Materials Science Forum Vols. 475-479

Abstract: The lifetime of organic light-emitting devices can be influenced by the OLED material and structure, electrode material, driving mode and so on. Among all these factors, OLED driving method has been regarded as one of the most important factors, and it is well known that ac-driving mode improves the lifetime of OLED, especially pulse-driving mode with a reversed-biased voltage on OLED. In this article, a new ac-driving mode for Active-Matrix OLED is proposed on basic fabrication of two-TFT current source pixel circuit. Simulation has been done on the pixel and 1×4 matrix circuits, and simulation results have demonstrated that OLED is in reversed-biased state during recovery time. At last, a practical peripheral circuit that can provide achieve an ac-driving mode has been designed.

Abstract: we designed and fabricated a white organic light-emitting device based on{[2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9yl)ethenyl]-4H-pyran-4-ylidene] propane-dinitrile}ultrathin layer and 4,4 ´ -bis(2,2 ˊ diphenylvinyl)-1,1 ˊ -biphenyl. It shows a maximum power efficiency of 1.8l m/W at 4 V (the brightness is 51 cd/m2). Its brightness reaches 8496 cd/m2 at 16 V. And the chromaticity coordinates varying from (0.42,0.34) to (0.32,0.28) with the forward bias from 4 to 16 V are well within the white region.

Abstract: Previous works on the kinetics of martensitic transformation in shape memory materials through Landau theory and the application of the phase field theory to study phase transformations in alloys are briefly reviewed. Based on field model to improper martensitic transformation proposed by Wang and Khachaturyan in 1997, a simpler model is suggested. Using this model, the motion speed and shape of parent/martensite and martensite-martensite interface are quantitatively described, which are important factors to be considered in design of smart device using shape memory materials as a main element.

Abstract: The superelasticity is one of the most important properties of TiNi alloy, which has been widely used in the smart systems of many fields, such as aerospace, aviation, biomedicine and energy etc. The current state of superelasticity of TiNi alloy has been reviewed with emphasis on the superelasticity, phase transformations, thermo-mechanical treatment and their relationship. The mechanisms of linear superelasticity and non-linear superelasticity have been revealed. Some successful applications based on the superelasticity of TiNi alloys in smart systems have been introduced.

Abstract: By using the discrete variational method and constructing cluster model, the effect of a few Hf、Zr addition on martensite transformation temperature of TiNi alloy was investigated in electronic level. It is found that the bond order of the strongest bond in the clusters is promoted by introducing the Hf、Zr atoms and the magnitude of bond order is ascendant with increasing number of Hf、Zr atoms in the cluster. At the same time, contour plots of valence charge density on the parent (110) plane show the variety on bond. The change of martensite transformation temperature of TiNi alloy with Hf、Zr concentrations can be reflected by the value of the density of states at the Fermi level for the (110) crystal plane.

Abstract: The microstructure and shape memory behavior of Ti-rich Ti-Ni melt-spun ribbons with various Ni-contents were investigated. Ti-xNi(x=40~48at%) ribbons were fabricated by the melt-spinning method at the rotation speed of 5000rpm. They were heat-treated at 1073K for 3.6ks. It was found that the Ti-40at%Ni as-spun ribbon exhibited almost complete amorphous structure, while the specimen with more Ni-content, such as 48at%Ni ribbon exhibited the coexistence of amorphous and crystalline structures. It was also found that the maximum shape recovery strain increased with increasing Ni-content. The Ti-40at%Ni ribbon was very brittle because of many Ti2Ni precipitates formed.

Abstract: The effects of bias springs with different coefficient on the actuation and transformation behaviors of TiNi wires were studied. Results showed that the maximum output stress increases with increasing spring coefficient. The reverse martensitic transformation starting temperature of the TiNi wires does not change with spring coefficient, but the reverse transformation finishing temperature increases with increasing spring coefficient.

Abstract: The contact force during impact of a NiTi alloy was studied in this paper. The contact force and contact time during impact between a spherical impactor and the specimen at different impact velocity and temperature were measured in real time. The maximum contact force and contact time of the NiTi alloy in the martensite state increased and decreased respectively with increasing temperature. The maximum contact force of the NiTi alloy in the parent phase state showed a plateau with increasing impact velocity of the impactor.

Abstract: In a constrained martensitic transformation of shape memory alloys, a fraction of martensite is always retained in the materials. Experimental results showed that the remaining martensite could be plastically deformed by the generated recovery stresses. The self-tension process elevated the reverse transformation temperatures of the remaining martensite, and the external constraint conditions had no significant effect on the self-tension process of the remaining martensite.

Abstract: . NiTi particles were prepared by the reaction between Ti and Ni powders in high temperature molten salts. Results of differential scanning calorimetry (DSC) confirmed the martensitic transformation of the prepared NiTi particles. Backscatter electron image of scanning electron microscopy (SEM) showed that the synthesized NiTi particles were captured by the molten salts, which revealed the mechanism of the chemical synthesis method in molten salts.