高熵合金(CoCrFeMnNi)/铜真空扩散连接的界面行为及接头性能研究

用固态扩散方法实现了CoCrFeMnNi高熵合金与铜在温度750~850℃下的良好连接,利用扫描电镜(Scanning electron microscope,SEM)、能谱(Energy disperse spectroscopy,EDS)分析、显微硬度测试及拉伸试验研究扩散反应温度对其界面反应行为和接头力学性能的影响,结合菲克扩散第二定律计算和分析Cu原子在高熵合金中的扩散系数。结果表明:Cu在高熵合金一侧的扩散速率大于高熵合金组元在Cu侧的扩散,随温度增加,高熵合金组元向Cu侧扩散时其在扩散区内原子浓度分布降低的程度按Mn>Cr>Fe>Co>Ni的顺序依次减小。理论计算表明,Cu在高熵合金中的平均扩散系数明显小于铜在不锈钢中的平均扩散系数。经扩散反应后,Cu/高熵合金界面附近均可形成FCC型固溶体组织的反应层,无金属间化合物产生。所有扩散连接接头拉伸后其断裂均发生在远离界面的铜侧,随扩散焊温度升高,其抗拉强度和应变有所降低,其中750℃时铜的抗拉强度与应变分别达到最大值224MPa和33%。

基于锰铜高阻尼合金弹簧的反作用轮隔振器性能研究

为解决反作用轮微振动引起卫星成像质量下降问题,依据反作用轮微振动特性,设计了一种汇聚式六自由度被动隔振系统。隔振系统通过弹簧刚度设计降低系统整体模态频率,结合高阻尼特性的锰铜合金作为隔振元件材料来提高振动能量衰减。首先,采用拉格朗日方程建立隔振系统动力学模型,考虑刚度对隔振性能影响,设计不同结构参数弹簧进行对照,分析弹簧径轴刚度比与系统基频关系,并确定最佳隔振结构参数;其次,利用有限元法分析隔振系统模态及振动传递特性,讨论各自由度下振动抑制性能;最后,搭建Kistler微振动试验平台对隔振前后的反作用轮微振动进行测量,分析与验证隔振器的减振效果。结果表明:隔振系统在六个扰动方向和中高频范围内隔振效果显著,在1000 Hz主频振动处隔振效果超过40 dB;在0~2500 r/min转速内F z方向上最大振动幅值的减振百分比达到92.42%。

高合金钢磨屑电选试验研究

分析了高合金钢磨屑的化学组成和物质组成 ,研究了其电选工艺参数 ,并进行了流程试验 ,得出了最佳分选参数及合理的试验流程。通过一粗一精一扫的流程试验 ,最终可得到产率为 70 6 5 % ,铁品位为78 2 2 % ,铁回收率为 98 6 0 %的导体产品。结果表明 。

Solitaire“超钻”与临床其它常用充填材料边缘微渗漏体外研究的比较

目的通过Solitaire"超钻"与临床常用充填材料边缘微渗漏体外研究,为临床冠部充填选择封闭性能较好的材料提供依据。方法选择因正畸需要拔除无龋前磨牙50颗,随机分成5组。在每颗牙的颊侧制备盒状洞形,分别用Solitaire"超钻"、GK高铜银汞合金、Spectrum TPH、DyractAP复合体、FujiⅡGC5种不同材料充填。之后,将根尖孔封闭置于5℃和55℃水浴1分钟,交替进行100次。然后将标本置入配有2%亚甲基蓝溶液中,在恒温37℃下保存15小时后沿牙体长轴纵行剖开,在体视显微镜观察壁和龈壁染料渗入情况。结果Solitaire"超钻"在壁微渗漏最小、FujiⅡGC在龈壁微渗漏最小,Ag-Hg合金与其他四组相比较微渗漏都更为明显。结论Solitaire"超钻"与牙釉质层具有良好的粘结能力,是临床上修复牙冠部可以应用的较好充填材料。

Modeling of whole process of ageing precipitation and strengthening in Al-Cu-Mg-Ag alloys with high Cu-to-Mg mass ratio

A physically based numerical model to predict the microstructure evolution and yield strength of high Cu-to-Mg mass ratio Al-Cu-Mg-Ag alloys during the whole ageing process was developed.A thermodynamically-based precipitation model,employing the classical nucleation and growth theories,was adapted to deal with the precipitation kinetics (evolution of radius and volume fraction of precipitates for Ω phase) of aged Al-Cu-Mg-Ag alloys.The model gives an estimation of the precipitation kinetics (evolution of radius and density of precipitates for both θ' and Ω phases) of the alloy.The strengthening model based on Orowan mechanism was deduced.The microstructural development and strength predictions of the model are generally in good agreement with the experimental data.

Modifying element diffusion pathway by transition layer structure in high-entropy alloy particle reinforced Cu matrix composites

The Al0.3CoCrFeNi high-entropy alloy(HEA)particles reinforced Cu matrix composites(CMCs)were fabricated by mechanical alloying and sintering.Transition layer structure was obtained by multi-step ball milling to investigate the related influence on element diffusion behavior and wear properties of CMCs.The results indicate that a new Cu transition layer is generated,and the thickness is about 5μm.Cr element diffuses into the interface via the transition layer,which forms the complex oxide.Because of the structure of Cu transition layer,the diffusion rates of Ni,Co and Fe increase,especially the Ni element.The wear resistance of CMCs is improved by 30%,which is due to the improvement of interface bonding strength,compared with the CMCs without transition layer.This method is applicable to the development of advanced HEA reinforced metallic matrix composites.

High Density Plasma Nitriding of Al-Cu Alloys for Automotive Parts

Duralumin alloys have been utilized as structural components and parts for aircrafts, train-cars and so forth. Their high specific strength was attractive to those applications; however, their little corrosion resistance and low wear endurance became a fatal demerit in practical applications. In order to overcome these issues of high strength aluminum alloys, high density plasma nitriding is proposed as an effective surface treatment for duralumin. This process has a capability to control the RF- and DC-plasmas independently for nitriding. This enables us to temporally control and describe the plasma state by in-situ plasma diagnosis. This plasma diagnosis was instrumented to search for optimum processing condition to plasma nitriding the duralumin alloys of type A2011. Both type A2011 aluminum alloy plates and pipes were employed to describe the inner nitriding behavior for hardening the duralumin alloys by the present plasma nitriding.