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NiTi/Stainless Steel (SS) sheets have been welded via a vacuum electron beam welding process, with three methods (offsetting electron beam to SS side without interlayer, adding Ni interlayer and adding FeNi interlayer), to promote mechanical properties of the NiTi/SS joints. The joints with different interlayers are all fractured in the weld zone near the NiTi side, which is attributed to the enrichment of intermetallic compounds including Fe2Ti and Ni3Ti. The fracture mechanisms of different joints are strongly dependent on the types of interlayers, and the joints without interlayer, adding Ni interlayer and adding FeNi interlayer exhibit cleavage fracture, intergranular fracture and mixed fracture composed of cleavage and tearing ridge, respectively. Compared with the brittle laves phase Fe2Ti, Ni3Ti phase can exhibit certain plasticity, block the crack propagation and change the direction of crack propagation. The composite structure of Ni3Ti and Fe2Ti will be formed when the FeNi alloy is taken as the interlayer, which provides the joint excellent mechanical properties, with rupture strength of 343 MPa.

As high-strength aluminum alloy for traction beam of high-speed rail, the fatigue strength of A7N01 aluminum alloy is particularly critical for its industrial application. In order to improve the fatigue strength of this aluminum alloy, three kinds of A7N01 aluminum alloy with different Si content were selected. The result indicates that, with the increase of Si element content, the fatigue strength is enhanced monotonously and meanwhile the dispersivity of S-N curves is largely reduced. Analyses of microstructure and the error of strength and hardness all indicate that the microstructure homogeneity of the alloy is improved when increasing the Si content, which is proved to be the main reason for the enhanced fatigue strength and reduced fatigue life dispersivity. Besides, it is found that the discontinuous distribution of the grain boundary precipitates due to the increase of Si content also contributes to the improved fatigue property.

Different artificial two-stage ageing behaviors and their effect on stress corrosion cracking (SCC) susceptibility of Al-Zn-Mg alloy have been investigated. The experimental results show that two hardness peaks present on the second-stage ageing-hardening curve when the first-stage ageing is dealt with comparatively lower temperature than the conventional one. The first peak is caused by dispersive and evenly distributed G.P. zones, while η′ phases and coarsened G.P. zones contribute to the second peak. Tensile strength of experimental alloy raises 9.6% (33.2 MPa) and SCC susceptibility decreases 38.9% by applying the second peak ageing regime instead of conventional T73. Al-Zn-Mg alloy obtains high strength and SCC resistance due to its finely dispersive matrix precipitates (MPts), coarsened and discontinuous grain boundary precipitates (GBPs), as well as the narrow precipitate free zone (PFZ) in the second peak ageing condition.

Influence of Sc content on microstructure and stress corrosion cracking behavior of medium strength Al–Zn–Mg alloy have been investigated by optical microscopy, scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy and slow strain rate test. The results indicate that the addition of Sc results in the formation of the quaternary coherent Al3(Sc, Zr, Ti) dispersoids during homogenization treatment, which will inhibit the dynamic recrystallization behavior. The number density of Al3(Sc, Zr, Ti) particles increases with the increase of Sc content, and thus the recrystallization fraction of hot-extruded alloy is reduced and the peak strength in two-stage artificial aging sample is enhanced. At the same time, the wide of precipitation free zone is reduced, and the content of Zn and Mg in grain boundary particles and precipitation free zone is increased with the increase of Sc content. In peak-aged state, the 0.06 wt% Sc added alloy shows the better stress corrosion cracking resistance than the Sc-free alloy because of the reduction of recrystallization fraction and the interrupted distribution of grain boundary precipitates along grain boundary. However, the further addition of Sc to 0.11 wt% will result in the deterioration of stress corrosion cracking resistance due to the increase of electrochemical activity of grain boundary particles and precipitation free zone as well as hydrogen embrittlement.

The microstructural evolution and mechanical properties of the 6082 alloys with different Mn content were systematically investigated to deeply understand the influence of Mn on the negative natural aging (NA) effect. It is found that α-Al(Mn,Fe)Si precipitated during homogenization is larger in size and less in amount in the alloy with lower Mn content, resulting in the less consumption of Si to create a relatively Si-rich environment in the matrix. The true Mg/Si ratio of alloy with higher Mn content is higher so that the alloy possesses a stronger negative natural aging effect. Additionally, four types of aggregates including clusters, GP zones, elongated β'' and β′ are present in the microstructures aged at 175 °C/8 h which is the peak artificial aging (AA) treatment in the two alloys. The number density of β'' and the total number density of the aggregates in alloy with lower Mn content is always higher than that in alloy with higher Mn content at the same heat treatment condition, which lead to the higher hardness and strength.

The effect of continuous extrusion forming (CEF) process on the microstructure and mechanical properties of a CuCrZr welding joint was investigated. The experimental results showed that after the CEF process the grains were refined to submicron-scale through dynamic recrystallization, which improved the mechanical properties of the welding joint as well as the base material. Meanwhile, the micron-scale precipitates aggregated at the grain boundaries in the welding process were broken down to smaller ones and recrystallized grains of several micrometers formed around the precipitates after CEF process, which could alleviate the negative effect induced by the micron-scale precipitates during plastic deforming process. Finer grains and smaller micron-scale precipitates made contributions to improve the properties of a CuCrZr alloy with a welding joint.

A Cu–0.16Cr–0.12Zr alloy with an initial grain size of about 400 μm was extruded by continuous extrusion forming (CEF), where severe plastic deformation and precipitation process occurred. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to examine the microstructure and morphology of the precipitates. Experimental results show that a notable grain size reduction to sub-micron scale is obtained through continuous dynamic recrystallization and precipitates maintain a fine and disperse morphology after the CEF process. These two features are considered as the effective ways to improve the strength and ductility of the CuCrZr alloy after cold deformation and subsequent aging process without a significant decrease of electrical conductivity.

Aluminium doping TaNx thin films were deposited on Al2O3 ceramic wafers by DC reactive magnetron sputtering. The influences of nitrogen partial flux on the phase structures and the electrical properties of the samples were investigated in detail. The results show that the main phases in the samples are gradually changed from poor nitrogen phases to rich nitrogen phases with the increase of the nitrogen partial flux. The deposition rate of the samples is decreased with the increase of the nitrogen partial flux. With the increase of the nitrogen partial flux, the resistivity and the absolute value of the temperature coefficient of resistance (TCR) of the samples increase slowly at lower nitrogen partial flux, and then increase remarkably at higher nitrogen partial flux. These experimental results can be explained by the presentation of rich nitrogen phases with higher resistivity and absolute value of the TCR when the samples were prepared at higher nitrogen partial flux.

NiCr-NiSi K-type thin film thermocouples with multi-layer structure were fabricated on Ni-based superalloy substrates (95 mm×35 mm×2 mm). The multi-layer structure contains NiCrAlY buffer layer (2 μm)/ thermally grown Al2O3 bond coating (200 nm)/ Al2O3 insulating layer (8 μm)/ NiCr-NiSi thin film thermocouples (1 μm)/ Al2O3 protecting layer (500 nm). The samples were statically calibrated in a tube furnace in the temperature range from 170 °C to 610 °C. The results show that the resistance of Al2O3 insulating layer is about 14.6 kΩ at 800 °C and exceeds 100 MΩ at room temperature. The Seebeck coefficient a of the samples is about 34 μV/°C, and the sensitivity coefficient K is greater than 0.8 in the temperature range from 170 °C to 610 °C. The maximal sensitivity coefficient is about 0.97 at 265 °C.

The effect of Mo addition on the microstructure, phase transformation, mechanical behavior and damping capacity has been investigated. It is found that the Mo addition depresses the solubility of Nb in the TiNi matrix and results in abundant dispersive Nb-rich precipitation. The R-phase transformation is induced in Ti-Ni-9.0 at.%Nb alloys by the substitution of Mo for Ni. The yield strength and rupture strength increase with increasing Mo content due to the precipitation strengthening of Nb-rich particles and the solution strengthening of the Mo, while the elongation remains at a high level. With the increment of Mo content, the damping in the martensitic state and the damping during the phase transformation are enhanced. The increment of the martensite volume fraction and the presence of abundant Nb-rich particles are responsible for the high damping in the martensitic state. The improvement of the damping properties during the phase transformation is related to the volume fraction of the transformed martensite phase per unit time and the contribution of the R-phase transformation. (C) 2009 Elsevier B.V. All rights reserved.

Self-propagating high-temperature synthesis (SHS) of porous NiTi alloy for hard tissue implants shows shape memory effect and superelasticity due to the B2 B19' transformation. In order to decrease the A(f) temperature to the human body temperature, 310 K, the effects of preheating temperature, thermal cycling and the third element Mo on the transformation temperatures were investigated using differential scanning calorimetry. The experimental results indicate that the preheating temperature has no obvious effect on the transformation temperatures; the transformation temperatures slightly decreased with increasing number of thermal cycles, but the At temperature was still above 310 K within 10 times; the addition of Mo decreased transformation temperatures considerably, and the R-phase transformation was induced during cooling. Transformation temperatures of porous TiNi(Mo) shape memory alloys with appropriate Mo contents fabricated by SHS meet the demands for human-body implants. (c) 2006 Elsevier B.V. All rights reserved.

The driving field of the magnetostrictive thin film actuator should be as small as possible in order to develop miniature devices. The aim of this paper is to reduce the driving field by varying the structural and the material parameters of the substrate of the cantilever in the actuator based on the finite element calculation. The influences of the geometric and the material parameters on the reference driving field have been studied. The results show that the reference driving field is sensitive to the length of the cantilever, the thickness of both the magnetostrictive film and the substrate, and also the Young's modulus of the substrate. The length of the cantilever should be long enough. In order to achieve a small driving field, the thickness of both the magnetostrictive film and the substrate should be carefully designed according to the ratio of the Young's modulus of the substrate to that of the film.

In this paper, the influences of depositing angles on TbFe film magnetic and magnetostrictive characteristics were discussed. TbFe films were deposited by DC magnetron sputtering. With the decrease of depositing angles from 900 to 150, TbFe film in-plane magnetization measured at 1600kA.m-1 external field is greatly increased. With the decrease of depositing angles from 900 to 150, the magnetostrictive saturation field is decreased. TbFe film in-plane magnetostriction is improved when depositing angles are changed from 900 to 150. Magnetic domain structures detected by MFM indicates that film easy magnetization direction is gradually changed from perpendicular to parallel with the decrease of depositing angles. The variation of film magnetic and magnetostrictive performances can be explained by the oblique anisotropy associated with columnar grain morphology of the films.

In this paper, the influences of annealing temperature on TbFe magnetostrictive film magnetic and magnetostrictive characteristics were discussed. TbFe films were prepared by RF magnetron sputtering. XRD patterns indicate that polycrystalline films consisting mainly of a-Fe and TbFe2 Laves phase could be obtained through rapid cycle annealing process (RCAP) at higher annealing temperature. Grain sizes could be controlled through varying annealing temperature. From film hysteresis loops measured by VSM, it has been found that the annealing treatment can improve TbFe film in-plane magnetization at 1600 kA.m-1 external field, and decrease in-plane coercivity. Magnetostriction of annealed TbFe films measured by optical cantilever deflectometer is better than as-deposited films at 40 kA.m-1 external magnetic field.