Applied Mechanics and Materials Vol. 248

Abstract: The melt-spinning technique was used to synthesize the Mg₂₀Ni₆M₄ (M=Co, Cu) alloys with nanocrystalline and amorphous structure. The microstructures of the as-spun alloys were characterized by XRD and TEM. The electrochemical hydrogen storage properties of the alloys were measured. The results show that the as-spun (M=Cu) alloys hold an entire nanocrystalline structure, whereas the as-spun (M=Co) alloys display a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni facilitates the glass formation in the Mg₂Ni-type alloy. The discharge capacity and high rate discharge ability (HRD) of the alloys notably augment with the rising of the spinning rate. The action of the melt spinning on the cycle stability of the alloys is associated with the substitution element. For the (M=Co) alloy, the melt spinning exerts a dramatically positive impact, whereas for the (M=Cu) alloy, its impact is negative.

Abstract: This study is to with system change the riser size and the casting geometry to find out the relation between thermal gradient and porosity formation in A201 aluminum alloy plate casting, which is discussed in this study. The results show that the porosity content was found to be relevant to the thermal gradient and riser system. The larger the thermal gradient (G), the lower the porosity content was found in this study.

Abstract: In this paper, we report the characterization of springback degradation of an Invar sheet with a combination of gamma-ray irradiation and repeated hot-then-cold stresses. The springback factor value of fresh Invar without radiation shows a linear increase with the number of hot-then-cold stress cycles. Continuous springback degradations are observed as the number of hot-then-cold stress cycles reaches 100. When the Invar sheet is subjected to gamma-ray irradiation, the springback factor is greater than that of the repeated hot-then-cold stressed samples. After applying the repeated hot-then-cold stresses to the post-irradiated Invar sheets, the springback factors are first restored to the value of fresh Invar, and then revert to an increasing trend. Our previous X-ray diffraction (XRD) analysis excluded the crystalline structural changes in the post-irradiated Invar. It is believed that the radiation-induced defects, which are closely related to the springback degradation, are possibly annealed during the first 20 hot-then-cold stress cycles. These cycles ultimately dominate the springback behavior of the stressed Invar sheets.

Abstract: Proper selection of drilling parameters is one of the significant challenges in drilling process. In this study, a new method for selection of optimal machining parameters during drilling operation is investigated. The present study deals with multiple-performance optimization of machining characteristics during drilling of 7075 aluminum alloy. The most commonly-used material in aerospace industry is aluminum alloy with zinc as the primary alloying element. The drilling parameters used for this experiment include cutting speed, feed rate and drill diameter while the two output parameters are surface roughness and dimension error. These outputs are specified to be optimized as a measure of process performance. The statistical model is generated from linear polynomial equations which are developed from different output responses when the machining parameters are changed. The Non-dominated Sorting Genetic Algorithm optimization results show high performance in solving the present problem.

Abstract: An investigation was made to determine the effect of austenizing temperature on microstructure and tensile properties of Cr-W-Ni-alloy steel. Correlations of microstructure tensile properties and austenizing temperature parameters were established. Analysis of optical and scanning electron microscope show that there were a lot of coarse spherical undissolved carbides dispersed on the lath martensitic matrix in as-quenched specimens when austenized at 900°C while there were only very little nanometer carbides when austenized at 1000°C and 1100°C. The tensile properties show that austenizing temperature had large effect on the mechanical property of the Cr-W-Ni-alloy steel. Oil quenching after austenized at 1100°C for 26 minutes followed with tempering at 260°C for 3h, Cr-W-Ni-alloy steel obtained best strength and ductility match.

Abstract: The effects of pressure, concentration and feed temperature using a high pressure membrane filtration test rig capable of handling nanofiltration and reverse osmosis separation was investigated. The experimental results indicated that the applied pressure across the membrane has a significant positive influence on the flux produced and increasing the pressure will rupture the membrane if excessive force or pressure is applied. The high concentrations of solutes/molecules inhibit the flow of fluid through the membrane consequently lower fluxes and improved separation is and subsequently all variables, including their interactions, examined was found to be significant.

Abstract: Nanocomposited and Functionally graded (FG) ZrN/hydroxyapatite coatings with good mechanical strength and biocompatibility were prepared on cp-Ti substrate for biomedical applications and detailed analysis of the nanocomposite coatings for its structural, morphological, topographical and biocompatibility properties were carried out. Crystallite size of the coating for the functionally graded coatings was smaller compared to that of nanocomposite coatings. The arrangement of grains was observed to be denser in the FG coatings due to the decrease in the grain size. Hardness and modulus of FG coatings were observed to be greater than those of nanocomposite coating, which was attributed to the reduction in the crystallite size in FG coatings. Both ZrN/HA nanocomposite and functionally graded coatings was found to induce biomineralization formation, suggesting both are promising candidates for the future biomedical applications.

Abstract: Room temperature rolling tests were performed on a bulk nanostructured Cu with an average grain size of 90 nm. The results indicated a high thickness reduction ( ) of 92% without crack and an increased {220} texture as the rolling processes continued. Microstructure evolution of the deformed nanostructured Cu could be characterized by several deformation stages. Grain growth and coalescence was prevalent in the early deformation stage, while grain boundaries were impaired and replaced by dislocation interactions when 24%. Microhardness of the deformed nanostructured Cu increased sharply to a maximum value of 1.61 GPa at 8% and then slightly decreased to 1.58 GPa at 92%.

Abstract: In this paper, the effect of CeO2 nanoparticles content in the bath on the weight percent of CeO2 particles, morphology, texture, and high temperature oxidation resistance of the nanocomposite coatings was examined. With a rise in the loadings of CeO2 particles in the bath from 10 gl-1 to 40 gl-1, the CeO2 particles weight percent in the nanocomposite coatings gradually increases. Further increased the loadings of particles in the bath to 50 gl-1, the weight percent reversely reduces. The maximum of CeO2 nano particles weight percent in the nanocomposite coatings is 4.98 wt% obtained at current density of 3 Adm-2 from the bath containing 40 gl-1 CeO2 particles. The high temperature oxidation resistance of Ni-CeO2 nanocomposite coatings significantly rise compared with that of bare nickel coatings, and enhanced with a rise in the loadings of CeO2 nano particles from 10 gl-1 to 30 gl-1. The wear resistance of deposits is also consist with the nanoparticles content in the bath。