Effects of ternary additions on the thermoelastic martensitic transformation of NiAl

Nickel-rich β-NiAl alloys, which are potential materials for high-temperature shape-memory alloys, show a thermoelastic martensitic transformation, which produces their shape memory effect. However, the transformation to Ni₅Al₃ phase during heating of NiAl martensite can interrupt the reversible martensitic transformation; consequently, the shape memory effect in NiAl martensite might not appear after heating. The phase transformation process in binary Ni-(34 to 37)Al martensite was investigated by differential thermal analysis (DTA) method, and we found that the condition of reversible martensitic transformation was not the β → Ni₅Al₃ transformation, but rather the M → Ni₅Al₃ transformation occurring at 250 °C to 300 °C. Therefore, the transformation temperature of M → Ni₅Al₃ determined the highest operating temperature for the shape memory effect. For verifying the critical temperature, the phase transformation process was investigated for eight ternary Ni-33Al-X alloys (X=Cu, Co, Fe, Mn, Cr, Ti, Si, and Nb). Only Ti, Si, and Nb additions were found to be effective in dropping the M _s temperature, and they facilitated the shape memory effect in Ni-33Al-X alloys. In particular, the addition of Si and Nb raised the transformation temperature of M → Ni₅Al₃, a potentially beneficial effect for shape memory at higher temperatures. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

An efficient implementation of surface impedance boundaryconditions for the finite-difference time-domain method

An efficient way to implement the surface impedance boundary conditions (SIBC) for the finite-difference time-domain (FDTD) method is presented in this paper. Surface impedance boundary conditions are first formulated for a lossy dielectric half-space in the frequency domain. The impedance function of a lossy medium is approximated with a series of first-order rational functions. Then, the resulting time-domain convolution integrals are computed using recursive formulas which are obtained by assuming that the fields are piecewise linear in time. Thus, the recursive formulas derived here are second-order accurate. Unlike a previously published method [7] which requires preprocessing to compute the exponential approximation prior to the FDTD simulation, the preprocessing time is eliminated by performing a rational approximation on the normalized frequency-domain impedance. This approximation is independent of material properties, and the results are tabulated for reference. The implementation of the SIBC for a PEC-backed lossy dielectric shell is also introduced     

Synthesis of ultrafine LiCoO2 powders by the sol-gel method

Ultrafine high-temperature (HT) LiCoO₂ powders were synthesized by the sol-gel method using polyacrylic acid (PAA) as a chelating agent. The decomposition process of the gel precursor was examined to determine the crystallization temperature and the dependence of the physicochemical properties of HT-LiCoO₂ powders on the PAA quantity was extensively investigated. Polycrystalline HT-LiCoO₂ powders, composed of very uniformly sized ultrafine particulates with an average particle size of 30–50 nm and a specific surface area of 2.3–17 m²g^–1, could be obtained at the lower calcination temperature of 550 °C and the shorter calcination time of 1 h compared to the solid-state reaction.     

A new Thermo-viscoplastic Material Model for Finite-Element-Analysis of the Chip Formation Process

A new material model for describing the thermo-viscoplastic flow behavior of workpiece material in metal cutting is presented. In order to express the complex flow behavior which depends on the local strain, strain rate and temperature, a new methodology for sequential formulation is proposed. The material parameters which are achieved by using the flow stress data available at low strain rates are enhanced by matching the results of the experimental investigations and finite element simulations of the orthogonal cutting process. As a result, a material model which has a wide validity range of strain, strain rate and temperature is established.     

Effective Reduction of Horizontal Error in Laser Scanning Information by Strip‐Wise Least Squares Adjustments

Though the airborne laser scanning (ALS) technique is becoming more popular in many applications, horizontal accuracy of points scanned by the ALS is not yet satisfactory when compared with the accuracy achieved for vertical positions. One of the major reasons is the drift that occurs in the inertial measurement unit (IMU) during the scanning. This paper presents an algorithm that adjusts for the error that is introduced mainly by the drift of the IMU that renders systematic differences between strips on the same area. For this, we set up an observation equation for strip‐wise adjustments and completed it with tie point and control point coordinates derived from the scanned strips and information from aerial photos. To effectively capture the tie points, we developed a set of procedures that constructs a digital surface model (DSM) with breaklines and then performed feature‐based matching on strips resulting in a set of reliable tie points. Solving the observation equations by the least squares method produced a set of affine transformation equations with 6 parameters that we used to transform the strips for adjusting the horizontal error. Experimental results after evaluation of the accuracy showed a root mean squared error (RMSE) of the adjusted strip points of 0.27 m, which is significant considering the RMSE before adjustment was 0.77 m.     

共面转换液晶显示器中获得对比度高于1:600的新技术

薄膜晶体管液晶电视(TFT-LCD TV)因为具有薄、轻、紧凑和可随意放置的特点，已经占据了大部分电视机市场。除了这些物理特性以外，最重要的特性是已具有了良好像质的对比度。为了将对比度提高到1：600以上，对偏振片膜、背光源板、滤色片树脂、电极锥角和摩擦条件等都进行了研究。优化的背光板组合，光滑的电极锥角和摩擦方法的控制是提高对比度的主要控制因素。应用新开发的滤色片树脂，对获得高对比度最为有效。     

Effects of potential and heat treatment on phase transition of alumina dielectric layer

The characteristics and growth behaviors of alumina dielectric layer formed by anodic oxidation were investigated. The aluminum oxide layer anodized at 400 V was predominantly amorphous alumina, but at the applied potentials more than 500 V, amorphous and crystalline γ-alumina were existed in anodic oxide layer and the ratio of γ-alumina increased with the increasing applied potential. During the heat treatment at 600^°C or higher temperature, amorphous alumina layer was transformed into the crystalline γ-alumina. The phase transition of anodic amorphous alumina into crystalline depends on anodic applied potentials and heat-treatment temperatures.     

Nanoporous activated carbon cloth for capacitive deionization of aqueous solution

Activated nanostructured-carbon cloths with a high ratio of surface area to volume are used as electrode for capacitive deionization. The electrochemical properties on capacitive deionization for NaCl solution have been investigated to improve efficiency of capacitive deionization properties from aqueous solution, employing chemical surface-modification by etching in alkaline and acidic solution. The removal efficiency of inorganic salts of activated carbon cloths by chemical modification significantly increased. Specially the carbon cloth surface modified in HNO₃ showed an effect of improvement in the CDI efficiency due to not only ion adsorption by an electric double layer, but also electron transfer by Faradaic reaction.     

A kinetic study on isothermal crystallization of palm oil by solid fat content measurements

Isothermal crystallization of plam oil was studied by means of differential scanning calorimetry (DSC) as well as by nuclear magnetic resonance spectrometry to monitor its solid fat content (SFC). The temperature of crystallization (Tc) varied from 0 to 30°C, depending on the method used. The plot of %SFC vs. time at 25°C was sigmoidal in shape. However, at lower temperatures, two consecutive curves were clearly visible. Results from DSC experiments showed the following interesting features. At each Tc, the crystals produced were of different compositions. From 0 to 8°C, the thermogram showed three peaks, with the first two peaks (I and II) sharp, and the third (III) rather broad. At elevated temperatures up to 20°C, peak II disappeared totally while peak III tended to shift toward peak I. Above 20°C, both peaks shifted downward to longer times. Peak I continued to be broadened, and then suddenly disappeared at Tc above 24°C. The melting thermograms of the crystals obtained above and below this cut-off point were distinctly different. Kinetic studies on isothermal crystallization based on the data of SFC measurements showed that the data fit well into the Avrami-Erofeev equation with n=3 over the first 70% of the crystallization.