Liste des documents
Effect of WC-Co cermet positioning and Ni-Cr interlayer on the microstructure and mechanical response of the dissimilar WC-Co / AISI 304 L rotary friction joint
In this work, incompatible properties of WC-Co cermet and AISI 304 steel were combined in the same component using rotary friction welding (RFW) process. The dissimilar joints were performed using a ductile NiCr interlayer with the change in the WC-Co cermet positioning i.e., fixed rotary side and feeding side. Similar microstructure across the weld joints was obtained of the different welding configurations that produced similar behavior in hardness and elastic modulus. A diffusion zone was formed at the weld interface as a result of the mutual inter-diffusion of both cermet (W and Co) and steel elements (Fe, Cr and Ni) that enhanced with the insertion of the interlayer when the cermet was fixed in rotary side. The introduction of the NiCr interlayer was beneficial to relax the residual stresses and improving the shear strength of the WC-Co cermet/AISI 304 L steel joints, which is promising technology for drilling tools industries. Voir les détails
Mots clés : Rotary friction welding WC-Co cermet NiCr interlayer Interface Microstructure Mechanical properties
Dissimilar FSW of AA2024 and AA7075: Effect of materials positioning and tool deviation value on microstructure, global and local mechanical behavior
In this work, the effect of material location and tool deviation on the global and local mechanical behavior of dissimilar AA2024/AA7075 friction stir weld joints was investigated. The results showed that increasing the tool deviation value up to 1mm towards the AA2024, fixed in advancing side, improved the material mixing quality and enhanced the grain refinement in the stir zone. It was found that the highest ultimate tensile strength was obtained when the AA2024 alloy was fixed in the advancing side for 1mm tool deviation towards this material. Above this deviation value, a gradual decrease of the global mechanical properties of the weld joints was noticed. Digital image correlation (DIC) technique coupled to tensile testing revealed an improvement of local strain in the stir zone and the heat affected zones of the dissimilar joints when AA2024 alloy was positioned in the advancing side. Voir les détails
Mots clés : Dissimilar friction stir welding, tool deviation, DIC, mechanical properties, microstructure
Rotary friction welded C45 to 16NiCr6 steel rods: statistical optimization coupled to mechanical and microstructure approaches
In the present work, the dissimilar joints between C45 carbon steel and nickel-chromium 16NiCr6 steel rods were produced usingrotary friction welding process. Statistical analysis based on response surface methodology (RSM), microstructural examinationusing scanning electron microscopy with backscattered electron diffraction (EBSD) and mechanical tests were performed toinvestigate the friction weld joints. The results showed that friction time and rotation speed were the most effective parameters onthe weld joint quality with the highest t-ration of − 4.27, where the maximum bending strength of 1406.9 MPa was obtained at2000 rpm for 13 s friction time. Increasing friction time to 13 s resulted in remarkable decrease in grain size (about 35%) at theweld interface, which increased the hardness (350HV0.1) and elastic modulus (260 GPa). Voir les détails
Mots clés : Rotary friction welding . RSM methodology . Microstructure
Effect of heat treatment on microstructure and tribological behavior of friction stir processed Al2O3-reinforced AA2024-T351 matrix
In the present work, 2024-T351 Al alloy reinforced with alumina particulates (Al2O3p) was elaborated using friction stir processing (FSP). The effect of solution heat treatment followed by subsequent aging on microstructure, hardness, and tribological behavior is discussed. It was noticed that the hardness of the as-FSPed 2024-T351/Al2O3p was slightly enhanced in comparison to the as-received AA2024-T351 material, whereas the resulting wear resistance was remarkably improved. After heat treatment process, the composite volume increased, and swelling and pores were created at the processed area. The heat treatment caused a degradation in wear resistance compared to as-FSPed composites. The precipitation mechanism changed forAA2024/Al2O3p; reactions occurred at grain boundaries between Al2O3 and Cu or Mg, causing their depletion from the Al matrix. Intriguingly, the precipitation mode in heat-affected zone of the matrix also changed to grain boundary precipitation. Voir les détails
Mots clés : Friction stir processing, Metalmatrix composites, wear, friction
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