Recently, porous NiTi shape memory alloys (SMAs) have drawn great interest in various engineering fields, in particular for biomedical applications as one of the promising biomaterials for hard-tissue replacements and orthopedic implants. It is well known that the porous NiTi SMAs exhibit three transformations, B2-B19', B2-R and R-B19'. Among these phase transformations B2-B19' and R-B19' involve high lattice distortion and large transformation hysteresis. Consequently, these distortion and transformations usually introduce structural defects which may result in degradation of mechanical stability for the functional application. On the contrary, B2-R transformation is governed by small lattice distortion which indicates less damage to the microstructure and lower sensitivity to the defects, and thus generates higher reversibility and mechanical stability. Due to these unique virtues, it is of great importance to study the R-phase transformation behavior in porous NiTi SMAs, since the pore has a significant influence on B19' martensitic transformation as well as the R-phase transformation. In this paper, a three-dimensional phase field model aiming at accounting for the pore effect on phase transformation in NiTi SMAs was developed to study the B2-R phase transformation behavior in porous NiTi SMAs. The model was applied to characterize the microstructure evolution of B2-R phase transformation as well as the influence of porosity ratio and pore size on growth kinetics of R-phase variants. The simulation results show that the R-phase variants can form three-dimensional banded structure and two-dimensional herring-bone microstructure through self-accommodation between R-phase variants. The R-phase variants nucleate preferentially around the pores, and there are more R-phase variants to nucleate around the large pores than the smaller ones. Two types of twinning planes are found, which are {101}B2 and {001}B2 respectively, and four variants meet at <010>B2. It has been shown that the average size of R-phase variants decreases with increasing porosity ratio, but increases with increasing pore size. Moreover, the average size of R-phase variants decreases in NiTi system containing irregular pores compared to that the system containing regular circular pores. The size uniformity of R-phase variants increases with increasing porosity ratio but shows no sensitivity to pore size and pore shape. It is also shown that the B2-R transformation can generate uniform and fine R--phase microstructure only when the NiTi matrix contains a large number of small size pores.

The deformation behavior of AZ31 Mg alloy was studied in the temperature range from 523 to 723 K under a strain rate of 3×10^-3 s^-1. Cuboid samples with different orientations were machined from an extruded rod along angles of 0^o, 45^o and 90^o to the extrusion direction, respectively. The effects of original orientation on microtexture evolution were analysed by OM and SEM/EBSD techniques. The results showed that the true stress-true strain curves were sensitive to original orientation especially below 623 K. Extensive {1012} tension twins were formed at 523 K in the 0^o samples and the volume fraction of twins increased rapidly to 90\% at a strain of ε=0.3. Namely, the basal planes initially parallel to the compression axis rotated quickly by twinning to an orientation perpendicular to the compression axis. In contrast, the volume fraction of {1012} twinning in the 45^o or 90^o samples was lower than 10%. The initial texture in the 90^o sample scarcely changes and the relative intensity decreased with increasing strain.

Ni-Cu-P steel is well known as a seawater corrosion resistance steel due to strong corrosion resistance in marine splash zone. However, corrosion resistance mechanisms of alloying elements in Ni-Cu-P steel remain unclear. Because the steel exhibits obvious characteristic of pitting corrosion in marine splash zone, rust layers and pitting corrosion resistance were investigated in this study. The experimental steels were smelted in vacuum induction melting furnace. In order to evaluate the corrosion resistance of Ni-Cu-P steel, hanging plate test was performed in marine splash zone for 660 d. Rust layers formed on the steel surfaces were studied by means of scanning electro microscopy (SEM), energy dispersive analysis of X-ray (EDAX), Fourier transform infrared resonance (FTIR) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The results indicated that average corrosion rate and pit penetration of Ni-Cu-P steel was obviously smaller than that of carbon steel after exposure test. For all the steels, the inner and outer rust layers were composed of α-FeOOH, β-FeOOH, γ-FeOOH, δ-FeOOH, Fe₃O₄ and a small amount of amorphous oxides. However, the inner rust layer exhibited higher content of Fe₃O₄ and lower content of γ-FeOOH and δ-FeOOH than the outer rust layer. Under the same condition, the rust layers both in macro cathodic region and pits of Ni-Cu-P steel were much more compact than those of carbon steel. According to the composition and distribution of alloying elements, Ni, Cu and P were mainly observed in the inner rust layer and pits, and Cu and P were found to enrich in pits. In macro cathodic region, alloying element Cu made inner rust grains small and dense.  In corrosive pits, Cu was observed to enrich around inclusions in the rust layer, which could repair and fill the slots and holes of the rust layer in pits. Additionally, addition of alloying elements Cu and Ni improved potential of matrix in pits, and alloy element P led to a decrease in the corrosion rate of matrix. Therefore, Ni-Cu-P steel exhibited stronger pitting corrosion resistance than carbon steel.

Low carbon steel has been studied as one candidate material of the outer container used in the geological disposal of the high-level radioactive nuclear waste. The active/passive state of the steel is the most important factor in maintaining the service life of the container. The active state will ensure that the container achieve the designed life under general corrosion, and moreover, the passive state will degrade the container's life under stress corrosion cracking (SCC) caused by pitting corrosion. In the groundwater, a lot of chemical compositions have very complicated effects on the active/passive state of the low carbon steel. Among these factors, obviously, the pH values of the ground water and the corrosion products of the low carbon steel would be the most important factors. In this paper, the influences of pH values and corrosion products on the susceptibility of the low carbon steel in the deaerated borate buffer solutions were studied. The results showed that the corrosion product did not change the corrosion potential of the low carbon steel at a pH value of 8, which means that the steel was in the active state, while the corrosion product made the corrosion potentials of low carbon steel move to the passive state at pH values of 9 and 10. XPS and XRD analyses indicated that the corrosion products were composed of Fe₆(OH)₁₂B₄O₇ and γ-FeOOH. The low carbon steel with corrosion products was passivated more easily than the naked steel substrate.

The effect of Cr addition on the transformation and the cyclic deformation characteristics in 550℃ annealed Ti-50.8Ni shape memory alloy (SMA) were investigated by differential scanning calorimetry (DSC) and tensile test. The B2→R→M/M→B2 type reversiable transformation occurred in Ti-50.8Ni alloy upon cooling/heating. After the addition of 0.3%Cr in Ti-50.8Ni alloy, the transformation type for Ti-50.8Ni-0.3Cr alloy was B2→R→M/M→R→B2, and the transformation temperatures decreased significantly. At room temperature, the phase composition was parent phase B2 for both Ti-50.8Ni and Ti-50.8Ni-0.3Cr alloys, while the former showed shape memory effect; the latter showed superelasticity. With increasing cyclic deformation number n, Ti-50.8Ni alloy evolved from shape memory effect to linear superelasticity, and its stress inducing martensitic critical stress and the accumulation residual strain increased rapidly; while Ti-50.8Ni-0.3Cr alloy evolved from incomplete superelastic to complete superelastic, and the stress-strain curve shape was stable. With increasing n, the superelastic residual strain ε_r decreased and the superelastic strain recovery ratio η_s of Ti-50.8Ni alloy increased, while the ε_r and η_s in Ti-50.8Ni-0.3Cr alloy kept at lower and higher values, respectively. The superelastic of Ti-50.8-0.3Cr alloy was stable.

The effect of Cu content on the corrosion resistance of Zr-1%Nb-xCu (x=0.05%-0.5%, mass fraction) was investigated in superheated steam at 500 ℃ and 10.3 MPa by autoclave tests. The microstructures of the alloys and oxide films on the corroded specimens were observed by TEM and SEM, respectively. The results showed that when the Cu content was below 0.2%, the corrosion resistance of the alloys was markedly improved with the increase of Cu content, while further addition of Cu did not lead to a further improvement in the corrosion resistance. When the Cu content was below 0.2%, the Cu mainly dissolved in the α-Zr matrix. And when the Cu content was more than 0.2%, part of Cu precipitated as Zr₂Cu second phase particles. When the α-Zr matrix was oxidized, the Cu dissolved in the α-Zr could delay the process that the vacancies in the oxide film diffused and coalesced to form pores, and the pores developed into micro-cracks. Therefore, the corrosion resistance of the alloys was enhanced. It can be concluded that the Cu concentration in the α-Zr matrix, rather than the second phase particles containing Cu, is the main reason that the addition of Cu improves the corrosion resistance of M5 alloy in superheated steam at 500 ℃ and 10.3 MPa.

The Fe₈₁Ga₁₉ single crystals were grown in a floating zone melting furnace at a growth rate of 4 mm/h by using a seed crystal. A single crystal was grown by using the seed crystal oriented 5^o from the <001> orientation. Pole figure tests were taken at different parts of the single crystal and showed that the start and end parts' axial orientations were 5^o and 4^o from the <001> orientation, respectively. Another single crystal was grown by using the seed crystal oriented <001> orientation. Magnetostrictive properties along the axis of the crystals λ_// were measured for the single crystal, and the saturated magnetostriction λ_// up to 0.0324% was achieved under the pre-stress of 60 MPa. Initial magnetization curves were measured in single crystals along <100>, <110> and <111> axis, respectively. From the magnetization curves, magnetocrystalline anisotropy constants of Fe₈₁Ga₁₉ alloys were calculated, and the values of K₁ and K₂ were 1.3×10⁴ and -2.6×10⁴ J/m³, respectively.

Mg-Li-Gd alloys were obtained by electrochemical codeposition method in LiCl-KCl-MgCl₂-Gd₂O₃ molten salt on molybdenum electrode at 1073 K. Transient electrochemical techniques, such as cyclic voltammetry and chronopotentiometry, were used in order to study the reaction mechanism. XRD, SEM, EDS and OM were employed to characterize Mg-Li-Gd alloys. The results suggested that Gd₂O₃ could dissolve in LiCl-KCl-MgCl₂ molten salt while it could not in LiCl-KCl melt. Cyclic voltammograms and chronopotentiometry measurements indicated that the potential of Li metal deposition, after the addition of MgCl₂ and Gd₂O₃, was more positive than the one of Li metal deposition before the addition. The codeposition of Mg, Li and Gd occurred when applied potentials were more negative than -2.30 V (vs. Ag/AgCl) or current densities were higher than 0.776 A/cm² in LiCl-KCl-MgCl₂-Gd₂O₃. Electrolysis temperature exerted a great influence on current efficiency, 78.87% current efficiency was obtained when electrolysis temperature was 873 K. Li content in Mg-Li-Gd alloys increased with the high current densities. XRD results showed that Mg₃Gd intermetallic compounds formed in Mg-Li-Gd alloys. Grain size became smaller as the Gd metal content increased in the alloy. The analysis of SEM and EDS demonstrated that the element of Gd was mainly distributed at grain boundaries.

Room temperature creep (RTC) behaviors of the as-rolled (AR) and normalized (Nor) X70 pipeline steel as well as the AISI304 stainless steel were investigated. At different stress levels, their RTCs mainly showed the feature of logarithmic creep with continuously falling rate. By comparing RTC with tensile tests, it was found that the loading process of RTC test was the same as the tensile test, and the strain rate at the start of RTC was equal to that at the end of loading process. Based on these results and by combining the constitutive equations of RTC with the Ramberg-Osgood equation, which is generally used to describe the stress-strain relationship in tensile tests, an approach to estimate RTC strain was presented as a function of the applied stress. On applying it to the X70 pipeline steel and AISI304 stainless steel, it was indicated that the estimated results of RTC were well consistent with the experimental data and that all the errors were within a factor of 2.

Microsegregation caused by the redistribution of alloying elements means the inhomogeneity of the chemical composition on the scale of a single grain. To decrease the degree of microsegregation is beneficial to avoiding ingots hot crack and shortening the homogenizing treatment time. In this study, the microsegregation of Cu element in the Al-4.5%Cu (mass fraction) alloy was investigated. Al-4.5%Cu ingots with diameter of 200 mm were prepared by the processes of conventional direct chill (DC) casting and low frequency electromagnetic casting (LFEC), respectively. The temperatures were measured during solidification processes. The effects of low frequency electromagnetic field on the microstructures and microsegregation of Cu element were investigated from eutectic analysis and electro probe microanalysis (EPMA). By the OM observations, it was found that the area fraction and dimensions of eutectic decreased markedly. The concentration profiles of Cu element were obtained with EPMA results, which showed that the profiles increased (i.e. the content of Cu element in α-Al phase increased) in the initial transit region due to the effect of low frequency electromagnetic field. The effective distribution coefficient k_e of Cu element was calculated. In the initial transit region, k_e increased to unit linearly. At the same time, the low frequency electromagnetic field made k_e a bigger value, and the value increased with the increasing of the current intensity. Because the cooling rate at the solidification front was promoted by the low frequency electromagnetic field, and there was more Cu element in α-Al, the microsegregation of Cu element in the ingot was alleviated by the LFEC process.

In order to realize accurate numerical simulation of rolling, forging, extrusion of Incoloy 800H superalloy and formulate reasonable process parameters of hot working, the flow stress behaviors of Incoloy 800H superalloy were investigated in the temperature range of 1273-1473 K and strain rate range of 0.01-10 s^-1 on Gleeble-1500 thermo-simulation machine. Utilizing hyperbolic sine function and introducing the strain factor with six polynomial fitting, the constitutive equations of flow stress of Incoloy 800H superalloy at high temperature were established, then the accuracy of the constitutive equation was verified. The results showed that during the hot compression deformation of Incoloy 800H superalloy, the characteristics of dynamic softening and dynamic recovery were observed at lower strain rates and high strain rates conditions, respectively, flow stress increased with increasing strain rate, decreased with increasing temperature; the flow stress of Incoloy 800H superalloy predicted by the proposed models with 6^th order polynomial fit agrees with the experimental value well, relative error is not more than 6.5% at the overwhelming majority (95%) cases of the deformation conditions, and average relative error is only 3.15%.

Magnetic pulse joining (MPJ) is a solid state joining technology, by which mechanical or metallurgical joint is obtained. It can be used to assemble and join dissimilar metals. In this work, by means of MPJ setup with low inductance coil, the effects of discharge voltage, radial gap between tubes and lap length on the tensile and peel testing strength of 3A21 aluminum alloy-20 steel tubes joint were investigated experimentally. The microstructural observation and the energy spectrum analysis (by linear scan) of basic elements distribution within the MPJ joint interface were performed by SEM. The results showed that an increasing discharge voltage contributed to the change of MPJ joint from mechanical joint to metallurgical one. The metallurgical joint with the small wave joining interface was obtained under a voltage of 5.5 kV, a radial gap of 1.5 mm, and a lap length of 3/4 coil length, where the mutual diffusion of Al and Fe elements occurred. The severe plastic deformation with sharp strain gradient, and the distinct grain refinement occurred in the matrix metals near the joining interface.

Due to the surface plasmon resonance (SPR) and enhanced local field effect of metal particles, nano-composite films exhibit a variety of properties, such as large third order nonlinear susceptibility, superfast response time and absorption peaks in the optical spectra at a special wavelength. Therefore they are attractive candidates for optical communication, such as information storage and optical device. In recent years, the metal nanoparticle nonlinear optical composite films have been developed rapidly, expanded from single metal nano particle dispersion system to the dual metal nano particle dispersion system. However, theoretical study on the nonlinear optical absorption of the dual metal nano particle dispersion system is quite rare. In this study, the optical absorption spectra of the (Ag, Cu)/SiO₂, (Au, Cu)/SiO₂ and (Ag, Au)/SiO₂ binary metals dispersed nano-composite films were simulated by modified Mie theory. When the metal particles with a low full factor are smaller than the incident wavelength in diameters, the optical spectra of (Ag, Cu)/SiO₂, (Au, Cu)/SiO₂ and (Ag, Au)/SiO₂ composite films in which the nanoparticles solely dispersed in each metal state, can be calculated and analyzed based on the modified Mie theory using the optical parameters of the component. Two SPR absorption peaks appear in the corresponding wavelength of the single metal dispersed nano-composite films. The intensities of SPR absorption peaks depend strongly on the relative content of binary metals, while their peak positions are constant regardless of the content. The calculated optical absorption spectra by proposed method in this study are in good agreement with the reported experiment results. It suggests that the linear superposition method is feasible to calculate the absorption spectra of other separated binary and/or multiplex metals dispersed nano--composite films.

By selecting complexing agent and the buffer agent, using square wave pulsed currents and optimizing electroplating process, the chromium-palladium alloy films were deposited on 316L stainless steel in acidic solution. By appropriate design for the plating bath composition and pulse electroplating, Cr-Pd alloy films were deposited on 316L stainless steel. The films were compact and homogeneous with good adherence to the substrate. By adjusting the composition of the plating bath, the ratio of Cr/Pd could be changed in a large range. The Cr-Pd films significantly improved corrosion resistance of 316L stainless steel in strong reducing mediums. In boiling 20% (mass fraction) H₂SO₄ solution, corrosion rates of the Cr-Pd plated samples were about four orders of magnitude lower than that of the original 316L stainless steel samples. A synergism effect was observed for Cr and Pd on passivation of stainless steel. When there was only 2.5%Pd (mass fraction) in the Cr-Pd film, corrosion resistance of the sample was obviously improved. The protection effect of Cr-33.3%Pd film was similar to that of pure Pd film on stainless steel.

The distribution of Co, the intrinsic magnetism and magnetostriction of quaternary Tb-Dy-Fe-Co alloy were investigated. The SEM image showed the matrix (Laves phase) and the rare-earth (RE) rich phase in the annealed samples. The Co content (atomic fraction) in the RE rich phase was 21.18%, much higher than that in the matrix (9.36%). XRD patterns showed that Co partial substitution for Fe did not change the structure of MgCu₂-type cubic Laves phase, contributing to the giant magnetostriction. Curie temperature T_c was increased remarkably with Co addition, resulting in wider operating temperature. The magnetocrystalline anisotropy compensation by Co addition was beneficial to improving the magnetostriction in low field. The solidified orientation influences the testing of intrinsic magnetostriction. In order to ensure the accuracy in the measurements, the equiaxed Tb-Dy-Fe-Co samples were prepared. The saturated magnetostrictive constant λ_s was tested. λ₁₁₁ and λ₁₀₀ were calculated by the cleavage of (440) diffraction peak of Laves phase. Compared with Terfenol-D alloy, λ₁₁₁ in the Co-doped sample decreased slightly, but λ₁₀₀ increased evidently and λ_s almost remained unchanged.

A new method (electromagnetic steel-teeming method) using electromagnetic induction heating in slide-gate was proposed to overcome the disadvantage of the pollution of the traditional nozzle sand on the molten steel. The basic idea of this new process is to melt part or whole of the new ladle well-packing material (i.e. Fe-C alloy with similar composition of the molten steel), which becomes the substitute of the traditional nozzle sand, and achieve smoothly molten steel-teeming. In the experiment, the state of the Fe-C alloy well-packed in the upper nozzle was examined when the ladle held molten steel using the self-designed electromagnetic steel-teeming simulation facility. The results showed that the F-C alloy in the upper nozzle were divided into liquid Fe-C alloy, solidified Fe-C alloy, liquid-sintered, solid-sintered and original layers. The solidified, liquid-sintered and solid-sintered layers could prevent the molten steel flow into the upper nozzle from destroing the slide plate. The blocking layers could be melted with induction heating to achieve electromagnetic steel-teeming. In addition, the position of the liquid/solid interface of the Fe-C alloy in the upper nozzle was investigated. The length of liquid Fe-C alloy increased with the increase of time after molten steel poured into the ladle and then kept in a certain length. Furthermore, the position of the interface increased with the increase of melting points which were related to the composition of the Fe-C alloy. The experimental results indicated that 100% automatically teeming of the ladle would be achieved after using the electromagnetic steel-teeming technology.

Friction stir welding (FSW) is a ideal method for joining light metal materials, especially for AA2000 and AA7000 series aluminum alloys. In the welding field, many aspects of FSW have been studied quite extensively and comprehensively. However, the origin of the banded texture is still a subject of current research. One of the phenomena that strike researchers today is the occurrence of banded texture on the top surface in FSW joints. Furthermore, many waves also emerged in shoulder affected zone (SAZ) after a joint being polished and etched. The correlation between the banded textures and the waves is not clear. In this paper, 1.6 mm thick 7075-T6 aluminum alloy sheets were friction stir welded, microstructures and hardness profile of banded textures on the top surface of the joint were investigated. The results of metallographic observation showed that alternately light and dark waves presented in SAZ, the light waves coincided with valleys of the banded textures, whereas the dark waves coincided with peaks. SEM and TEM analyses revealed that compared with the valleys, the peaks were characterized by more secondary phase particles and small grains, resulting in higher hardness at the peaks.

The Al-Cr coating exhibits a good steam oxidation resistance and can act as tritium permeation barrier. It is necessary to prepare Al-Cr coating at low temperatures to avoid detrimental effect on the mechanical properties of the substrate. In the present study, a new process was proposed to prepare Al-Cr coating by electrodeposition of Cr/Al composite coatings firstly, and then heat treatment at low temperatures. The Cr/Al composite coatings were obtained by electrodepositing Cr from aqueous solution followed by electrodepositing Al from AlCl₃-EMIC ionic liquid. Effects of the temperature of heat treatment on the composition and phase of alloy layers were studied by using OM, SEM, BSE, EDS and XRD. The results showed that an Al-Cr alloy layer at the Cr/Al interface was formed even at low temperature of 540 ℃ by the interdiffuse between Al and Cr coating. The different Al-Cr alloy layers could be formed by controlling the thickness of Cr and Al in Cr/Al composite coatings. For 6.5 μm Cr/15 μm Al composite coating, the main phase was Al₈Cr₅ for 960 min heat treatment at 640 ℃, and for 1.6 μm Cr/15 μm Al composite coatings treated at 600 ℃ for 30 min, the main phase of alloy layer was Al₄Cr.

A series of lightweight Ti-based ductile in-situ dendrite-reinforced metallic-glass-matrix composites were synthesized by Bridgman solidification. Compared to Cu-mould suction casting, the $\beta$-Ti dendrites were uniformly distributed within the glass matrix by this method. Through tailoring the withdrawal velocity, the volume fraction and the characteristic spanning length of dendrites could be changed, which provides a way to optimize the mechanical properties of the composites. The Ti-based composite with excellent mechanical performances (high ultimate strength of 2706 MPa and large plasticity of 18.0% with apparent work-hardening behavior) was synthesized when the withdrawal velocity was fixed at 1.4 mm/s. The relationship between the size of the dendrites and the mechanical properties was investigated, and it was found that the improved mechanical properties were obtained when the size of the dendrited approached about 40 μm.

The displacements of vectors in a habit plane (HP) are assumed to lie along a particular Burgers vector, so that the misfit in the interface can be fully accommodated by a set of dislocations with that Burgers vector. This assumption is consistent with many models and experimental observations. Based on this assumption, a simple method based on vector analysis has been developed. By applying this method to fcc/bcc system, the classical solutions from the phenomenal theory of martensite crystallography can be reproduced. In addition, a simple form of equation for general HP orientations satisfying the above assumption has also been derived. The present method provides a simple but general tool for analysis of irrational HP generated from either martensitic or diffusional transformations.

By using uniaxial tensile test combining the $in~situ$ electrical resistance change method, the influence of modulation period with a wide range spanning from 10 to 250 nm on the ductility and fracture toughness of Cu/Nb nanostructured metallic multilayers on polyimide substrate was measured. The microstructural analysis revealed that the modulation structure of Cu/Nb metallic multilayers was clear and no intermixing between Cu and Nb was been found by using line scanning analysis. The experimental results indicated that both ductility and fracture toughness of the multilayer film exhibited a nonmonotonic change with decreasing modulation period, and reached maximum values at a critical modulation period of about 50 nm. This was attributed to the competing effect between the size of the microcracks initiated in the Nb layer and the role of the Cu layer in blocking crack propagation. This competing effect was qualitatively assessed on basis of fracture mechanics.

The morphology, size, distribution and types of precipitate particles were studied by using OM, SEM, TEM, EDS and SAEDP for Ti-Mo low-carbon ferrite matrix micro-alloy steel with four different titanium contents. Experimental results indicated that there were two kinds of particles with obvious different sizes in ferrite matrix, one was nanometer sized particles, which were smaller than 10 nm, the composition of these particles was compound carbonitride of Ti and Mo. These particles precipitated in chains or dispersed in the interior of grains. Dislocation nodes and the dislocation network were preferential nucleation sites for these particles. Another kind of particles was titanium carbonitride larger particles with a “cap” and few in number in ferrite matrix. Their size was about 200 to 300 nm and morphology was square. Tensile experimental results at room temperature and high temperatures showed that ferrite matrix micro-alloy steel with nanometer sized had good mechanical properties. No.4 steel had good performance at 600 ℃ with a yield strength of about\linebreak 300 MPa.