旋转造粒制备Al—Pb合金颗粒

研究了用旋转造粒法制备Al-8Pb-3Si-2Sn-Cu合金颗粒的宏观特征与微观组织，研究结果表明：Al-Pb合金颗粒的形状受合金熔体表面张力的影响，呈近球形，颗粒直径随熔体旋转速度的提高而减少；当颗粒直径小于3.9mm时，合金的非平衡凝固可以克服Pb重力偏析，随颗粒直径的减小，合金凝固过程从非平衡过偏晶状态转变为非平衡亚偏晶状态，在微观上Pb分布更加均匀。     

旋转磁场对无铅钎料组织及显微硬度的影响

为改善无铅钎料组织性能,研究了在0.125T、1250r/min的情况下旋转磁场对Sn3.0Ag0.5Cu、Sn-9Zn钎料组织和显微硬度的影响.结果表明：旋转磁场作用对Sn3.0Ag0.5Cu、Sn-9Zn钎料的物相构成没有影响,但可使钎料构成相的尺寸、形状及分布发生明显变化,其中部分Ag3Sn相发生弯曲,富Zn相变为细小且分布呈一定的旋转状.与未经旋转磁场作用相比,磁场作用后Sn3.0Ag0.5Cu、Sn-9Zn和Sn-9Zn钎料的显微硬度分别提高15.6%和10.2%,达到HV 24.5和HV 19.3.旋转磁场与感应电流间的Lorentz力具有驱动熔体随电磁场运动的趋势,将影响钎料组织凝固及其显微硬度.     

变质处理对新型 Al-10Sn-4Si 合金结晶组织的影响

采用钠盐变质剂对新型Ａｌ－１０Ｓｎ－４Ｓｉ轴承合金熔体进行变质处理,结果发现：变质处理不仅可以细化共晶Ｓｉ相,而且可以明显地改善共晶β（Ｓｎ）相的结晶行为,使得β（Ｓｎ）相环绕Ｓｉ粒子凝固并且以近似网状分布于晶界,为均匀化后形成均匀的β（Ｓｎ）包Ｓｉ的“包晶”式相组织创造了有利的条件。     

熔体过热处理作用机制的新认识

从液-液结构转变的角度探讨了熔体过热处理对CuSn18.7(at.%)和BiPb20.1(at.%)合金凝固组织和凝固行为的作用机制.实验表明:在升温过程中,合金熔体的某些物理性能(例如内耗,电阻率,热电势和热)在特定的温度区间都发生了异常的变化,而在降温过程中没有异常变化,揭示了熔体中在这些温度区间内发生了不连续的液-液结构转变.随后的凝固实验表明结构转变对合金的凝固有着很大的影响,例如形核过冷度显著增大,CuSn18.7合金的凝固组织明显细化,而BiPb20.1合金的初生相形态由鱼骨状树枝晶变成无序的等轴晶.分析认为熔体结构转变使得熔体结构趋于均匀和无序,在凝固中抑制了初生相的形核,进而细化凝固组织.而BiPb20.1合金组织形态的变化则是由熔体结构转变改变了界面溶质分配系数导致的.     

双频电磁约束成形过程的温度场研究

以耐热不锈钢为实验材料，利用自制的真空电磁约束成形定向凝固实验设备，测试并分析了双频电磁成形过程中样件的温度场及其影响因素，结果表明：合理的预热感应圈结构使送入固态料棒的温度分布合理；在预热感应圈不影响成形感应圈的磁场分布的情况下，预热感应圈能调整熔体的温度分布，提高熔体的过热度；屏蔽罩能够调节成形感应圈内熔体的温度分布，使熔体的下固／液界面上移，使成形感应圈内的熔体处于理想状态，侧表面垂直，位于电磁压力最大作用范围内；在其他条件一定时，抽拉速度争电源功率必须良好匹配，才能实现使金属熔化争凝固的动态平衡。     

磁场电流对AZ31镁合金组织与性能的影响

为了改善AZ31镁合金的综合性能并提高其利用价值,通过在AZ31镁合金整个凝固过程施加旋转磁场制备镁合金管坯.通过改变磁场电流对磁场与自然凝固条件下获得的AZ31镁合金铸锭的微观组织及力学性能进行了观察与测试,研究了磁场电流对AZ31镁合金显微组织和力学性能的影响.结果表明,随着磁场电流的增大,合金晶粒逐渐细化,晶粒内部出现较多的孪晶,且β-Mg17Al12相逐渐减少并细化.磁场电流越大,AZ31镁合金的力学性能越好.当磁场电流为150 A时,AZ31镁合金的抗拉强度为194 MPa,屈服强度为98 MPa,伸长率为14. 8%,与自然凝固状态相比分别提高了23. 6%、32. 4%和57. 4%.     

场致排列CrO2/Polystyrence复合材料结构及磁性分析

研究了CrO2/Polystyrence（聚苯乙烯简称PS）的场致排列复合材料的结构与磁性.通过对场致排列CrO2/PS复合样品与随机样品XRD的比较分析显示复合排列样品具有明显的各向异性特征,PS的加入并没有改变晶体的结构.磁滞洄线分析显示磁场平行于样品的易磁化轴时样品的磁矩很容易饱且剩磁较大,垂直时样品的磁矩不容易饱且剩磁较小.     

脉冲电场和稀土对Fe-C-S系合金凝固过程的影响

以工业纯铁、石墨、硫化亚铁等为原料制备Fe-C-S系合金熔体,开展在Fe-C-S系合金熔体的凝固过程中施加脉冲电场及添加稀土的实验,分析脉冲电场和稀土对Fe-C-S系合金熔体凝固组织、S元素的分布特性及夹杂物性状的影响。结果表明:脉冲电场和稀土有利于减轻晶界偏聚,细化和改善Fe-C-S系合金凝固组织,优化S元素分布,共同作用效果比稀土的单独作用效果明显;且有效减小和细化夹杂物,夹杂物的直径由35-50μm下降到25μm以下,夹杂物形貌得到较好控制,由条状硫化物大部分转变为球状硫化物。     

基于磁流变液的客车缓速器设计

首先,分析传统电涡流缓速器及液力缓速器优缺点,电涡流缓速器工作时没有时间上的滞后性,但工作电流非常大,使蓄电池很快损坏;液力缓速器能以较小的质量提供较高的制动力矩,维修成本低,但液力缓速器结构复杂,加工装配困难,开始工作及断开时有时间滞后性。其次,阐述磁流变液组成及效应,在零磁场下磁流变液中的磁性颗粒杂乱无章随机分布,在施加磁场后颗粒规则排列,沿着磁力线方向显示出成束的链状分布。磁场越强,颗粒的链状排列越明显,磁流变液的剪切屈服强度越强。最后,设计客车磁流变缓速器结构原理图,该磁流变缓速器工作在压缩与剪切相结合的模式下。据估计,该客车磁流变缓速器能够克服电涡流缓速器工作电流大及液力缓速器时间滞后的缺点。     

常规和快速凝固Al－3．18Ti－0．65C合金中TiC相的形成机理

采用快速凝固技术在ＡＬ－３．１８Ｔｉ－０．６５Ｃ合金（Ｗｔ％）合金中获得了是弥散分布的ＴｉＣ相颗粒．结合常规和快速凝固组织的分析对比，研究和探讨了相的形成过程和机制；快凝技术为研制ＡＬ／ＴｉＣ自生复合材料开辟了新的途径．     

Instability of TiC and TiAl3 compounds in Al-10Mg and Al-5Cu alloys by addition of Al-Ti-C master alloy

The performance of Al-Ti-C master alloy in refining Al-10Mg and Al-5Cu alloys was studied by using electron probe micro-analyzer （EPMA） and X-ray diffractometer （XRD） analysis. The results indicate that there are obvious fading phenomena in both Al-10Mg and Al-5Cu alloys with the addition of Al-5Ti-0.4C refiner which contains TiC and TiAl3 compounds. Mg element has no influence on the stability of TiC and TiAl3, while TiC particles in Al-10Mg alloy react with Al to form Al4C3 particles, resulting in the refinement fading. However, TiC particles are relatively stable in Al-5Cu alloy, while TiAl3 phase reacts with Al2Cu to produce a new phase Ti（Al, Cu）2, which is responsible for the refinement fading in Al-5Cu alloy. These indicate that the refinement fading will not occur only when both the TiC particles and TiAl3 compound of Al-Ti-C refiner are stable in Al alloys.     

Fabrication and Mechanical Properties of TiC／TiAl Composites

TiC/ TiAl composites with different TiC content were fabricated by rapid heating technique of spark plasma sintering ( SPS ). The effect of TiC purticles on microstructure and mechanical properties of TiAl matrix was imestigated. The results indicate that grain sizes of TiAl matrix decrease and mechanical properties are improved because of the addition of TiC particles. The composites display a 26.8% increase in bending strength when 10wt% TiC is added and 43.8% improvement in fracture toughness when 5ut% TiC is added compared to values of TiC-free materials. Grain-refinement and dispersion-strengthening were the main strengthening mechanism. The improvement of fracture toughness was due to the deflexion of TiC particles to the crack.     

Preparation of TiAl/Al_2O_3 composites by combustion synthesis

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掺杂对Al_2O_3/TiAl复合材料性能的影响

本研究采用Ti-Al-TiO2-La2O3体系,通过热压烧结工艺原位合成了Al2O3/TiAl复合材料.借助X射线衍射(XRD)、扫描电镜(SEM)等分析研究了材料的物相组成和微观组织结构,同时分别将掺杂La2O3和掺杂Fe2O3对合成Al2O3/TiAl复合材料微观结构和力学性能的影响进行了对比.结果表明:掺杂La2O3合成的Al2O3/TiAl复合材料基体尺寸相对掺杂Fe2O3合成产物较小,分散更加均匀,致密度更高.当La2O3掺杂量为3.93wt%时,Al2O3/TiAl复合材料的抗弯强度和断裂韧性达到最大值,分别为701.95MPa和7.79MPa·m1/2.由于稀土氧化物具有对基体和增强颗粒的净化,细化晶粒等作用,因此提高了TiAl基体与Al2O3增强颗粒结合强度,所以掺杂La2O3合成材料的力学性能相比掺杂Fe2O3合成的产物较高.     

Fabrication of in situ Ti2AlN/TiAl composites by reaction hot pressing and their properties

Ti2AIN/TiAI composites with different volume fractions of reinforcement were successfully fabricated by hot-pressing sintering method （reaction hot pressing） using Ti, Al and TiN powders as starting materials. The synthesis process includes four stages： first, the reactions between Al and Ti powers and between Al and TiN powders respectively occur and result in TiAl3 phase; secondly, AI powders in the sample are exhausted; the remaining Ti cores react with TiAl3 layer to form Ti-Al intermetallics; moreover, a few Ti2AlN particles precipitate from the TiAl3 phase; thirdly, Ti-Al intermetallics react with the remaining Ti cores to form Ti3Al and TiAl phases. TiAl phase and original TiN powers are in direct contact each other; finally, the residual TiN powers react with TiAl phase and result in a plenty of TizAIN phase. Compared with TiAl matrix, the hardness, elastic modulus and high-temperature compressive strength of Ti2AlN/TiAl composite are improved obviously and they are all enhanced with increasing the volume fraction of Ti2AlN phase.     

Microstructural evolution during self-propagating high-temperature synthesis of Ti-Al system

In order to investigate the microstructural evolution during self-propagating high-temperature synthesis （SHS） of Ti-Al powder mixture with an atomic ratio of Ti： Al=1：1, a combustion front quenching method （CFQM） was used for extinguishing the propagating combustion wave, and the microstructures on the quenched sample were observed with scanning electron microscope （SEM） and analyzed with energy dispersive spectrometry （EDS）. In addition, the combustion temperature of the reaction was measured, and the phase constituent of the synthesized product was inspected by X-ray diffraction （XRD）. The results showed that the combustion reaction started from melting of the Al particles, and the melting resulted in dissolving of the Ti particles and forming of Al3Ti grains. As the Al liquid was depleted, the combustion reaction proceeded through solid-state diffusion between the solid Al3Ti and the solid Ti. This led to the forming of TiAl and Ti3Al diffusing layers. In addition, the combustion reaction is incomplete besides TiAl, there are a large amount of Ti3Al and TiAl3 and a small amount of Ti in the final product. This incompleteness chiefly results from the using of coarser Ti powder.     

Al-Ti-C grain refiner made by ultrasonic levitation

An electrostrictive uniaxial ultrasonic levitation reaction system was designed to perform TiC synthesis reaction by suspending graphite powder in Al-3Ti melt and an Al-3Ti-0.15C grain refiner alloy was obtained. The results show that sound pressure node in which graphite suspends is formed in the melt between radiation block and reflecting board by ultrasonic and TiAl3 particles congregate around C powder. Meanwhile, due to ultrasonic cavitation, dissolved TiAl3 provides better surface condition for the synthesis reaction of TiC. The reaction route is that C and dissolved Ti react to form TiC. Ultrasonic cavitation has a thermal activation effect on TiC particles and Al-3Ti-0.15C refiner has excellent microstructural refining effect on α-Al.     

外加Al2O3颗粒对Ti-Al-TiO2系合成产物微观结构的影响

Ti-Al-TiO2体系外加不同含量的Al2O3颗粒获得了Al2O3／TiAl基复合材料,研究了产物的相组成及微观组织。结果表明：Al2O3颗粒多分布在基体晶界处。随外加Al2O3含量的增大,晶粒变小,但增强相颗粒团聚严重。外加Al2O3量存在一个临界值。含量过高,易造成结构疏松,不致密,形成大的气孔,且由于TiO2的活化作用,会造成外加的Al2O3颗粒烧结呈板状联结分布;含量较低,颗粒与界面的结合不够紧凑,但颗粒的结晶度较好。     

Alignment of primary Al<Subscript>3</Subscript>Ni phases in hypereutectic Al-Ni alloys with various compositions under high magnetic fields

Al-Ni hypereutectic alloys with various compositions were solidified under various magnetic field con- ditions to investigate the alignment of primary Al3Ni phases. The results showed that the application of high magnetic fields could improve the homogeneity of the primary Al3Ni phase distribution and induce the alignment of primary Al3Ni phases in the direction perpendicular to the magnetic field direction to form chain-like structures. However, the alignment was different from the orientation of the Al3Ni...     

Effect of HIPing time on the properties of TiAl alloys

The compacted TiAl alloys were prepared and the effects of HIPing time on their properties were studied. At 1100 ℃, 80 Mpa, the density of TiAl alloy reached up to 3.46 g/cm3 after 10 min HIPing. The densities of TiAl alloys did not significantly increase with the time increasing from 10 min to 70 min. Under the experimental conditions, the TiAl alloys obtained is an unstable state alloy, and the effect of HIPing time on the TiAl phase is not significant. The micro-cracks appear in inner of TiAl alloy with the HIPing time increase. At 1380 ℃, after one hour heat treatment, the micro-cracks disappear and the phase changes into stable state and its microstructure changs into lamella.