Ni-Cr合金与金刚石和钢基体界面微区的分析研究

利用扫描电镜 X射线能谱 ,结合金相及试样逐层的 X射线结构分析 ,剖析了 Ni-Cr合金与金刚石和钢基体钎焊界面的微区组织结构 ;揭示了 Ni-Cr合金对金刚石和钢基体表面的浸润和钎焊机理。即在钎焊过程中 ,Ni-Cr合金中的 Cr元素分离出在金刚石界面形成富 Cr层并与金刚石表面的 C元素反应生成 Cr7C3,在钢基体结合界面上 Ni-Cr合金和钢基体中的元素相互扩散形成冶金结合 ,这是实现合金层与金刚石和钢基体都有较高结合强度的主要因素。

AuGeNi－n型GaAs欧姆接触界面微区结构与接触电阻率的关系

欧姆接触是砷化镓器件中的基本单元，它的电性能极大地影响器件的质量。在众多的欧姆接触系统中，ＡｕＧｅＮｉ系统应用最为广泛。利用扫描俄歇电子微探针对离子注入重掺杂的ｎ型ＧａＡｓ上利用快速热合金制备的ＡｕＧｅＮｉ欧姆接触进行了研究，比较了不同退火温度下欧姆接触的电性能和微区界面结构，对界面微区结构与接触电阻的关系进行了探讨，提出了产生低阻接触的理想微区结构，为工艺参数的选择提供了有益的依据。

SiC_(f)/SiC陶瓷基复合材料增韧机理及界面相微区性能测试方法研究进展

作为一种典型的陶瓷基复合材料(ceramic matrix composites,CMC),SiC_(f)/SiC复合材料具有高比强度、耐高温、抗氧化和抗热震等优点,在航空航天领域应用前景广阔。纤维和基体中间的界面相具有保护纤维、传递载荷、偏转裂纹等作用,赋予SiC_(f)/SiC复合材料伪塑性断裂特征。界面相的设计方案会显著影响其微区性能,进而影响SiC_(f)/SiC复合材料宏观力学性能和损伤失效模式。近年来发展的基于聚焦离子束(focused ion beam,FIB)的微纳加工技术和基于纳米压痕的微观力学测试技术是表征SiC_(f)/SiC复合材料界面相微区性能的有效手段。本文综述了SiC_(f)/SiC界面相现有设计方案及界面相微区性能对增韧效果的影响机制,重点总结了单纤维顶出/顶入、微柱压缩等小尺寸力学测试(small-scale mechanical testing,SSMT)技术的应用现状及各方法的适用条件和优缺点。最后,对CMC界面相微区性能研究的发展趋势做了初步展望,并指出测试方法的标准化、测试环境的高温化及测试数据的模型化是未来的主要发展方向。

面向航空航天的金属多孔夹层结构钎焊研究现状及发展趋势

金属多孔夹层结构具有质轻,比强度、比刚度高,耐高温、耐腐蚀,消音、隔热等优异性能,在航空航天领域高端装备的应用受到越来越多的关注。钎焊法是实现金属多孔夹层结构芯体与面板连接的首选方法。然而夹芯与面板大面积钎焊过程中易产生钎料对薄壁母材溶蚀、焊合率低、焊接变形大、界面易形成连续脆性反应产物等缺陷,因此金属多孔夹层大面积钎焊仍有较大难度,迫切需要开展金属多孔夹层钎焊基础研究。国内外学者针对连接界面微区反应产物的种类和分布调控、薄壁母材的溶解预测、薄壁夹芯的焊接热变形控制等难题,研究了钎焊界面组织调控新方法、钎焊工艺–钎角形态–接头组织–接头力学性能的整体对应关系,阐明接头的组织演化规律,优化接头的力学性能,具有重要的科学意义及工程应用价值。本文从金属多孔夹层结构钎焊接头界面微区调控、基于力学性能优化的钎焊接头微观形态设计、钎焊过程对结构力学性能的影响及焊后强化方法和液态钎料对母材的溶解预测模型等国内外研究进展进行综述。

Improving performance of recycled aggregate concrete with superfine pozzolanic powders

Phosphorous slag （PHS）, ground granulated blast-furnace slag （GGBS） and fly ash （FA） were used as replacements of Portland cement to modify the microstruc^xe of recycled aggregate concrete （RAC）. A new manufacturing method named ＂W3T4＂ was proposed to improve the performances of interracial transition zone （ITZ） between recycled aggregate and mortar. The mechanical properties and the durability of RAC were tested, which show that this new manufacturing method improves the properties of RAC, and the GGBS with finest size makes a great contribution to the performance of RAC due to its better filling effect and much earlier pozzolanic reaction. Combined with GGBS, the effects of PHS on the retardation of setting time can be alleviated and the synergistic effect helps to make a more compact RAC. For the RAC with 25% of the recycled aggregate （RA） replacement and 10% PHS ＋ 10% GGBS additives, the compressive strength increases by 25.4%, but the permeability decreases by 64.3% with respect to the reference concrete made with nature aggregates. The micro-mechanisms of these improvements were investigated by the scanning electron microscope （SEM）. The SEM images show that the new manufacturing method, adding superfine pozzolanic powders and super-plasticizer benefits, makes a much denser ITZ in RAC.

Diffusion bonding of Al 7075 and Mg AZ31 alloys:Process parameters, microstructural analysis and mechanical properties

Al 7075 and Mg AZ31 alloys were joined by diffusion bonding method. Joining process was performed in pressure range of 10-35 MPa at temperatures of 430-450 ℃ for 60 min under a vacuum of 13.3 MPa. The microstructure evaluation, phase analysis and distribution of elements at the interface were done using scanning electron microscopy （SEM）, energy-dispersive X-ray spectroscopy （EDS） and X-ray diffraction （XRD）. The pressure of 25 MPa was determined as the optimum pressure in which the minimum amount of plastic deformation takes place at the joint. Different reaction layers containing intermetallic compounds, such as Al12Mg17, Al3Mg2 andα（Al） solid solution, were observed, in interfacial transition zone （ITZ）. Thickness of layers was increased with increasing the operating temperature. According to the results, diffusion of aluminum atoms into magnesium alloy was more and the interface movement towards the Al alloy was observed. The maximum bond strength of 38 MPa was achieved at the temperature of 440 ℃ and pressure of 25 MPa. Fractography studies indicated that the brittle fracture originated from Al3Mg2 phase.

Experimental study on the shear behavior of grout-infilled specimens and micromechanical properties of grout-rock interface

The grout-rock interfacial property is one of the key factors associated with the strength of grouted rock masses.In this study,direct shear tests and nanoindentation tests were adopted to investigate the mechanical properties of the grout-rock interface at both the macroscale and microscale.The cohesion of the cement specimens was higher than that of the grout-infilled joint specimens,while their internal friction angle was lower than that of the grout-infilled joint specimens.A“separation method”for identifying the different phases according to the qualitative and quantitative estimations was introduced,and the irregular interfacial transition zone(ITZ)thickness and elastic modulus were estimated.The ITZ thickness of the grout-infilled sandstone specimen ranged from 0 to 30μm,whereas it was within the range of 10-40μm for the grout-infilled mudstone specimen.The average elastic modulus of the ITZ in grout-infilled sandstone and mudstone specimens was approximately 58.2%and 54.1%lower than that of the bulk grout,respectively.Regarding the incidence of the rock type,the interlacing between the grout and sandstone was better developed.The ITZ with a higher porosity and lower modulus had a significant effect on the mechanical properties of the grout-infilled specimens.