مسعود مصلایی پور

In the present study, friction stir processing (FSP) technique was carried out on the AA2024 sheet at different traverse speed (63 to 250 mm/min) and rotation speed (315 to 800 rpm). The temperature and grain size of stirred zone (SZ) were measured and their relationship was analyzed and effect of FSP parameters on the grain size of SZ was determined. Experiment and analytical investigations revealed that SZ grain size complies the exponential temperature-dependent relationship and can be defined the mathematical equation. Calculations indicate that a change in operational variables (rotation and traverse speeds) makes no variation in strain rate, and it is constant.

In the present study, the microstructure and mechanical properties of the dissimilar joint of Inconel 625 (IN-625) superalloy to austenitic stainless steel AISI316L (SS-316L) via AWS-BNi3 interface layer and transient liquid phase (TLP) bonding process were evaluated and necessary conditions for creating an efficient joint were determined. TLP bonding was performed in temperature and time range of 1050-1150ºC and 5-20min, respectively, under the protection of argon shielding gas with a purity of 99.9995%. Microstructural (OM and SEM) and phase (XRD) studies revealed that bonding at 1150 ° C for 20 min results in completion of isothermal solidification and develops a uniform gamma (γ) phase at the bonding zone. Cooling the samples before completion of isothermal solidification results in the formation of chromium and molybdenum-rich eutectic compounds at the bonding centerline. The continuous morphology of the eutectic compounds caused a sharp drop in the shear strength of the specimens (~50% reduction of shear strength). The inter-diffusion of alloying elements between the bonding area and the surrounding base metal results in the formation of chromium carbide in the IN-625 and chromium- boron compounds in the SS-316L, which increased the microhardness of these areas compared to the base metals and the bonding zone.

Friction stir processing (FSP) was performed on a 2024 aluminum alloy sheet with a thickness of 2.5 mm. Determination of the parameters affecting on the microstructure is very important to investigate the grain size changes in Thermo-Mechanically Affected Zone (TMAZ). In this study, were investigated the effect of tool rotation speed on the microstructure and mechanical properties of the areas around the stir zone when keeping the traverse speed constant. The average grain size in advancing side were decreased from 6 μ to 3 μ by increasing rotation speed from 315 to 500 rpm and were increased from 3μ to 7μ by increasing rotation speed from 500 to 800 rpm. The average grain size in retreating side were decreased from 7μ to 4μ by increasing rotation speed from 315 to 500 rpm and were increased from 4μ to 8μ by increasing rotation speed from 500 to 800 rpm. Also the advancing side’s grain size was smaller than that of the retreatin side. The mechanical properties of advancing and retreating sides were semillar.

In the present study, the effect of completion of isothermal solidification (IS) and NaCl concentration on potentiodynamic polarization behavior (PDP) of transient liquid phase bonded (TLP) 2205 duplex stainless steel (DSS) was investigated. The PDP results indicated that the pitting potential was decreased from 1.171VAg/AgCl in the as-received base metal to 0.373VAg/AgCl in the TLP bonded specimen before completing the IS in 0.1M NaCl test solution. By completion of the IS, the pitting potential of TLP bonded specimen increased to 1.180VAg/AgCl which was similar to that of the as-received base metal (1.171VAg/AgCl). This improve of pitting potential was strongly related to the uniform distribution of Cr and Mo across the bonding zone due to removing (Mo, Cr)-rich secondary phases from the bonding zone after completion of the IS. Before completion of the IS, the pitting potential of TLP bonded specimen decreased significantly with the increasing chloride concentration, while after it, the pitting potential was almost equal to that of the as-received base metal until 1.5M NaCl, but with increasing to 2.5M NaCl, the stable pitting attack occurred in the bonding zone and therefore, the pitting potential was decreased in the TLP bonded specimen. Furthermore, with increasing chloride concentration from 0.1 to 2.5M, the pitting corrosion was extended in the bonding zone before completing the isothermal solidification, which could be due to decreasing the pitting potential of TLP bonded specimen with increasing the NaCl concentration.

In the present study, the transient liquid phase bonding of AISI 2205 dual phase stainless steel with amorphous BNi-3 interlayer was carried out. Based on the initial experimental and analytical studies, the parameters of temperature and bonding time were determined. In order to investigate the effect of bonding temperature on the microstructural changes of the joint, bonding was performed in the temperature range of 1050-1200℃ for 20 min. The microstructural and phase analyses indicated the completion of isothermal solidification and the formation of a uniform Ni-solid solution in the bonding zone centerline. The interdiffusion between the bonding zone and the adjacent base metal resulted in the formation of boride and nitride intermetallic compounds in the base metal adjacent to the bonding zone, which the area fraction of this intermetallics significantly decreased with increasing bonding temperature from 1050℃ to 1200℃ (reduction of the intermetallic area fraction from 85% to 40%). Evaluation of shear strength of samples showed that despite the completion of isothermal solidification in all samples and shear strength of bonded samples significantly depends of amount and morphology of intermetallic compounds on the transient liquid phase bonding shear strength. By increasing the bonding temperature to 1200℃ and reducing the area fraction of intermetallic compounds up to 40% of the shear strength of the samples increased from 450 MPa of TLP bonded specimen of 1050℃ to about 85% of base metal shear strength.

In the present study, the effect of chromium carbide element on microstructure, hardness and abrasive properties of welded coating on the DIN-25CrMo4 substrate was investigated. For this purpose, three groups of roughing electrodes with different chromium content (0-13 wt%) were made and roughing operation was performed by hand electrode arc process (SMAW). Optical and scanning microstructural studies (SEM) along with XRD fuzzy analyzes showed that with increasing chromium content the microstructure of the coating is varied from a ferritic field with needle and morphology morphologies into a rich austenite field of carbide phases such as (FeCr) 7C3. The evaluation of the characteristics of roughened samples showed that the coating hardness increased by about 350% with increasing chromium content (the hardness of the chromium-plated coating and the hardness of the metal substrate were 875 ± 5HV and 200 ± 5HV respectively). Examining the wear behavior of the samples indicates a significant improvement in the wear resistance of the chromium-rich coating (an 80% reduction in the coefficient of friction and a 90% reduction in the amount of lost weight relative to the metal-tensile properties) The SEM study of washed surfaces implying a change in the wear mechanism from the two-body scrubbing wear to the cutting mechanism by increasing the volume fraction of carbide compounds in higher-chromium specimens.

In-situ synthesizing of Al/Cr was carried out to improve the strength of spot joining of Al plates. For this purpose, 0.03gr Cr powder with 10 μm particle size was inserted in the spot joining zone and the assembly was subjected to the Friction Stir Spot Welding Process (FSSW). Microstructure, formation of intermetallic compounds and mechanical properties of samples were investigated by optical microscopy (OM), scanning electron microscopy with spot and line EDS, tensile and microhardness measurements. Spot and line scan chemical analysis (Spot-EDS and Line-EDS) of joining area indicated that minimal tool rotation speed for formation of Al-Cr intermetallic compounds (Al13Cr2) is around 2500 rpm. Formation of Al-Cr rich intermetallic compounds in the joining area increased the hardness of joining zone more than two times of hardness of join without this components (140±5 HV and 60±5 HV). Furthermore, in-situ synthesis joining increase ultimate tensile strength of the joint from 40±5 Mpa to 130±10 Mpa

Aluminum and its alloys have an ever growing demand in many industries such as aerospace, automotive due to their high strength to weight ratio and corrosion resistance. In this research, in order to improve the wettability and distribution of nano-sized Al2O3particles within the matrix with low agglomeration and to achieve the good mechanical properties, injection of the milled nano- Al2O3/Al composite powder within the molten and mechanical stirring was used. Different mass fractions of nano alumina particles up to 0/3, 0/5, 0/7 and 0/9 wt% were injected into the melt under stirring. The microstructure and mechanical properties of the fabricated nanocomposites were studied. The density measurements showed that the porosity in the composites increased with increasing the mass fraction of Al2O3 Hardness, yield and ultimate tensile strengths of the composites increased with increasing Al2O3 particles up to 0/5 wt% The increase in mechanical properties can be explained by more uniform distribution of Al2O3 in the matrix, and grain refinement. The further addition of Al2O3 particles (>0/5%) particle agglomeration and porosity were the two important factors for decreasing strength and ductility.

In this study, Al/(SiCӘ) hybrid composite was produced on the surface of Al-1050 substrate via friction stir processing to achieve the high hardness of SiC particle and lubricating property of BNh simultaneously. Microstructural studies revealed that grain refinement was occurred in the stir zone (22% reduction of grain size in comparison to base metal). Closer microstructural studies by using scanning electron microscope equipped to Map-EDS analyzer illustrate the relatively uniform distribution of SiC and BNh particles in the Al-1050 matrix. Microstructural studies indicated that increasing FSP passes increased the grain sizes of TMAZ and HAZ more than 20% of base metal grain size. Microhardness evaluation showed that increasing the number of FSP passes resulted in increasing hardness of stir zone (100± 5HV in 8 pass sample in comparison with 60± 5 in 1 pass sample) that was ~70% more than hardness of base metal.

In the present study, the combination of cladding and carburization process for reconstructing of gears made of DIN - 25CrMo4 steel was evaluated. Therefore, at fist weld cladding was carried out by using E - 7018-1 basic electrode to compensate the lost thickness. Subsequently, the cladded specimens was subjected to carburization process to increase the hardness and wear resistance of the coating. Microstructural and phase studies indicated that ferrite microstructure of base metal converted to the martensite accompanied with residual austenite and Fe-C carbides such as Fe3C that increased surface hardness ~300. Wear evaluations indicated significant improvement of wearing resistance of carbonized specimens (80% reduction in friction coefficient and 90% reduction in lost weight).the microscopy SEM study of worn surfaces implying a change in the wear mechanism from the two-body scrub bing wear to the cutting mechanism by increasing the volume fraction of the martensitic phase in the carbonized specimens.

In order to improve the structural and mechanical properties of Al-1050, Al/Mg composite was processed on the surface of this alloy by using friction stir processing. Structural studies showed that one pass FSP on the as-received aluminum substrate changed the grain shape from stretched grains to equiaxed. Microstructural studies by scanning electron microscope equipped with EDS spot analysis and X-ray diffraction phase analysis revealed the formation of Al3Mg2 intermetallic compound in the 4-pass FS-processed sample. Microstructural studies revealed the significant effect of number of FSP passes and using of Mg particles on the grain size of the FSP area, i.e. grain size in this area changed from 5010 μm in the FS-processed sample with one pass and without Mg particles to 62 μm in FS-Processed sample with four passes and Mg particles. Tensile strength test showed a 70% improvement of tensile strength of the composite compared to that of the base metal.

In this study, the microstructural and tribological properties of surface Al/(SiCӘ) hybrid composite was investigated. Al/(SiCӘ) hybrid composite was produced on the surface of Al-1050 substrate via friction stir processing to achieve simultaneous high hardness of SiC particle and lubricating property of BNh particles. Microstructural studied revealed that grain refinement and significant reduction of grain size occurred in the stirred zone. Micro hardness evaluation illustrated that friction stir processing (FSP) increased hardness of stirred zone to about 60± 5HV that was 70% more than the hardness of base metal. Wearing and corrosion properties of Al/(SiCӘ) hybrid composite were investigated and compared with those of base metal, friction stir processed, Al/SiC and Al/BNh surface composite. Evaluation of wearing property indicated that the wear rate of base metal, Al/SiC surface composite, Al/BNh surface composite and Al/(SiCӘ) surface composite were 0.075, 0.047, 0.046 and 0.039mg/m, respectively which indicated the highest wearing resistance of Al/(SiCӘ) in comparison to the base metal and mono SiC or BNh surface composite. This could be related to the simultaneous increase of hardness and reduction in the friction coefficient of hybrid surface composite. . Investigations of corrosion properties showed that FSP improved the corrosion resistance of base metal more than 30%.

In this research, friction stir processing (FSP) was carried out to modify the microstructure and mechanical properties of gas metal arc (GMA) welded St37 base metal. Microstructural studies revealed that with applying FSP on the GMA-weld metalsignificant microstructural modification occurred and as-cast coarsegrains of weld metal modify to the fine grain, i.e. a reduction of weld metal grain size about 50% occur after FSP. This variation of grain sizes could be contributed to the recrystallization inFS-processed zone, i.e. high temperature accompany with significant deformation during FSP resulted in recrystallization and formation of fire grains in weld metal. Evaluation of mechanical properties indicated that applying FSP on the GMA-weld metal caused increasing ductility and uniform hardness profile of modified specimens that was in harmony with microstructural results.

In this study, mechanical milling has been applied to fabricate Ni-Al coating on the surface of a nickel-based superalloy (Inconel 617). In order to form the coating layer, Al powders accompanying the substrate (Inconel 617) and balls with different ball size and ball-to-powder weight ratio were placed and then ball milling was done for 5, 10, 15, and 20 h. During the mechanical milling process, due to the cold welding between powder particles and surface of substrate, coating layer was formed. . To form the intermetallic compositions, all samples were annealed at 550 °C for 120 min. In additions, to optimize of thickness and coating hardness the ball-to-powder weight ratio, milling duration, and ball size as effective parameters were investigated. The microstructure studies of samples was investigated by using of scanning electron microscopy (SEM).The results showed that the formation of Ni-Al intermetallic coatings on nickel-based superalloy (Inconel 617) have been formed. Also, the best coating was formed in milling duration of 15 h and ball to powder weight ratio of 10:1 and mixing ball 8, 12, and 16 mm diameter. Also, the maximum hardness of the formed coatings reached 1270 HV for sample ball milled for 15 hr.

Abstract In this research alumina sol-gel coating was applied on St44 steel by dipping, that sintered at temperatures of 300, 400 and 500?? after drying. Phase and micro structure analysis, corrosion resistance, adhesive strength and wear resistance were evaluated by XRD, SEM, electrochemical tests in 3.5% NaCl solution, pull off test and wear tester respectively. The results of DTA and XRD indicate that coating structure was amorphous at sintering temperature of 300?? and transformed to ?-Al2O3 completely at 500?? and transformed to ?-Al2O3 completely up to 1200??. Microscopic observation indicate minimum defects and maximum compaction for interface of sample sintered at 400??. The best wear and corrosion resistance obtained at 400?? and the decrease properties of sample sintered at 500?? could be due to cracks and holes caused by the phase transformation from amorphous to crystalline structure.