Surface properties of CaNi5 hydrogen storage alloy

The Ca 2p, Ni 2p and O 1s emissions of the air-exposed sample of CaNi₅ indicate that all the calcium and most of the nickel are present in the oxidized state. Interestingly, it is observed that all the peaks are shifted by 3 to 4 eV towards higher binding energy values. This observation has been attributed to the presence of insulating oxide phases leading to partial charging of the sample during the experiment. Depth profiling by argon-ion sputtering removes the insulating oxide species and the sample etched for 7300 sec shows the presence of metallic nickel and mostly metallic calcium. XPS analysis indicates that preferential segregation of calcium in the CaNi₅ alloy is mainly due to induced surface reaction with oxygen.     

High temperature interaction of hydrogen with intermetallic compound CaNi5

The intermetallic compound CaNi₅ disproportionates rapidly into CaH₂ and Ni when treated with hydrogen above 350° C. The kinetics of this reaction in the initial stages follows the nucleation and growth mechanism. The pressure-composition-temperature isotherms for hydrogen interaction with CaNi₅ in the temperature range 640°C to 725°C have been determined and the ΔH_f for CaNi₅ is calculated to be 12.9 kcal/mol. Differential thermal analysis confirms the scheme proposed for the CaNi₅-H₂ reaction. Even a 5% disproportionation of the alloy drastically affects the kinetics of hydrogen Sorption at room temperature.     

Fabrication of porous NiTi-shape memory alloy objects by partially hydrided titanium powder for biomedical applications

Porous NiTi-shape memory alloy (SMA) is a promising biomaterial with desirable mechanical property and appropriate biocompatibility for human implant manufacturing. In this research, porous NiTi-SMAs have been successfully produced by using thermohydrogen process (THP). This process has capability of production of homogenous structures, appropriate pore-size distributions and short sintering times. The THP-SMA samples produced in this research have a low Young’s modulus (19.8 GPa) and a high tensile strength of 255 MPa. These properties are close to those of the natural bone and can meet the mechanical property demands of the hard-tissue implants for heavy load-bearing applications. The samples produced exhibit sufficient thermoelastic effect distinguished by a 1.2% mean recoverable strain.     

第一性原理计算CaNi_2和CaMgNi_4合金的相稳定性

利用第一性原理计算方法计算了CaNi2和CaMgNi4合金的相稳定性、弹性和电子结构。计算结果显示,由于原子间作用力得到释放,CaMgNi4更稳定。弹性系数计算结果显示,CaMgNi4的体模量远大于CaNi2。利用弹性系数、体模量的经验公式计算了合金的熔点,结果显示,CaMgNi4的熔点(1379.6K或1458.4K)大于CaNi2的熔点(1075.4K或979.37K)。     

Structure and bonding configuration of hydrided ErNi3 and CeCo3

The intermetallic compounds ErNi₃ and CeCo₃ has been hydrided at low (p _{H 2} ≤ 0.01 GPa) and high (p _{H 2} up to 0.2 GPa) hydrogen pressures. X-ray and neutron diffraction characterization has shown that the resultant hydrides have structures of the same type (PuNi₃) as the parent intermetallics and have a larger unitcell volume. We have identified the positions occupied by the metal and hydrogen atoms and have determined their positional parameters. The lattice anisotropy has been shown to vary little at high hydrogen concentrations. Our results indicate that the metal-hydrogen bonds in the hydrides studied are predominantly ionic for the rare-earth metals (Er and Ce) and predominantly metallic for the transition metals (Ni and Co).     

Structure and mechanical properties of internally hydrided Mg-IIIa transition metal alloys

Magnesium alloys containing III_a transition metals, such as Sc, Y and Ho, respectively, were hydrogenated at 773 K and examined for microstructure, X-ray diffraction pattern, micro-Vickers hardness, and tensile properties at room and high temperatures. Results obtained are as follows:

1. The alloys, respectively, have been internally hydrided and have precipitated hydrides of the III_a transition metals as small flake-like particles in the matrix and at grain boundaries, as well as twin boundaries.
2. The dispersed hydride particles do not necessarily contribute to further hardening of the alloys at room temperature and up to near 673 K.
3. However, the dispersed particles are very stable and seem to improve mechanical properties of the alloys above 673 K.
4. Presumed relationships of crystallographic coincidence between the matrix and hydrides have been obtained.

     

Surface studies on untreated and plasma-treated carbon fibers

XPS and contact-angle measurements have been performed on a number of untreated and plasma-treated commercial carbon fibers.

In the case of untreated unsized fiber, correlations between surface composition, modulus and wettability were observed. Sized fibers had similar surface compositions and contact angles.

Plasma treatment resulted in decisive improvements in wettability. Sized fibers underwent hydrophobic recovery as a result of segmental motions within the sizing layer. Unsized fibers did not change their wettability upon aging in air, while dramatic increases in advancing angles and decreases in surface-oxygen composition were observed upon aging in water, possibly owing to treatment-induced solubilization of oxidized species.     

Corrosion and impedance studies on magnesium alloy in oxalate solution

Corrosion behavior of AZ91E alloy was investigated in oxalate solution using potentiodynamic polarization and electrochemical impedance measurements (EIS). The effect of oxalate concentration was studied, where the corrosion rate increases with increasing oxalate concentration. The effect of added ions (Br⁻, Cl⁻ or SiO₃²⁻) on the electrochemical behavior of magnesium alloy in 0.1 M Na₂C₂O₄ solution at 298 K, was investigated. It was found that the corrosion rate of 0.1 M oxalate solution containing silicate ion is lower than the blank (0.1 M Na₂C₂O₄). This was confirmed by scanning electron microscope (SEM) observations. However, for the other added ions Br⁻ or Cl⁻, the corrosion rate is higher than the blank.     

Experimental and simulation studies on thixoforming of AA 2017 alloy

Thixoforming is one of the near net shaped manufacturing processes which in the product will be formed between the solidus and the liquidus temperatures of the alloy. In the present work, a finite element based simulation study has been performed to simulate the thixoextrusion of AA 2017 alloy in the semisolid range. The alloy has been heated between 570 and 610°C and it was extruded in a die having die cone angles of 30, 45 and 60°. Simulation studies have been performed by using the constitutive relation that was developed by performing disc compression tests at different temperatures and strain rates. A good agreement was found between the experimental and the simulation results.     

Surface characterization of activated Ti-Zr-V NEG coatings

The thermally activated Ti-Zr-V non-evaporable getter (NEG) film has been studied by means of X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). Depth profiling technique has been used to establish the location of different components in the near-surface region. It was found that the top surface layer of the activated Ti-Zr-V NEG film is zirconium and titanium enriched. Residual oxide observed even on fully activated NEG surface consists mostly of zirconium and titanium low valence suboxides that are located mainly in the top surface layer. Carbides formed during the activation process remain on the surface and their concentration drops strongly with depth.     

Surface and bulk properties of mechanically activated zinc sulphide

BET, scanning electron microscopy, X-ray photoelectron, infrared, X-ray diffraction and Mössbauer spectroscopy methods were used to identify changes in surface, structural and spectroscopic properties of sphalerite produced by mechanical activation. Activated samples exhibit amorphization of crystallographic structure of the mineral, as well as of hyperfine structure of the accessory manganese. The presence of a new magnetic phase was disclosed in the samples activated for longer periods of time. Changes in structure are accompanied by mechanochemical oxidation of the surface layer of sphalerite.     

Surface resistivity studies on leached E-glass fabric

The direct-current resistivity of leached E-glass fabric was measured. The surface resistivity of the fabric increased on removing the alkali ions. The removal of the ions depended on the concentration of the acid and the leaching time. The surface resistivity of the fabric increased as the post heat-treatment temperature increased. However, on exposure to the atmosphere the surface resistivity decreased. The re-adsorption of water and the decrease in surface resistivity were found to be reduced in fabrics which were heated to higher temperatures. The residual alkali ions and the protons (of H₂O) were the conducting species.     

Interface studies on crystallized alumina-silica fibre-reinforced Al-Si alloy composites

On applying heat treatments to the amorphous alumina-silica fibre (55% Al₂O₃, 45% SiO₂), the mullite crystal is separated out, and the crystallinity depends on the heat treatment parameters. The crystallized alumina-silica fibre shows higher hardness than amorphous alumina-silica fibre and a remarkable stability to chemical reaction with molten metal. The primary interfacial reaction zone product was found to be 2MgO · SiO₂.     

二元合金薄膜的表面偏析

本文评述了广泛应用于描述平衡态和动态偏析的修正Darken模型。该模型首次提出了偏析的驱动力是化学势梯度,并成功地应用于定量描述体块材料的平衡态和动态的表面偏析。在考虑到薄膜体系中的尺寸效应后,引入了一个约束条件,再将其应用于修正的Darken模型,实现了在所有的浓度和薄膜厚度范围内,对合金薄膜体系的平衡态和动态的表面偏析的模拟计算。并利用该模型模拟了N(i111)Cu二元合金薄膜系统的平衡态和动态的表面偏析。     

Wear and microstructural studies of alloy sintered steels

Abstract

Crossed cylinder abrasive wear tests were carried out on alloy sintered steels T15, M2, and M42. The test parameters necessary for reproducible and reliable wear data have been studied. These parameters include applied load, time of test, abrasive grit size, speed of abrasion, and hardness of test specimen. Use has been made of the hypothesis of Archard to relate the test parameters to the wear rates found for these steels. Results show that Archard's hypothesis of abrasive wear holds for the conditions used in the test. The wear rates determined using this test method were found to be comparable to those observed in the use of these steels in industry and, therefore; it is considered that this method could be used to predict wear behaviour in service conditions. Using a replica technique on the polished and etched surfaces of these steels, it has been possible to make an assessment of the carbide size and distribution, both as number per cent and volume per cent. Examination of the microstructures of these steels showed a uniform distribution of carbide with a maximum size of 8 μm in a hardened and tempered steel matrix. The importance of microstructure in the characterisation of the wear behaviour of these alloy steels is discussed.

MST/1369