Advanced Materials Research Vol. 829

Abstract: Al-Cu joints have been widely used in electronic and heat exchanger industries due to their excellent electrical and thermal conductivity. Meanwhile, the use of Al in the Al-Cu joints can result in lower weight and cost of the final structure. The purpose of the current study is to join Al to Cu by furnace brazing using ultrafine Al-Si powder. To study the microstructure of the join area, the brazing tests were conducted in the range of 590 to 610°C for 5 to 15 minutes under inert atmosphere. The microstructure of Al/Cu joints was studied by scanning electron microscopy (SEM). The elemental analysis was conducted using an energy dispersive spectrometry (EDS) system. Experimental results show that two kinds of intermetallic compounds (IMCs) mainly Cu₃Al₂ and CuAl₂ phases are formed near the interface of copper and in the braze layer region. The bulky prismatic structure which is formed on the side of Al substrate was found to be α-Al+CuAl₂ eutectic.

Abstract: In this study, Al-6Zn-2.5Mg-1.5Cu alloy powders were synthesized by mechanical alloying of the elemental powders of Al, Zn, Mg and Cu at different milling times. The 60 h milled powders were isothermally annealed at 380 °C for 30 min under argon atmosphere. The microstructure and mechanical properties of the as-milled and annealed powders were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness test. The crystallite size and lattice strain of Al were estimated from the broadening of XRD peaks using WilliamsonHall method. The results showed that the crystallite size of Al decreases with increasing milling time and after milling up to 60 h, the crystallite size reduced to 76 nm. Due to formation of intermetallic phases such as MgZn₂ during annealing, an increase in the hardness of the alloy powders was achieved.

Abstract: It is the objective of this study to investigate the effect of ECAP processing and heat treatment on the mechanical properties of the UFG 7075 alloy. Also the effect of post ECAP heat treatment is investigated. The alloy is processed by ECAP after annealing as well as solution treatment to produce an UFG structure. Furthermore mechanical properties and their variations during annealing and aging are investigated. The hardness of the pre-ECAP annealed and the pre-ECAP solutionised 7075 aluminum alloy has increased significantly compared with that of the CG sample. Also hardness of ECAPed specimen has not experienced significant changes in post-ECAP heat treatment and indicated that the alloy had approximately good thermal stability.

Abstract: Because of corrosion resistance and antibacterial effects, shape memory Ni-Ti-Ag alloy can be considered for different biomedical applications. Mechanical alloying is used to produce nanostructured Ni-Ti-Ag alloy from elemental powders. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) are used to characterize the product. Results show that after 1h milling, homogenous distribution of the elements occurs; while no intermetallic compounds is observed. After 3h milling, titanium dissolves in nickel to form amorphous and nanostructured solid phases. Peaks of B2 phase appear in the XRD pattern after the 3h milling of the powder mixture. Sintering of the 3h-milled mixture at 1223 K leads to the formation of NiTi intermetallic compound; while titanium disappears, the content of the element nickel reduces and grain growth takes place.

Abstract: FeCuCo alloys are the new generation of metal matrix for diamonds in PM processed cutting tools. These alloys were created with the purpose of reducing the cobalt content in diamond tools. Nevertheless, little have been published, once this is a matter of industrial interest. In this work, samples of Fe (10-20) wt. %Cu and Fe (10-20) wt. %Cu 1%wt SiCp alloys were processed by cold pressing at 350 MPa, followed by sintering at 1150 C/30 min. under argon atmosphere. After sintering, a study of structural and microstructural analyses was conducted. Brinell hardness and wear tests were carried out in the metal matrix, as well as the wear resistance of the metal matrix composites. The composition Fe-20%wt Cu-1%wt SiCp was the best among the studied ones, because it presented the best results of hardness and wear resistance.

Abstract: Recently some nanocrystalline soft magnetic materials containing nanosized α-Fe grains have been obtained by crystallization of amorphous melt-spun ribbons. These structures are nanocomposites in which nanosized grains are distributed within an amorphous matrix. The soft magnetic ribbons composed of Fe₈₀B₁₀Si₈Nb₁Cu₁ alloy were prepared by melt spinning method with different quenching rates (wheel speed of 10, 20 and 40 m/s). The XRD results exhibit an increase in the copper wheel speed (quenching rate) causes the fraction of crystallinity and grain size to decrease. The grain size varies in the range of 20 to 200 nm that is in good agreement with TEM results. The VSM results show that these nanostructured samples exhibit coercivity in the range of 10 to 30 A/m and magnetic saturation in the range of 1.5 to 1.7 T.

Abstract: Hydrogenation is one of the most important transformation reactions widely used in a large variety of areas such as Chemical, pharmaceutical and agricultural industries. Granulated carbon supported palladium catalysts have been used here for hydrogenation of carbon-carbon triple bonds. Catalyst composites and granules were produced by using sodium alginate binder under the certain thermal treatment process. After that, metal salt precursors were deposited using impregnation method. The final catalysts obtained through reduction of metal oxides by hydrazine as reducing agent. After that, metal particles loaded catalysts were utilized to perform hydrogenation reaction. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques applied for investigation of catalysts. Reaction products were evaluated by High Performance Liquid Chromatography (HPLC) technique. It has been concluded that MWCNT as support exhibits high conversion in the hydrogenation of 2-butyne-1, 4-diol as a typical triple bond carbon-carbon precursor.

Abstract: The present paper describes the effect of severe plastic deformation on the microstructure and mechanical properties of AISI type 304 stainless steel by equal channel angular pressing (ECAP) at room temperature. The strain-induced martensitic transformation occurred in the specimens, and martensite phase increased with increasing strain up to 42% for three passes of ECAP. X ray diffraction was used to identify the strain-induced martensite phase and its volume fraction. The martensite phase, mechanical twins and micro hardness have increased with increasing passes of ECAP. Microstructures of specimens show that with increasing strain, subgrains less than microns are susceptible to be created by fragmentation of twins.

Abstract: The present study describes synthesis of highly active copper nanoparticles by a green and economically viable approach. The highly stable colloidal dispersions of copper nanoparticles ( Cu NPs) were prepared via modified sodium borohydride reduction route with controlled morphology in a aqueous phase using anionic surfactant, Sodium dodecyl sulfate (SDS), as directing agent and vitamin-C as a Quenching agent. The characterization studies like optimization of various parameters for preparation of nanoscale copper NPs, surface binding interactions, size and morphology of the fabricated Cu NPs were carried out using UV-Visible Spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy, X-Ray Diffraction (XRD) Analysis and Tunneling Electron Microscopy (TEM). The results of study revealed that CuNPs has ultra fast catalytic activity for the degradation of some frequently used organic dyes such as methylene blue (MB) and rose bengal (RB).

Abstract: The Quenching and Partitioning (Q&P) process is known as a promising method for producing steels with superior mechanical properties. Developing Q&P steels with optimized mechanical properties requires well understanding of the relation between their microstructural and mechanical properties. The microstructural evolution during different Q&P processes in a 0.3C-1.5Si-3.5Mn (wt.%) steel was analysed. Mechanical properties of the developed microstructures were measured by using microtensile test. The influence of volume fractions and carbon contents of the phases on the ductility and strength of the microstructures was investigated. Furthermore, the effect of the specimen size on the tensile properties was discussed and a correction procedure was applied to convert the measured microtensile properties to the standard ones. A comparison with the measured mechanical properties of other type of Advanced High Strength Steels (AHSS) shows the improved properties of the Q&P steels.