Key Engineering Materials Vol. 796

Abstract: This paper reviews the manufacturing of magnesium-based alloys prepared by powder metallurgy (PM) technique and analysis of the effects of PM parameter on the developed microstructure, texture and mechanical properties. Powder metallurgy (PM) technique has been considered to produce magnesium product with consideration of less complex, finer grain and improved mechanical properties. Selection of PM route especially sintering to full densification determines a good diffusion path of alloy for interparticle bonding. This paper discusses the preparation and process parameter of each process in powder metallurgy routes, and the evolved microstructure including the crystallography texture and mechanical properties of the magnesium-based alloy product.

Abstract: A carbon nanosphere has been used in various applications such as supercapacitors, lithium batteries, fuel cells and catalyst carriers due to their outstanding properties. The precursors commonly used to synthesize carbon nanospheres are methane, polymer and alginate solution. These precursors come from fossil fuels which are non-renewable resources where future access is limited. Hence, alternatives of renewable natural resources to develop carbon-based precursors should be studied. The aim of this work is to study properties of carbon nanospheres synthesized from sugar by using chemical reduction method. The surface morphology of mesoporous carbon nanospheres were observed by field emission scanning electron microscopy (FESEM) and the expected elemental composition by energy dispersive X-ray (EDX) analysis. The FESEM images showed carbon nanospheres having irregular spherical nanostructures with a range of diameter from 84.04 – 834.86 nm. The formation of carbon nanospheres with highly carbon content can be observed from EDX spectrum.

Abstract: Conductive polymer composites start to gain its attention towards many industries. Widely, it is used in producing electrical components such as microchips and semiconductor electronics. Most of the highly conductive polymer composites are used to produce solar panels, which convert thermal energy into electrical energy to generate electricity. It can also diffuse heat faster to avoid overheating of components that can cause degradation of the composites in the component. Thus, this short review describes the various effects that affect the thermal conductivity of natural fiber reinforced polymer matrix composites with additions of metallic filler. The outcome of this short review helps identify the important keys that influence the conductive polymer composites as functional materials.

Abstract: Blended polymer composites are prepared based on linear low density polyethylene (LLDPE) and mixed with polysulfone (PSU) using solvent casting technique. LLDPE is functionalized with carbonyl functional groups to enable it to interact with PSU from the molecular level. Various weight percent of PSU is added into LLDPE to find the optimum weight percent ratio between LLDPE and PSU. The highest glass transition temperature obtained is 47.58°C for ratio LLDPE to PSU of 7:3. In addition, value for decomposition temperature is increased up to 490.16°C with the increasing of PSU content. SEM observation of the blended polymer films shows that glass transition and decomposition temperature depend on morphology of the blended polymers.

Abstract: In this paper, the effect of carbon fiber hybridization on the compressive strength of glass-carbon/epoxy hybrid filament wound pipes before and after low velocity impact was investigated experimentally. Specifically, the effects of different stacking sequence and fiber content ratio on the compression and compression after impact (CAI) behavior of hybrid glass-carbon fiber reinforced polymer pipes were analyzed. Hybrid composite pipes composed of eight layers of / reinforced with thin HDPE liner were manufactured utilizing filament winding technique. A series of axial compressive tests were carried out on the composite pipes for the non-impacted and impacted specimens under 100 J of impact energy. Residual compressive strength, damage tolerance and failure modes were examined and analyzed for different pipe configurations, before and after the impact. The failure modes of non-impacted and impacted composite pipes under compressive loading were analyzed visually. The results show that, under the same conditions of impact energy, specimens with alternative fibers exhibited better impact resistance regardless of fiber content ratio. Moreover, carbon fiber reinforced epoxy specimens exhibited the worst impact damage tolerance for a given impact energy level although having the highest compressive strength before impact among the samples, with the highest percentage reduction of 62% in residual compressive force after impact.

Abstract: In this study, the mechanical disc milling of coal fly ash (CFA) produced by ESKOM thermal station in South Africa has been investigated. The present work covers the effects of milling time on the characteristics such as crystal phases, particle sizes, morphology and physiology of the powder. The produced nanoparticle powders were characterized by SEM-EDX, XRD, and XRF. The milling time was carried out at (t=0, 20, 40, and 60 minutes) at a constant milling speed of 940 rpm. The results showed that mean area of the particles of the particle sizes increased from 75 µm size to approximately 200 nm which revealed that there was 62.5 % increase in the number of particle size as a result of the disintegration of the area of particle sizes. The crystal phases detected by the XRD in CFA are hexagonal, orthorhombic, rhombohedral and anorthic. XRD analysis showed that the most dominant minerals in coal fly ash are Quartz (SiO₂), Mullite (Al_2.32Si_0.68O_4.84), Sillimanite (Al₂(SiO₄)O, Calcite high (CaCO₃), Hematite (Fe₂O₃), Microcline (KAlSi₃O₈). It was also revealed by EDX that the main elemental compositions present in CFA are silicon, aluminium, calcium, iron, titanium and magnesium. It was established in the study that the duration of the milling affects volume, surface area, particle size, pore size distributions, as well as the microstructure

Abstract: The purpose of this study is to extract natural hydroxyapatite (HAP) from cow bone. The hydrothermal method followed by calcination treatment at different temperatures is used in this current research. Cow bone has the potential for producing hydroxyapatite, a chief component present in bone and teeth of vertebrates. HAP is an excellent material used in bone restoration and tissue regeneration. Characterizations of the cow bone natural HAP powder were done by X-ray diffraction (XRD) and Thermogravimetric analysis (TGA). TGA data revealed that biological apatite is thermally stable at 1100°C. XRD data showed that the extracted HAP is, highly crystalline and hexagonal crystal structure having a crystallite size in the range of 10-83 nm. The extracted HAP material is found to be thermally stable up to 1300°C.

Abstract: Titanium and titanium alloys have a large array applications attributed to its low density, good corrosion resistance and high specific strength. Damage to the surface can be improved by surface modification for extended application. Direct laser metal deposition (DLMD) technique can be used to address the limitations associated with titanium alloy. This is mostly achieved by integration of reinforcement materials into the main matrix to form coating. Thereby inducing microstructural changes to the material. The morphology and also the hardness property of the various composite coatings were examined. The hardness of the composite coating was found to range between 450.64 and 638.22 HV, and the hardness obtained for 10% SiC reinforcement coating was 638.22 HV. For all the coatings, the hardness was established to be much higher than that of the substrate, which was averaged 304.21 HV. Hardness value increases with increase in SiC content. The enhanced hardness values were due to refined grains and intermetallics in the microstructure of the coatings. Moreover, the highest tensile and yield strengths was found at 10 wt.% SiC due to the uniform particle dispersion that can impede dislocation movement. The uniform distribution of SiC particles in the Al-Sn matrix had a good effect on its mechanical properties.

Abstract: The effect of rare earth metal erbium (Er) modification on the microstructure and mechanical properties of aluminium alloys (A380) were investigated using Optical Microscope (OM), Scanning Electronic Microscope (SEM) attached with Electron Dispersive Scanning (EDS), Vicker’s hardness test and Ultimate Tensile Test (UTS). The results show that the addition of Er reduces the size of the silicon particle and improve mechanical properties of the aluminium alloy. In addition, by adding 0.1 wt. % of Er, the mean area (μm²) and aspect ratio value decreased. The coarse plate like existed in the unmodified alloy transformed into fine particle and short rod. The mechanical properties were investigated by using tensile test and Vicker’s hardness test. The ultimate tensile strength test shows that the tensile and the elongation increased 1.32 % and 9.1 % with 0.1 wt. % Er content of the aluminium alloys, respectively. The hardness improved from the addition of 0.1% Er aluminium A380 alloy.