Advanced Materials Research Vols. 1025-1026

Abstract: This research has an aim to modify and improve the microstructures and hardness property of cast nickel-based superalloy, IN-738 by modified chemical composition of various Al additions as well as different reheat treatment conditions. IN-738 was modified by adding aluminium in 1, 2 and 3% by weight and casting with vacuum arc melting process. Then all casted alloys were performed with 5 different solutioning temperatures of 1125°C, 1145°C, 1165°C, 1185°C and 1205°C for 6 hours and all following with the same precipitation aging temperature of 845°C for 24 hours. The various obtained microstructures of the casting and reheat treatments were observed and investigated by SEM to evaluate the average area fraction and size of γ’ precipitated particles. The mechanical property was evaluated by Vickers hardness. From the obtained results, it was found that fine microstructure, which would be the most appropriate for using at elevated temperature, was obtained by the Al addition with 1%wt. following with solutioning temperature range between 1125°C – 1145°C/6 hours and precipitation aging at 845°C/24 hours. The microstructures received consist of high area fraction of γ’ particles in cubic shape with the proper size. However, the maximum hardness value of 683 HV was obtained from the alloy with 3%wt. Al addition following with solutioning temperature of 1205°C.

Abstract: The experimental study deals with the effect of modification of the surface layer by irradiation cross-linking on the micromechanical properties of the low-density polyethylene (LDPE) tested using the instrumented nanohardness test. The surface layer of LDPE specimen made by injection technology was modified by irradiation cross-linking using beta irradiation, which significantly influences micromechanical properties of the surface layer. Compared to the heat and chemical-heat treatment of metal materials (e.g. hardening, nitridation, case hardening), cross-linking in polymers affects the surfaces in micro layers. These micromechanical changes of the surface layer are observed in the instrumented microhardness test. Our research confirms the comparable properties of surface layer of irradiated LDPE with highly efficient polymers. The subject of this research is the influence of irradiation dosage on the changes of micromechanical properties of surface layer of LDPE.

Abstract: Micromechanical changes in the surface layer of High-density polyethylene HDPE modified by beta radiation were measured by instrumented test of nanohardness. The specimens were prepared by injection technology and subjected to radiation doses of 0, 132, 165, 198 kGy. Measurements of nanohardness showed considerable changes of behavior of surface layer in middle as well as high radiation doses with higher values of indentation hardness and stiffness.

Abstract: The presented article deals with the research of micro-mechanical properties in the surface layer of modified Polyamide 66 filled by 30% of glass fibers. These micro-mechanical properties were measured by the Depth Sensing Indentation - DSI method on samples which were non-irradiated and irradiated by different doses of the β - radiation. Radiation doses used were 0, 15, 30 and 45 kGy for filled Polyamide 66 with the 6% cross-linking agent (triallyl isocyanurate). Individual radiation doses caused structural and micro-mechanical changes which have a significant effect on the final properties of the polyamide 66 tested. The highest values of micro-mechanical properties were reached at radiation dose of 30 kGy, when the micro-hardness values increased by about 64%. The aim of the article is to find out the influence of the radiation on the micro-hardness of the modified glass fiber-filled Polyamide 66 (PA66).

Abstract: Nickel phosphide Ni₂P catalysts supported on TiO₂-Al₂O₃ support were prepared by co-impregnation. The catalysts were characterized by XRD, BET, and XPS. The effects of calcination temperature on catalyst structure and HDS activity were studied. The results indicated that the catalyst prepared with calcination temperature of 773 K exhibited the best performance. At a reaction temperature of 606 K, a pressure of 3.0 MPa, a hydrogen/oil ratio of 500 (V/V), and a weight hourly space velocity (WHSV) of 2.0 h^-1, the conversion of DBT HDS was 96.0%.

Abstract: One of the disadvantages of β-Ti alloys is rapidgrain coarsening at elevated temperatures due to accelerated diffusion in the βphase region. Microstructural stability of β-Ti alloys would depend on theirability to maintain refined grains or microstructures at high temperatures. Thebeta grain growth kinetics of a newly designed beta titanium alloy has beensystematically investigated in this research. The grain growth exponent (n) value is at the range of 0.1-0.2,about 0.1 at low temperatures and about 0.2 at high temperatures over 950°C. Itis lower than other beta titanium alloys. The reason of lower n values can be investigated in the viewof the solute and the diffusivity in the titanium matrix.

Abstract: Orthorhombic HoMnO₃ films were prepared epitaxially on Nb-doped SrTiO₃ single crystal substrates by using pulsed laser deposition technique. The films showed perfectly a-axis crystallographic orientations. X-ray diffraction and atomic force microscopy were used to characterize the films. The complex dielectric properties were measured as functions of frequency (40 Hz~1 MHz) and temperature (80 K~300 K) with a signal amplitude of 50 mv. The respective dielectric relaxation peaks shifted to higher frequency as the measuring temperature increased, with the same development of real part of the complex permittivity. The cole-cole diagram was obtained according to the Debye model, and the effects of relaxation process were discussed.

Abstract: The bamboo waste can be an alternative material to sustain the crescent demand for particleboards, also bringing ecological benefits as reduction of the pressure for raw materials and landfill space demands. In this context, this research aimed to manufacture and determine some physical and mechanical properties of particleboards with bamboo waste particles (Dendrocalamus giganteus), obtained from different sources, bonded with four different percentages of urea–formaldehyde (UF) based resin (6%, 8%, 10% and 12% related to dry material of particles). Response variables investigated were: density; moisture content; thickness swelling in 2 and 24 hours; water absorption in 2 and 24 hours; internal adhesion (STpe); strength in tension parallel to faces (STpa); modulus of elasticity (MOE) and modulus of rupture (MOR). Results permitted to conclude that particleboards as mentioned showed good performance only in the physical properties requirements imposed by Brazilian Standard NBR 14810, but this was not observed to mechanical properties considered. New researches are needed in order to optimize the producing process parameters.

Abstract: The problem of proper disposal of solid waste generated in different industrial processes is one of worldwide environmental concerns nowadays. Thus, this study aimed to establish a new alternative for the disposal of two agro-industrial residues employing them to produce particleboard for different purposes in building construction. The focus was given to the reuse of the sugarcane bagasse (SB) originated during the processing of Saccharum officinarum for sugar and ethanol production, and bamboo stem leaves of Dendrocalamus giganteus(BB). For this, six particleboards were produced in the following compositions: with 100% SB, 75% SB + 25% BB, 50% SB+50% BB, 40% SB +60 BB, 25% SB+ 75% BB and 100% BB in the total mass of the composites. The particleboards physical characterization followed Brazilian Standard ABNT NBR 14810-3 to density, moisture content and water absorption. Results showed these raw materials are compatible to particleboard production.

Abstract: Pr substituted barium hexaferrite, Ba_1-xPr_xFe₁₂O₁₉ with x = 0.00-0.20 were synthesized by Oxide One Pot Synthesis (OOPS) process. The phase composition of Ba_1-xPr_xFe₁₂O₁₉ were characterized by X-ray diffraction analysis (XRD). The phase morphology of the barium hexaferrite powder was studied by scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectroscopy confirmed that the Pr completely substituted into barium ferrite. The magnetic properties was investigated by vibrating sample magnetometry (VSM). It was found that saturation magnetisation and coercive field can be improved by the substitution of Ba with Pr in BaFe₁₂O₁₉ powder. The saturation magnetisation increased at first to the maximum of 50 emu g^-1 (x = 0.15) and then decreased to the 34 emu g^-1 (x = 0.20), while the coercive field increased remarkably with increasing Pr ions content.