Advanced Materials Research Vol. 974

Abstract: Advanced industrial applications require materials with special surface properties such as high hardness and high wear resistance. In this study, copper substrate samples where coated by Fe-Si by using thermal evaporation technique under high vacuum, then subjected to surface laser treatment by using 720 watt CO₂ laser beam. The purpose was to perform local alloying in the form of surface network of four tracks (each two are parallel and perpendicular to the other two) to produce a good thermal and electrical properties bulk material with reasonable surface hardness properties. The morphological features of the subsurface laser treated layers and their mechanical properties (microhardness) have been studied on oblique sections through the laser fused tracks. The results show that there were an intensive re-evaporation of the coating material, probably because of the high laser power density applied and the use of deep vacuum during the laser surface alloying process. Generally hardness recorded to be increased in the laser-fused tracks locations, but the bottom of the laser fused tracks showed a number of spherical voids causing a drastic decrease in the hardness values. The middle parts of the tracks showed columnar structure and elevated hardness values.

Abstract: In the present study, high-power CO₂ laser cutting of steel plates has been investigated and the effect of the input laser cutting parameters on the cut surface quality is analyzed. The average roughness of the cut surface of the specimens, produced by different laser beam diameter and laser power, were measured by using roughness tester. The scanning electron microscopy SEM is used to record possible metallurgical alterations on the cut edge. The aim of this work is to investigate the effect of laser beam diameter and laser power on the cut surface roughness and on the heat affected zone width HAZ of steel plates obtained by CO2 laser cutting. An overall optimization was applied to find out the optimal cutting setting that would improve the cut surface quality. It was found that laser beam diameter has a negligible effect on surface roughness but laser power had major effect on roughness. The cut surface roughness decreases as laser power increases. Improved surface roughness can be obtained at higher laser power. Also, laser beam diameter and laser power had major effect on HAZ width. It increases as laser power increases.

Abstract: Metal foams are widely produced by using different techniques such as compaction and replication method. In this study, slurry method also known as replication method has been used to produce SS316L foams. SS316L powders (50wt% and 60wt%) were mixed with the binders and distilled water by using mechanical stirrer. Polyethylene Glycol (PEG) and Carboxyl Methyl Cellulose (CMC) were used as binders. Polyurethane (PU) foam was used as scaffold and dipped into SS316L slurry then dried in room temperature for 24 hours. Sintering process has been done in two different temperatures which were 1200°C and 1300°C in vacuum furnace. The morphological study was performed using Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray (EDX). The SEM micrograph showed that the cells were interconnected and the structures become denser as the sintering temperature increase. The average pores size is ranging from 252.8 μm-353.8 μm, while strut size ranging from 50.2 μm-79.9 μm based on SEM micrograph analysis. The elemental analysis from EDX showed the element presence in the SS316L foam remain from SS316L powder which are Chromium (Cr), Nickel (Ni), Molybdenum (Mo), Cooper (Cu), Nitrogen (N₂), Sulphur (S) and Silicon (Si). Higher sintering temperature contributes better grain growth between particles where the point-contact between the particles expanded and disappear the small pores.

Abstract: The escalating issues on sustainable environment such as the necessity to reduce CO2 emission and fuel consumption including new regulations to improve the safety of passengers car had brought up the application of new innovative materials and manufacturing process in the automotive industry called hot press forming operation. By using this new technique, the manufacturers can produce more lightweight and high strength car parts such as the B-pillars with tensile strength ranging from 1200MPa to 1600MPa. Hot press forming is done by rapidly heating up Ultra High Strength Steels (UHSS) made of boron steel material in a furnace to austenization temperature of about 950°C for 5 minutes, then transferred it quickly to the hot press die where rapid quenching occurred during the die closed with the aid of cooling channel. This experiment investigates the effects of varying combination of hot press forming parameters to final tensile strength of boron steel and had been carried out without use of cooling channel. The studied parameters are the air cooling time, cooling rate, cooling time in die and stamping pressure. The type of boron steel material with trade name of Usibor® 1500 was used as the test specimens while for punch and die material, High Thermal Conductivity Tool Steel (HTCS-150) made by Rovalma was used. Both are common materials used in the automotive industry for hot press forming operation. A preliminary experiment had been conducted where ten flat tensile strength specimens of Usibor 1500 were heated to the austenization temperature of 950°C and immediately quenched in a tank of water to confirm the material ability to achieve the minimum tensile strength of 1500MPa. All specimens achieved average tensile strength of 1550MPa in this most ideal cooling rate condition. In the experimental hot press forming operation, result shows that the flat blank specimens of Usibor 1500 able to obtain ultimate tensile strength of 1400MPa after quenching in die without use of cooling channels when suitable process parameters were used during. Overall ,faster air cooling time, higher stamping pressure applied to the blank, and longer cooling time in die improve the cooling rate. Highest tensile strength of 1400MPa was achieved in the experiment when cooling rate was 95°C/s, air cooling time of 3.83s, stamping pressure of 50bar and cooling time in die of 30s.

Abstract: Thermal spray coatings have become one of the most potential for hard chrome replacement, particularly for wear and corrosion applications. In this study four types of hard coating materials were selected and thermally sprayed by suitable processes as the following designated codes (material/spray technique): Cr-Fe/HVOF, Cr-Ni/HVOF, WC-Ni/SF and Cr-Fe/AS. All of starting materials were characterized in order to create a correlation between spray materials and coating characteristics. SEM was employed for morphology and microstructure investigation. Particle size analysis was investigated by SEM and laser particle size analyzer. Coating characterization included surface roughness measurment by profilometer, porosity evaluation by image analysis and hardness test by Vicker microhardness tester. Microstructure of coatings was also revealed by SEM. Wear performance was evaluated by pin on disc test and dry sand rubber wheel abrasion test. Corrosion resistance was tested by potentiodynamic method. The results showed that particle size and morphology of starting powders were various depending on manufacturing method. Chemical compositions of starting materials showed great effect on coating properties and performance. Coatings deposited by HVOF and spray & fuse (SF) method showed typically dense and homogeneous structure than arc sprayed coating. WC-Ni/SF coating showed lowest abrasive wear rate compared to other thermally sprayed coatings. All Ni base coatings had significantly lower corrosion rates while Cr-Ni/HVOF coating had lowest corrosion rate. Although Cr-Ni/HVOF and WC-Ni/SF could be applicable for both wear and corrosion applications, for heat sensitive parts, Cr-Ni/HVOF coating could be a better alternative to spray and fuse.

Abstract: This paper presents the results of an experimental investigation into the Ultimate Elastic Wall Stress (UEWS) of ±55° filament wound composite pipes. The UEWS test appears to provide an attractive alternative to the current method, and has proved to be one of the most effective in term of accuracy and speed. Moreover, it has been found to be sensitive to changes in key manufacturing and raw material parameters. The pipes were subjected to biaxial loading, which was achieved by combinations of hoop and axial stress. Loads were applied as groups of cycles which, were gradually increased until the UEWS had been determined. Various ratios of hoop to axial stress were applied to the pipes, ranging from pure axial to pure hoop loading at room temperature and at 65°C. These ratios were investigated by applying different pressures in both the main and small chambers built inside the pipe, and therefore it was unnecessary to add any external loads to the pipe wall. Tests were also conducted to observe leakage through the pipe wall. The main failure mode observed was weepage through the pipe wall, which was due to intensive matrix microcracking. The results from the UEWS tests are presented in the form of failure envelopes showing the effects of testing at an elevated temperature. Finally, degradation in the elastic properties of the pipe wall is also discussed and plotted against wall stress.

Abstract: Rheological studies of polymers are of great importance in optimizing the processing conditions and in designing processing equipments like injection molding machines, extruders, and dies required for various products. Melt rheological studies give us valuable viscosity data that will be helpful in optimizing the processing conditions. Parameters like melt viscosity as a function of shear rate or shear stress and temperature have become more and more important. Previous study indicated that the flow behaviour of the compound depends on the filler loading. Lesser elastic torque was found with compound containing lower filler content as compared to higher filler content. In this work, effect of dual filler, based on Carbon Black / Silica filled Epoxidised Natural Rubber (ENR) compound was investigated. A total of 80phr of filler content based on passenger tyre tread formulation was used in the experiment. The compounds were prepared by melt mixing in tangential type of an internal mixer. The rheological and the processability properties of the compounds were determined using three different testing instruments namely Capillary Rheometer, Mooney viscometer and Rubber Process Analyzer (RPA). A variation of shear rates (ranging from low to high) was performed, in order to better reflect the actual processing condition in rubber manufacturing. It was found that ENR mix with ratio silica to carbon black 70:10 exhibited the best flow behaviour and processability properties as compared to control and other mixes.

Abstract: The objective of this work was to examine the microstructure, interdiffusion of elements, and hardness of joining sialon to AISI 420 martensitic stainless steel using diffusion bonding process. These materials were diffusion bonded at 1200^oC for one hour under 20 MPa in a vacuum of 2.1x10^-6 Torr. The microstructural analyses showed that joining sialon to nitrided steel produced thinner reaction layers and no gap or crack were formed on the sample. Gaps were produced in joining sialon to as-received steel. From the elemental analyses, alumina and iron silicides were formed at the interface layer of sialon/as-received steel joint. Alumina and smaller amount of silicides were detected at the interface layer of sialon/nitrided steel joint. Diffusion layer and parent steel of the sialon/nitrided steel joining contained nitrides. The hardness test across the joints indicated that reaction layers possessed intermediate hardness between sialon and steel. The layers contributed to ductility of the joint that help to attain the joint.

Abstract: We have studied tunneling current in a p-n junction based on armchair graphene nanoribbon (AGNR) by using the relativistic Dirac equation and a transfer matrix method (TMM). The electron wave function was derived by solving the relativistic Dirac equation. The TMM, which is a numerical approach, was used to calculate electron transmittance and the tunneling current. The results showed that the tunneling current increases with the bias voltage. On the other hand, the tunneling current increases with the decreases in the electron incidence angle and temperature. Moreover, the increases in the AGNR width and electric field in the p-n junction result in the increase in the tunneling current.

Abstract: The present work attempts to investigate the interfacial phenomenon occurring between two dissimilar materials and in particular organic and inorganic hybrid materials. Layer by layer hybrid heterostructures are fabricated by electro-deposition technique. Here, ZnO thin films are deposited using potentiostatic mode using regulated DC voltage supply fixed at-1.0 V (with respect to the reference electrode) with platinum sheet (99.99% purity) used as the counter electrode and ITO-coated glass used as a working electrode. The as obtained ZnO films are then used as substrates for deposition of organic layer. Two conducting polymers namely polyaniline (PANI) and polypyrrole (PPy) are deposited by electro-deposition method on ZnO to form ZnO/PANI and ZnO/PPy interfaces. The two interfaces are compared for their photoconducting response. These studies are further correlated with the properties that the two interfaces share.