Jiuzhou Zhao

Effect of the introduction of H atoms on magnetic properties and magnetic entropy change in metamagnetic Heusler alloys Ni–Mn–In

By hydrogen insertion into Ni51Mn49−xInx (x=16.2,16.6) Heusler alloys, the interstitial compounds Ni51Mn49−xInxHδ were fabricated. The introduction of H atoms does not change the L21 structure of the alloys but shifts martensitic temperature (TM) to lower temperature. Magnetic measurements indicated the hydrogenated Ni51Mn49−xInxHδ compounds retain the metamagnetic properties although the ferromagnetic behavior of martensitic phases is slightly enhanced due to the introduction of H atoms. The strong metamagnetic behaviors result in large magnetocaloric effect (MCE). By controlling H content an extended temperature range having large MCE can be achieved.

Hot Rolling Characteristics of spray-formed AZ91 Magnesium Alloy

AZ91 magnesium alloy was prepared by spray forming. The spray-deposited alloy was subsequently hot-rolled with a 80% reduction at 350 degrees C. The microstructural features of the as-spray-deposited and hot-rolled alloy were examined by optical microscopy, scanning electron microscopy and X-ray diffractometry. The results show that the spray-formed AZ91 magnesium alloy has, compared with the as-cast ingot, a finer microstructure with less intermetallic phase Mg17Al(12) dispersed in the matrix due to fast cooling and solidification rates of spray forming process, and, therefore showing excellent workability. It can be hot-rolled with nearly 20% reduction for one pass at lower temperatures (330-360 degrees C), and the total reduction can reach 50% prior to annealing. After proper thermo-mechanical treatment, the spray-formed AZ91 magnesium alloy exhibits outstanding mechanical properties.

Tuning martensitic transformation and magnetoresistance effect by low temperature annealing in Ni45Co5Mn36.6In13.4 alloys

We studied the influence of post-annealing on magnetic and transport properties in Ni45Co5Mn36.6In13.4 alloys. Our results demonstrate that post-annealing at low temperatures, ≤300u2009°C, can lead to a significant change in magnetic properties, martensitic temperature (TM) and magnetoresistance effect through structure relaxations and possible change in atomic order. It was found that TM shifts from 314 to 283u2009K but the strong metamagnetic behaviour is still retained when the sample is annealed at 300u2009°C for 3u2009h. Thereupon, a large magnetoresistance effect over an extended temperature range can be achieved through controlling the heat treatment conditions. Meanwhile, the thermal stability of the novel composition is also disclosed through the investigations on low temperature annealing effect.

Production of Al-B master alloys by mixing KBF4 salt into molten aluminum

Abstract Two mixing techniques, the immersion method and the vortex method, were adopted in the production of Al–3%B master alloys since the generally used production route involving the direct addition of KBF 4 salt to molten aluminum has several drawbacks. The experimental results demonstrate that the Al–B master alloys produced by the immersion method show a microstructure characterized by the appearances of AlB 12 phase and many agglomerations of boride particles, while the Al–B master alloy produced by the vortex method exhibits a well dispersed microstructure of AlB 2 particles in the matrix. The distinct microstructure features result from the differences in the stirring speed during the salt additions and the average size of the salt droplets achieved by the salt additions.

The effects of interstitial atoms H and B on magnetic properties and magnetocaloric effect in LaFe11.5Al1.5 compound

The changes in magnetic properties of LaFe11.5Al1.5Hx and LaFe11.5Al1.5By have been investigated. By introducing interstitial atoms H or B, the magnetic ground state is changed from the antiferromagnetic to the ferromagnetic state, accompanied by significant increases in the saturated magnetization (Ms) and the Curie temperature (TC). An attractive feature is that the magnetic transition from the second-order to the weakly first-order with increasing hydrogen content compared to the magnetic transition from the weakly first-order to the second-order with increasing boron content. The maximum magnetic entropy change (−ΔSM) under a field change of 0–5u2009T increases from 10.1u2009J/kgu2009·u2009K for hydrogen content xu2009=u20090.12 to 12.3u2009J/kgu2009·u2009K for xu2009=u20091.3, while decreases from 9.6u2009J/kgu2009·u2009K for boron content yu2009=u20090.1 to 9.2u2009J/kgu2009·u2009K for yu2009=u20090.3.

Surface electronic inhomogeneity of the (001)-SrTiO3:Nb crystal with a terrace-structured morphology

Local surface conduction of the (001)-orientated SrTiO3:Nb crystal with a terrace-structured morphology has been studied by means of conductive atomic force microscope analysis. We found that the surface conductance is inhomogeneous on the atomic scale; it is high near step edges and low on terrace plateaus. The surface conductance fluctuation is susceptible to post annealing, first enhancing and then weakening while repeatedly annealed at 700u2009°C in vacuum. Considering the fact that the oxygen content is most sensitive to vacuum annealing for the temperatures adopted here, the inhomogeneous conductance implies the difference of oxygen vacancy content at step edges and terrace plateaus. The present work clearly demonstrated the influence of surface microstructure on physical properties, and could be helpful for the understanding of the atomic scale non-uniformity of the ultrathin films fabricated on step-featured SrTiO3 surface.

Modeling and experimental verification of tubular product formation during spray forming

A mathematical model is formulated to predict the shape evolution and the final geometry of a tubular product prepared by spray forming. The effects of several important processing parameters oil the shape evolution of the tube are investigated. The model is validated against experiments of spray formed large diameter tubes. The experimental and the modeling results show that there are three distinct regions in the preform, i.e., the left transition region, the middle uniform diameter region and the right transition region. The results show that the atomization parameters a(s) and b(s), traversing speed nu of the Substrate, the outer diameter D(0) of the substrate, and the initial deposition distance d(0) play important roles in the contour and the wall thickness of the spray formed tube. But the angular velocity omega of the substrate has little effect on the buildup of the deposit. After a certain time from the beginning of the process, the deposit will come into a steady growth state. In addition, an equation is provided to estimate the wall thickness of the deposit under the steady growth state based on the mass conservation.