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The effects of thermomechanical treatment on microstructure, mechanical properties and shape memory effect of Ti–13V–3Al alloy were investigated. A dual-phase structure which consists of α phase and α″ martensite phase forms after thermomechanical treatment. As annealing temperature increases, the amount of α phase decreases and its morphology changes. Stress plateau decreases when annealing temperature increases and elongation shows the opposite trend. Ti–13V–3Al alloy annealed at 700 °C has the best comprehensive mechanical property. Recoverable strain first increases then decreases as annealing temperature increases. Ti–13V–3Al alloy annealed at 700 °C for 0.5 h displays a large fully recoverable strain of 7.5%. It is believed that small, uniformly distributed α phase benefits the shape memory effect. With the help of α phase, martensite variants become small. The variants are supposed to have a good mobility and that reduces the chance of introducing irrecoverable strain during tensile test. The microstructure evolution of Ti–13V–3Al alloy annealed at 700 °C during deformation was investigated. When the pre-strain is less than 7.5%, the recoverable martensite reorientation process contributes to the deformation. When the pre-strain exceeds 7.5%, the crossover of martensite plates leads to the deterioration of shape memory effect.

The effects of aging on martensitic transformation, thermoelastic and fracture behavior were investigated in the Mn 53 Ni 25 Ga 22 ferromagnetic shape memory alloy. The results show that precipitation has obvious effects on the phase transformation behavior and fracture behavior. The transformation temperature gradually decreases and then increases when the samples are aged at increasing temperatures, reaching the minimum value at an aging temperature of 773 K for 3 h, which is mainly attributable to elemental diffusion between the matrix and the precipitate. The enthalpy and entropy changes rapidly increase and then gradually decrease with an increase in the aging temperature, reaching their minimum values at an aging temperature of 573 K. Moreover, the brittleness, low strength and poor processability of Mn–Ni–Ga alloys greatly limit their application. We attempted to improve the mechanical properties without sacrificing the magnetic and thermoelastic properties by using appropriate aging treatments. The highest compressive strength and compression strain of 1594 MPa and 20.3% were obtained in alloys aged at 673 K and 573 K for 3 h, respectively. These values are approximately 750 MPa and 8% higher than the solution-treated Mn 53 Ni 25 Ga 22 alloy. As a result, the improvements in the mechanical properties of Mn 53 Ni 25 Ga 22 alloys from the aging treatments are mainly due to changes in the fracture type from intergranular brittleness to a quasi-cleavage ductile fracture. By controlling the number and the size of the precipitates and aging at a temperature no higher than 773 K for no more than 3 h, a significant improvement in the compressive strength and ductility of the alloys can be expected through the fine-tuning of the small precipitates.

A Heusler Ni 50 Mn 30 Ga 1 Cu 4 alloy with the highest compressive strength has been obtained by substituting 4 at% Cu for Ga in a ternary Ni 50 Mn 30 Ga 20 ferromagnetic shape memory alloy. It is shown that the highest compressive strength of 3178.9 MPa with a fracture strain up to 13.6% can be achieved at room temperature. To date, this is the highest compressive strength reported in the Ni–Mn–Ga alloy system. The martensitic structure changes from 7M with 0 at% Cu to non-modulated T martensite with 4 at% Cu . In addition, the Cu doping markedly increases the martensitic transformation temperature from 82.1 °C to 136.6 °C. At the same time, the Curie temperature and saturation magnetization for the Ni 50 Mn 30 Ga 16 Cu 4 alloy slowly decrease due to the 4 at% Cu addition.

The influence of Co on the microstructure, phase transformation temperature, mechanical properties and shape memory effect of TiNiNb alloys has been investigated by X-ray diffraction, differential scanning calorimetry, tensile stress–strain measurements and bending tests, respectively. The results show that the addition of Co suppresses the brittle (Ti,Nb) 2 Ni phase of NiTiNb alloys, and the phase transformation temperature and lattice parameter of Ni 46.5− x Ti 44.5 Nb 9 Co x alloys are decreased with the increase of Co content. The yield strength of NiTiNb alloys has been improved due to the addition of Co. In particular, Ni 45.5 Ti 44.5 Nb 9 Co 1 alloy exhibits highest yield strength among the Ni 46.5− x Ti 44.5 Nb 9 Co x (Co = 0.5, 1, 1.5, 2) alloys, and a maximum completely recoverable strain of 7.8% has been achieved.

The martensitic transformation and shape memory effect of Ni 54.75 Mn 13.25 Fe 7 Ga 25 (at.%) alloy are studied in the present paper. It is shown that tetragonal martensite with parallel bands substructure transforms to parent phase heated by electron beam. It can be clearly observed that the martensite band becomes smaller and smaller, then transforms to parent phase completely in the end. A large reversible transformation strain, about 1.5%, is obtained in this undeformed polycrystalline alloy due to martensitic transformation and its reverse transformation. This transformation strain is also increased to 1.8% by the external magnetic field. It is believed that the effect of the magnetic field on the preferential orientation of martensitic variants increases the transformation strain.

Diamond-like carbon films with different bias voltages were deposited on polished NiTi alloys by plasma immersion ion implantation and deposition (PIIID) using acetylene as precursor. The chemical structure of the DLC films was characterized by Raman scattering spectroscopy. The electrochemical behavior and blood compatibility of the DLC coated and uncoated NiTi alloys were investigated by means of potentiodynamic polarization tests, clotting time measurement, and platelets adhesion. The results show the corrosion resistance and blood compatibility of the NiTi alloys is improved due to the DLC films, and the sp 3 /sp 2 ratio and the corrosion resistance of the DLC films on the NiTi alloys first increases and then decreases with the increase of the bias voltage. Thus, it can be inferred that the corrosion resistance of the DLC films is influenced by the sp 3 /sp 2 ratio.

A dense and well-adhered diamond-like carbon (DLC) coating was prepared on NiTi alloys by plasma immersion ion implantation and deposition (PIIID). Electrochemical impedance spectroscopy and potentiodynamic polarization tests indicated the corrosion resistance of the NiTi alloys was markedly improved by DLC coating.

The influence of pre-deformation on the martensitic transformation behavior and its microstructure has been put forward in a Ni55Mn20Ga25 (at.%) ferromagnetic shape memory alloy. It is found that the reverse martensitic transformation temperatures (As and Af) increase linearly with increasing amount of deformation, while the martensitic transformation temperatures (Ms and Mf) are not changed even when the deformation is up to 6%. However, the effect of the pre-deformation on the reverse martensitic transformation disappears in the following heating process. Transmission electron microscopy shows well-accommodated martensite variants in the undeformed specimen and interfacial boundaries are straight and well-defined. After deformation, the reorientation of martensite variants occurs at the expense of the unfavorable martensite variants, and the interfacial boundary changes from a sharp and straight morphology to a curved and irregular one. Meanwhile, some lattice defects are formed inside the variants even in slightly compressed samples. With increasing deformation, more lattice defects are generated inside the variants as well as in the interfacial boundaries between variants. Based on the analysis of the experimental results, the micromechanism of the effect of pre-deformation on martensitic transformation behavior has been clarified.

Effect of aging on transformation temperatures and microstructure of an Fe-doped Ni–Mn–Ga alloy has been studied by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). DSC results show the transformation temperatures can be obviously raised by aging. When the aging temperature increases, the transformation temperatures gradually decrease to the minimum values and then increase slightly upon further increasing the aging temperature. The defects introduced by aging should be responsible for the change of transformation temperatures. In the sample aged at 573 K for 30 min, a large number of stacking faults are observed by TEM.

Diamond-like carbon (DLC) films were produced on NiTi substrate by plasma immersion ion implantation and deposition (PIIID) at room temperature. Surface morphology and roughness were analyzed by atomic force microscopy. Film microstructure and hardness were characterized by Raman scattering spectroscopy and nano-indentation, respectively. The corrosion resistance in Hank's solution was evaluated by means of open-circuit potential (OCP) and potentiodynamic polarization techniques. It was found that, according to the corrosion potential ( E OCP ), the coated sample is always more noble than the uncoated one. For the polarization curves, the shift of the breakdown potential to more positive values and the reduction of the current densities give evidence that the coating with DLC is a useful method for reducing the corrosion attack of the NiTi alloy in Hank's solution.

The effect of Fe content on hardness and toughness of Ni48.7Mn30.1−xFexGa21.2 (x = 0–11, number indicates at.%) alloys is investigated and the relationship between the fracture toughness and the fractography is discussed by observing the fracture morphology and analyzing the propagation of the crack. The micro-Vickers hardness results indicate that the hardness increases with increasing Fe content. The fracture toughness results indicate that Fe doping has improved the toughness of Ni–Mn–Ga alloys, and the toughness increases with increasing Fe content in Ni48.7Mn30.1−xFexGa21.2 (x = 0–11) alloys. Fracture morphology shows typical intergranular fracture with rock candy pattern in the Ni48.7Mn30.1Ga21.2 (x = 0) and river pattern cleavage fracture facets in the Ni48.7Mn19.1Fe11Ga21.2 (x = 11) alloy. The fracture type changing from intergranular fracture to transgranular fracture is the main reason for the improved toughness of Ni–Mn–Ga alloys by addition of Fe.

Chemical composition and surface morphology of Ni–Ga–Fe thin films grown under various sputtering powers and argon gas pressures by r.f. magnetron sputtering technique are studied. X-ray fluorescence results show that the sputtering power has obvious effect on the chemical composition of Ni–Ga–Fe thin films. The argon gas pressure has little effect on the composition of Ni–Ga–Fe thin films. The change in surface morphology of Ni–Ga–Fe films is discussed in terms of root-mean-square (rms) surface roughness values. The grain size and the rms of Ni–Ga–Fe thin films increase with the increase of sputtering power and argon gas pressure. The film deposited at room temperature has a cubic L2 1 structure and the annealed film shows martensitic structure.

More attention has been paid to ternary Ti–Ni–Hf high-temperature shape memory alloys (SMAs) due to their high phase transformation temperatures, good thermal stability and low cost. However, the Ti–Ni–Hf alloys have been found to have low ductility and only about 3% shape memory effect and these have hampered their applications. It is well known that there are three methods to improve the shape memory properties of high-temperature SMAs: (a) cold rolling + annealing; (b) adding another element to the alloy; (c) aging. These methods are not suitable to improve the properties of Ti–Ni–Hf alloys. In this paper, a method of conditioning Ni-rich Ti–Ni–Hf alloys as high-temperature SMAs by aging is presented. For Ni-rich Ti80−xNixHf20 alloys (numbers indicate at.%) the phase transformation temperatures are on average increased by more than 100 K by aging at 823 K for 2 h. Especially for those alloys with Ni contents less than 50.6 at.%, the martensitic transformation start temperatures (Ms) are higher than 473 K after aging. Transmission electron microscopy shows the presence of (Ti + Hf)3Ni4 precipitates after aging. Compared with the precipitation of Ti3Ni4 particles in Ni-rich Ti–Ni alloys, the precipitation of (Ti + Hf)3Ni4 particles in Ni-rich Ti–Ni–Hf alloys needs higher temperatures and longer times.

Ni 53.97 Mn 25.67 Ga 20.36 high temperature shape memory thin film was deposited onto silicon substrates using radio-frequency magnetron sputtering. Crystallographic structure, surface morphology, compositions and martensitic transformation of Ni–Mn–Ga thin films were investigated by means of X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, and differential scanning calorimetry. The results show that Ni 53.97 Mn 25.67 Ga 20.36 thin film with excellent surface quality is 7M structure at room temperature. The martensite transformation temperature M s can be increased to 100 °C through selecting a suitable composition of the Ni–Mn–Ga target and appropriate sputtering parameters.

The interface structure and its mobility in the martensites of shape memory alloys (SMAs) are reviewed. The emphasis is placed on the evolution of interface structure during deformation and the relations of interface characteristics to the mobility in cold-deformed TiNi-based alloys and the types, structure and mobility of interfaces in Cu-based SMAs. With the increase of deformation strain in the cold-deformed TiNi alloys, the interface type of martensite variants changes and their mobility becomes bad gradually. For the Cu-based SMAs, the A/C and A/B interfaces have effective mobility and may move smoothly and become straight during motion. On the contrary, the mobility is not effective for the A/D interface.

Poly( l -lactide-co-ɛ-caprolactone) (PCLA) copolymers were prepared by ring-opening polymerization using stannous octaoate as catalyst. Their thermal properties and crystallinity were determined by using differential scanning calorimetry and X-ray diffraction. The mechanical properties are significantly affected by the copolymer composition. With increasing ɛ-caprolactone (ɛ-CL) content, the tensile strength of copolymers decreases and the maximum strain increases gradually. The shape memory property of PCLA copolymers was investigated by tensile test and its dependence on the composition and the deformation strain was also revealed. The crystallinity poly( l -lactide) (PLLA) or the entanglement of molecular chains is considered as physical cross-links, while the amorphous fraction acts as reversible phase and is responsible for the shape memory property of PCLA copolymers.

The damping behavior of TiNi-based alloys has been investigated by dynamic mechanical analyzer (DMA) instruments. It shows that an appropriate cold-rolling deformation on the martensitic Ti50Ni50 alloy can enhance its damping capacity. The damping behavior of the Ti49.2Ni50.8 alloy is aging condition dependent and the damping capacity peak value corresponding to the phase transformation increases due to the increase of the amount of boundaries between the martensite and parent phase as a result of the existence of the Ti3Ni4 particles. The Ti44Ni47Nb9 alloy possesses high damping capacity either during phase transformation or in the parent phase, which is very important for the engineering application.

In this paper, ZnO ultrafine particles (UFPs) were prepared by the thermal decomposition method of the precursor, zinc carbonate hydroxide. The structure and properties of the as-prepared ZnO UFPs were studied using TEM, XRD, BET, SPS, ESR, Raman, XPS and UV–Vis absorption spectroscopy. It was found that the prepared ZnO UFPs exhibited obvious quantum size effect and surface effect. In addition, there were many active species on the surface of ZnO UFPs such as oxygen deficiencies and hydroxyls, both of which can improve the photocatalytic activities of ZnO UFPs.

The R-phase transformation in a Ti–50.7at%Ni alloy was investigated by in-situ transmission electron microscopy (TEM) observations using double-tilt cooling stages, and the incommensurability of 1/3 diffuse scattering in the process of the transformation was examined by using imaging plates. It is shown that the incommensurate diffuse scattering exists in the parent phase within a wide temperature range above the Rs temperature and that the incommensurability decreases with decreasing temperature. The R-phase transformation starts at the Rs temperature where the electrical resistance starts to increase and the R-phase is commensurate even in the state just after formation.

The A/D type twin boundary between 18R martensite plates in a Cu–Zn–Al alloy has been studied by both transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). It is curved in TEM and has irregularly serrated steps in HREM. The randomly distributed faults have no obvious influence on the boundary orientation. The boundary segments consist of respective basal planes of the two variants. Crystallographic analysis shows that the macroscopic curve results from the non-self-accommodation of transformation strain of the two variants. The calculated boundary energies based upon the model of a small-angle tilt grain boundary indicate that the deviation from the exact twin orientation and the irregularly serrated steps result from energy minimization.

The microstructure and phase evolution in a rapidly-solidified Ti24Al11Nb alloy have been studied using X-ray diffraction, and scanning and transmission electron microscopy. Two forms of this alloy, plasma rotary electrode process powder and plasma-sprayed foil, were used for this investigation. While a β phase was the only phase found in the powder, several different phases were observed in the foil. These included ordered β (B2), ordered b.c.t. (T), ordered orthorhombic (O) and ordered h.c.p. (α2) phases. Phase transitions occurred when the rapidly-solidified alloy was isothermally aged. The phase transition sequences that took place during isothermal aging depended upon temperature range. For T(°C) β/ B 2 a ω and β/ B 2 a α 2 occurred. For 650 β/ B 2 a α 2 was prevalent. A complex reaction sequence was found for the β/ B 2 a α 2 transition: β/ B 2 a T a O a α 2 . For 900 β a α 2 (niobium-lean) + β(niobium-rich) took place. A preliminary time-temperature-transformation diagram for the Ti24Al11Nb alloy is proposed.