Advanced Materials Research Vol. 845

Abstract: In the present study, we have successfully grown Si-doped AlN developed by solution growth technique using Ga-Al melt as a solvent under nitrogen atmosphere at 1300 °C. Si doping was introduced to the Ga-Al melt by adding pure Si metal. To allow homoepitaxial growth during solution growth experiment, sapphire substrate were nitrided with precise control to produce hiqh quality single crystalline AlN films with low dislocation density. With the help of AlN film template from above methods, we have successfully grown Si-doped AlN single crystalline layer with a flat surface and almost free from cracks. The full width at half maximum (FWHM) of x-ray rocking curve values for (0002) and (10-12) diffraction from the Si-doped AlN film were 43,2 and 594 arcsec, respectively.

Abstract: Recently, Zn-based alloys were introduced as alternative biodegradable metals to the well-studied Mg and Fe based alloys for temporary implants. In this work, Zn-3Mg alloy was developed using a conventional casting method followed by heat treatment with different cooling media. As-cast samples were heat treated at 370 oC for 10 hours then cooled in open air, water bath and inside furnace environments. The microstructure of as-cast alloy was characterized under optical microscope and phase analysis was evaluated using X-ray diffraction (XRD) technique. Potentiodynamic polarization tests were carried out on the heat treated samples for evaluating the degradation rate. It was observed that as-cast Zn-3Mg alloy consists of star-like-shape of primary Zn-rich dendrites which are segregated in the eutectic mixture of Mg₂Zn₁₁ phase. The segregation of these dendrites has been significantly reduced under water bath cooled treatment as compared to open air and inside furnace cooling. It is also found that the microstructure of the water cooled samples is more homogenous with less porosity than the as-cast, air or furnace cooled samples. The water cooled sample exhibits better degradation resistance for at least 2 folds than other treatments.

Abstract: As the study of fatigue failure of composite materials needs a large number of experiments as well as long time, so there is a need for new computational technique to expand the spectrum of the results and to save time. The present work represents a new technique to predict the fatigue life of Woven Roving Glass Fiber Reinforced Epoxy (GFRE) subjected to combined completely reversed bending moments and internal hydrostatic pressure, with different pressure ratios (P_r) between the applied pressure and burst pressure equal to (0, 0.25, 0.5 and 0.75). Two fiber orientations (θ), [0^o,90^o]_3s and [±45^o]_3s are considered. Two neural network structures, feed-forward (FFNN) and generalized regression (GRNN), are designed, trained and tested. The groups of data considered are the maximum stress and the Pressure ratio with the different fiber orientation. On the other hand, more accurate prediction method is obtained by using a useful expert system which is designed to aid the designer to decide whether his suggested data for the composite structure is suitable or not. In this expert system a neural network is designed to consider the design data as input and to get yes or no as output. The results show the feed-forward neural network is better results than that given by the generalized regression neural network. The designed expert system helped the designer with reliable conclusions about his decision of the combination of the proposed data.

Abstract: Ash is a by-product of solid fuels (eg. coal, biomass, petroleum coke) gasification, which can contribute to the gasifier performance. Continuous formation of ash slag will further accumulate and cause plant outage. In relation to that problem, this study is conducted to mitigate the formation of ash slag in gasifier. Adaro coal from Indonesia and empty fruit bunch (EFB) were used as blends. EFB is used to promote the utilisation of renewable energy source and to reduce the Green House Gas Emission (eg. CO₂). Adaro coal and EFB; and 4 blended fuels from Adaro:EFB at blending ratios of 80:20, 85:15, 90:10 and 95:5 were prepared in laboratory. Prediction of slagging tendency for Adaro:EFB blends were conducted using two slagging indices, which are slagging index, Basic/Acidic (B/A) and ratio-slag viscosity index (S_R). Mineral oxides (eg. SiO₂, Al₂O₃, Fe₂O₃) from the ashes of single and blended fuels were determined using Filed-Element Scanning Electron Microscopy (FESEM) and were used as input for the prediction of slagging tendency. The results showed that Adaro:EFB with blend ratio of 80:20 and 85:15 had low slagging tendency based on slagging index (B/A) and S_R. Therefore, these two blending ratios are suitable to be used in the gasification system to avoid the ash slagging problem.

Abstract: Al-Mg₂Si in-situ composite as a class of advanced engineering materials has possessed better properties which enhanced them to be potential candidate to manufacture most of automotive and aerospace components. Melt treatment of the in-situ composite by addition of bismuth, Bi has resulted in a change of primary Mg₂Si reinforcement to a refined morphology which would expect to improve mechanical properties of the composite. Characteristics parameters of Mg₂Si particles have been investigated via thermal and microstructural analysis. It has revealed that 0.4wt.% Bi addition produced optimum refinement effect on the morphology since coarse structure has been change to polygon one and reduced most in size. The result also showed depression in nucleation temperature, T_N and growth temperature, T_G which also correspond to the refinement effect.

Abstract: This paper reviews the effect of rare earth addition on aluminium-silicon (Al-Si) alloys of hypoeutectic, eutectic, and hypereutectic types. The effects of rare earth on metallurgy, tensile strength, tensile fracture surface and wear behaviour of Al-Si alloys are highlighted and discussed in this paper. It was concluded that adding rare earth element to Al-Si alloys reduces the grain size of primary Si, increases the tensile strength and decreases the friction coefficient decreases. These indicate enhanced mechanical properties for rare earth modified Al-Si alloys are likely.

Abstract: This paper examines the performance of a new type of static mixer known as Fractal Plate Static Mixers. A simulation study was performed to investigate the pressure drop across different numbers of mixing elements (1, 2 and 3). The effectiveness of mixing was assessed by analyzing the coefficient of variation (CoV) of the flow within the range of 0 to 1. The value of CoV that approaching 1 is categorized as a total segregation, while close to 0 indicates a good mixing. The Reynolds number of the study was chosen between 500 and 2000 based on the unobstructed pipe diameter. Results showed that the mixing elements in the flow stream promote a non-laminar, turbulent-like flow which substantially enhances the mixing. By adding more mixing element, it was found that the flow mixing was enhanced in particular at lower Reynolds numbers. In spite of this advantage, the pressure drop was found increased in proportional to the number of mixing elements. This work presents an initial stage of ongoing work to develop a new type of static mixers that based on perforated plate.

Abstract: Multi-layer alternating nanocrystalline diamond (NCD) layer and polycrystalline diamond (PCD) layer was successfully deposited on pretreated tungsten carbide (WC) substrates with various seeding sizes (<0.1μm synthetic, <0.5μm synthetic, <0.25μm natural, <0.5μm natural, and <1μm natural) diamond with and without hammering by silicon carbide. X-rays penetrate through the coating to the substrate from XRD method was able to show strong peaks of diamond relative to WC despite the diamond film being 4μm thick only. It is found that substrates with no hammering produce stronger signals. The coating was cross sectioned and analysed using field emission scanning electron microscopy showing the multi-layer with NCD grains that has coalesced and columnar structure for PCD. None of the diamond coating delaminated during cross sectioning showing good adhesion. Raman was able to capture data from the 1-1.6μm thick NCD layer only while AFM measured the extreme low roughness of the NCD surface.

Abstract: Growing demand of machines such as gas turbine, pump, and compressor in power generation, aircraft, and other fields have yielded the transformation of machine maintenance strategy from corrective and preventive to condition-based maintenance. Real-time fault diagnosis has grabbed attention of researchers in looking for a better approach to overcome current limitation. The parameters of health condition in machinery could be monitored thus faults could be detected and diagnosed by using signal analysis approach. Since some fault signals are non-stationary or time dependent in nature, therefore time-frequency signal analysis is crucial for machinery fault diagnosis. Common time-frequency signal analysis methods are such as short time Fourier transform (STFT), wavelets analysis, empirical mode decomposition (EMD), Hilbert-Huang transform (HHT), etc. This review provides a summary of the basic principle of signal analysis, the most recent researches, and some advantages and limitations associated to each types of time-frequency signal analysis method.