Observations on the mechanical properties of nickel oxide scales

The mechanical properties of NiO scales produced by the complete oxidation of high-purity (grade-1) Ni and commercial-purity (grade-A) Ni have been investigated at 700 to 1000 C. The modulus of elasticity of both grades of oxide decreased with increasing temperature, whereas the modulus of rupture for grade-A oxide exhibited a maximum at 850 C and that for grade-1 oxide decreased with increasing temperature. At 700 C, elastic deformation to fracture occurred with both oxides, whereas, at temperatures 850 C, plasticity was also observed. The plasticity of grade-1 oxide was 3 times greater than that of grade-A oxide.Creep behaviour of the oxides was studied at 900 and 1000 C. Primary and secondary creep was observed and, in both oxides, the creep rates increased with increasing temperature and load. The creep rate of grade-1 oxide was 10 to 20 times greater than that for grade-A oxide.     

Effect of Ni interlayer on strength and microstructure of diffusion-bonded Mo/Cu joints

Mo and Cu were bonded successfully by means of diffusion bonding using a Ni interlayer. The tensile strength of the joint increases firstly and then decreases with the bonding temperature or holding time increases. Compared with 79 MPa which was the maximum value of Mo/Cu joint, the maximum tensile strength of joint with Ni interlayer was 97 MPa. The interfacial structure of the joints was studied by SEM, EPMA, EDS and XRD, the results showed that the different atoms diffused to each other in the bonding process and no intermetallic compound appeared. MoNi and NiCu solid solutions formed in the joint. The fracture of the joint had taken place in the Mo/Ni interface rather than in the Ni/Cu interface and the fracture way of the joints was brittle fracture.     

Nucleation and growth of ion beam sputtered metal films

Transmission electron microscope observations have been made on ion beam sputtered (IBS) films of Cu, Au, Pt and Ni (of predetermined thicknesst 0.5 nm) deposited on amorphous carbon substrates. The influence of IBS parameters on particle size distribution and deposition rate has been measured, also the fractional substrate coveragef as a function oft which indicates three-dimensional island growth in Au, Cu films and two-dimensional growth in Pt, Ni films. Electron diffraction measurements appear to show that the f.c.c. metal particles grow with (1 1 0) parallel to the substrate with, in the case of Ni, a critical island thickness of 0.8 nm.     

Electrical and optical properties of vacuum-evaporated CdS films

1 m CdS films for the window layer of CdS/CulnSe₂ solar cells have been prepared by vacuum evaporation at various deposition conditions. Deposition rates were 0.73 and 3.3 nms^–1, and substrate temperature ranged from 50 to 225 C. The effect of the deposition conditions on the properties of CdS films was investigated by measuring electrical resistivity, optical transmittance and reflectance.The resistivity of the evaporated CdS films strongly decreased as substrate temperature decreased and the films with high deposition rate showed lower resistivity compared to the films with low deposition rate. Interestingly, the combination of high deposition rate and very low substrate temperature resulted in an increase of resistivity. The optical transmittance of CdS films increased as substrate temperature decreased and then decreased with further decrease in substrate temperature. The transmittance strongly depended on deposition rate at low substrate temperature (<100C), while it was independent of deposition rate at high substrate temperature (>100C). In particular, high transmittance can be extended to lower substrate temperature by reducing deposition rate. Low optical reflectance can be obtained by lowering substrate temperature. The results indicate that CdS films of low resistivity and high transmittance can be produced by vacuum evaporation at low substrate temperature and low deposition rate.     

Copper coating on carbon fibres and their composites with aluminium matrix

A uniform and continuous coating of copper was given to carbon fibres by cementation or electroless techniques. In both cases, when coating thicknesses were less than 0.2 m, copper deposition was discontinuous over the fibres, and above 0.2 m, coatings were continuous. In electroless coating, about 75% of the continuously coated fibres had a coating thickness range 0.2–0.5 m and above this showed isolated dendrite deposits of copper. In the cementation process, about 75% of the continuously coated fibres had a coating thickness range 0.2–0.6 m, and above this thickness, fine crystallite-type copper deposition was found over smoothly coated copper. The ultimate tensile strength of continuously electroless-coated fibres were nearer to the uncoated fibres, suggesting defect-free coating, while fibres coated by the cementation process exhibited lower ultimate tensile strength values. The tensile fracture of both electroless- and cementation-coated fibres showed delamination of the coating, suggesting poor bonding between coating and the fibre. In composites, prepared by dispersing the coated chopped fibres in a pure aluminium matrix, uniform and random distribution of the fibres were observed without appreciable fibre-metal interaction. The CuAl₂ intermetallics were largely found in the matrix and only very small amounts were observed at fibre/matrix interfaces. Additions of about 2 wt% Mg to the matrix prior to the fibre dispersion did not appreciably change the distribution pattern of the fibres, but in addition to CuAl₂ phase, Mg₂Si phases were observed in the matrix as well as at the interface.     

Effect of composition and grain size on slow plastic flow properties of NiAl between 1200 and 1400 K

A series of 15 m diameter, polycrystalline B2 crystal structure NiAl alloys ranging in composition from 43.9 to 52.7 Al (at%) have been compression tested at constant velocities in air between 1200 and 1400 K. All materials were fabricated via powder metallurgy techniques with hot extrustion as the densification process. Seven intermediate compositions were produced by blending various amounts of two master heats of prealloyed powder; in addition a tenth alloy of identical composition, 48.25 AI, as one of the blended materials was produced from a third master heat. Comparison of the flow stress-strain rate behaviour for the two 48.25 AI alloys revealed that their properties were identical. The creep strength of materials for AI/Ni 1.03 was essentially equal, and deformation could be described by a single stress exponent and activation energy. Creep at low temperatures and faster strain rates is independent of grain sizes and appears to be controlled by a subgrain mechanism. However, at higher temperatures and slower strain rates, diffusional creep seems to contribute to the overall deformation rate.     

Preparation and properties of ZnS thin films by low-pressure metalorganic chemical vapour deposition

Low-pressure metalorganic chemical vapour deposition of ZnS thin films on silicon, oxidized silicon and glass substrates using Zn (C₂H₅)₂ and C₄H₄S as source chemicals was investigated. The growth process and the film properties were characterized as functions of process parameters including substrate temperature, reactant ratio and reaction pressure. In general, growth rates as a function of substrate temperature were found to reach a maximum at a much lower temperature than that for growth at atmospheric pressure. In addition, growth rates increased with reaction pressure and thiophene flow rate depending on the temperature condition. The microstructure indicated that growths above 250°C possess a cubic (zincblende) structure, while growths below 150°C are polycrystalline of wurtzite structure. The resistivity varies from 10⁴ cm to a maximum of about 3×10⁵ cm for growth at 250°C, depending on the reactant ratio. The details are discussed in the text.     

Structural and optical properties of microcrystalline silicon films deposited by plasma enhanced chemical vapour deposition

Hydrogenated microcrystalline (c) silicon films were prepared by plasma enhanced chemical vapour deposition using an Ar-diluted SiH₄ gas at various deposition conditions. The substrate temperature and RF power were varied from 150 to 400 C and from 10 to 120 W, respectively. Structure and microstructure were examined by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Hydrogen bonding and optical properties were investigated by FTIR spectra and UV transmission spectra. The crystal fraction of the films increased as the deposition temperature decreased and RF power increased. More definite columnar morphology was developed with increasing crystal fraction. The existence of c-Si above a critical RF power (>30 W) suggests that SiH₂ radical in plasma plays an important role for the formation of columnar morphology and c-Si. IR absorption analysis showed that the SiH₂/SiH bonding ratio in the silicon films increased as the crystal fraction increased. The UV absorption coefficient of the films became smaller as the deposition temperature and RF power increased.     

Ni-Cu-P化学镀工艺及组织结构的研究

研究了Ni-Cu-P化学镀液主要成分、PH值、温度以及时间等工艺参数对化学沉积Ni-Cu-P合金镀层成分及镀速的影响。通过选择适当的镀液成分及工艺参数,得到了Cu含量从0到56．18wt%的Ni-Cu-P合金镀层。利用EDS和XRD研究了镀液中硫酸铜浓度对Ni-Cu-P合金镀层组织结构的影响。在硫酸铜浓度低于3g/L时,Ni-Cu-P合金镀层中P含量高于7．05wt%,合金镀层是非晶态结构。     

High-temperature flow behaviour and concurrent microstructural evolution in an Al-24 wt% Cu alloy

Tensile specimens of an Al-24 wt% Cu alloy of grain sizes in the range 7.6–20.6 m were deformed at 400–540 °C using constant initial strain rates ranging from 5×10^–6 to 2×10^–2 s^–1. Initially the stress-strain (-) curves show work hardening which is followed by strain softening at higher strain rates and lower temperatures. At lower strain rates and higher temperatures, on the other hand, continues to increase with strain or tends to be independent of strain. Grain growth and cavitation occur to varying extents depending on strain rate and test temperature. While the grain growth can account for the work hardening at higher temperatures as well as at lower strain rates, it fails to do so at higher strain rates. The strain softening is associated with cavitation. The presence of non-steady-state flow influences the parameters of the constitutive relation to varying extents.     

Formation,thermal stability and mechanical properties of amorphous alloys in the Mg-transition metal(Ni,Cu)-alkaline-earth metal(Ca,Sr, Ba) system

Mg-Ni-Ca, Mg-Ni-Sr, Mg-Ni-Ba and Mg-Cu-Ca alloys were found to be amorphized by melt-spinning in the compositional ranges 0 to 30% Ni and O to 40% Ca, 5 to 20% Ni and 0 to 15% Sr, 10 to 25% Ni and 0 to 15% Ba, and 0 to 50% Cu and 0 to 35% Ca, respectively. In the amorphous Mg-Ni-Ca and Mg-Cu-Ca alloys, the glass transition was observed in the ranges of 7.5 to 15% Ni and 2.5 to 5% Ca and 10 to 40% Cu and 2.5 to 7.5% Ca, respectively. The crystallization temperature (T _x) of amorphous Mg-Cu-Ca alloys increases with increasing Cu content, while T _x for amorphous Mg-Ni-Ca and Mg-Ni-Sr alloys shows a maximum value of 459 and 471 K, respectively, at 15% Ni. The glass transition temperature (T _g) increases monotonously with increasing Ni or Cu content. Amorphous Mg-Ni-Ca and Mg-Ni-Sr ribbons containing more than 80% Mg have a good bending ductility and the highest tensile fracture strength (_f) reaches 690 and 680 MPa, respectively. The ratios of _f to density are nearly equal to those for previously reported Mg-Ni-(Y or Ln) amorphous alloys with higher _f values because of the low densities of the present Mg-based alloys.On leave from Yoshida Kogyo K.K., Yoshida Krobe Toyama Pref. 938, Japan.     

Computer simulation of the interface in Cu/Ni multilayer films

X-ray diffraction of Cu/Ni (1 0 0) bicrystalline multilayer thin films was studied by atomistic simulation. Atomic position equilibrium was reached by using a molecular dynamics method to simulate interface structure with Morse potentials to model interatomic interactions. It was found that X-ray profiles were sensitive to the interface structure and some extra peaks appeared other than the regular peaks of copper or nickel crystals. The number of extra peaks increased with increasing modulation length of the multilayer. The extra peaks result from the diffraction between interfaces and also from the diffraction of the modulated structure. The variation of spacing normal to the interface could be described as a near-square wave. The interface region approximately includes five atomic layers for Cu/Ni (1 0 0) multilayer thin film when its modulation length is not too small. When the modulation length is small enough, the interface regions overlap, and the average atom potential energy is high.     

Effect of the surface oxide layer on transformation behavior and shape memory characteristics of Ti-Ni and Ti-Ni-Mo alloys

Oxidation behaviors of Ti-49Ni and Ti-48.3Ni-0.7Mo (at.%) alloys in dry air from 723 K to 1273 K have been investigated by means of scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, and then effects of oxidation on transformation behavior and shape memory characteristics of the alloys were studied by means of differential scanning calorimetry and thermal cycling tests under constant load. Three-layered surface scale was formed in both alloys oxidized at temperatures higher than 1023 K, consisting of an outer TiO₂ layer, an intermediate layer of mixture of TiO₂ and Ni and an inner TiNi₃ layer. Thickness of the surface oxide layer increased from 1 m to 50 m with raising oxidation temperature from 923 K to 1273 K. The surface oxide layer raised transformation temperatures associated with the B2-B19 and the R-B19 transformation, while it did not almost change transformation temperatures associated with the B2-R transformation. Recoverable elongation was not changed in the alloys oxidized at temperatures below 823 K with raising oxidation temperature, whereas it decreased in the alloys oxidized at temperatures above 923 K. Transformation hysteresis was not almost changed by oxidation in a Ti-49Ni alloy, but it decreased largely in a Ti-48.3Ni-0.7Mo alloy.     

The effect of silica characterization on the microstructure of BaFe12O19 ferrites

The anisotropically formed BaFe₁₂O₁₉ ferrites were prepared from the hot-rolled mill scale and silica was added to the ferrite during fine milling in the range 0.15 to 0.50 wt%. These ferrites were sintered at 1220° C for 2 h. The grain growth of the ferrites is dominantly influenced by the sizes of the silica added. Coarse-grain ( 1m) silica tends to promote discontinuous grain growth, which increases drastically with slightly increasing amounts of silica added, while fine-grain ( 0.013m) silica tends to retain fine grain microstructures with the same increasing amount of silica. The average grain size of the ferrite without silica addition was 8 to 10m. The size was increased to as large as 30m on addition of 0.15% coarse-grain silica and the microstructure was full of extremely large grains on the addition of 0.50% coarse-grain silica.     

An investigation of the effects of thickness on mechanical properties of LIGA nickel MEMS structures

This paper examines the effects of thickness on the mechanical properties of LIGA Ni MEMS structures plated from sulfamate baths. The as-plated LIGA Ni specimens of different thickness (50 m, 100 m and 200 m) were utilized in the microtensile experiments. Optical microscopy, orientation imaging microscopy and scanning electron microscopy were used to characterize the microstructure of the LIGA Ni specimens. Fracture Modes obtained from specimens with different thickness were revealed by scanning electron microscopy. The effects of specimen thickness are then discussed within the context of strain gradient plasticity theories.     

Ni-doping effect on the anisotropic resistivity in Bi2Sr2Ca(Cu1−xNix)2Oy single crystals

When Ni is substituted for Cu in Bi-2212 single crystals, the in-plane resistivity is increased with maintaining the linear temperature dependence while the out-of-plane resistivity is decreased. The anisotropy parameter estimated from the angular dependence of the flux flow resistivity is also decreased from 250 for undoped sample to 80 for a sample doped with 2.4% of Ni. The doping dependence of _ab and _c is discussed on the basis of the t-J model and the Fermi liquid theory.     

Hardness of bi-layer films on a leadframe substrate

The indentation hardness and elastic modulus of leadframe materials that consist of Cu alloy substrate and Ni/Pd bi-layer films of differing thicknesses are characterised using the micro-hardness and nano-indentation tests. The true hardness of the individual substrate and film layers is evaluated based on the empirical relationship between the measured composite hardness and the volume of plastically deformed material of film layers. It is found that the composite hardness determined from the nano-indentation test increases rapidly toward a peak at extremely low indentation depth of less than about 20–30 m for all materials studied, due mainly to the finite value of the indenter tip radius and the rough surface of the specimen on the nano-scale. The composite hardness for the coated specimens decreases with further increasing indentation depth toward the hardness value of the substrate, because of the strong influence of the film/substrate interaction and the indentation size effect. The nano-indentation test in general gives higher true hardness values than those obtained from the micro-hardness test. Nevertheless, the relative hardness values of the substrate and films determined from the two tests are consistent. The hardness of Ni film is about 20 to 50% greater than that of Cu alloy, whereas the hardness of Pd film is 7 to 11 times the Ni film in the nano-indentation test.     

Microstructural characteristics and carbon content of Al2O3 films as a function of deposition parameters

Microstructural characteristics and carbon content in aluminum oxide thin films deposited on silicon substrates are reported as a function of deposition parameters such as substrate temperature and molar concentration of the spraying solution. The films were deposited using the spray pyrolysis technique from a spraying solution of aluminum acetylacetonate (Al(acac)₃), dissolved in N,N-dimethylformamide (N,N-DMF), at temperatures in the range from 500 to 650 °C. Water mist was added during the deposition process and no further post deposition thermal treatments were given to these films. The films have a stoichiometry close to that expected for Al₂O₃, although, residual carbon from the deposition process was found to be present in these films. The surface roughness of the films was less than 20 , with deposition rates up to 540 /min, low chemical etch rates and activation energies around 27.6 kJ/mol were also determined. High resolution transmission electron microscopy observation of these films show the presence of a tiny 5Al₂O₃ : H₂O crystalline phase embedded in a dense amorphous matrix. It was found that the average crystallite diameter of this phase depended on the deposition temperature as well as on the molar concentration of the spraying solution.     

Preparation of CuInSe2 thin films by selenization of co-sputtered Cu–In precursors

CuInSe2 thin films have been prepared by high Se vapor selenization of co-sputtered Cu–In alloy precursors within a partially closed graphite container. Cu–In alloys with different compositions were investigated. X-ray diffraction (XRD) analysis of the films showed mainly CuIn2 and Cu11In9 phases and the Cu11In9 peak intensity was found to increase as the alloy composition tended towards Cu-rich. A linear dependence of the alloy composition on the Cu/In deposition power was observed from energy dispersive analysis by X-rays (EDX). A three-fold volume expansion was exhibited by all the CuInSe2 films after selenization at 500–550 °C. Scanning electron microscopy (SEM) analysis of the films showed large and densely packed crystal structures with sizes above 5 m. The CuInSe2 films exhibited single phase chalcopyrite structure with preferential orientation in the (1 1 2) direction. The EDX composition analyses of the films showed Cu/In ratio ranging from 0.43 to 1.2, and Se/(Cu+In) ratios from 0.92 to 1.47. The measured film resistivities varied from 10-1 to 105 cm. The Cu–In alloy precursors with Cu/In ratio less than 0.70 were found to form CuIn3Se5 a defect chalcopyrite compound. All films were Se rich, with the exception of samples with very high Cu content.© 1998 Kluwer Academic Publishers     

The solidification and mechanical properties of chill-cast AI-AI3IMi and AI-AI2Cu eutectic alloys

This paper describes the effect of chill-casting on the solidification behaviour and mechanical properties of the AI-AI₃Ni and AI-AI₂Cu eutectic alloys. Cellular microstructures were obtained by casting the eutectic alloys into preheated split-steel moulds mounted on either a water-cooled or plain copper chill, to promote growth along the length of the ingot and not radially from the mould wall. This produced the required cellular microstructure with good alignment of AI₃Ni fibres or AI₂Cu lamellae within the cells, with an interfibre/interlamellar spacing of 1 m. The experimental solidification results showed an increase in solidification rate with increasing distance from the chill associated with a decrease in interfibre/interlamellar spacing along the length of the solidifying ingot. There were no significant variations in the room-temperature tensile properties of the two chill-cast aluminium based eutectic alloys for the various casting conditions. Variations in solidification rate along the ingots for the different chill-casting conditions were not sufficient to affect the stress-strain behaviour of the chill-cast alloys. The room-temperature tensile behaviour of the chill-cast AI-AI₃Ni eutectic alloy was very similar to, and that of the AI-AI₂Cu eutectic alloy significantly different from, those obtained by Lawson and Kerr. The ultimate tensile strengths of the chill-cast eutectic alloys were not as high as those of the corresponding unidirectionally-solidified eutectic alloys prepared at a slow and constant solidification rate although the reasons for this were different for the two alloys. The ultimate tensile strength of the chill-cast AI-AI₃Ni eutectic alloy was found to be in reasonable agreement with that expected from the rule of mixtures for discontinuous fibre reinforcement.