Effect of high undercooling on Co-Ni-Ga ferromagnetic shape memory alloys

Co₄₅Ni₂₅Ga₃₀ ferromagnetic shape memory alloys were treated by glass fluxing combined with superheating cycling. The effect of high undercooling on solidified microstructure and transformation temperatures was investigated. The martensite lath is obviously refined and a mass of sub-grains are produced with the increase of undercooling. Undercooling rapid solidification introduces a number of dislocations and large internal stress, which give rise to the production of sub-grains in recovery. During the following annealing process, these sub-grains can gradually recrystallize and grow up with an amount of γ′ phase precipitated. Meanwhile, transformation temperatures of undercooled alloys are greatly elevated compared with those of as cast, which results from the large internal stress, and gradually reduce with the heating time.     

Dislocation analysis of a complex sub-grain boundary in UO2 ceramic using accurate electron channelling contrast imaging in a scanning electron microscope

In this work, accurate electron channelling contrast imaging (A-ECCI) assisted by high resolution selected area channelling patterns (HR-SACP) was used to characterize the structure of a complex low sub-grain boundary in a creep deformed uranium dioxide (UO₂) ceramic. The dislocations were characterized using TEM-style g·b = 0 and g·b × u = 0 contrast criteria. Misorientations across the boundary were measured using HR-SACPs with 0.04° precision and high accuracy EBSD. The boundary was determined to be asymmetric and mixed in nature, composed of two distinct regions with different dislocation morphologies and a misorientation below 0.5°. The A-ECCI, HR-SACP, and HR-EBSD results are consistent, confirming A-ECCI as a powerful tool for characterizing even complex dislocations structures using scanning electron microscopy. This is particularly true for UO₂, since this material is very difficult to thin, which makes TEM examination of sub-boundaries over the scale of several micrometers difficult. Furthermore, in this study, the change in dislocations arrangement along the breath of the complex low angle sub-grain boundary is related to the misorientation across the boundary.     

Microstructure evolution of the undercooled Co-Ni-Ga magnetic shape memory alloy

Microstructure evolution of the martensite Co₅₀Ni₂₂Ga₂₈ magnetic shape memory alloy was investigated by the method of glass fluxing combined with superheating cycling. A maximum bulk undercooling of 220 K is achieved and a mass of sub-grains are introduced by the undercooling. A number of dislocations and large internal stress, due to the undercooling rapid solidification, give rise to the production of sub-grains during the recovery process. These sub-grains, as well as martensite variants, are remarkably refined with the increase of undercooling. The recrystallization and growth of sub-grains during the following annealing are also discussed.     

低电压压敏电阻

介绍了适于小型化、集成化需要的ZnO低电压压敏电阻制作的国内外发展动态。     

高镁低钪Al-Mg-Sc-Zr合金强韧化机理研究

本文通过常规轧制与退火工艺制备了具有高抗拉强度(~502MPa)和高断后延伸率(~22%)的高镁低钪Al-Mg-Sc-Zr合金,退火工艺为673K/1h。通过X射线衍射仪(XRD)、电子背散射衍射仪(EBSD)和透射电子显微镜(TEM)等手段,研究了合金退火后的组织及其强化机制。结果表明：Al-Mg-Sc-Zr合金在退火后获得了具有尺寸为0.42 μm的小晶粒和尺寸为16.2μm的大晶粒的双峰晶粒组织,固溶镁原子与Al₃(Sc,Zr)相的存在与共同作用促进了具有较大晶格畸变、存在大量亚晶及均匀弥散分布析出相的双峰晶粒组织的形成;合金主要强化方式为镁原子的固溶强化、亚晶界阻碍位错引起的亚晶界强化、细晶强化和Al₃(Sc,Zr)相的弥散强化,且合金计算与实测屈服强度相吻合;高镁固溶度、Al₃(Sc,Zr)相、双峰晶粒及再结晶织构的存在为位错增殖提供了空间,提高了合金加工硬化率,进而提高了合金的延伸率。     

取向Galfenol合金的结构与磁致伸缩应变

采用非自耗真空电弧熔炼方式制备了不同Ga含量的Fe100-XGaX(X=17、19)合金铸锭,利用定向凝固的方法试验研究了取向多晶Fe-Ga合金的结构与磁致伸缩应变。研究发现,采用定向凝固工艺制备的Fe83Ga17合金试样沿轴向呈现出明显的{110}织构特征。在低场下不同成分两种试样的磁致伸缩随磁场的增加迅速增大,在磁场强度大约为40 kA/m时Fe83Ga17合金的磁致伸缩λ达到饱和,为55×10-6。Ga含量为19%的定向凝固试样沿轴向取向性有所降低,晶粒中存在很多的亚晶界。富Ga相的析出和亚晶界的出现不利于磁致伸缩性能的提高。     

同时添加钪、锆对Al-10Mg合金再结晶机制的影响

利用电子背散射衍射(EBSD)和透射电子显微镜(TEM)研究了Al-10Mg及Al-10Mg-0.1Sc-0.1Zr合金在热压缩过程中的组织演变及动态再结晶机制。结果表明：同时添加Sc、Zr能够明显细化Al-10Mg合金的铸态晶粒,热处理后,Sc、Zr能够形成与α-Al基体共格的Al₃(Sc,Zr) 相,这些沉淀相能够提高合金的热变形抗力;在变形过程中,Al₃(Sc,Zr)相能够钉扎位错运动、降低晶界及变形带处的位错密度,使位错在沉淀相周围聚集,因而改变了Al-10Mg合金内部位错增殖与湮灭的过程、进而使Al-10Mg合金动态再结晶方式由不连续动态再结晶(DDRX)转变为连续动态再结晶(CDRX)。