电流作用对铜镁合金弯曲微动疲劳损伤特性的影响

采用自主研制的试验装置，研究了铜镁合金在不同电流强度条件下的弯曲微动疲劳损伤演变规律. 运用红外线热成像仪测试电流条件下微动接触区温度分布情况；利用白光干涉仪、扫描电镜、电子探针、X射线光电子能谱仪对试样接触损伤区的微观形貌和化学行为进行分析. 试验结果表明:在相同循环次数下，随着电流强度的增加，铜镁合金弯曲微动疲劳寿命逐渐降低，接触区温度逐渐上升，接触损伤区尺寸增大，剥落层逐渐细化，接触损伤区氧化程度越来越严重，氧化磨屑的主要成分为CuO和Cu₂O；主要损伤机制为氧化磨损、黏着磨损和剥落.      

7075铝合金扭转微动疲劳行为研究

在基于多轴疲劳试验机上自主设计的扭转微动疲劳装置上,对7075铝合金材料进行了扭转微动疲劳试验,讨论了相同法向载荷下不同扭转切应力对扭转微动疲劳寿命的影响,建立了7075铝合金扭转微动疲劳S-N曲线,并采用SEM,EDS,EPMA等分析方法对扭转微动疲劳的损伤区域进行了分析,建立了扭转微动疲劳混合区接触表面损伤和裂纹萌生及扩展的物理模型,揭示了7075铝合金扭转微动疲劳的损伤机理.试验结果表明:微动作用导致疲劳寿命大大降低;扭转微动疲劳S-N曲线呈"ε"型曲线特征;损伤区靠加载端位置氧化严重,氧化程度随着循环次数增加而增加;微动疲劳的裂纹萌生于次表面,接触区中心两侧主裂纹扩展交叉后垂直于接触表面扩展至试样断裂.     

Electromagnetic wave absorption properties of Ba(CoTi)xFe12-2xO19@BiFeO3 in hundreds of megahertz band

The high-performance electromagnetic (EM) wave absorption material Ba(CoTi)$_{x}$Fe$_{12-2x}$O$_{19}$@BiFeO$_{3}$ was prepared by solid-state reaction, and its EM wave absorption properties were deeply studied. The results revealed that Ba(CoTi)$_{x}$Fe$_{12-2x}$O$_{19}$@BiFeO$_{3}$ could obtain excellent absorption properties in hundreds of megahertz by adjusting the Co$^{2+}$-Ti$^{4+}$ content. The best comprehensive property was obtained for $x=1.2$, where the optimal reflection loss ($RL$) value reaches $-30.42$ dB at about 600 MHz with thickness of 3.5 mm, and the corresponding effective absorption band covers the frequency range of 437 MHz-1 GHz. Moreover, the EM wave absorption mechanism was studied based on the simulation methods. The simulated results showed that the excellent EM wave absorption properties of Ba(CoTi)$_{x}$Fe$_{12-2x}$O$_{19}$@BiFeO$_{3}$ mainly originated from the internal loss caused by natural resonance, and the interface cancelation further improved the absorption properties and resulted in $RL$ peaks.     

Inconel 718激光熔覆合金层切向微动磨损特性研究

采用激光熔覆沉积技术制备Inconel 718合金试样，通过自主研制的多功能复合微动摩擦磨损试验机，在平面/球的点接触模式下进行切向微动磨损试验，探究合金试样在不同法向载荷和不同位移幅值下的磨损特性.试验结束后，对获得的摩擦力-位移曲线、摩擦系数曲线和耗散能等结果进行详细的动力学特性分析，再采用扫描电子显微镜和三维形貌仪对磨损表面及磨痕截面进行微观分析，得到其磨损形貌及主要的磨损机制.结果表明：当位移幅值不变时，随着法向载荷的增加，微动运行状态由完全滑移区转变成混合区，材料的磨损损伤逐渐加剧，微动磨损导致的能量耗散增加；随着位移幅值增加，材料的磨损损伤同样加剧；微动磨损区域出现裂纹的萌生和扩展现象，其主要的磨损机制为疲劳磨损、氧化磨损和磨粒磨损.