Zr-xNb-4Sn alloys with low Young’s modulus and magnetic susceptibility for biomedical implants

The microstructure, mechanical and magnetic properties of Zr–x (8, 9, 10, wt.%)Nb–4Sn alloys were investigated to obtain novel Zr-based alloy with low Young’s modulus and magnetic susceptibility for biomedical implants. After homogenization annealing, hot forging and solution annealing, Zr–8Nb–4Sn, Zr–9Nb–4Sn and Zr–10Nb–4Sn alloys were composed of β+α″ phase, β+α″ phase, β+ω phase, respectively. The temperature at which the α" and ω phase were transformed into β phase during the heating process was about 200 ​°C, and the phase transformation temperature decreased with the increase of Nb element. Among all the Zr–x (x ​= ​8,9,10)Nb–4Sn(wt.%) alloys, Zr–9Nb–4Sn alloy had the lowest Young's modulus of 46.6 ​GPa and the low magnetic susceptibility of 1.294 ​× ​10⁻⁶ cm³g⁻¹, which has a good application prospect for biomedical applications.     

Tailoring of microstructure and martensitic transformation of nanocrystalline Ti–Ni-Hf shape memory thin film

The amorphous Ti-Ni-Hf thin films with the specific compositions were prepared from single Ti-Ni-Hf alloy target by adjusting processing parameters of direct current magnetron sputtering deposition. Prior to the crystallization,a glass transition occurred in the present Ti-Ni-Hf thin films. The annealed Ti-Ni-Hf thin films were characterized by the nano-crystalline. With the annealing temperature increasing, the grain size firstly increased and then decreased owing to the presence of(Ti,Hf)_2Ni precipitate. Two endothermic and exothermic peaks corresponding to B19'■B2 martensitic transformation in heating and cooling curves were observed for the Ti-Ni-Hf thin films with the lower annealing temperature and shorter annealing time, which was closely related to the inhomogeneous composition. However, the Ti-Ni-Hf thin films annealed at higher annealing temperature and longer annealing time showed the single stage B19'■B2 martensitic transformation. In addition, the martensitic transformation temperatures firstly increased and then decreased with the annealing temperatures rising.     

Characteristic investigation of trilayered Cu/Al8011/Al1060 composite: Interface morphology,microstructure, and in-situ tensile deformation

In this work, Cu/Al8011/Al1060 trilayered composite with an ultrathin copper layer was fabricated successfully by the hybrid process of cast-rolling and hot-roll-bonding. The effects of heat treatment were investigated on the microstructure and mechanical behavior of the composite. The results showed that annealing temperatures above 300 ​°C led to the formation of new intermetallic compounds that joined their initial counterparts. Also, the interface growth was fast above 340 ​°C. It was found that the annealing temperature of 320 ​°C led to the optimal tensile properties of the composite. Through rolling, hard-brittle IMCs imposed intense plastic strains on the surrounding regions, resulting in further grain refinement of both metals in the vicinity of the interface. Although the kernel average misorientation of the trilayered composite was almost identical with the Cu/Al8011 bimetal, its amount was considerably decreased after heat treatment, as the distorted structure changed into a nearly strain-free one using the restoration phenomenon. The SEM-based in-situ tensile test showed that crack initiation occurred within the IMCs and propagated into the Cu strip, leading to its early fracture. However, the strength-displacement curve during in-situ tensile deformation did not decrease significantly due to the ultrathin copper layer.     

Effects of heat treatment on microstructure and mechanical properties of SLMed Sc-modified AlSi10Mg alloy

The influence of heat treatments on the microstructures and mechanical properties of the selective laser melting manufactured AlSi10Mg alloy modified with Sc was systematically investigated. The results showed that the addition of Sc element introduced primary Al₃Sc, which increased the heterogeneous nucleation during the solidification of AlSi10Mg alloy, and then the ultrafine network eutectic structure was obtained, and hence the tensile strength was improved significantly (nearly 23 ​%). During the heat treatment process, the network eutectic structure transformed from continuous to discontinuous, and the grain refinement was weakened with an increasing heating temperature, both of which affected the mechanical properties of the Sc modified AlSi10Mg alloy. The tensile strength decreased from 438 ​± ​10 ​MPa for the Sc-modified alloy to 208 ​± ​6 ​MPa, while the fracture strain significantly increased from 6 ​± ​0.2 ​% to 30.2 ​± ​1.2 ​% when the Sc-modified alloy was heat-treated at 325 ​°C for 12 ​h. It has been found that the desirable microstructure and mechanical properties of SLM Sc-modified AlSi10Mg alloy can be realized by controlling the heat treatment process parameters.     

Near-microscopic grain boundary facilitates fatigue crack propagation in a polycrystalline Al–Zn–Mg–Cu alloy

In present study, grain characteristics with sizes within 10–30 μm were fabricated from a same Al–Zn–Mg–Cu alloy, FCP behaviors of the alloys with small grain(SG alloy), medium grain(MG alloy) and large grain(LG alloy)were investigated and related fatigue fracture morphology was analyzed. With the enhancement of stress intensity factor range(ΔK), the alloy with larger grains possessed faster FCP rate, which were successively arranged as SG alloy > MG alloy > LG alloy at initial stage while...     

Flexible free-standing polyaniline/poly(vinyl alcohol) composite electrode with good capacitance performance and shape memory behavior

The increasing demand for portable and flexible energy storage devices drives the development of flexible electrodes and electrolytes. The aim of this work is to fabricate the flexible free-standing polyaniline/poly (vinyl alcohol) (PANI/PVA) composite electrode with good capacitance performance and shape memory behavior. The electrodes were fabricated by chemical oxidation polymerization of aniline in porous PVA (P-PVA) films. The morphology, electrochemical and mechanical properties of PANI/P-PVA electrodes were studied by scanning electron microscope, cyclic voltammetry, galvanostatic charge-discharge, and tensile test etc. The results revealed that the flexible PANI/P-PVA-1 electrode had good specific capacitance of 173.86 ​mF ​cm⁻² at 1 ​mA ​cm⁻², with the capacitance retention of 70.16% after 4000 charge-discharge cycles. Besides, it had excellent heat-induced shape memory effect. The fixed shape could completely recover to its original shape within 10 ​s at 80 ​°C, which is above the glass transition temperature (75.89 ​°C) of PANI/P-PVA-1. The comparatively tensile strength (2.86 ​MPa) and high elongation at break (315.72%) indicated its outstanding flexibility. Up to 200 times folding had no effect on the electrochemical properties. The free-standing polymer electrodes with excellent comprehensive performance provide potential applications in flexible energy-storage devices, electronic encapsulation and high stretchable electric devices etc.     

Synthesis of amorphous SeP2/C composite by plasma assisted ball milling for high-performance anode materials of lithium and sodium-ion batteries

To promote substantially the performances of red phosphorous (P) anode for lithium and sodium-ion batteries, a simple plasma assisted milling (P-milling) method was used to in-situ synthesize SeP₂/C composite. The results showed that the amorphous SeP₂/C composite exhibits the excellent lithium and sodium storage performances duo to the small nano-granules size and complete combination of selenium (Se) and phosphorous (P) to generate Se–P alloy phase. It was observed that inside the granules of SeP₂/C composite the nanometer size of the SeP₂ particles ensured the fast kinetics for Li⁺ and Na⁺ ​transfer, and the amorphous carbon wrapping the SeP₂ particles relieved volume expansion during lithium/sodium storage processes and enhances electric conductivity. Therefore, the SeP₂/C electrode retained reversible capacities of 700 ​mA ​h ​g⁻¹ at 2 ​A ​g⁻¹ after 500 cycles and 400 ​mA ​h ​g⁻¹ at 0.5 ​A ​g⁻¹ after 400 cycles as anode for LIBs and SIBs, respectively. The result proves that the amorphous SeP₂/C composite can be a new type of anode material with great potential for lithium and sodium-ion batteries.     

Creep behavior and dislocation mechanism of Ni3Al based single crystal alloy IC6SX at 760°C

The creep behavior and dislocation mechanism of Ni₃Al-based single crystal alloys IC6SX with crystal orientation [001] which was prepared by seed crystal method under the testing conditions of 760 ​°C/500 ​MPa,760 ​°C/540 ​MPa and 760 ​°C/580 ​MPa were investigated. The experimental results showed that the creep properties, dislocation morphology and mechanism of this alloy were different under different stress conditions. With the stress increasing from 500 ​MPa to 580 ​MPa, the creep life decreased from more than 1000h to 32.64h. The cubic degree of γ′ phase in single crystal alloy decreased obviously and the size of γ′ phase increased. The mechanism of dislocation movement also changed with the increasing stress. It was found that after the specimen was tested under the condition of 760 ​°C/500 ​MPa the dislocation network prevented the movement of dislocations and it was difficult for dislocations to enter the γ′ phase from the γ/γ′ interface. When the stress was 540 ​MPa, the dislocations cut into the γ′ phase by stacking fault. Furthermore, with the stress increasing to 580 ​MPa, the dislocation entered the γ′ phase in the form of extended dislocation and Lomer-Cottrell dislocation.     

Dependence of mechanical behavior on grain size of metastable Ti–Nb–O titanium alloy

Cold-rolled metastable β-type Ti–38Nb-0.2O alloy was subjected to annealing treatment to obtain different precipitates and grain sizes. The influence of annealing on microstructure and mechanical properties was investigated. The alloy annealed at 673 ?K or 773 ?K exhibited a single-stage yielding with high strength and low uniform elongation, due to the residual work hardening and the precipitation of ω or α phases. The alloy annealed at above 873 ?K exhibited an obvious double yielding behavior resulting from the stress-induced martensitic transformation. The grain growth kinetics of single β phase alloy is sensitive to temperature, and it is suggested that the existence of oxygen decreases the grain growth exponent and increases the required activation energy for grain growth. The critical stress for slip decreased monotonously with the increase of grain size, following the classic Hall-Petch relationship. However, the critical stress for martensitic transformation decreased to a minimum and then increased again, as the grain size increased. The results are worth for design of the heat-treatment parameters of the Ti–38Nb-0.2O alloy for engineering applications.     

Effect of carbon addition on microstructure and mechanical properties of a typical hard-to-deform Ni-base superalloy

In this paper, the as-cast microstructure, microsegregation, and mechanical properties of GH4151 superalloys with a carbon addition were studied by scanner electron microscopy(SEM), transmission electron microscope(TEM), electron probe microanalysis(EPMA), differential thermal analyzer(DSC), and electron backscattered diffraction(EBSD). The results show that the solid solution effect of carbon in alloys is limited, the addition of C from 0.01 to 0.08 wt% significantly refines the secondary dendr...     

TiNi形状记忆合金低速冲击响应行为的研究

利用单摆冲击试验设备，对TiNi合金不同冲击能量及温度条件下的冲击响应行为进行了研究。冲击过程中的接触载荷由压力传感器及数字信号处理系统实时测量。根据接触载荷数据，可计算得到接触载荷与样品表面变形的关系。结果表明，同一冲击高度时，随温度升高马氏体TiNi合金的最大接触载荷增加，而接触时问降低；母相TiNi合金的最大接触载荷随冲击高度的增加会出现载荷平台段即伪弹变形段，处于平台段时母相TiNi合金吸收冲击能量，且不产生不可恢复的塑性变形，最大接触载荷降低，从而可减轻材料损伤。     

Microstructure and electrical conductivity of 10% Yb-doped SrCeO3 ceramics

As a candidate material for hydrogen separation, Yb-doped SrCeO₃ has attracted increasing attention in recent decades. In the present study, Yb-doped SrCe_0.9Yb_0.1O_3-α ceramics were prepared by the dry pressing and sintering approach, with the microstructure evolution and the micro morphology investigated. It was indicated that the ceramics sintered in air were of a pure perovskite structure, and that the sintering temperature had a significant effect on the growth of ceramic grains. The average grain size increased from 1 ​μm to 10 ​μm with an increase in sintering temperature from 1300 to 1500 ​°C. Further investigation of the thermodynamics and kinetics of grain growth revealed that the grain boundary diffusion was the main driving force of grain growth during solid phase sintering, with a grain growth index of 4 and an activation energy of approximately 61.23 ​kJ ​mol⁻¹. These results illustrate an obvious tendency of grain size growth. By electrochemical workstation with different atmospheres the effects of sintering temperature on the conductivity were characterized in the temperature range of 700–900 ​°C. The electrical conductivities σ of SrCe_0.9Yb_0.1O_3-α ceramics in different atmospheres were as follows: σ(wet hydrogen) ​> ​σ(dry hydrogen) ​> ​σ(dry air) ​> ​σ(wet air). In the test atmosphere containing water and hydrogen the conductivity of protons increased with increasing temperature because of the protons jump between lattices in the form of interstitial hydrogen ions or bare protons.     

Ni—Ti合金马氏体相变的位错模型

根据实验结果,建立了一个Ｎｉ－Ｔｉ合金马氏体相变的位错模型,认为该相变是以母相阵点到马氏体阵点的矢量ｂ１或ｂ２为Ｂｕｒｇｅｒｓ矢量的相变位错在母相（１１０）ｐ面上交替地运动,形成一对对（００１）Ｍ孪晶,马氏体以形成孪晶对的形式生长,这样的马氏体具有最小的弹性应变能。利用此模型提出了马氏体的热弹性行为和形状记忆效应的物理机制。     

CuZnAl形状记忆合金马氏体相变内耗

研究了从高温淬火的ＣｕＺｎＡｌ合金的马氏体相变内耗；提出了新的内耗表达式： 认为马氏体相变内耗与整体模量 Ｇ 相对于发生马氏体相变的局部区域的模量Ｇ′的 比值有关，淬火缺陷影响局部模量软化；并研究了不完全转变对正、逆马氏体相变内 耗的影响。     

Improvement in hydrogen storage performance of Mg by mechanical grinding with molten salt etching Ti3C2Clx

Mg-based materials are currently a hot research topic as hydrogen storage materials due to their considerable theoretical hydrogen storage capacity. However, the kinetic performance of hydrogen absorption and desorption of Mg is too slow and requires high temperature, which seriously hinders the application of this material. MXene is a new type of two-dimensional material with significant role in improving thermodynamics and kinetics. In this experiment, a two-dimensional layered MXene containing Cl functional group was prepared by molten salt etching using the Ti-containing MAX phase as the raw material. Then different ratios of Ti₃C₂Cl_x were uniformly dispersed onto the surface of Mg by high energy ball milling. The samples were characterized by hydrogen absorption and desorption kinetics, SEM, XRD, XPS, and DSC to investigate the effect of Ti₃C₂Cl_x on the hydrogen absorption and desorption performance of Mg. The onset hydrogen absorption temperature can be reduced to room temperature and the hydrogen release temperature is reduced by 200 ​°C by doping Ti₃C₂Cl_x. And there is also 5.4 ​wt% hydrogen storage in the isothermal hydrogen absorption test at 400 ​°C. The results of DSC demonstrate that the E_a of Mg+15 ​wt% Ti₃C₂Cl_x was reduced by 12.6% compared to pristine Mg. The ΔH is almost invariable. The results of XPS show that the presence of multivalent Ti promotes electron transfer and thus improves the conversion between Mg²⁺/Mg and H⁻/H. This study provides a guideline for further improving the hydrogen absorption and desorption performance of Mg-based hydrogen storage materials.     

Current Research Progress in Magnesium Borohydride for Hydrogen Storage (A review)

Hydrogen storage in solid-state materials is believed to be a most promising hydrogen-storage technology for high efficiency, low risk and low cost. Mg(BH₄)₂ is regarded as one of most potential materials in hydrogen storage areas in view of its high hydrogen capacities (14.9 ​wt% and 145–147 ​kg ​cm⁻³). However, the drawbacks of Mg(BH₄)₂ including high desorption temperatures (about 250 ​°C–580 ​°C), sluggish kinetics, and poor reversibility make it difficult to be used for onboard hydrogen storage of fuel cell vehicles. A lot of researches on improving the dehydrogenation reaction thermodynamics and kinetics have been done, mainly including: additives or catalysts doping, nanoconfining Mg(BH₄)₂ in nanoporous hosts, forming reactive hydrides systems, multi-cation/anion composites or other derivatives of Mg(BH₄)₂. Some favorable results have been obtained. This review provides an overview of current research progress in magnesium borohydride, including: synthesis methods, crystal structures, decomposition behaviors, as well as emphasized performance improvements for hydrogen storage.     

Martensitic transfor mation involved mechanical behaviors and wide hysteresis of NiTiNb shape memory alloys

On the basis of thermoelastic martensitic transformation involved,the mechanical behaviors of NiTiNb shape memory alloys were experimentally studied and their wide hysteresis effect was theoretically d...     

Effect of thermo-mechanical treatment on Ti–Ta-Hf high temperature shape memory alloy

The microstructure, martensitic transformation and mechanical/functional properties of Ti–Ta-Hf alloys with various thermo-mechanical treatments were investigated. The results reveal that the hot-rolling could refine the grain size and introduce a certain number of defects, resulting in the disappearance of martensitic transformation. The as-casted and solution treated Ti–Ta-Hf alloys were composed of α'' martensite phase and smaller volume of β phase. In contrast, the grain size of solution treated Ti–Ta-Hf alloy was slightly less than that of as-casted Ti–Ta-Hf alloy. This should be responsible to the higher yield stress and superior strain recovery characteristics for solution treated Ti–Ta-Hf alloy. The yield stress for the dislocation slip and the maximum recoverable strain of solution treated Ti–Ta-Hf alloy were 723 ​MPa and 5.06%, respectively.     

Improving on calculation of martensitic phenomenological theory

Exemplified by the martensitic transformation from DO3 to 18R in Cu-14.2Al-4.3Ni alloy and according to the principle that invariant-habit-plane can be obtained by self-accommodation between variants with twin relationships, and on the basis of displacement vector, volume fractions of two variants with twin relationships in martensitic transformation, habit-plane indexes, and orientation relationships between martensite and austenite after phase transformation can be calculated. Because no additional rotation matrixes are needed to be considered and mirror symmetric operations are used, the calculation process is simple and the results are accurate.     

Microstructure and elevated-temperature mechanical properties of dispersoid-strengthened Al-Mg-Si-Mn alloys produced by twin roll casting

The microstructure and elevated-temperature mechanical properties of dispersoid-strengthened Al-Mg-Si-Mn alloys produced by twin roll casting (TRC) and conventional mold casting (MC) were studied. A specific heat treatment at 430 ​°C for 6 ​h was applied, followed by rolling. Tensile tests were carried out at 300 ​°C. The results show that in the as-cast microstructures, equiaxed grains formed in the MC sample while elongated grains with substructures formed in the TRC sample. The eutectics in the TRC sample were much finer than those in the MC sample. Upon heat treatment, large numbers of α-Al(Fe, Mn)Si dispersoids precipitated, and the TRC sample had a greater number density of dispersoids than those in the MC sample. During the tensile test after rolling, the TRC samples exhibited higher strength than the MC samples, which resulted from the combination of the strengthening effect of the stronger dispersoids and the greater substructure hardening effect in the TRC sample; the TRC sample exhibited better ductility due to its finer initial eutectic than that in the MC sample, which depressed the stress concentration and delayed the occurrence of microcracks and fracture in the TRC sample.