Shuiyuan Yang

Ni56Mn25-xCrxGa19 (x=0, 2, 4, 6) high temperature shape memory alloys

National Natural Science Foundation of China [50771086]; Program for New Century Excellent Talents in University (NCET), China [NCET-09-0676]; Program for New Century Excellent Talents in Fujian Provincial University (NCETFJ), China; Fujian Provincial Dep

Microstructure, mechanical and shape memory properties of Ti-55Ta-xSi biomedical alloys

National Natural Science Foundation of China [50771086]; Program for New Century Excellent Talents in University, China; Program for New Century Excellent Talents in Fujian Province University, China; Fujian Provincial Department of Science and Technology

Giant phase shift effect in Tb0.3Dy0.7Fe2/Pb(Zr,Ti)O3 laminated composite

In this letter we present a magnetic field-induced giant phase shift effect under resonant frequency in the bilayered magnetoelectric composite of Tb0.3Dy0.7Fe2(Terfenol-D) and Pb(Zr,Ti)O3. When the bias magnetic field is varied from 0.1 T to 0.3 T, the phase shift of the magnetoelectric effect under 83.2 kHz was as large as 180°, which implies a complete transformation from capacitor behavior to inductor behavior. The phase shift was analyzed in the polar coordinates, and the mechanism of this giant phase shift was considered as the ΔE effect of Terfenol-D. This giant phase shift effect may benefit existing phase modulation techniques.

A Novel Self-Assembling Al-based Composite Powder with High Hydrogen Generation Efficiency.

In this study, a novel self-assembling hydrogen generation powder comprised of 80Al-10Bi-10Sn wt.% was prepared using the gas atomization method and then collected in an air environment. The morphological and hydrolysis properties of the powders were investigated. The results indicated that the powders formed unique core/shell microstructures with cracked surfaces and (Bi, Sn)-rich phases distributed on the Al grain boundaries. The powders exhibited good oxidation resistance and reacted violently with distilled water at temperatures as low as 0 °C. Furthermore, at 30 °C, the powders exhibited a hydrogen conversion yield of 91.30% within 16 minutes. The hydrogen produced by this powder could be directly used in proton exchange membrane fuel cells. The mechanisms of the hydrolysis reactions were also analyzed.

The Influence of Flexural Deformation on the Static Magnetoelectric Coefficient of a Bilayered Magnetoelectric Composite

In the bilayered Ni/Pb(Zr, Ti)O3 (PZT) composite, upon the application of a magnetic field, a strong flexural deformation was observed. Using an analogous scenario involving a known thermo bimetal, a simple formula for the curvature in the bilayered Ni/PZT composite was obtained. This result permitted the strain distribution and the static magnetoelectric (ME) coefficient in the bilayer composite to be easily solved. Experimental and theoretical results quantitatively explained how the flexural deformation weakened the ME effect in the bilayer composite, which agreed well with the experimental results from many previous experiments.

Experimental investigation of phase equilibria in the Co–Cr–W ternary system

Abstract The phase equilibria in the Co–Cr–W ternary system were experimentally investigated by using optical microscopy, electron probe microanalysis and X-ray diffraction on equilibrated alloys. In this study, isothermal sections of the Co–Cr–W ternary system at 1000°C, 1100°C and 1200°C were determined. The intermetallic compound R phase with its composition region were determined in the isothermal section at 1200°C, whereas it was absent at 1000°C and 1100°C. The Co7W6 phase was found to possess a large solubility of Cr. The trapezoid-shaped composition region of σ phase was determined from 1000°C to 1200°C in the present work. The newly determined phase equilibria of the Co–Cr–W in the present study will provide useful information for Co-based alloys and Co–W base cemented carbides.

A jumping shape memory alloy under heat

Shape memory alloys are typical temperature-sensitive metallic functional materials due to superelasticity and shape recovery characteristics. The conventional shape memory effect involves the formation and deformation of thermally induced martensite and its reverse transformation. The shape recovery process usually takes place over a temperature range, showing relatively low temperature-sensitivity. Here we report novel Cu-Al-Fe-Mn shape memory alloys. Their stress-strain and shape recovery behaviors are clearly different from the conventional shape memory alloys. In this study, although the Cu-12.2Al-4.3Fe-6.6Mn and Cu-12.9Al-3.8Fe-5.6Mn alloys possess predominantly L21 parent before deformation, the 2H martensite stress-induced from L21 parent could be retained after unloading. Furthermore, their shape recovery response is extremely temperature-sensitive, in which a giant residual strain of about 9% recovers instantly and completely during heating. At the same time, the phenomenon of the jumping of the sample occurs. It is originated from the instantaneous completion of the reverse transformation of the stabilized 2H martensite. This novel Cu-Al-Fe-Mn shape memory alloys have great potentials as new temperature-sensitive functional materials.

Microstructure characterization, stress–strain behavior, superelasticity and shape memory effect of Cu–Al–Mn–Cr shape memory alloys

In this study, the Cr was added into Cu–Al–Mn alloys for replacing Cu and Mn, and the microstructure, martensitic transformation, stress–strain behavior, superelasticity and shape memory effect of quaternary Cu–Al–Mn–Cr shape memory alloys were investigated. All the studied alloys exhibit a mixed microstructure consisted of dominant L21 parent, small amounts of A2(Cr) and 2H(γ1′) martensite, as well as a reversible martensitic transformation. Although the alloys are main L21 parent before deformation, partial stress-induced 2H(γ1′) martensite can be stabilized and retained after unloading. Therefore, the same alloy under a certain deformation temperature not only exhibits superelasticity property during deformation, but also the deformed alloy also shows shape memory effect when heated. The results further show that Cu–12.8Al–7.5Mn–2.5Cr alloy has a good superelasticity strain of 2.9% as well as a shape memory effect of 1.5%. Cu–12.7Al–6.9Mn–1.8Cr alloy possesses much the best superelasticity strain close to 5.0% under a pre-deformation of 10% and a shape memory effect of 2.0%. The best shape memory effect up to 2.5% with 10% of pre-deformation and a superelasticity strain of 2.8% are obtained in Cu–12.5Al–5.8Mn–4.1Cr alloy.

Experimental investigation of phase equilibria in the Nb–Si–Ta ternary system

Abstract The phase equilibria in the Nb–Si–Ta ternary system at 1 373 K, 1 473 K and 1 573 K were investigated by means of back-scattered electron imaging, electron probe microanalysis and X-ray diffraction. The isothermal sections at 1 373 K, 1 473 K and 1 573 K consist of two three-phase regions and seven two-phase regions, without any ternary compounds. The compounds of NbSi2 and TaSi2, αNb5Si3 and αTa5Si3 form continuous solid solutions, respectively. The solubilities of Nb in Ta3Si and Ta2Si phases are extremely large, whereas the solubility of Si in the β(Nb, Ta) phase is relatively small.

Improved polycrystalline Ni54Mn16Fe9Ga21 high-temperature shape memory alloy by γ phase distributing along grain boundaries

Abstract In this study, the shape recovery and mechanical properties of Ni54Mn16Fe9Ga21 high-temperature shape memory alloy are improved simultaneously. This results from the low, about 4.4%, volume fraction of γ phase being almost completely distributed along grain boundaries. The recovery strain gradually increases with the increase in residual strain with a shape recovery rate of above 68%, up to a maximum value of 5.3%. The compressive fracture strain of Ni54Mn16Fe9Ga21 alloy is about 35%. The results further reveal that when applying a high compression deformation two types of cracks form and propagate either within martensite grains (type I) or along the boundaries between martensite phase and γ phase (type II) in the present two-phase alloy.