Liste des publications
HEAT TREATMENT AND WELDING EFFECTS ON MECHANICAL PROPERTIES AND MICROSTRUCTURE EVOLUTION OF 2024 AND7075 Aluminum ALLOYS
Aluminum alloys are sensitive to hot cracking during the welding operation, both liquidation cracking in the heat affected zone (HAZ) and solidification cracking in the weld can occur. The GTA Welding results of aluminum alloys 2024 T3 and 7075 T6 for 2 mm plate thickness with different parameters of welding are presented in this paper. Before welding, different alloys were heat treated at different temperature to follow the evolution of microstructure and mechanical properties. After welding, the strength of the materials in heat affected zone (HAZ) is reduced. This reduction on properties is due to the different phenomenon that occurs during welding Voir les détails
Mots clés : heat treatment, Aluminium alloys welding, hardness, Precipitation, tensile strength, yield strength, Microstructures
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
Microstructure and Tribological Behavior of In SituTiC-Ni(Si,Ti) Composites Elaborated from Ni and Ti3SiC2 Powders
Herein, we study the effect of Ti3SiC2 on the microstructures and tribological properties of an in situ TiC reinforced Ni(Si, Ti) composites elaborated from Ni and Ti3SiC2 MAX phase powders against steel(100Cr6). Pressureless sintering at 1080 C for 4 h of Ni and Ti3SiC2 powders was used to elaborate these composites with 10, 20 and 30 wt.% of Ti3SiC2. The microstructures of the composites were investigated by scanning electron microscopy (SEM), x-rays diffraction and Raman spectroscopy. Standard ball-on-disk friction wear tests under different applied loads were conducted on the composites surfaces at room temperature. For the three elaborated composites, Ti3SiC2 was totally decomposed and transformed to TiC phase, while the released Si and Ti atoms from Ti3SiC2 diffused into Ni matrix forming Ni(Si, Ti) solid solution. As compared with reference (Ni) sinter, the addition of 20 wt.% Ti3SiC2 in the Ni matrix improved the hardness by 250%. The addition of Ti3SiC2 particles also had a beneficial effect on the tribological performance of these composites against steel. The worn surfaces of the elaborated composites under all applied loads are characterized by the presence of a lubricious Fe3O4-aFe2O3 tribofilms. The effect of chemical compositions and different applied loads on the wear mechanisms of the three elaborated composites is discussed. Voir les détails
Mots clés : In situ composites, MAX phase, Microstructures, wear
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
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
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
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
Influence of isothermal aging in LDX 2101 duplex stainless steel on the microstructure and local properties
In the present work, the interface morphology and the evolution of nitride precipitates in LDX 2101 stainless steel isothermally treated at 750 °C for various aging times were investigated. The microstructure results showed that the Cr2N nitrides precipitated along the δ/γ interface with 200 nm in length and continue to grow to 2 μm after 240 h of aging. However, only Cr2N nitrides were found at the δ/δ interface after long term of aging. Atomic force microscopy (AFM) analysis revealed that Cr2N nitrides andCr23C6 carbides started to precipitate after the first 10 min of aging with a small needle shape of the former and specific triangular morphology of the latter. The evolution of hardness and Young’s modulus of the interfaces, performed with nano-indentation measurements, showed that the δ/γ interface became harder (4.1 ± 0.2 GPa) with increasing aging times, whereas negligible changes in the hardness and elastic modulus were recorded at the δ/δ interface. 3D topographic analysis of the immersed surfaces revealed that the susceptibility of δ phase to preferential dissolution in 3.5% NaCl solution increased with aging time. This behavior was manifested by the important imperfections of δ phase, the high surface roughness (55.7 nm), and the deep corrosion pits (30 nm) along the δ/γ interface and around the Cr2N nitrides. Voir les détails
Mots clés : microstructure, Interface, precipitates, Nano-hardness, Surface degradation
Effect of aging temperature on the microstructure, local-mechanical properties and wear behavior of a UNS S32750 super-duplex stainless steel
In this paper, the effect of aging temperature on the microstructure, local-mechanical properties and wear behavior of a UNS S32750 super-duplex stainless steel is investigated. A massive preferential precipitation of σ phase and Cr2N is detected at the periphery of ferrite with an increase in their extent as aging temperature increases. Simultaneously, the δ phase decomposition is accentuated with temperature and reaches its maximum at 850°C.This behavior results in an enhancement in hardness and Young’s modulus accompanied by a higher plasticity ratio. The wear resistance of the aged samples is investigated in terms of friction coefficients and wear rates against two counterparts. The wear performance follows σ phase presence, the higher σ phase extent, the higher the wear resistance. It is found that the change in wear mechanisms in the 850°C aged samples from abrasive against AISI-304L counterpart to adhesive-oxidative against Al2O3 counterpart is responsible in the increase in wear resistance. Voir les détails
Mots clés : 2507 SDSS, Aging temperature, microstructure, precipitates, Nano-indentation, Wear resistance.
Effect of WC-Co cermet positioning and NiCr 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 304L steel joints, which is promising technology for drilling tools industries. Voir les détails
Mots clés : Rotary friction welding, WC-Co cermet, mechanical properties, NiCr interlayer, Interface