轧制和热处理对Bi系超导体高温超导相组成的影响

对Ｂｉ系超导体热处理前后的轧制试样的高温超导相组成进行了分析。结果表明,轻过轧制和热自理后,超导体的高温超导相组成发生了变化,其中１１０Ｌ相含量大大提高。热自理工艺所具有的较高的保温温度以及轧制工艺引起的超导晶粒的碎化是１１０Ｋ相含量提高的主要原因。     

初始晶粒尺寸对高温交叉轧制镁合金板材组织和力学性能的影响

目的 揭示晶粒尺寸对多道次高温交叉轧制AZ31镁合金板材组织和力学性能的影响规律及机制.方法 通过对不同初始晶粒尺寸的镁合金板材进行高温交叉轧制变形及热处理,获得不同状态的镁合金板材,采用金相显微分析、X射线衍射(XRD)分析及室温拉伸实验等手段研究镁合金板材的晶粒组织(形态、尺寸、取向)及力学性能.结果 经过多道次交叉轧制后,不同初始晶粒尺寸的板材均发生了孪生现象,但粗晶板材的晶粒尺寸仍明显大于细晶板材.退火处理后,细晶退火态板材组织均匀性较好,而粗晶退火态板材的组织虽有细化,但并不均匀.随着交叉轧制次数的增加,两种板材内非基面取向晶粒都有所增加.退火后粗晶板材中非基面取向晶粒更多.结论 晶粒细化和晶粒取向强化导致退火后的交叉轧制细晶镁合金板材具有更高的强度.粗晶板材伸长率较高主要与其具有更多的非基面取向晶粒有关.     

择优蚀坑表征立方晶系冷轧电工硅钢取向性

为确定电工硅钢的晶粒取向性,应用蚀坑技术研究了冷轧无取向硅钢、取向硅钢因择优腐蚀所形成的蚀坑与晶粒取向的关系,分析了{100}面系蚀坑形貌的演变过程,从晶体学角度建立了蚀坑形貌与晶面指数的对应关系.结果发现:无取向硅钢形成不同形貌的蚀坑,其晶面指数为(001)、(011)和(111),或是由它们演变形成的其他晶面指数;取向硅钢形成的蚀坑为同一类型,晶面指数为(011)或由其演变形成的其他晶面指数;晶界也会形成蚀坑,其形貌与相邻晶粒间的取向差有关,取向差大,形成{100}、{110}和{111}面系的蚀坑,取向差小,形成{110}面系的蚀坑.取向硅钢的蚀坑分布具有连续性,晶界的存在并不改变蚀坑的基本特征;取向硅钢蚀坑的底棱相互平行,相差不超过5°,底棱延伸方向与硅钢的轧制方向即[001]方向一致,偏离角度不超过5°.     

热处理对短碳纤维表面镍磷涂层形貌和结构的影响

对不同工艺条件下所得的碳纤维表面化学镀镍涂层进行热处理,利用SEM和XRD对热处理前后镀层形貌、物相组成及微观结构的变化进行了分析比较。实验结果表明,热处理对镀层形貌影响明显;镀层的存在对碳纤维的微结构并未造成影响;热处理后镀层的晶粒较未热处理增大近3倍,并且镀层结晶度提高近1倍;550℃热处理后镀层物相组成由初始的沿(111)晶面择优取向的金属Ni和少量的P转变为无序取向的Ni和Ni3P。     

金刚石膜内晶粒尺寸和取向对其热导率的影响

研究了金刚石膜内晶粒尺寸和取向程度对金刚石膜热导率的影响。通过对衬底表面进行不同研磨时间的处理和适当的工艺条件，采用灯丝热解化学气相沉积（ＨＦＣＶＤ）的方法在单晶硅衬底上形成了具有不同晶粒尺寸和不同程度（１００）晶面取向的金刚石膜，并研究了其热导率。结果表明，由大晶粒和较高程度（１００）晶面取向的晶粒构成的金刚石膜具有热导率特性。     

Y—Ba—Cu—O超导陶瓷的热压研究

用热压技术制备了高密度的 Y-Ba-Cu-O 材料,在适当条件下热处理,可以形成与烧结材料相同的高 T_c超导体。显微结构和 X-光衍射分析表明:在热压的 Y-Ba-Cu-O 超导陶瓷中,晶粒成片状生长,优先生长的方向与正交晶系中的 c 轴向垂直。片状晶体在一定的近程内平行排列,远程范围内无定向性,本文还对此类显微结构的取向特征与材料的超导特性进行了讨论。     

金属铝箔冷轧过程中的特性研究

利用多辊冷轧技术对金属铝进行轧制，研究了1.8μm以下金属铝箔的轧制工艺，轧制出了厚度为1.6μm高纯铝摘要箔，分析了影响铝箔表面质量的主要因素。XRD分析表明轧制过程可以使铝箔晶粒细化，晶面偏转，并形成不同类型的变形织构。同时研究了轧制过程中其力学性能的变化。     

高牌号冷轧无取向硅钢片磁畴,晶粒尺寸对铁损的影响

本文用粉纹法观察磁畴与腐蚀坑相结合的方法,研究了冷轧无取向硅钢片晶粒不同晶面,在轧面上呈现的磁畴及该畴结构对应的蚀坑坑形。进一步计算出各种畴所占百分比及其对磁性的影响。用真空热处理作了不同温度的热处理后对每种工艺统计出不同尺寸晶粒占的百分比,并与原始态作比较,阐述了各种状态下晶粒尺寸对铁损的影响。获得了接近临界平均晶粒尺寸的最佳值及其热处理工艺。     

取向硅钢易磁化方向对轧向偏离角α和β的测定方法

利用X射线衍射的方法测定取向硅钢易磁化方向[001]晶向对轧制方向(RD)的偏离角α和β。通过测定(110)晶面在轧面内的转动角度,以及其对轧面的倾斜角度,并根据晶体结构中(110)晶面与[001]晶向的关系,得到[001]晶向相对于轧向的偏离角α和β。对某取向硅钢中的4个晶粒的α和β角进行了测定,并提出了计算α和β角平均值的方法。     

(Ba,K)Fe2As2铁基超导多芯线材的晶间耦合强化与性能提高(英文)

铁基超导材料在高场超导磁体领域具有很大的应用潜力,而研究具有高传输临界电流密度的多芯复合包套线材对于其实际应用至关重要.本研究基于粉末装管法,结合孔型轧制工艺和热等静压烧结工艺制备了多芯Cu/Ag复合包套(Ba,K)Fe₂As₂ (Ba-122)超导线材.通过对不同直径线材中Ba-122超导芯的质量密度、晶粒取向、晶粒尺寸、元素分布与线材的电流传输性能之间的关系进行系统研究,我们发现线径较小的样品中超导晶粒间的耦合得到了显著增强,其传输临界电流密度在4.2 K, 10 T下达到3.3×10⁴A cm^-2,同时由于晶粒尺寸和超导芯丝的均匀性得到改善,其电流传输的一致性(n值)也获得有效提高.本研究为制备高性能、高度均匀的铁基超导多芯线材提供了一种可规模化的工艺路线,对促进铁基超导材料的高场强电应用有重要意义.     

Bi-Sr-Ca-Cu-O系高温超导体结构的电子显微镜研究

本文用透射电子显微术和 EDAX 对 Bi 系超导体的成份和晶体结构进行了分析研究。结果表明该 Bi 系超导体中存在 a=b=5.41(?)c=24.21(?)四方结构超导相,为改进成份、热处理工艺提供了依据。     

The influence of filament bundle location on coupling losses in superconducting composites. part i: mixed matrix conductor

The ac losses in mixed matrix multifilamentary superconducting composites with different superconducting filament bundle positions have been measured using the magnetization method to establish the relation between filament bundle position and coupling losses. Experimental results indicate that coupling losses between filaments in the composite with the filament bundle located in the central region is smaller than the composite with the filament bundle located in the outer region. It is also pointed out that a copper stabilizer, divided by the CuNi barrier into small regions, like a honeycomb, shows anomalous increase in its resistivity due to Ni duffusion during heat treatment.     

轴坯校直断裂分析

材料为3Cr13钢的轴坯在进行机械校直时，有30%的轴坯发生了横向断裂。经分析，轴坯的化学成分符合技术条件要求。经宏、微观检验，发现轴坯的外表面有数条裂纹；其显微组织为位向明显的回火索氏体，裂纹表面有轻微的氧化脱碳；轴坯断口为萘状断口，其微观断裂途径为沿晶断裂。通过对断裂轴坯表面裂纹的分析，认为轴坯表面裂纹分为两类：一类裂纹是由于轴坯原材料表面有较深的纵向划伤缺陷，热处理时沿缺陷处进一步扩展形成的；另一类裂纹是轴坯在淬火加热过程中由于温度偏高而形成的过热裂纹。因此，淬火加热时的过热导致轴坯在淬火冷却时形成表面裂纹，这样在轴坯机械校直时表面裂纹又诱发轴坯发生断裂。     

Transient heat transfer model for normal zone propagation. Part 1 — theory of a bare helium-cooled superconductor

The paper presents a physical model, involving no adjustable parameters of transient heat transfer for normal zone propagation in a composite helium-cooled superconductor. Evaluations are given showing that the main contribution to transient heat flux is made by transverse heat conduction in the coolant. When the zone front passes through a fixed point, the temperature at that point increases drastically, a great temperature gradient appears in coolant which results in transient cooling of the superconductor. The zone propagation equation becomes an integro-differential with a convolution integral. The transient heat transfer intensity is characterized by the introduced dimensionless parameter ?.The problem has been solved analytically for the model with constant coefficients and jump-wise heat release. Formulae have been obtained for the propagation and recovery velocities describing the effect of transient heat transfer (via parameter ?).     

Minimum heat pulse to quench a superconducting magnet

The minimum energy required to quench a fully impregnated superconducting winding has been measured at a constant field of 5 T for various currents. Great care has been taken to match the experimental conditions with those presumed in the minimum propagating zone (MPZ) treatments of the situation. In particular the winding has been designed so that the MPZ is smaller than the heat source thus satisfying the requirement for a point disturbance. The adiabatic requirement has been met with an inductive heating technique in place of the usual resistive heating. As a consequence of these features the minimum quench energies are much smaller than those obtained in previous experiments and agree well with Wilson's theoretical treatment for a point disturbance.     

Fluctuations contribution to the specific heat of a van hove superconductor

The fluctuation contribution to the specific heat of a two-dimensionai superconductor has been calculated, taking into consideration a logarithmic density of states. The specific heat correction contains a term proportional to (T-T _c)^-1 and a logarithmic contribution. It has been shown that this contribution represents a very small correction. The specific heat correction is analyzed in the critical region where the fluctuations interact strongly.     

A simple heat switch for use at millikelvin temperatures

A simple technique is described for fabricating a high conductivity silver-aluminium joint for use in the construction of an aluminium superconducting heat switch which can be operated in the millikelvin temperature range.     

Fabrication of Grain-oriented (Bi,Pb)_2Sr_2Ca_2Cu_3O_x Superconducting Tapes Using Magnetic Field and Vibration Technique

Highly textured (Bi,Pb)2Sr2Ca2Cu3Ox superconducting tapes have been fabricated by means of magnetic-field and vibration technique. This method is an effective way of improving the degree of grain alignment and density of oxide core in tapes after heat treatment and pressing cycles.Jc of above 20% was increased than that without treatment.     

Heat transfer characteristics of flat plate finned-tube heat exchangers with large fin pitch

The objective of this study is to provide experimental data that can be used in the optimal design of flat plate finned-tube heat exchangers with large fin pitch. In this study, 22 heat exchangers were tested with a variation of fin pitch, number of tube row, and tube alignment. The air-side heat transfer coefficient decreased with a reduction of the fin pitch and an increase of the number of tube row. The reduction in the heat transfer coefficient of the four-row heat exchanger coil was approximately 10% as the fin pitch decreased from 15.0 to 7.5 mm over the Reynolds number range of 500–900 that was calculated based on the tube diameter. For all fin pitches, the heat transfer coefficient decreased as the number of tube row increased from 1 to 4. The staggered tube alignment improved heat transfer performance more than 10% compared to the inline tube alignment. A heat transfer correlation was developed from the measured data for flat plate finned-tubes with large fin pitch. The correlation yielded good predictions of the measured data with mean deviations of 3.8 and 6.2% for the inline and staggered tube alignment, respectively.