 JR steel specimens, is to evaluate the surfacehardness Hv, the rupture strength Rm, the energy absorbed W during the impact test, and the work-hardened thickness e after theburnishing operation. Factorial designs were used for the test organization and mathematical models were established for theprediction of Hv, Rm, W, and “e” in function on treatment parameters considered: number of tool passes (i) and the pressure force(Py). The results show that the surface hardness increases by 30.46%. The high levels of Py and i were allowed to improve Rm by30.8% as well as an increase in tenacity of only 3.6%. Increasing the force to 20kgf promotes mixed rupture under the effect ofimpact to shock. The quenching and tempering improve the Rupture strength Rm by 183% and 119%, respectively, while theeffect of burnishing was limited to a rate of increase of this property of 28% compared to machining. Voir les détails
Mots clés : Tensile resistance . Burnishing . Heat treatment . Superficial hardness . Absorbed energy . Penetration depth . Ruptures facies
Investigation оn Dry Sliding Wear Performance and Corrosion Resistance of 13Cr5Ni2Mo Supermartensitic Stainless Steel
This work aimed to study the microstructure, wear and corrosion resistance of supermartensitic stainless steel (SMSS). Heat treatment applied to samples consists of quenching after austenitization at elevated temperature (1250 °C) followed by a double tempering at 650 °C. Conventional mechanical properties, scanning electron microscopy (SEM/EDS) analysis and X-ray diffraction methods (XRD) are used to analyze the microstructure and to evaluate the wear mechanisms. The potentiodynamic polarisation and the electrochemical impedance spectroscoopy (EIS) methods are used to evaluate the corrosion resistance in both the 0.5M H2SO4 and 0.5M NaCl aggressive media. The microstructure is mainly composed with tempered lath martensite, small quantity of retained austenite and carbides. Oxidative and abrasive wear dominated the wear process in dry condition. During the corrosion process, the same mechanism of degradation was found in both the 0.5M NaCl and 0.5M H2SO4. Voir les détails
Mots clés : Supermartensitic steel, microstructure, friction, wear, corrosion
Effect of annealing temperature on the microstructureevolution, mechanical and wear behavior of NiCr–WC–CoHVOF-sprayed coatings
In the present work, the effect of annealing temperature on the microstructure, mechanical and tribological properties of NiCr–WC–Co coatings produced by the high-velocity oxy-fuel (HVOF) technique has been investigated. X-ray diffraction and scanning electron microscopy revealed the dissolution of WC into the NiCr matrix to form W2C and Cr3C2 with the annealing process. This dissolution became complete at 800 °C. The mechanical properties of the coatings were investigated using nano-indentation and Vickers fracture toughness measurements. These measurements suggested that the hardness, Young’s modulus, and fracture toughness values increased because of the newly formed carbide phases as a result of the dissolution of the WC particles.The overall properties of the coatings were found to be optimum for annealing temperatures of 800 °C. The wear mechanism appears to be abrasive in the as-sprayed coating, and it becomes a combination of an abrasive and oxidative wear with increasing the annealing temperature Voir les détails
Mots clés : HVOF;, WC coating:, Annealing;, Wear resistance;, Nano-indentation