微椭圆孔轴面织构油封密封性能仿真模拟及机理探究

提出轴面微椭圆孔织构油封运行时的理论分析模型,通过仿真模拟得到微孔结构参数对其性能的影响规律。结果表明：微椭圆孔轴面织构的润滑减摩性主要体现在相对运动的过程中微织构会使液膜产生显著的动压润滑效应,致使界面间形成非接触式密封和润滑状态;在研究的工况条件下,密封可靠性在微椭圆孔的方向性方面有所体现,合适的方向性能使流体在孔区流程变长,且其受边界阻挠在孔区一侧动压增强另一侧形成空化区,低压的空化区会快速抽吸即将泄漏出的流体从而提高密封可靠性,故而通过改变织构结构尺寸可控制油封的性能。为提高油封的寿命并降低泄漏率,在研究范围内,选用半轴比γ≥0.8（在面积比固定不变的情况下）、孔深h₁=1.5~4μm和旋转角α₁=0°~45°或175°~215°的轴面微椭圆孔织构较为合适。     

Air exposure improving hydrogen desorption behavior of Mg–Ni-based hydrides

It is well established that H₂O and O₂ have an inauspicious influence on hydrogen reactivity of hydrogen storage alloys. In this work, an unexpected improvement of the desorption behavior was discovered by just exposing the magnesium rich Mg–Ni hydrides into the air for a certain period. Upon an exposure duration of 4 months, the dehydrogenation peak and onset temperature were sharply lowered by 150 °C and 130 °C. Furthermore, the air-exposed sample could quickly absorb 3.08 wt% H₂ and desorb 2.81 wt% H₂ within 400 s at 300 °C. Besides the refinement of the powders due to the spontaneous hydrolysis reaction, the in-situ formed magnesium hydroxide layer and Ni are thought to be responsible for the remarkable improvement. This work gives interesting insights that the self-generating surface passivation is not necessarily harmful in the solid-state hydrogen storage area, especially for the cases where active sites of catalysis are present.     

Development of a powerful miniature hydrogen catalytic combustion powered thermoelectric generator

Rapid development of portable electronics promotes the R&D of micro/miniature power sources with high energy density. The high mass energy density and zero emission characteristic of hydrogen show a huge potential to develop powerful portable hydrogen-based power sources. A miniature hydrogen catalytic combustion powered thermoelectric generator (CCP-TEG) is designed and tested in detail. An outstanding catalytic core is prepared with a newly proposed method on the basis of combining H₂PtCl₆ solution and foamed transition metal. Such catalytic core is demonstrated to provide high combustion temperature, complete combustion, and sufficient heat flux for power generation. Several parameters including input power, equivalent ratio, cooling mode, and load resistance are investigated to clarify their influences on the combustion temperature, electric power, and various efficiencies (combustion, heat collection, TE, and overall efficiencies) of the hydrogen CCP-TEG. The developed hydrogen CCP-TEG is able to generate an electric power of 20.7 W with an overall efficiency of 2.04%, filling the research gap of generating large electric power (>10 W) with sufficiently high overall efficiency (>2%) in the research field of hydrogen CCP-TEG. The generated electric power and overall efficiency are much higher than those in previous hydrogen CCP-TEGs. The prepared catalytic core remains excellent functionality after running for 30 h, and the combustion temperature is as high as 918 K, which ensures the sufficiently high temperature difference for powerful power generation. This study is conducted to illustrate a concrete method on developing a powerful hydrogen CCP-TEG, and to identify further research directions.     

刻蚀工艺对四面体非晶碳膜生长及其性能的影响

目的研究不同等离子体刻蚀工艺对基体和四面体非晶碳膜(ta-C)的影响,并进一步考察不同电弧等离子体刻蚀时间对ta-C薄膜结构的影响。方法采用自主设计研制的45°单弯曲磁过滤阴极真空电弧镀膜设备,进行不同等离子体刻蚀以及ta-C薄膜的沉积。使用等离子体发射光谱仪表征离子种类及其密度,使用椭偏仪表征薄膜厚度,原子力显微镜表征刻蚀后的基体粗糙度,拉曼光谱仪和XPS表征薄膜结构,TEM分析薄膜的膜基界面结构。结果辉光刻蚀工艺中,作用的等离子体离子以低密度的Ar离子为主;而电弧刻蚀时,作用的等离子体离子为高密度的Ar离子和少量的C离子,并且能够在基体表面形成约15 nm的界面层,并实现非晶碳膜(a-C)的预沉积。随电弧等离子体刻蚀时间增加,ta-C薄膜的sp3含量有所降低。结论相比于辉光刻蚀,电弧刻蚀利于制备较厚的ta-C薄膜。这主要是因为电弧刻蚀时,基体表面形成良好的界面混合层,并预沉积了非晶碳膜,形成a-C/ta-C的梯度结构,有助于增强膜基结合力。     

In situ straining in the transmission electron microscope of an L12-ordered γ′-intermetallic strengthened by disordered γ-particles

Single crystal samples of quaternary alloy Ni₆₉Co₉Al₁₈Ti₄ were in situ strained in a transmission electron microscope. The alloy consists of an L1₂-long-range ordered γ′matrix strengthened by particles of the disordered γ-phase. During in situ straining the interaction of the dislocations with the γ-particles was investigated under stress. Microscopic features such as the dissociation width of the superpartial dislocations, bending of the dislocations between the γ-particles and the pinning of the dislocations at the departure side of the γ-particles are in excellent agreement with computer simulations performed recently.     

Shear strength and fracture surface analysis of Sn58Bi/Cu solder joints under a wide range of strain rates

The influences of the strain rate on the shear strength and failure mode of Sn58Bi/Cu solder joints were investigated. After reflowing, some Kirkendall voids were observed at the neighborhood of the Cu₃Sn/Cu interface or in the inner Cu₃Sn layer. In addition, another type of void could also be observed inside the Sn58Bi eutectic solders, and its size was much larger than that of Kirkendall voids. Some Bi particles were obviously found to segregate at the interface between the Cu-Sn IMC and the Sn58Bi solder. The single lap shear test results indicated that the strain rate had an important influence on the shear strength and failure mode of Sn58Bi/Cu solder joints. The shear strength of joints demonstrated increment at first and then decrement as the strain rate increased from 3.33 × 10⁻⁴ s⁻¹ to 3.33 s⁻¹. It was observed that all Sn58Bi/Cu solder joints broke in a mixed-type fracture mode under a wide range of strain rates. Additionally, more broken IMC grains were exposed on the fracture face and more fracture occurred within the IMC layer with increasing strain rate. Furthermore, the fracture path gradually moved from the solder side to the inner IMC side as the strain rate increased.     

干式切削条件下自润滑复合涂层技术

随着现代汽车、航空等领域轻合金及难加工材料的应用,干式切削加工越来越受重视。但干式切削没有冷却液的作用,因此对刀具涂层技术提出了新的要求。由于固体自润滑可以很好地解决这一问题,因此近年来回体自润滑复合涂层研究成为热点。在综合大量文献资料的基础上,对自润滑复合涂层特性、制备技术的研究进行综述,并提出了目前制备复合涂层存在的问题及发展趋势。     

Effect of TiC whisker addition on properties of YG10F alloy

The cemented carbide material （YG10F） with different additions of TiC whisker （0%, 0.3%, 0.6%, mass fraction） was prepared by different techniques. The effect of TiC whisker addition on the density, microhardness and toughness of the experimental material was investigated. The results indicate that after the wet-milling for 8 h and sintering in vacuum at 1 440 ℃, the toughness of YG10F is remarkably improved and meanwhile higher microhardness is obtained by 0.3% TiC whisker addition. Preliminary analysis suggests that the main toughening mechanism of TiC whisker in YG10F is whisker pull-out and bridging phenomena.     

Microstructure evolution during cold rolling in a nanocrystalline Ni–Fe alloy determined by synchrotron X-ray diffraction

Stress softening after cold rolling is observed in an electrodeposited nanocrystalline Ni–Fe alloy. The grain-size distribution becomes much broader after the cold rolling. Microstructure changes, though moderate, such as simultaneously decreased dislocation and twin densities with grain growth during cold rolling, are systematically proved by synchrotron high-energy X-ray diffraction, transmission electron microscopy and differential scanning calorimetry (DSC). The amorphous fractions in the form of grain boundaries are evidenced by the diffuse-background scatterings and large DSC values. Partial dislocation separation calculation, a dislocation mean free path and annihilation model, and texture development together reveal that the current nanocrystalline Ni–Fe alloy exhibits the combined behavior of perfect dislocation slip and grain-boundary mediated deformation.