Key Engineering Materials Vol. 835

Abstract: New series of spinel LiNi_0.25Fe_0.2Mˊ_0.05Mn_1.5O₄ (Mˊ = Cu, Mg or Zn) cathode materials have been purposefully tailored using sol-gel auto-combustion method at low annealing temperature ~ 700°C for 3 h. The XRD analysis showed that all substituted (LNFMO-Mˊ) samples are comported with the main structure of undoped (LNFMO) with crystalline disordered spinel Fd-3m structure. TEM images revealed the octahedron-shape like morphology for the particles and the LNFMO-Zn sample has the widest particle size distribution. EIS spectra evidenced that a typical one semicircle (LNFMO-Mg) was revealed for each cell, suggesting the absence of ionic conductivity contribution. The values of charge transfer resistance (R_ct) were equal to 9.3, 6.7, 6.0 and 4.4 kΩ for LNFMO, LNFMO-Cu, LNFMO-Mg indicating that the Zn-doped sample has the fastest kinetic diffusion rate and lowest activation energy of conduction.

Abstract: An attempt has been made to investigate the microstructures and wear behavior of magnesium alloy AM100 (Mg-Al-Mn) based composites reinforced with 7 vol. % of ZrB₂, graphite or hybrid of (1:1) ZrB₂ and graphite particles as well as the unreinforced magnesium alloy. Magnesium alloy was melt under shield of inert gases and composites were prepared using stir casting method. Optical microscopy was used to study the microstructures of the unreinforced alloy and composites. The composites characterized primarily by the uniform distribution of particles in the matrix and a good adherence between the particles and matrix. XRD analysis was used to identify the phases of the unreinforced alloy and composites. The XRD diffraction pattern of AM100 matrix reveals different phases, namely, Mg, AlMn and Al₁₂Mg_17. Formation of these phases is due to the reaction between alloy constituents. Dry sliding wear tests were conducted by using a pin-on-ring apparatus. The wear rates of the composites and matrix alloy were measured at loads of 10, 20 and 30 N, and sliding speed of 0.7 m/s. The worn surfaces of the composite pins were examined by scanning electron microscopy (SEM). The experimental results of the wear tests showed that the magnesium based composites exhibited higher wear rate at all the applied loads when compared to those of the unreinforced magnesium alloy. The ZrB₂ reinforced magnesium composite exhibited the lowest wear rate amongst the composites material investigated in the present work.

Abstract: This study aimed at optimizing impact toughness and high wear resistant carbidic austempered ductile iron (CADI) by controlling the morphology, size and quantity of carbides. The effects of dynamic solidification, niobium addition, combined action of them and heat treatment have been investigated. Investigations were performed by means of the image analyzer, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and X-ray diffraction. Impact toughness, hardness and abrasion wear resistance tests were conducted. Fracture surfaces were studied. Results indicated that microstructural control during solidification is the most valuable tool to attain the optimum combination between impact toughness and wear resistance in CADI. Combined action of Nb addition and dynamic solidification improves impact toughness, hardness and wear resistance even more than the action of each individual factor. In the as-cast condition, impact toughness, hardness and abrasion resistance were improved after dynamic solidification compared to statically solidify one by 31.2%, 18.75% and 87.96% respectively. This enhancement was increased to 36.9%, 25.93% and 128. % by adding 1% Nb. Lower tempering temperature of 275°C exhibit best hardness and abrasion resistance better than higher tempering temperature of 375°C.

Abstract: The present study was undertaken to investigate the effect of different metallurgical parameters such as casting techniques, wall thickness, inoculant technique, carbon equivalent, nodule count, ferrite and pearlite percent on the mechanical properties of thin wall ductile iron castings (TWDI). Understanding of the effect of chemistry, casting techniques, melting and molten treatment on the mechanical properties and microstructural features of TWDI castings would help in selecting conditions required to achieve optimum mechanical properties and alloy high strength to weight ratio. The use of the design of experiment (DOE) and the analysis of variance (ANOVA) can be a useful methodology to reach this objective. The analysis of the effects of each variable and their interaction on the mechanical properties of TWDI castings using green sand, green sand with insulation and investment casting techniques plays a key role in improved materials performance.The results indicate that nodule count, pearlite content and the interaction between carbon equivalent, nodule count and pearlite content have a significant effect on the tensile strength of TWDI castings. The impact toughness values decrease with smaller section thickness and increased nodule count. Using investment casting technique, decreasing the pearlite percent and nodule count, and increasing the wall thickness and ferrite percent reduce the values of ultimate tensile strength and yield strength. The results of percent elongation and impact toughness show a reverse trend compared with those of ultimate tensile strength and yield strength in terms with different metallurgical parameters.

Abstract: This manuscript investigates the Fabrication and Microstructure of Automotive Brake Rotor Made of AlSi-SiC Composites. This work is oriented toward fabrication of automotive brake rotors from Al-9Si and Al-12Si reinforced with 10 and 20% SiC particles using stir-casting method. The brake rotors were subjected to heat treatment. Aging behavior showed that hardness increased with the addition of SiC reinforcements by 104%, comparing to solution treatment condition. Also, the addition of SiC particles accelerates formation of precipitates. Microstructure of brake rotors made of composite revealed uniform distribution of SiC particles, primary phase (⍺-Al) and modified eutectic Si. EDX analysis showed the presence of Al, Mg and O at the interface between matrix and SiC particles.

Abstract: Cyclic extrusion compression (CEC) is one of the well-known techniques in metal forming processes under the severe plastic deformation process (SPD) in which an ultra-large plastic strain is imposed on a bulk material in order to make ultra-fine grained (UFG) metals, alloys and composites. In this work, the mechanical properties of the aluminum alloy (6061) before and after CEC process were examined. A special CEC die was design and fabricated for the present work which achieved an effective plastic strain of about 0.62 after each separate cycle of CEC. The microstructure was effectively refined with increasing the number of CEC cycles as the grain size was reduced from ≈250μm to ≈30 μm after 6 cycles of CEC. The mechanical properties were tremendously increased in comparison with those of as cast and annealed condition. The micro-hardness increased from 25 Hv to 56 Hv, while the yield and the ultimate tensile strengths increased from 60 MPa to 198 MPa and 85 MPa to 204 MPa respectively, the ductility increased from 2.97% to 4.6% with the number of CEC cycles increasing up to six cycles.

Abstract: The deposition of composites with tailored optical properties is investigated. This would employ structures consisting of combined metallic and oxides nature. A thin layer of TiNi is obtained by using RF magnetron sputtering on a stainless-steel substrate, followed by oxidation at 400°C and 800°C for four and one hours, respectively. The optical properties of the thin films were characterized by optical spectrophotometer, and Fourier Transform Infrared Spectroscopy (FTIR). The morphology, topography, and structure were studied by scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD). The results show that TiO₂ has been produced through the oxidation process of the sputter-deposited TiNi thin film at high oxidation temperature. The TiNi thin films showed a significant improvement in optical properties after oxidation, as the absorbance increased, and the emittance was reduced. This work introduces oxidized TiNi thin films as candidates for solar selective absorber.

Abstract: Polyaniline (PANI) has been considered for thermoelectric (T.E) applications due to its facile preparation methods, easy doping-dedoping processes and its environmental stability. Like other conducting polymers (CPs), it has low thermal conductivity (usually below 1 Wm^-1K^-1) which is favorable for T.E applications, however studies have shown that it still suffers from low power factors as a result of low electrical conductivity. For this reason, PANI has been compounded with other materials such as polymers, inorganic nanoparticles and carbon nanoparticles to enhance its electrical conductivity, power factors (PF) and ultimately zT value.This work is focused on the synthesis and characterization of n-type polyaniline nanocomposites doped with reduced graphene oxide (rGO). The rGO was prepared through oxidation of graphite and subsequent reduction and incorporated into polyaniline through in situ polymerization and the resulting nanocomposites were characterized. Addition of rGO resulted in enhancement of the electrical conductivity of polyaniline from 10^-3 S/cm to 10^-1 S/cm which is two orders of magnitude higher. This contributed to the enhanced PF, an indication that thermoelectric behavior of conducting polymers can be boosted through compounding with inorganic materials.

Abstract: The demand for tantalum and niobium has increased steadily due to their importance in the production of modern industrial materials and high tech consumer products such as super alloys and cell phones. This work aims at recovery of tantalum and niobium from Abu Dabbab deposits at the Eastern Desert of Egypt. The beneficiation was successfully performed using shaking table concentrator and carpco magnetic separator. The enrichment ratio reached up to 160-times for both Ta₂O₅ and Nb₂O₅. Aliquat 336 ionic liquid was used for separating Ta₂O₅ with purity of 90%. Amberlite anion exchanger was used for separating Nb₂O₅ with purity of 87%.

Abstract: The characteristics of Ni-Cr porous alloys containing 0.5 wt%Cr up to 12 wt%Cr were determined. The alloys were prepared from a mix of Ni-particles with filamentary shape and Cr-particles with irregular shape which then mixed with 0.5 wt% paraffin wax as a binder. The samples were formed by compaction and then sintered at 1200 °C for 1 h. The microstructure of samples was found to consist of a Ni-Cr solid solution matrix with X-ray energy dispersive analysis of Cr% less than 0.33 wt%. The matrix microstructure which composed of equiaxed grains (20-60 μm) surrounded high Cr content islands which also contained γ phase (Ni_2.88 Cr_1.22). The apparent density of the alloys was found to decrease with Cr content from 8.32 g/cm³ for samples containing 0.5 wt%Cr to 7.26 g/cm³ for samples containing 12 wt%Cr. Therefore, the estimated porosity was found to increase from 6.4% to 16.6% with increasing Cr content from 0.5 wt% to 12 wt%. The microhardness of the samples varied from 153.6 to 284.2 VHN for the equiaxed grains and from 119.6 to 240.6 VHN for the island areas.