Advanced Materials Research Vols. 391-392

Abstract: Tooth morphogenesis results from reciprocal interactions between oral epithelium and ectomesenchyme culminating in the formation of mineralized tissues, enamel, and dentin. Based on these basic theory, we design a organic molecules model to induced the crystallization of hydroxyapatite to synthesized tooth-like calcium phosphate/hydroxyapatite with 3D-structure in a controllable way in vitro. We observed that hydroxyapatite nanorods can be controlled followed by in situ phosphorylation process and triggered by conditions of pH and ionic strength. The results showed that he dentinal tubule were blocked by neonatal hydroxyapatite layer and this composite a continuous structure of columns crystal with size of 30-80nm. At the same time, XRD showed that the precipitation was calcium fluoride phosphate and Ca:P was 1.6. Furthermore, there were column crystal with parallel direction inside, as same as the crystal array in the top of enamel rod. The results suggest that collagen monolayer may be useful in the modulation of mineral behavior during in situ dental tissue engineering.

Abstract: Mg_-1Mn_-0.6Ce_-xY (x=0, 1, 2 and 3, mass fraction, %) magnesium alloys were prepared by casting method. And the influences of yttrium on microstructure and mechanical properties of the Mg_-1Mn_-0.6Ce magnesium alloy were investigated. The results reveal that the addition of yttrium to the Mg_-1Mn_-0.6Ce alloy could reduce the grain size of the as-cast alloys and improve mechanical properties during the investigated temperature range. The Mg_-1Mn_-0.6Ce_-1Y alloy exhibits maximum ultimate strength, yield strength, elongation and the values are 152 MPa, 72 MPa and 13.4% and enhanced about 23.1%, 63.6% and 38.1% compared with those of Mg_-1Mn_-0.6Ce alloy at room temperature, respectively. The improvement of mechanical properties are attributed to the grain refinement and the precipitation strengthening generated by the Mg₁₂Ce phase particles and the fine Mg₂₄Y₅ precipitations.

Abstract: The temperature field and stress field of laser welding were simulated by "ansys" analysis soft of finite element for different thickness aluminum alloy plate. The results show that quasi steady state temperature field were formed after laser act on aluminum alloy plate for a certain time. Because heating volume of thin plate is small than one of thickness plate under the same amount of heat input, thin plate has greater grads of temperature and melting pool size. Distribution law of heat stress is similarity with common melt welding. However. heat stress filed area and its peak value of thin plate is greater than one of thickness plate.

Abstract: 0.25Li₂MnO₃•0.75LiNi_1/2Mn_1/2O₂ solid solution was prepared via a two-step calcination technique. No appreciable difference between the end products can be detected from the X-ray diffraction patterns including the superstructure reflections. However, the material prepared from preheating the precursor at 450°C for 4h in N2 delivers a high first charge capacity of 287mAhg^-1 between 2.5and 4.8V at 0.5C, while the samples obtained from preheating the precursor for 10h in air exhibit a low capacity of 199 mAhg^-1 and an undetectable plateau around 4.5V in the initial charge curve. With an aim to identify the influence of preparation process on the structural and electrochemical properties, Rietveld refinement method was performed on the detailed structure testing with the model integrating R m layered rock salts and Fd m cubic ones. The end products prepared from precalcining the precursor in N2 shows low proportion of Fd m domain about 8.0% and larger Li-O slab space in dominating R m rock salts. By contrast, the samples obtained from prolonging the process-prheating time to 10h in air consists of 12.7% Fd m cubic rock salts and 87.3% R m layered ones. The observations indicate that the samples obtained from different precursor-preheating process appear a variation in the local environment of Li+ insertion/extraction, which give an evidence on their electrochemical lithiation/delithiation process shown in the CV curves.

Abstract: Residual stresses are determined by different materials and processing parameters so that it is hard to systematically carry on the experimental testing, and it also spends a plenty of time and running costs. Therefore, it is necessary to estimate the residual stresses by mathematical techniques. In this paper, a mathematical method is proposed, and the calculating results are compared with the testing results of alumina and W coatings on various matrixes (process: plasma spraying) that are highly consistent. The calculating results show that the thermal expansion coefficient, substrate preheating temperature and thickness of coating have significant effects on the residual stresses.

Abstract: A series of spot welding technology, joint mechanical properties and microhardness test analysis of TRIP800 high strength steel were researched. Based on these experiments and analysis, effect of spot welding parameters such as welding current, welding time and electrode pressure on joint mechanical properties were explored. The relevant spot welding parameters of TRIP800 high strength steel of spot welding were recommended, such as welding current is7.5~8.0KA, electrode pressure is 450 kgf and welding time is 20cyc. Welding electrode should be to ensure that as much as possible and clean the surface,to avoid welding current and welding time is too high or too long, as well as forging lack of power, to prevent the occurrence of welding defects.

Abstract: Dual phase steel resistance spot welding process is transient, rapid, invisible, complex, which makes the physical process of welding not yet be fully understood. Both the preprocessing contact stress field and thermo - electric transient process under alternative current(AC)load of the resistance spot welding of DP1000 dual - phase steel are analyzed by ANSYS12.0 finite-element analysis software. The fusion zone formation process and the contact situation of electrode and workpiece, between workpieces, lamination surface is investigated through numerical simulation. The project can help understand the phenomenon and essence of the DP1000 spot welding optimize the structure design and process design, quality control, for the dual-phase steel in vehicle body spot welding quality control to provide theoretical guidance.

Abstract: After being plasma carburized, the surface of AISI 316 austenitic stainless steel was covered with a layer of compact black thin-film. The surface polishing treatment, electrochemical brightening was carried out to remove the black thin-film and renew the original color of the stainless steel. The surface appearance, microstructures, micro hardness, surface roughness and corrosion resistance of the samples treated by electrochemical brightening process were analyzed. Experimental results show that the electrochemical brightening treatment can remove the black thin-film from and restore the original color of the plasma carburized stainless steel. After electrochemical brightening treatment, the thickness and surface hardness of the carburized layer were all decreased little, but the corrosion resistance was improved significantly. And the surface roughness (Ra) was lower than before. Therefore, the electrochemical surface brightening treatment can be used to improve the surface quality of the austenitic stainless steel treated by plasma carburizing.

Abstract: The light transmitting cement-based material (LTCM) is a kind of light transmitting new materials. A large number of optical fiber was embedded in the block and transfer light from the light side surface to the dark side. While at present, the composition, structure and performance of LTCM have been reported rarely. The paper studied the preparation method, light transmitting property and compressive strength of LTCM with optical fiber embedded by means of parallel arrange. The results show that, LTCM gets higher light transmitting ratio with appropriate optical fiber filamentous by means of parallel arrange along the light direction. This kind of LTCM can also achieve, even exceed the light transmitting ratio of the 70g A4 print paper in the light wavelength range of 580~640nm.The light transmitting ratio increases and the compressive strength decreases along with the increase of the optical fiber content in volume.

Abstract: B₄C-CeB₆/Al composite was fabricated by pressureless infiltration technology. It is composed of the phases of Al, B₄C, AlB₂, Al₃BC and CeB₆, and Al₄C₃ is not found because of the existence of CeB₆. It could identify that AlB₂, CeB₆, and Al₃BC were formed as interfacial reaction products. Al3BC is formed on the interface of B₄C and Al; therefore it connects the aluminum with the ceramic toughly. AlB₂ as strip crystal is formed between B₄C and Al, which has higher fracture toughness.CeB6 particles in B₄C grain boundary are discovered by TEM, which caused intercrystalline rupture. Grain toughening and reinforcing, crack deflection, crack bridging is the main toughening and reinforcing mechanisms of B₄C-CeB₆/Al composites.