Ion mixing of the interface between TiNi films and glass substrates

Atomic mixing between TiNi metallic thin films and glass substrates, silica glass and borosilicate glass was induced by argon ion bombardment and investigated by means of Auger electron spectroscopy. 150 keV argon ion bombardment was carried out at room temperature to doses of 5x10¹⁶ and 1x10¹⁷ ions cm^-2. The Auger analysis demonstrated that significant intermixing occured at the TiNi-glass interface after argon ion bombardment and that the degree of atomic mixing varied, depending on the species of the constituent atoms. It was found that the titanium atoms were always transported deeper into the glass substrates than nickel atoms, and silicon atoms diffused into the TiNi overlayer more than oxygen atoms. The light boron atoms in borosilicate glass were found to diffuse least during argon ion bombardment. It was suggested that some metal silicides and oxides were formed in the reacted interface regions. Indentation-fracture tests revealed that the adhesion between the TiNi films and the glass substrates was improved substantially by argon ion mixing. The atomic mixing of each constituent atom was discussed qualitatively using a model of isotropic cascade mixing. The improved adhesion of the interface was thought to result from the interface mixing and the resultant formation of metal silicides and titanium oxides of various valence states in the interface region.     

Ion beam mixing of Ni/Ti bilayer thin films

Amorphization by ion beam mixing of bilayered samples consisting of nickel and titanium layers, each 50 nm thick, has been studied by selected area electron diffraction, plan and cross-sectional view transmission electron microscopy and Rutherford backscattering spectroscopy. Amorphization occurred on irradiation with 1 MeV Au⁺ ions at fluences ranging from 3 × 10¹⁹ to 2 × 10²⁰ m ⁻². Cross-sectional transmission electron microscopy revealed that amorphization starts close to the original Ni-Ti interface. It has been shown that collisional processes alone cannot account for the observed amount of mixing. A model based on thermodynamics has been found to predict an amount of mixing higher than that observed experimentally.     

Transformation characteristics of TiNi/TiNi alloys synthesized by explosive welding

Effects of severe deformation and heat treatment on the transformation behaviors of explosively welded duplex TiNi/TiNi shape memory alloys (SMAs) were investigated by the differential scanning calorimeter (DSC). The explosively welded duplex TiNi/TiNi plate of 0.7 mm in thickness was cold-rolled at room temperature to the extent of 60% reduction in thickness and then annealed at different temperatures (573–973 K) for different time (15 min–10 h). Low temperature (623–723 K) heat treatment led to amorphous crystallization. At higher temperature (873 K), the re-crystallization took place in the specimens. Analysis showed that the change of internal stresses is just the root cause of the change of transformation temperature. The relationships between the transformation behaviors and the heat treatment were discussed in the present report.     

Ni implantation-induced enhancement of the crystallisation of amorphous Si

We report on the effect of Ni implantation on the crystallisation process of amorphous Si formed by ion implantation during excimer laser annealing. Scanning transmission electron microscopy and X-ray photoemission spectroscopy results show that NiSi₂ precipitates are formed in the Si–Ni-implanted samples. It is shown that the Ni implantation results in the enhanced crystallisation of amorphous Si during laser annealing. The Si–Ni-implanted samples become epitaxial to the Si substrate at 600 mJ/cm², while the Si-implanted samples produce epitaxial relationship at 800 mJ/cm². Possible mechanisms by which implanted Ni atoms play a role are given to describe the enhanced crystallisation process of amorphous Si.     

Crystallization of amorphous Ni60Nb40

The crystallization of Ni₆₀Nb₄₀ metallic glass during continuous heating and isothermal annealing at temperatures from 845 to 904 K, was studied by differential scanning calorimetry (DSC), electrical resistance measurements, X-ray diffraction and transmission electron microscopy. Crystallization occurred in four clearly defined stages. In the initial stage a metastable phase, with structure similar to the M-phase in the Ni-Nb-Al ternary system, forms in the amorphous matrix. In the two subsequent stages the remaining glass crystallizes to the Ni₃Nb- and-phases found in the equilibrium Ni-Nb phase diagram. The M-phase transforms into the equilibrium Ni₃Nb- and-phases only at high temperature. The crystallization of the M-phase could be described by Johnson-Mehl-Avrami kinetics with the time exponentn=1.3 and activation energyE ₁=628 kJ mol^–1. M-phase crystal growth was apparently diffusion controlled and the diffusion coefficient was estimated to be 4.2×10^–20 m² sec^–1. Activation energies for the second and third stages of crystallization were found to beE ₂=446 kJ mol^–1 andE ₃ = 430 kJ mol^–1.     

Martensitic Transformation of TiNi Shape Memory Alloy Fiber Reinforced Ni Matrix Composites

In this paper, a TiNi shape memory alloy fiber Ni matrix composite was fabricated by an electroplating method using TiNi alloy as the cathode and Ni as the anode. The constrained martensitic transformation behaviors of the TiNi alloy were studied by differential scanning calorimeter (DSC), and the results showed that two endothermic peaks appear on the DSC heating curves and the reverse transformation temperatures increase with increasing prestrain levels. Moreover, comparing to the free transformation, the temperature window of the constrained reverse transformation is widely expanded due to the influence of recovery stress.     

Transformation behavior of explosively welded TiNi/TiNi laminate after diffusion annealing and aging

This paper reports the creation of compositionally graded NiTi plates with widened transformation temperature windows by means of diffusion annealing and aging of explosively welded (Ti-50.4 at.%Ni)/(Ti-49.8 at.%Ni) laminates. The transformation behavior of the laminate was investigated by means of differential scanning calorimetry. The laminate samples after diffusion annealing and aging showed greatly enlarged reverse transformation temperature window of 70–90 °C, about twice wide as that of the Ti-50.4 at.%Ni alloy.     

Laser welding of TiNi shape memory alloy and stainless steel using Ni interlayer

Laser welding of TiNi shape memory alloy wire to stainless steel wire using Ni interlayer was investigated. The results indicated that the Ni interlayer thickness had great effects on the chemical composition, microstructure, gas-pore susceptibility and mechanical properties of laser-welded joints. With an increase of Ni interlayer thickness, the weld Ni content increased and the joint properties increased due to decreasing brittle intermetallic compounds (TiFe₂ and TiCr₂). The joint fracture occurred in the fusion zone with a brittle intermetallic compound layer. The tensile strength and elongation of the joints reached the maximum values (372 MPa and 4.4%) when weld Ni content was 47.25 wt.%. Further increasing weld Ni content resulted in decreasing the joint properties because of forming more TiNi₃ phase, gas-pores and shrinkage cavities in the weld metals. It is necessary to select suitable Ni interlayer thickness (weld composition) for improving the mechanical properties of laser-welded joints.     

Reaction zone formed during diffusion bonding of TiNi to Ti6Al4V using Ni/Ti nanolayers

This study investigated the interfacial structure of solid state diffusion bonding of TiNi to Ti6Al4V using reactive Ni/Ti multilayer thin films. The TiNi and Ti6Al4V surfaces were modified by sputtering, by deposition of alternated Ni and Ti nanolayers, to increase the diffusivity at the interface. Bonding experiments were performed at 750, 800 and 900 °C at a pressure of 10 MPa with a dwell time of 60 min. The reaction zone was characterized by high-resolution scanning and transmission electron microscopy. Joints free from porosity and cracks were produced with Ni/Ti reactive multilayer thin films. Several phases formed at the interface, ensuring the bonding of these alloys. The reaction zone was constituted by columnar grains of Ti₂Ni and AlNi₂Ti, close to the Ti6Al4V base material, and by alternate layers of Ti₂Ni and TiNi equiaxed grains. The grain size decreased from Ti6Al4V to TiNi base materials. Nanometric grains were observed in the layers closest to the TiNi base material.     

Electronic structure of amorphous semiconductors

The effect of light soaking and thermal quenching on the electronic structure of hydrogenated amorphous silicon (a-Si:H) and chalcogenide glasses was studied. It was found that lithium dopeda-Si:H shows both light and thermal induced changes in electronic transport properties. In contrast, chalcogenides do not show any effect of thermal quenching, although they exhibit changes upon light soaking. By analysing the conductivity and thermopower data we have concluded that the light soaking increases the potential fluctuations present in lithium dopeda-Si:H, whereas quenching does not change them. A model qualitatively explaining these effects is presented.     

Formation of Ni2Si silicide in Ni/Si bilayers by ion beam mixing

We have studied ion mixing in Ni-Si(1 1 1) bilayers using noble gas ions. Thin Ni films of 45 nm thickness, deposited on a Si (1 1 1) substrate, were irradiated with 175 keV Kr and 110 keV Ar ions at the same fluence of 4×10¹⁶ ions/cm² at room temperature. The formation of the mixing and the elemental depth profile were investigated by Rutherford backscattering spectrometry. In the Ar irradiated sample, there was no structural change. On the other hand, we have noted the formation of Ni₂Si for the sample irradiated with Kr ions. X-ray diffraction measurements confirmed the formation of the Ni₂Si phase. The surface morphology of the Kr irradiated sample was also studied by scanning electron microscopy.     

Hydrogen embrittlement fracture of notched amorphous Ni alloy specimens

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

大块非晶合金Zr55Cu30Al10Ni5的电子结构特征及电击穿行为

测定了大块非晶合金Zr55Cu30Al10Ni5晶化前后的费米能级和各元素的电子结合能,研究了非品合金的电子结构特征和电击穿行为．测试并讨论了非晶材料场发射能力和耐电压强度的关系．结果表明,对于Zr基合金,非品态比品态合金具有更大的功函数．比较了Zr55Cu30Al10Ni5合金非晶态与晶态的耐电压强度数值,发现非晶态合金的耐电压强度数值比较分散,品化合金的耐电压强度相对比较集中．耐电压强度平均值表明,Zr基合金非晶态具有更好的耐电压能力．     

Electric and magnetic properties of ferromagnetic/piezoelectric bilayered composite

One of the most promising ways for the realization of multi-functional materials is the integration of oxides with different properties in artificial heterostructures. In this paper, a novel piezoelectric–ferromagnetic heterostructure consisting of 0.92Na_0.5Bi_0.5TiO₃–0.08BaTiO₃ (abbreviated as BNT–BT_0.08) and CoFe₂O₄ layers is fabricated on Si–Pt substrate, by sol–gel method coupled with spin-coating technique. The composite thin film shows only perovskite Bi_0.5Na_0.5TiO₃-like rhombohedral phase and CoFe₂O₄ cubic phase. The thickness of CoFe₂O₄ and BNT–BT_0.08 layers is ~?280 and?~?400 nm, respectively. BNT–BT_0.08/CoFe₂O₄ heterostructure thin film shows a saturation magnetization of 0.11 emu/g at 5 K and 0.07 emu/g at 295 K, dielectric constant of 235 at 1 kHz and tunability of 70% at 1 kHz and an electric field E?=?110 kV/cm. The results reveal that the investigated hybrid piezoelectric/ferromagnetic structure shows piezoelectric behavior, good ferroelectric and ferromagnetic properties. This bilayer composite can be used in miniature low-frequency magnetic sensor and piezoelectric sensor for biomedical domain.     

The structure of amorphous silicon telluride

The radial distribution functions which were obtained from X-ray diffraction measurements of Te₇₈Si₇₂ and Te₈₇Si₁₃ between 6.5 and 470 K compared well with those calculated from a model based on the intersection of Te, Si chains, where Si is common to both chains. Si has four Te neighbours in tetrahedral coordination and Te has two neighbours. The mean-square displacements of the atoms were calculated from the widths of the peaks in the radial distribution function and from the Debye-Waller factor.     

Ion-beam-induced modification of the electrical properties of vacancy-doped mercury cadmium telluride

The effect of ion-beam milling (IBM) on the electrical properties of vacancy-doped mercury cadmium telluride (MCT) p-Hg_1−x Cd _x Te (x ∼ 0.22) has been studied. The samples were prepared by thermal annealing of molecular beam epitaxy (MBE)-grown heterostructures and the films and single crystals grown by liquid-phase epitaxy (LPE). The etching of samples by IBM resulted in the formation of donor centers. In MBE-grown heterostructures (but not in LPE-grown samples), the concentration of these centers reached ∼10¹⁷ cm⁻³. It is established that the appearance of a high concentration of donor centers in the heterostructures is caused by the IBM-induced activation of neutral defects formed during epitaxial growth. The probable nature of defects is discussed.