Applied Mechanics and Materials Vol. 372

Abstract: Ni doped amorphous mesoporous titaniasilica with Ti/Si mass ratio of 0.8 (NiTiO₂SiO₂) was synthesized, and this material was characterized by a combination of various physicochemical techniques, such as N₂ physisorption, diffuse reflectance UVvis, X-ray diffraction, and FT-IR. Interestingly, and some of this material showed sphere shape.

Abstract: The phase composition of the AlNiMnFeSiZr system is analyzed as applied to heat resistant nikalines (aluminum alloys of a new generation based on Ni containing eutectic), which are strengthened by the Al₃Zr (L12) nanoparticles. It is shown that the presence of iron and silicon considerably complicates the phase analysis when compared with the AN4Mts2 base alloy. Silicon strongly widens the crystallization range, which increases the tendency of the alloy to form hot cracks during casting. It is shown that economically doped nikaline AN2ZhMts substantially exceeds the most heat resistant cast aluminum alloys of the AM5 grade in the totality of its main characteristics (heat resistance and mechanical and production properties).

Abstract: The occurrence of high temperatures in combustion chambers of jet engines and gas turbines has led to the demand for new technologies and new materials for the manufacture of one of the most critical elements of these systems - the turbine blades. These elements have to withstand extreme temperatures for extended periods without loss of mechanical strength, conditions under which many alloys fail. Such failure is ascribed to the combination of high temperatures and high centrifugal forces, resulting in creep. This is especially prevalent in multi-crystalline structures in which grain boundaries present weaknesses in the structure. High temperature resistant alloys formed as single crystal (SX) structures offer the necessary material properties for safe performance under such extreme conditions. Modelling and simulation techniques were first used to study the directional solidification (DS) of crystal structures during vacuum investment casting. These models allowed the study of the dendritic growth rate, the formation of new grains ahead of the solid/liquid interface and the morphology of the dendritic microstructure. These studies indicated the opportunity to optimise the velocity of the solidification front (solidification rate) for single crystal structures. The aim of this study was therefore to investigate the effect of the solidification rate on the quality of SX castings. The investigations were carried out for nickel-based superalloy CMSX-4 turbine blade casts and rods using the Bridgman process for vacuum investment casting.

Abstract: In this study, the mechanochemical method was employed to synthesize hydroxyapatite (HA) and magnesium (Mg) doped hydroxyapatite (HA) powders. The effect of Mg²⁺ into the synthesized HA powder properties were investigated. Characterization of the synthesized HA and Mg doped HA at various concentrations (1% - 5% MgHA) were accomplished through X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses. nanosize of HA and Mg doped HA powders were successfully synthesized through the present method as indicated from the different peaks intensity and adsorption bands obtained in XRD pattern and FTIR respectively.

Abstract: The effect of trace Sc and Zr on grain refinement of Al-7.2Zn-2.2Mg-1.8Cu as-cast ingot was studied by using optical microscopy and scanning electron microscopy with EDS. The results show that addition of only 0.20% Zr or 0. 20% Sc to Al-7.2Zn-2.2Mg-1.8Cu alloy can refine grains to a certain degree, and the addition of 0.10% Sc+0.20%Zr leads to stronger grain refinement, the average grain size is only 10-15μm. Al₃Sc/Al₃Zr composite particles in the melt work as the nucleation of heterogeneous nucleation during solidification.

Abstract: It is imperative to determine the dependence of the quality and characteristics of the epitaxial film on different growth parameters. A mathematical model has been developed showing the effect of different growth parameters e.g. temperature, TMI and TEG flow rate, molar ratio on epitaxial film. This model is considered for InGaN film on GaN template with an Indium mole fraction up to 0.4 by Metal Organic Vapor Phase Epitaxy (MOVPE). The results obtained from this model has been compared and fitted with experimentally obtained data through XRD, RSM, PL, SEM etc. Finally, a phase diagram has been proposed to interpret the phase separation and Indium content evolution under the influence of growth temperature and precursor gas flow.

Abstract: Epitaxial bilayer structure consisting of ferromagnetic (FM) metallic Pr_0.7Sr_0.3MnO₃ (PSMO) and antiferromagnetic (AFM) insulator La_0.5Ca_0.5MnO₃ (LCMO) was fabricated on (001)-oriented single crystal SrTiO₃ (STO) substrate by pulsed laser deposition technique. We studied the surface structure and interdiffusion at interface between PSMO and LCMO by using atomic force microscope and grazing incident x-ray reflectivity (GIXRR). The perfect data fitting result of GIXRR indicated that interdiffusion at the interface of Pr_0.7Sr_0.3MnO₃/La_0.5Ca_0.5MnO₃ (PSMO/LCMO) could not be negligible; there was a large interdiffusion zone at the PSMO/LCMO interfaces with a thickness of about 7 nm. We found that the thickness of the top layer at air/PSMO interface was about 2.5 nm and the mass density of the top layer was about 76.53% of that of PSMO layer. The surface roughness was about 1.6 nm which was consistent with observation by atomic force microscopy. Normal X-ray diffraction (NXRD) was also employed to investigate the average structure. Except from PSMO and LCMO layer diffraction peaks, we observed another additional peak, which was developed from the large disordered layer resulting from interdiffusion at the interface of PSMO/LCMO. This implied that the variation of crystalline structure of PSMO/LCMO film occurred due to interdiffusion. Surface roughness and interdiffusion played an important role in magnetic properties of FM/AFM bilayer.

Abstract: A new complex crystal [Co₂(Hdmg)₂(dien)₂](ClO₄)₂4.5(H₂O) (H₂dmg= dimethylglyoxime, dien = diethylenetriamine) had been synthesised in aqueous solution and was characterized by X-ray diffraction and IR spectrum. The complex crystallizes in monoclinic space group C₂/c with cell constants =20.868(7)Å, =11.408(4)Å, =15.816(4)Å, =90.00°, =116.97(2)°, =90.00°, =3355.8(17)ų, =4, (000)=1732. The cobalt atom lies in a distorted octahedron environment and coordinates with one oxygen atom from neighbour Hdmg and five nitrogen atoms from bidentate chelate Hdmg and tridentate chelate dien. The two Hdmgs bridge two cobalt atoms to form a six-number Co₂O₂N₂ ring.

Abstract: Inconel alloy 690 which contains high chromium concentration, has replaced Inconel alloy 600 because of its high resistance of stress corrosion cracking (SCC). Inconel alloy 690 is an austenite nickel-based alloy and it has intergranular chromium carbide (M₂₃C₆). Alloy should be maintained to be nearly free from fretting wear, corrosion, and hydrogen brittleness for a several decades. Main factors controlling deterioration are initial chromium carbide size and their distribution along austenite grain boundary and chromium concentration distribution inside of grain. The precipitated carbide along grain boundary are modeled by KJMA(Kolmogorov-Johnson-Mehl-Avrami) equation. The model is based on the classical nucleation theory, and Cr diffusion controlled growth followed by coarsening. The distribution of the chromium concentration near grain boundary with time is based on diffusion of chromium. The simulated results are compared with the experiments from literatures to confirm the validity of model.

Abstract: Lime, a traditional calcium based stabilizer, had been widely used in chemical stabilization to improve the strength of soil. Past researches had shown that the major reaction product of lime and soil such as Calcium Silicate Hydrate (CSH) was formed abundantly under the observation of microscopic studies. However, sometimes it will be quite difficult to confirm the existence of CSH phase if solely based on its needle like structures, especially when other rod like structures will also exist. Practically, the recognition of the CSH phase by using XRD spectrum through matching with published data had speed up the process of identification. If the method is viable, then theoretically, the molecular weight ratio of silica and calcium, S/C of CSH gel is specific and can be determined based on its possible chemical compound. Hence, this study was carried out in an attempt to examine the possibility use of its S/C ratio as a quick method to confirm the existence of CSH gel. Two types of artificial organic soils were formed by admixing kaolin (inorganic matter) and humic acid (organic matter) with the ratio of 7:3 and 5:5. Four types of admixtures with different percentages ratio of lime and zeolite (a kind of pozzolan) were used to stabilize the soils. The specimens were cured at elevated temperature of 50°c in order to accelerate the development of reaction products. Field Emission Scanning Electron Microscope with attached Energy Dispersive Analyzer (FESEM-EDX) was utilized to observe and determine the existence of reaction products and its bulk chemical composition. The S/C ratio of needle like structures were determined and it is found that the S/C ratio fluctuates and varies significantly from one specimen to another. It is believed that due to the limitations of the experimental setup, the EDX analysis can only serve as semi-quantitative and act as a reference guide on the existence of element. Despite of its limitations, the EDX analysis is useful in distinguish the CSH from other structure which is physically un-identical.