X. Xu

Ferritic Alloys with Extreme Creep Resistance via Coherent Hierarchical Precipitates.

There have been numerous efforts to develop creep-resistant materials strengthened by incoherent particles at high temperatures and stresses in response to future energy needs for steam turbines in thermal-power plants. However, the microstructural instability of the incoherent-particle-strengthened ferritic steels limits their application to temperatures below 900 K. Here, we report a novel ferritic alloy with the excellent creep resistance enhanced by coherent hierarchical precipitates, using the integrated experimental (transmission-electron microscopy/scanning-transmission-electron microscopy, in-situ neutron diffraction, and atom-probe tomography) and theoretical (crystal-plasticity finite-element modeling) approaches. This alloy is strengthened by nano-scaled L21-Ni2TiAl (Heusler phase)-based precipitates, which themselves contain coherent nano-scaled B2 zones. These coherent hierarchical precipitates are uniformly distributed within the Fe matrix. Our hierarchical structure material exhibits the superior creep resistance at 973 K in terms of the minimal creep rate, which is four orders of magnitude lower than that of conventional ferritic steels. These results provide a new alloy-design strategy using the novel concept of hierarchical precipitates and the fundamental science for developing creep-resistant ferritic alloys. The present research will broaden the applications of ferritic alloys to higher temperatures.

Nanoporous metal/oxide hybrid materials for rechargeable lithium–oxygen batteries

Lithium–oxygen batteries have attracted considerable attention due to their expected specific energy being far higher than that of lithium-ion batteries. The high charge overpotentials of the cathodic oxygen evolution reaction of insulator lithium peroxide is one of the critical challenges for practical implementation of lithium–oxygen batteries, which results in low energy efficiency and poor stability of cathodes and electrolytes. Transition metal oxides are known to be the most active electrocatalysts that can dramatically decrease the charging overpotentials of rechargeable lithium–air batteries. However, the poor electrical conductivity of these oxide electrocatalysts, such as RuO2, MnO2 and Co3O4, limits the charge transport of cathodic reactions and the full utilization of their catalytic activities. Herein, we exploit the high oxygen evolution reaction activities of oxides by incorporating insulator oxides into the pore channels of highly conductive nanoporous gold to form three-dimensional nanoporous core–shell composites. The hybrid catalysts as the cathodes of rechargeable lithium–oxygen batteries show highly reversible cathodic reactions at extremely lower overpotentials for high efficiency lithium–air batteries, arising from the synergistic effect of high conductive nanoporous gold (NPG) and catalytically active metal oxides.

Stress-induced transformations at low temperatures in a Ni45Co5Mn36In14 metamagnetic shape memory alloy

The martensitic transformation behavior in a Ni45Co5Mn36In14 was investigated at low temperatures. Almost perfect superelasticity was confirmed below 200 K. The reverse transformation finishing stress monotonically decreased with decreasing temperature and the forward transformation starting stress changed from a decrease to an increase at ∼125 K. The temperature dependence of equilibrium stress had the same tendency as that of equilibrium magnetic field, allowing the thermal transformation arrest temperature to be determined. The temperature dependence of hysteresis in stress-induced transformation was also similar to that in magnetic-field-induced transformation, and the levels of dissipation energy yielded by the stress and magnetic field were intrinsically equivalent.

Electric Properties of Dirac Fermions Captured into 3D Nanoporous Graphene Networks.

Nanoporous graphene- based electric-double-layer transistors (EDLTs) are successfully fabricated. Transport measurements of the EDLTs demonstrate that the ambipolar electronic states of massless Dirac fermions with a high carrier mobility are well preserved in 3D nanoporous graphene along with anomalous nonlinear Hall resistance and exceptional transistor on/off ratio. This study may open a new avenue for device applications of graphene.

Scanning Distortion Correction in STEM Images

Various disturbances do exist in the image taking process of scanning transmission electron microscopes (STEM), which seriously reduces the resolution and accuracy of STEM images. In this paper, a deep understanding of the scanning distortion influence on the real and reciprocal spaces of STEM images is achieved via theoretical modeling and simulation. A scanning distortion correction algorithm is further developed based on two images scanned along perpendicular directions, which is able to effectively correct scanning distortion induced deviations and significantly increase the signal to noise ratio of STEM images.

Concentration dependence of magnetic moment in Ni50Mn50−xInx/2Sbx/2 alloys with Heusler structure

The concentration dependence of magnetic properties in the austenite phase of Ni50Mn50−xInx/2 Sbx/2 Heusler alloys was systematically investigated by magnetization measurements. The Curie temperature for Ni50Mn50−xInx/2Sbx/2 alloys is almost independent of content x. On the other hand, the concentration dependence on magnetic moment shows a concave curve similar to that of Ni50Mn50−xSnx alloys, which have the same number of valence electrons. This tendency suggests that the magnetic moment continues to increase with decreasing content x and reaches that of the metastable ferromagnetic NiMn-B2 phase.