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The ordered Pt-based intermetallic nanoparticles (NPs) with small size show superior magnetic or catalytic properties, but the synthesis of these NPs still remains a great challenge due to the requirement of high temperature annealing for the formation of the ordered phase, which usually leads to sintering of the NPs. Here, we report a simple approach to directly synthesize monodisperse ordered L10-FePt NPs with average size 10.7 nm without further annealing or doping the third metal atoms, in which hexadecyltrimethylammonium chloride (CTAC) was found to be the key inducing agent for the thermodynamic growth of the Fe and Pt atoms into the ordered intermetallic structure in the synthetic process. In particular, 10.7 nm L10-FePt NPs synthesized by the proper amount of CTAC show a coercivity of 3.15 kOe and saturation magnetization of 45 emu/g at room temperature. The current CTAC-assisted synthetic strategy makes it possible to deeply understand the formation of the ordered Pt-based intermetallic NP in solution phase synthesis.

A β-solidifying TiAl alloy with a refined microstructure and ultra-fine yttrium-rich precipitates that was consolidated by spark plasma sintering was investigated by scanning and transmission electron microscopies. Two categories of yttrium-rich precipitates, Y2O3 and YAl2, with sizes ranging from tens to hundreds of nanometers were found to be dispersed within the matrix uniformly. The crystallographic relationship between the two precipitates and the γ-TiAl matrix was determined by the selected area electron diffraction and high-resolution transmission electron microscopy. This spark plasma sintered TiAl alloy was characterized by a uniform duplex microstructure, and it exhibited excellent tensile properties at room temperature. Typically, specimen sintered at 1150°C has an ultimate tensile strength of 1113.1 MPa, yield strength of 881MPa, and a moderate plastic elongation of 1.41%.

The incipient plasticity of an amorphous solid represents the onset of shear deformation, which is a stochastic progress closely related to microstructure evolution. It is well known that the cooling rate plays a crucial role in the microstructure evolution of a glass. Nevertheless, how the cooling rate affects the incipient plasticity is still unclear. In this work, the incipient plastic deformation of the amorphous phase in Cu47.5Zr48Al4Nb0.5 bulk metallic glass composites (BMGCs) cast with different cooling rates is systematically studied. The incipient plasticity of the glassy matrix of the BMGCs is found to occur via a first displacement burst, the occurrence of which is more stochastic as the cooling rate decreases. According to the auto-correlation functions and cooperative shear model, the stochastic behavior is attributed to the effects of the cooling rate on the initial free volume and subsequent activated shear transformation zones (STZs). A higher content of free volume is present in the glassy matrix of the studied samples cooled at a faster rate, which facilitates the operation of STZs. Moreover, the larger incipient burst size is correlated with the higher content of free volume and larger STZs in the glassy matrix. The larger STZs result in more preferable propagation of multiple shear bands, leading to less stochastic deformation and more obvious plastic deformation. This study provides further understanding on the incipient plasticity of glassy matrix in BMGCs.

In this paper, we report the results obtained from the hot compression behaviour of co-spray-formed Al-Si/7075 bimetallic gradient alloys by investigating the five selected layers divided evenly from top to bottom. It was found that with a decrease in the strain rate and an increase in temperature, the hot compression flow stress of deposited alloys decreases gradually, as expected. The relationship between flow stress, temperature and strain rate follows the Arrhenius relationship. The deformation activation energy of the co-spray formed gradient alloy gradually increases from bottom to top in the height direction, which are 100.15, 167.35, 185.54, 208.78 and 220.83 KJ/mol, indicating that the degree of difficulty in the deformation of the alloy is affected by changes in the silicon content of the alloy. Finally, the flow stress constitutive equation is calculated for each layer of alloy material, which is instructive for the subsequent study of the densification process of co-spray-formed gradient alloys.

Bimetallic gradient alloys have attracted research attention recently due to their potential applications in the aerospace and automobile industries. In this study, Al-20Si/7075 bimetallic gradient alloys were successfully manufactured by co-spray forming and the roll process. We investigated the thermal expansion behavior of the gradient alloy. It was found that the coefficients of thermal expansion increased with silicon content and increased temperature, reaching the highest point at 573 K, after which they decreased on account of the relaxation of residual thermal stress and the silicon desolvation from the supersaturated aluminum phase. The measured thermal expansion coefficient can be roughly predicted through the traditional theoretical models. Our results revealed the thermal expansion behavior of Al-20Si/7075 bimetallic gradient alloys and would improve the development of new type aluminum–silicon alloy for electronic packaging.

The influence of surface microstructural regulation mechanisms on the mechanical and giant magneto-impedance (GMI) properties of as-cast melt-extracted CoFe-based wires has been systematically researched based on morphology, phase distribution and domain structure parameters. A series of statistical models were applied to analyze the mechanical properties and followed by mapping the curve of cumulative failure rate for wire application. It was found that the average and highest fracture strengths, average tensile strain increased with Cu substitution and reached peaks of ~3725 MPa, ~4250 MPa and ~2.7%, respectively. Verified structure-simulation experiments revealed that surface Rayleigh waves effectively split the main crack and the diffusely distributed nanocrystalline in surface area acted as a pinning point to impede the crack growth, enhancing the mechanical properties. The GMI ratio displayed similar variations and attained a maximum value of 700 ± 5% as well as the resistance and reactance ratios improved to ~687% and ~2206%, respectively. The enhanced relative dielectric permeability μs resulting from the increased domain wall energy density and the decreased surface domain width. The unique synchronous enhancement of CoFe-based wires satisfies the demand for emerging magnetoelectric sensor applications, e.g. flexible and wearable sensors, equipment self-monitoring sensors, and array robotic skin sensors under harsh working environments.

The improvement of mechanical properties must be achieved by designing and constructing more suitable microstructure, such as hierarchical microstructure. In order to significantly enhance the creep resistance of titanium matrix composites (TMCs), two-scale network microstructure was constructed including the first-scale network (

The plastic deformation of metallic glasses (MG) is well-known to occur via shear transformation zones (STZs) on the scale of atomic clusters, yet fracture of MG takes place via shear bands of the micron scale. So far, understanding on how the operation of STZs leads to shear localization and fracture remains limited. In this work, tensile tests on Cu/Zr-based MG micro-wires show that both the first-yield and fracture stress exhibit the Weibull distribution, and fractography reveals that shear localization in the form of intense shear bands leads to shear fracture. Molecular dynamics (MD) simulations show that shear bands form via the correlated emergence and operation of discrete STZs close to one another. To describe how the stochastic yet correlated occurrence of the discrete STZs leads to shear localization, a model is constructed to relate the probability of the successive operation of discrete STZs, to their nucleation density. The model predicts that, if nucleation density of the STZs grows along the strain path, as prior shear events triggers the emergence of new STZs, then successive occurrence of discrete shear events speeds up rapidly to an asymptotic state which is exactly the condition of shear localization and shear banding. Furthermore, the MD results suggest an exponential growth law for the occurrence of the STZs along the strain path, which also gives predictions in good agreement with the experimental Weibull distributions of the first-yield stress of Cu/Zr-based MGs.

The atomic structure evolution of Gd36Tb20Co20Al24 high entropy metallic glass microwire from room to cryogenic temperature has been studied by in-situ high energy synchrotron X-ray diffraction. During the cooling process, the atomic volume decreases. For short-range order, the coordination numbers of all atomic pairs increase. As the temperature decreases, bond lengths of large atom-small atom and small atom-small atom pairs keep decreasing whereas that of large atom-large atom pairs unexpectedly increases continuously. The mechanism of atomic structure evolution is proposed, which might be helpful for better understanding the low temperature magnetocaloric effect of high entropy metallic glasses.

Through designing the composition and processing approach, the non-equiatomic (Gd36Tb20Co20Al24)100- xFex (x = 0, 1, 2 and 3 at.%) high-entropy-metallic-glass (HE-MG) alloy microwires were successfully fabricated by melt-extraction technique. The microstructure and magnetocaloric properties of the microwires were systematically investigated. The microwires possess tunable Curie temperatures, i.e. 81– 108 K, above the typical rare-earth (RE) containing HE-MG reports. The high Curie temperatures are attributed to the designed composition. Magnetocaloric response peak values of Fe-containing GdTbCoAl alloy microwires range 7.6–8.9 J kg1 K1 (5 T), which are comparable to those of many outstanding RE-containing magnetocaloric HE-MGs. The characteristics of the melt-extraction method, combining with compositional effects, favor the formation of amorphous and nanocrystalline phases. The increase in the cooling efficiency for microwires with higher Fe content can be attributed to the broadening of the Curie temperature distribution induced by the composition difference between nanocrystalline phase and amorphous matrix. The designed composition and the melt-extraction processing approach for Fe-containing GdTbCoAl alloys can tune their Curie temperatures towards a temperature range of natural gas liquefaction and improve their magnetocaloric properties. This demonstrates that Fe-containing GdTbCoAl HE-MG composite microwires have great potential as high-performance magnetic refrigerants

The understanding of the fracture mechanism of amorphous alloys (AAs) is of importance for their engineering applications as advanced structural materials. In this study, a series of micro-tensions of Cu45Zr45Co10 AA microwires were conducted under different strain rates ranging from 5 × 10−5 s−1 to 1 × 10−2 s−1. It is found that all microwires fracture by shear cracking, but the shear fracture strengths exhibit pronounced rate-dependent uncertainties. Based on both lognormal and Weibull statistical analyses, the studied AA microwires reveal a positive rate-sensitivity of fracture strengths. However, increasing strain rates incurs the decrease in the fracture reliability. We demonstrate that the fracture reliability of AA microwires is dominated by a square root singularity of the characteristic lengths of shear offset on fracture surfaces, which satisfies linear elastic fracture mechanics.

A novel type of bi-constituent wire composite was obtained by combining melt-extracted Gd50Al30Co20 and Gd55Al20Co25 microwire components with Curie temperature (TC) of 86 K and 110 K, respectively. For a field change of 5 T, the wire composite possesses a table-like feature spanning a temperature interval of 30 K with value of ∼8.6 J kg−1 K−1, and enhanced refrigerant capacity (RC) and relative cooling power (RCP) values of ∼680 J kg−1 and ∼863 J kg−1, respectively. The experimental results agree well with those calculated by a simple bi-composition model, demonstrating the possibility of designing wire-based composites with desirable magnetocaloric effects (MCE) for active magnetic refrigeration.

Small-sized materials with large surface to volume ratio favor heat transfer during magnetic refrigeration cycling and thus may help enhancing the refrigeration efficiency. Here, high Fe content Ni44.9Fe4.3Mn38.3Sn12.5 polycrystalline microwires were prepared by a melt-extraction technique. The as-extracted microwires were annealed at 1173 K for 60 min, leading to significant grain growth and formation of a secondary Fe-rich γ phase. The annealed microwire exhibits larger magnetization difference (ΔM) between the austenite and martensite phases and smaller thermal hysteresis compared to the as-extracted microwire. The annealed microwire possesses a magnetic transition to austenite at 299 K, followed by a martensitic transformation (MT) from a ferromagnetic austenite to a weak-magnetic martensite at 208 K upon cooling. Under a magnetic field of 50 kOe, the annealed microwires show a maximum magnetic entropy change ΔSm of 6.9 J/kg·K and an effective refrigeration capacity RCeff of 78.0 J/kg over a broad working temperature span ΔTFWHM of 20 K around the MT. In addition, magnetic transition of the austenite gives rise to ΔSm −3.7 J/kg·K and RCmag 232.5 J/kg with ΔTFWHM of 85 K under 50 kOe. Keywords: Ferromagnetic shape memory alloys, Microwires, Martensitic transformation, Magnetocaloric effect, Ni-Fe-Mn-Sn

The data in this article is the supplementary data of the research article entitled “Comparable magnetocaloric properties of melt-extracted Gd36Tb20Co20Al24 metallic glass microwires” (Yin et al., 2020). The data shows the circular cross section of Gd36Tb20Co20Al24 metallic glass microwires with a diameter of ∼55 μm. The data also shows that the chemical compositions of microwires are basically uniform on macro-scale and micro-scale.

Techniques to fabricate patterned sapphire substrates (PSSs) have attracted much attention in recent decades. Wet etching behaviors and crystalline sapphire processes are critical for PSSs applications to improve the performance of light-emitting diodes. This study investigated the shape evolution behaviors and associated kinetics of cavities on the c-{0001} plane in crystalline sapphire during wet etching. It was revealed that wet etching reduces the cavity aspect ratio, and the cavity shape is a complicated structure constructed by 15 faceted planes of c-{0001}, r-{1 1 ¯ 02}, p-{11 2 ¯ 3}, m-{10 1 ¯ 0}, and s-{1 1 ¯ 01} families. A constant etching rate was demonstrated, suggesting the step flow mechanism of etching. The etching activation energy of crystalline sapphire is reduced by preformation of cavities as elucidated by the Arrhenius kinetic model followed during the etching process. This study provides new insight into wet etching behaviors of crystalline sapphire and might open up a way for fabricating sapphire substrate with large aspect ratio patterns.

Chemical wet etching technology is widely applied in semiconductor device fabrication such as the patterned sapphire substrates. However, the etching of pre-formed structure is still lack of investigations, which has potential applications in the preparation of particular devices. By using molten KOH etchant, the present work studied the wet etching behaviors of cavity on the A-plane of sapphire crystal in three-dimensional space and revealed the etching kinetics. It was demonstrated that the cavity will evolve into a complicate symmetric shape with multiple facet planes during etching. The width of the cavity is gradually expanded however the depth of the cavity is stable during etching, where the Arrhenius model was held, indicating that the etching process is realized by step flow removal of atoms. The present results improve the understanding of the morphology evolution and relevant kinetics of a pre-formed structure on sapphire crystal during wet etching, which shed further light on the single crystal wet etching technology for device fabrication.

The effects of trace Fe-doping on the magnetic and magnetocaloric performances of Gd-based metallic microfibers were systematically and detailedly investigated in this article. Experimental results indicated that the Gd-based microfibers prepared by the rotated-dipping process are uniform and continuous, with typically amorphous structure characteristics and favorable thermal stability. Curie temperature TC of Gd-based amorphous microfibers increases with the rising of Fe content, and the TC of GdAlCoFe3 microfibers is the highest at 128.7 K (relatively increased by 15.3 K than before doping). Among the general magnetic performance indicators, the saturation magnetization Ms of GdAlCoFe2 microfibers reaches a peak at 264.04 emu/g. Furthermore, the values of magnetocaloric performance indexes of Gd-based amorphous microfibers increase firstly and then decrease with the rising of Fe-doping amount. When the external magnetic field Hex = 50,000 Oe, the maximum magnetic entropy change -ΔSmmax, refrigeration capacity RC and relative cooling power RCP of GdAlCoFe1 microfibers are 10.33 J/kg·K, 748.22 J/kg and 1006.90 J/kg, which increased by 0.07 times, 0.13 times and 0.16 times, respectively than before Fe-doping (namely -ΔSmmax = 9.68 J/kg·K, RC = 663.79 J/kg, RCP = 871.73 J/kg). From the perspective of microstructural changes, Fe-doping results in the formation tendency of atomic clusters and nanocrystals in micro-regions, the orderly orientation of atoms appears, and the magnetic anisotropy increases accordingly. In addition, the 3d electron layer of the doped Fe element in Gd-Al-Co-Fe quaternary alloy system enhances the RKKY indirectly exchange coupling interaction and changes the state of magnetic entropy, which in turn leads to an increase in Curie temperature and an improvement in magnetocaloric performance. Since RC and RCP are the main indicators in engineering applications, the GdAlCoFe1 amorphous microfibers can be selected as a low-temperature magnetic refrigeration working medium to provide technical guarantee for the application of magnetic refrigeration technology.

We have proposed a series of novel tailoring techniques for integrating conventional vacuum annealing (CVA) and the specific (e.g. transverse- and rotated-) magnetic field annealing (as denoted by TMFA and RMFA respectively), and systematically investigated the impacts of them on the giant magnetoimpedance (GMI) properties and domain microstructure of Co-based amorphous wires. Experimental results indicated that a multiplex MFA treatment i.e, two-step CVA annealing under a rotated magnetic field of 4000Oe, can realize remarkable enhancement of GMI in comparison with the as-prepared, CVA-treated and MFA-treated wires. The GMI ratio increased firstly and then tended to be stable with increasing frequency, moreover, both permeability and GMI ratio decreased with the increase of DC magnetic field. At 13 MHz, the maximum GMI ratio [ΔZ/Zmax]max and field response sensitivity ξmax of RMFA-ed wires increased to 398.39% and 21.84%/Oe, respectively, which is 2.41 times and 3.17 times than those of 165.18% and 6.88%/Oe for the as-prepared wires. Essentially, the physical process of RMFA action is mainly described as the multi-angle induced magnetic anisotropy and atomic reordering dynamic process due to the co-action of rotatory variation magnetic field energy and thermal activation. Meanwhile, the GMI behavior of TMFA evolving from single peak (SP) to double peaks (DPs) is attributed to the increase of magnetic domain driving force (namely domain wall movement increment) and uni-directional inducing magnetic anisotropy at relatively high frequency, which modified the GMI ratio and field sensitivity to 334.61% and 33.51%/Oe, respectively. Therefore, it can be concluded that both RMFA & TMFA would be used to explore microwires with enhanced GMI property for high-performance sensor applications.

Impedance output stability of Co-rich amorphous wires depends largely on the wire-terminal-connection, which can be accomplished by composite electroplating towards a robust sensor application. The present experimental results indicated that Ni/Cu composite layer composed of Ni, Cu plating and passivating treatment show a homogeneous microstructure, and excellent surface wettability, weldability and thermal expansion coefficient matching under variable temperature of wire-terminal-connecting. The properties of composite electroplated layer are mainly influenced by cathode current density, electroplating time and electrolyte temperature. The inhomogeneous distributed clustering-regions, disproportionated reaction, tendency of hydrogen brittleness and crack have been reduced by optimized coactions of intermolecular Van der Waals force, inner diffusion and mechanical bonding of electroplated layer. Therefore, the wire-terminal-connection is able to effectively improve impedance output stability by minimizing the disturbance of stray capacity, decreasing radio-frequency wave emission and electromagnetic signal attenuation, and suppressing the destabilization or concussion. Keywords: Amorphous wires, Wire-terminal-connection, Ni/Cu composite electroplating, Impedance output stability

We report upon the excellent magnetocaloric effect in melt-extracted DyHoCo medium entropy microwires. The magnetic entropy change (-ΔSM) reaches a large value of ∼11.2 J kg−1 K−1 for a field change (μ0ΔH) of 5 T. The large value of -ΔSM is resulted from the large magnetic moments of Dy and Ho. In addition, the DyHoCo microwires show a good cooling efficiency; RC1, RC2 and RC3 are evaluated to be ∼530 J kg−1, ∼417 J kg−1 and ∼279 J kg−1, respectively, at μ0ΔH = 5 T. The DyHoCo microwires undergo a second-order paramagnetic-ferromagnetic transition at the Curie temperature of ∼35 K. The excellent magnetocaloric property makes the melt-extracted DyHoCo microwires a promising refrigerant for cryogenic cooling application.

In this paper, the magnetocaloric effect (MCE) of a high-entropy Gd19Tb19Er18Fe19Al25 amorphous microwires fabricated by melt-extracted method are investigated systematically. These microwires exhibit a second-order phase transition from ferromagnetic to paramagnetic states at the Curie temperature of 97 K. The zero-field-cooling (ZFC) and field-cooling (FC) magnetization curves are irreversible when the temperature lower than the Curie temperature due to the spin glassy freezing behavior. The peak magnetic entropy change ( Δ S M pk ) for a field change from 0 to 5 T reaches ~5.94 J/kg∙K. In accordance to two criteria refrigerant capacity, the values of refrigerant capacity (RC) and relative cooling power (RCP) reach ~569 J/kg and ~733 J/kg at a field change of 5 T, respectively. These results suggest that the melt-extracted Gd19Tb19Er18Fe19Al25 microwires exhibit good MCE and have great potential to use as one kind of high temperature magnetic refrigeration material.

Compare with Ce–Fe–B crystalline magnets, the amorphous alloy exhibit interesting properties due to their domains, low anisotropy energy, and microstructure contribution. In order to investigate magnetic properties and microstructures of the amorphous Ce–Fe–B system with Co substituting for Fe, the ribbons with a nominal composition of Ce13.5(Fe79.5-xCox)B7 (x = 0, 3, 6, 9, 12) were prepared using vacuum melt spinner at a wheel speed of 50 m/s. The XRD and the corresponding SAED Pattern indicate the uniform amorphous microstructure is well maintained in each sample. These ribbons are magnetically soft and undergo a second order phase transition from ferromagnetic to paramagnetic state. With the increasing Co content, the Curie temperature almost linearly increases with temperature during 270 K and 410 K. Results from Lorentz Transmission Electron Microscopy (L-TEM) and micromagnetic simulation prove that the vortex domains can form spontaneously and stability in Ce–Fe–B amorphous materials no matter doping Co or not. The nontrivial topological domain structures found in experiments and numerical calculations have potential applications in the field of information storage, which is helpful to develop new applications of high abundance rare earth elements in functional materials.

The data in this article is the supplementary data of the research article entitled "Comparable magnetocaloric properties of melt-extracted Gd36Tb20Co20Al24 metallic glass microwires" (Yin et al., 2020). The data shows the circular cross section of Gd36Tb20Co20Al24 metallic glass microwires with a diameter of ∼55 μm. The data also shows that the chemical compositions of microwires are basically uniform on macro-scale and micro-scale.

The enhanced magnetocaloric properties are studied in melt-extracted Gd36Tb20Co20Al24 metallic glass microwires. The Curie temperature is ∼91 K for these microwires which show promising applications at liquid nitrogen range. The microwires possess spin glass phase in low temperature and spin freezing temperature is 60 K. Notably, the maximum magnetic entropy change (–ΔSMmax), the relative cooling power (RCP) and the refrigerant capacity (RC) reach high values of 12.36 J kg−1K−1, 948 J kg−1 and 731 J kg−1, respectively, under a field change of 5 T. The large –ΔSMmax originates from the high effective magnetic moment. Meanwhile, the spin fluctuation, the exchange integral fluctuation of metallic glass and the second order paramagnetic-ferromagnetic transition enlarge the phase transition range.

Herein, we reported the influences of accumulated direct current annealing (ADA) on the GMI properties and microstructures of Zr-doped melt-extracted (Co 68.15 Fe 4.35 Si 12.25 B 12.25 Zr 3 ) amorphous microwires. There indicated that ADA-ed wires enhanced GMI properties and improved the microstructures remarkably in comparison with as-fabricated wires. The maximum GMI ratio [Δ Z / Z 0 ] max and equivalent magnetic circumferential anisotropy field (EMCAF) of ADA-ed microwires were increased to 256.01% and 4 Oe at 20 MHz, respectively, which are more than nearly 8 and 2 times of 33.62% and 1.6 Oe for as-fabricated wires, respectively. Moreover, the maximum magnetic field response sensitivity ( ξ max ) increased to 372.57%/Oe, which is much higher than the as-fabricated wires of 44.71%/Oe. The remarkable enhancement of GMI performance was considered as the microstructural evolution including structural relaxation, appearance of nano-crystallization, and circumferential arrangement of surface magnetic domains. Nano-crystallization degree and circumferential magnetic domains arrangement were effectively improved by actions of Joule thermal energy and circular magnetic field generated ADA as shown in HRTEM and magnetic force microscope (MFM) analysis. Based on above, both the excellent GMI performances and relatively large ξ max values indicate the ADA is an effective annealing technique for thermal treating the melt-extracted amorphous wires which applied for potentially magnetic sensor in detecting low-intensity magnetic fields.

Herein, we systematically studied the effect of a novel square-wave pulse current annealing (SPCA) on the magnetic properties and microstructure of Co-based melt-extracted amorphous wires, and efficiently tailored the related experimental parameters by using numerical calculation of transient temperature rise during SPCA process. We obtained the optimal SPCA treatment (at 50 Hz, with amplitude of 90 mA for 480 s) can remarkably enhance the GMI property of as-prepared wires. At 10 MHz, the maximum GMI ratio [Δ Z / Z 0 ] max and maxima response sensitivity ξ max of SPCA-treated wire increases to 202.60% and 305.74%/Oe, which is nearly two times and 1.5 times of 104.80% and 208.14%/Oe for as-cast wire, respectively. Especially, at 5 MHz, [Δ Z / Z 0 ] max of SPCA-treated wire increases to 185.81%, which is 2.5 times of 73.69% for as-cast wire, and ξ max of SPCA-treated wire increases to 346.65%/Oe by less than two times of 190.16%/Oe for as-cast wire. From mictrostructural perspective, the notably observed role of atomic order orientation regimes and circular magnetic domain during stress releasing or structural relaxation by the co-action of high-density pulse magnetic field energy and thermal activation energy determines the optimum efficiency of SPCA, further to enhance circumferential permeability. In conclusion, SPCA treatment is expected to effectively improve GMI property of microwires, which can be used as sensitive materials for potential sensor application in detecting weak magnetic field.

High-quality Gd60Co15Al25 microwires with an average diameter of 40 µm were successfully fabricated by the melt-extraction method. The as-cast microwires undergo a second-order paramagnetic to ferromagnetic (PM–FM) transition at ∼100 K. Large values of the magnetic entropy change (−ΔSM ∼9.73 J kg−1 K−1) and the refrigerant capacity (RC ∼732 J kg−1) are achieved for a field change of 5 T. A careful analysis of critical exponents near the PM–FM transition indicates the significant effects of structural disorder on the long-range ferromagnetic interaction and the magnetocaloric response of the microwires. The excellent magnetocaloric properties make the Gd60Co15Al25 microwires very promising for use in magnetic refrigerators operating in the liquid nitrogen temperature range.

Based on a comprehensive study of the effect of progressive DC Joule-heating annealing (DJA) on giant magneto-impedance (GMI) properties of melt-extracted amorphous microwires, we systematically analysed the different mechanisms for two types of GMI effect definition. Experimental results show that DJA can improve GMI response characteristics and magnetic field sensitivity (MFS) effectively for both definitions, but ΔZ/Z0 is enhanced much more than ΔZ/Zmax of the as-cast wires. At 20 MHz, the maximum GMI ratios, as denoted by ΔZ/Z0 and ΔZ/Zmax, of DJA microwires are enhanced to 582.59% and 639.13%, while the values for the as-cast wires are 69.09% and 520.48% respectively. Meanwhile, the MFS (ξmax) and equivalent magnetic anisotropy field (Hk) increase to 1346.4%/Oe (ΔZ/Z0), 2927.9%/Oe (ΔZ/Zmax) and 1.1 Oe, respectively. These significant effects of GMI properties as denoted by Z0 are mainly attributed to the change of resistivity (ρdc) for amorphous microwires induced by DJA. Revealing the mechanism of different effects can also result in the development of a micromagnetic field sensor, especially for geomagnetic sensor applications (∼±1.0 Oe).

To improve oxidation resistance of the titanium matrix composites, the network structured Ti-Al-Si coating was successfully prepared on TiBw/Ti6Al4V composites with network microstructure utilizing hot dip siliconizing and subsequent heat treatment. The cycle oxidation tests showed that the weight gains of the Ti-Al-Si coating were only 8.98%, 5.99% and 3.65% of the TiBw/Ti6Al4V composites at 973K, 1073K and 1173K for 100 h. This result indicates super oxidation resistance of the network structured Ti-Al-Si of TiBw/Ti6Al4V composites, which can be ascribed to the three reasons: (1) the continuous Al2O3 oxide scale was formed in the outermost layer, (2) there were no cracks existed in the oxidized coating due to the unique network structure of the coating, (3) the Ti5Si4 layer in the interface could effectively retard the interfacial reaction between the Ti(Al,Si)3 coating and composite substrate.

The effects of pulse current on the deformation behavior, dislocation structure, microstructural evolution and cavity morphology of the coarse-grained (25 μm) AZ31 magnesium alloy during gas bulging process were investigated. The tests of pulse current auxiliary bulging (PCAB) showed that the formability of the alloy was improved as the increase in the peak current density. The results of TEM and SEM analysis showed that the dislocation motion was mainly glide, and the dislocation lines were approximate parallel with few dislocation tangles observed. Moreover, a part of cavity tips turned into circular bead by the concentration of the pulse current, and the rounding effect would lead to the relaxing of the high stress concentrated near the cavity tips. These phenomena indicated that the pulse current not only increased the dislocation motion but also restrained the cavity growing during PCAB process. In addition, the asymmetrical contours of the free bulging samples were observed and their forming mechanism was analyzed.

The high temperatures and extended times involved with superplastic forming titanium mean that conventional die-steels are not suitable. Although dies manufactured from nickel-based alloys are used frequently, these are expensive, and more importantly, the coefficient of thermal expansion (CTE) of this materials are bigger than that of Ti–6Al–4V, which causes the dimensional inaccuracy between the dies and workpieces. The aim of this paper is to control the CTE of ZrO2–TiO2 ceramic die by adjusting the volume fraction of TiO2 and the relative density, and then controlling its’ CTE to be similar to Ti–6Al–4V alloy. In this paper, firstly, the relation between the expansion coefficient and the volume fraction of TiO2 and ceramic relative density was investigated. The results showed that with the increment of the volume fraction of TiO2, the expansion coefficient decreased. And with the rising of the relative density, the expansion coefficient increased. Secondly, based on the Turner Equation, a modified theoretical model was proposed in which the relative density of ceramic was considered. Using the model, the comparison was made between the experimental data and calculated data. The result showed that the linear CTE of ZrO2–TiO2 can be controlled by adjusting the volume fraction of TiO2 and corresponding relative density. Thirdly, to evaluate the practicability of the ZrO2–TiO2 ceramic die on superplastic forming, the ZrO2–TiO2 ceramic die (volume fraction of TiO2 is 27%, relative density is 93%) with the expansion coefficient (8.92 × 10−6 °C−1) similar to Ti–6Al–4V was fabricated by sintering at 1520 °C for 2 h. The experiment of superplastically forming Ti–6Al–4V using ZrO2–TiO2 cylinder ceramic die was carried out, also. The Ti–6Al–4V cylinder shows better shape retention, surface quality and high dimensional accuracy, and the ceramic die seems adequate for superplastically forming the high accurate Ti–6Al–4V.