Advanced Materials Research Vol. 410

Abstract: This study reports the synthesis and characterization of Al-alloy/SiC_p metal matrix nanocomposite, synthesized using high energy ball milling followed by sintering employing spark plasma sintering (SPS). In the present investigation, Al 5083 alloy powder (15 μm) and 10wt.% SiC particulates (~20 nm) were milled in a high-energy planetary ball mill to produce nanocrystalline Al-alloy/SiC nanocomposite powders. X-ray diffraction analysis (XRD) was carried out for milled and un-milled powder and it was observed that, as the time of milling increased, the crystallite size of Al-alloy matrix decreased sharply. The average crystallite size of Al-matrix from XRD analysis was observed to be ~ 25 nm after 15 h of ball milling. Ball milled nanocomposite powders were consolidated and sintered employing SPS at a temperature range of 500°C with a heating rate of 300°C/min and the total sintering cycle was completed in 8 min. The mechanical properties were found to substantially increase after sintering employing SPS. Morphology of as received (un-milled) powders, milled powders and sintered nanocomposites were investigated by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). The mechanical property evaluation of the sintered nanocomposite was done by measuring nanoindentation, micro-hardness and compressive strength.

Abstract: In this work, PCC was prepared from chicken eggshell powder (ESP) by dissolving 100 g ESP in 1 M hydrochloric acid at room temperature. Under vigorous stirring, PCC was precipitated from the ESP-dissolved solution using 1 M sodium carbonate solution. The dried PESP (precipitated eggshell powder) was then characterized by particle size analyzer, X-ray diffractometer, Brunauer-Emmett-Teller surface analyzer and thermogravimetric analyzer. The particle shape of the PESP was revealed using scanning electron microscope. It was found that PESP was a binary mixer of calcite and vaterite. The particles were in cubic and spherical shape. In addition, PESP had a volume average diameter of 8.16 μm, D[V, 0.5] of 7.22 μm, D[V,0.9] of 16.57 μm, and the specific surface area of 4.38 m²/g. The average particle size was lower than and the specific surface area was higher than that of ESP. The decomposition process of PESP occured in a single step between 610 and 770 °C, with 44.43% weight loss.

Abstract: Anisotropic plastic behavior of advanced high strength steel sheet of grade TRIP780 (Transformation Induced Plasticity) was investigated using three different yield functions, namely, the von Mises’s isotropic, Hill’s anisotropic (Hill’48), and Barlat’s anisotropic (Yld2000-2d) criterion. Uniaxial tensile and balanced biaxial test were conducted for the examined steel in order to characterize flow behavior and plastic anisotropy for different stress states. Especially, disk compression test was performed for obtaining balanced r-value. All these data were used to determine the anisotropic coefficients. As a result, yield stresses and r-values for different directions were calculated according to these yield criteria. The results were compared with experimental data. To verify the modelling accuracy, tensile tests of various notched samples were carried out and stress-strain distributions in the critical area were characterized. By this manner, the effect of stress triaxiality due to different notched shapes on the strain localization calculated by the investigated yield criteria could be studied.

Abstract: In this experimental study attempt has been made to realize potential of cryogenic treatment in enhancing surface quality with fine aluminum and graphite additives powders in AEDM of nickel based super alloy Inconel 718. L₃₆ (2³x3⁶) Orthogonal Array has been selected to conduct and analyze experiments based on Taguchi methodology. Polarity, peak current, pulse on time, duty cycle, gap voltage, retract distance, concentration of fine aluminum and graphite powder added into the dielectric fluid are chosen as input process variables to study performance in terms of surface roughness (SR) using copper and deep cryogenically treated copper electrode. It is found experimentally that deep cryogenically treated copper electrode with addition of 6g/l graphite powder improves surface roughness appreciably. The same has been supported by SEM analysis of the machined surface.

Abstract: In the present research the aging behavior of Al6061 alloy and Al6061/SiCp composite fabricated by powder metallurgy method was investigated. The solution treatment of the samples were carried out at 527°C for 2, 3and 4 h followed by aging at 180°C for different aging times between 1 and 10 h. The existence of SiC particles led to increasing the peak hardness of the composite. The peak hardness of the composite took place at shorter times than that of the 6061 alloy for the samples solution treated for 3and 4 h, but took place at longer times for the samples solution treated for 2 h. The optimum solution treating time was about 3 h for both the composite and the 6061 alloy that led to the fastest aging kinetics and the maximum hardness. At the solution treating time shorter than 3h due to incomplete dissolution of precipitates, the aging kinetics decelerated and the hardness values decreased. For the composites solution treated more than 3 h, hardness values decreased due to the grain growth of matrix while changing in the aging kinetics was not significant. EDS and SEM studies indicated the presence of bight enrichment zones including Mg and Si elements in the composite in solution treatment conditions.

Abstract: In recent years, researchers have reported powder metallurgy processed electrodes as alternative tooling for electrical discharge machining (EDM). The present experimental study evaluates the quality of machined surface during electrical discharge machining (EDM) of Inconel 718 alloy steel with powder metallurgy (PM) processed electrodes. The investigated process parameters were polarity, electrode type, peek current, pulse on time, duty cycle, gap voltage, retract distance and flushing pressure. The surface quality was measured in terms of surface roughness (Ra). An orthogonal array L₃₆ (2¹X 3⁷) based on Taguchi methodology was applied to plan and design experiments. Experimental data was statistically analyzed using analysis of variance (ANOVA) and optimum condition was achieved for evaluation criteria. It was concluded that polarity, electrode type, peek current, have significant effect on surface quality and minimum Ra is obtained with CuW2080 electrode at minimum current and negative polarity. Deposition of tungsten with CuW2080 (80%W 20%Cu) electrode was confirmed by energy dispersion spectrum (EDS) of the machined surface.

Abstract: Drilling of MMCs is considerably difficult due to the presence of extremely hard reinforcement which causes rapid tool wear and influences the cutting forces and quality characteristics. The present investigation aims at studying the effect of drilling parameters (cutting speed, feed rate and the drill point geometry) on the output responses such as, thrust force (TF), specific cutting pressure (SCP) and surface roughness (SR). Taguchi’s technique has been applied to obtain an optimal setting for drilling process parameters for optimizing the output quality characteristics.

Abstract: In this study, Al-20Si-5Fe-3Cu-1Mg-XMn (X=0,1.5,3) alloys were synthesized by the gas atomizing technique. The microstructure and mechanical properties of the powders were investigated using optical microscopy, scanning electron microscopy, X-ray diffractometery method, and microhardness test. Microstructure of the powders composed of α-Al, Si and iron intermetallic compounds. As the powder particle size decreases, the phases become finer. A significant refinement in the size of iron-containing compounds was observed by addition of Mn. The microstructural refinement by controlling the particle size leads to an increase in the hardness of the powder particles in the amount of 33-45% dependent on the composition. Keywords: Al-20Si-5Fe-3Cu-1Mg alloy, Gas atomizing, microstructure, mechanical properties

Abstract: SMAT is applied as an innovation surface enhancement technology to introduce compressive stress in metallic materials. The strengthening effects of SMAT in mechanical properties were investigated on aluminium alloy. The yield strength obtained under tensile test had significant improvement which may achieve up to 440 MPa. In this paper, the experimental setup and results will be briefly described. Tensile properties measured before and after SMAT at ambient temperature. Results show that the highest strength that can be attained is 544 MPa by SMATed sheet of 1 mm thickness for 15 minutes and 518 MPa for the 2.5 mm one SMATed with 45 minutes, with the desirable ductility. The present study demonstrates this high strength and corrosion resistance aluminium alloy can be a potential candidate for applications in aviation industries.

Abstract: Hot forging is a common, but important manufacturing process in metal forming industries. Forming at high temperature, flow stress of material decreases and thus lower load is required. Furthermore, mechanical properties of material regarding its microstructure characteristics can be improved according to heating and cooling conditions. Hot forging process for a spacer wheel made of steel AISI 4340 was investigated by means of FE simulation. Initially, hot compression test was performed using a thermo-mechanical simulator for determining flow curves. Different temperatures and strain rates within the process range were considered. A Zener-Hollomon parameter was applied to describe the experimentally obtained flow curves. To verify accuracy of the FE simulations, multi-step hot compression test was carried out at different forming temperatures. Subsequently, force development and final shape calculated for the investigated part were analyzed. Reliability of the FE results was significantly influenced by the defined flow curve or hot deformation behavior of material.