Advanced Materials Research Vol. 983

Abstract: Epoxy resin (EP) nanocomposites reinforced with different contents of core-shell structured Ni@NiO nanoparticles (NPs) were fabricated by using a surface wetting method. The nanoindentation and nanoscratch properties of Ni@NiO/EP nanocomposites were comparatively studied based on nanoindentation technique. Results revealed that 5 wt.% content of Ni@NiO NPs was the optimal concentration for Ni@NiO/EP composites to obtain the best improvement of nanomechanical properties. In comparison with pristine EP, the highest enhancements of hardness and elastic modulus of 5 wt.% Ni@NiO/EP nanocomposites were increased by 37.8% and 16.3%, respectively.

Abstract: Multiwalled carbon nanotubes/Polycarbonate (MWCNTs/PC) nanocomposites were successfully prepared by melting mixing. With the injection speed and temperature changed, different MWCNTs contents MWCNTs/ PC composites were prepared. The electrical conductivity of nanocomposites was compared with different injection speeds and injection temperatures. It was found that the electrical conductivity of the MWCNTs/PC nanocomposites was decreased with MWNTs content increasing, and were both affected by the injection speed and temperature. Besides, at the vicinity of the surface of samples, the resistivity of MWCNTs/PC nanocomposites was the maximum; the closer to the samples inner, the resistivity was smaller and more stabilized. The microstructure and morphology of composites were analyzed by Scanning Electron Microscopy (SEM) techniques, and the MWCNTs’ dispersion in PC matrix and the interfacial interaction between MWCNTs and PC were analyzed.

Abstract: In this paper the effect of production method and heat treatment of magnesium alloys to their corrosion resistance is presented. The study was carried out on the AZ91D alloy obtained by permanent mould casting, pressure die casting and pressure die casting with the subsequent heat treatment. Studies of the microstructure were carried out using a light microscope. The corrosion resistance was examined using the Potentiodynamic Test. The surface observations after corrosion tests were carried out using the Scanning Electron Microscope (SEM). It was stated that the best corrosion resistance is typical for AZ91D alloy produced by pressure die casting method with heat treatment. The alloy after permanent mould casting has got the worst corrosive properties.

Abstract: Molybdenum disilicide (MoSi₂) matrix composites with various contents of carbon nanotubes (CNTs) were fabricated by sintering in vacuum at 1550 °C for 1 h. The oxidation behaviors of CNTs/MoSi₂ composites at 400 °C and 500 °C for 200 h in air were studied. Results showed that the weight loss of CNTs/MoSi₂ composites increased with the increase of CNTs content. “Pest” phenomenon happened at 400 °C but not at 500 °C. Phase identification and microstructure of the samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that many MoO₃ whiskers and microcracks only occurred on the surface of CNTs/MoSi₂ composites when oxidized at 400 °C in air, which leaded to the catastrophic disintegration of CNTs/MoSi₂ composites.

Abstract: The major advancements in some mechanical properties of single crystal superalloys can be attributed to the carbon addition. The present study investigated the effect of carbon addition levels on the microsegregation behavior of single crystal superalloys. Quantitatative partitioning results indicated that typical single crystal superalloy segregation behavior for some elements such as W, Ni, Co, are all towards the dendrite core regions, while for elements of Al, Mo, Ta, Ti, Cr, partition towards the interdendrite regions. For all the alloys studied, the baseline alloy showed the most severe segregation degree, while the no carbon alloy the slightest. Furthermore, the segregation behavior of Ti and Ta were affected by the carbon additions, and that of W was greatly affected by the carbon levels.

Abstract: In this work, a relational model was established correlating microstructure and tensile properties for the Ti-17 alloy using a back-propagation (BP) neural network technique. In the proposed model, the input data consisted of quantitative microstructural feature parameters, including the volume fraction, thickness and Ferret ratio of α phase. Meanwhile, the tensile properties are the outputs of the model, such as ultimate tensile strength, yield strength, elongation and reduction in area. The coefficient of determination is more than 0.900, which indicates that the developed model possesses the excellent ability to predict the internal relationship of the microstructure and tensile properties of Ti-17 alloy.

Abstract: The microscopic morphologies of Bi₃₀Ga₇₀ immiscible alloy particles were investigated. Monosized microparticles with similar core-shell structures were fabricated for the first time by one step using the Pulsated Orifice Ejection Method. The EDS revels that the core and the shell consist of a Ga-rich phase (＞90 at. %) and a Bi-rich phase (＞80 at. %), respectively. The DSC testing at different temperatures is performed. Core-shell microstructures as well as endothermic peaks and exothermic peaks are observed after heating-cooling cycles when the working temperature is below the temperature of spinodal line, indicating good thermal stability after phase transformation. The thermal energy storage was preliminary tested, which is a good attempt for thermal energy storage. It is likely to use core-shell structures as microencapsulated phase change materials.

Abstract: Ti-based bulk metallic glass (BMG) is a new class of titanium alloys that exhibits excellent properties for biomedical applications. They have high strength, good corrosion resistance, low elastic modulus and satisfactory biocompatibility. Therefore, Ti-based BMG is an excellent alternative material to be used in biomedical application. Titanium alloy with a nominal composition of the Ti₄₀Zr₁₀Co₃₆Pd₁₄ was synthesized by replacing Cu with Co in a better-known bulk glass forming composition. Coin-shape samples with a diameter of 15 mm and thickness of 1 mm were prepared by arc-melting and casting into copper mold. The coin-shape samples were polished, then followed by blasting with 50 μm and 250 μm average particle sizes of alumina. Alumina blasting caused plastic deformation at the surface and induced change in surface roughness. The larger size of alumina particle, the higher the R_a, R_q and R_t with significant difference. Some abrasive alumina particles were found to be embedded onto the blasted surface. The blasted Ti₄₀Zr₁₀Co₃₆Pd₁₄ sample showed lower roughness values than those blasted Ti-6Al-4V samples. This may be because of the higher hardness values of Ti₄₀Zr₁₀Co₃₆Pd₁₄ sample, when compared to the softer Ti-6Al-4V samples. The contact angle measurement which demonstrated wettability of all samples did not show significant difference in a tested range of R_a (from 40 to 428 nm).

Abstract: The technical and economic feasibility of high strength low alloy structural steel is analyzed used in highway semi-rigid guardrail. In principle of improving safety performance and reducing cost, a kind of high strength low alloy structural steel guardrail is designed. Through the finite element simulation method, the safety performance of this guardrail structure is validated to satisfy the grade-A conditions (160kJ kinetic energy). Compared with the guardrail of same protection level made of ordinary carbon structural steel, high strength low alloy structural steel guardrail can reduce the probability of penetrating when the accident vehicle impact the guardrail and decrease the accident damage, the steel consumption is above 20% lower and the construction cost can be saved as well, thus, remarkable economic and social benefits can be obtained.

Abstract: Co/Pd bi metallic catalyst supported on MgO has been prepared by sol gel method, at different calcination temperatures of 250 and 550 C. They were introduced in to the reactor for 5 hrs of reaction. The CNTs were collected. The obtained CNTs were characterized by XRD and SEM and the yield was observed. It has been concluded that the catalyst calcined at higher temperature will lead to higher yield and more uniform and smaller diameter CNTs.