【摘要】 对材料中由塑性形变引起的表面及亚表面残余应力进行测定是材料科学及工程应用关注的重要问题之一 .一种将扫描电子显微镜和声学技术结合而研制成的扫描电子声显微镜技术 (SEAM )可用于残余应力的定征 ,由此得到的电子声图象显示了在金属中由韦氏硬度压痕引起的残余应力的横向分布 ,并且利用扫描电子声显微镜独特的分层成象能力 ,揭示了残余应力的深度分布状况 .此外 ,还讨论了扫描电子声技术定征残余应力的机理及实验条件对电子声信号的影响更多还原

【Abstract】 Characterization of the residual stress has been proved to be useful to evaluate elastic modulus, yield strength and hardness of materials. Although the practical importance of the distributions of residual stress field has been well recognized, most experimental methods only show surface distribution of residual stress fields around a sharp crossed indentation. This work describes a nondestructive method, a scanning electron acoustic microscopy (SEAM), for detecting the 3 dimensional distribution of residual stress in materials. SEAM is established by modifying a scanning electronic microscopy (SEM), in which the intensity modulated electron beam is used to generate an acoustic signal within the specimen and a PZT transducer is used to detect the acoustic signal. In order to improve the signal to noise ratio, a lock in amplifier and a computer data processing system are employed. The amplitude and phase of these signals reflect different information coming from different depths. Therefore, it can be used for identification and location of many parameters of materials, for instance the distribution of residual stress. By the laminated imaging method with either changing frequency or reference phase shift of modulation signal, it becomes possible to get distributions of the residual stress in different depths. Not only can the 2 dimensional distribution of the residual stress be revealed by electron acoustic (EA) images, but also 3 dimesional distribution of it. From the imaging results, it is shown clearly that the residual stress is diffused and homogenized form the surface to subsurface around the crossed indentation. Besides, some subsurface defects have been observed in the laminated SEAM images. In addition, the EA signal generation mechanism in residual stress field and the dependencies of EA signal on experimental parameters are also discussed briefly, which is helpful for the understanding of the imaging principle. Likewise, the capability of SEAM in residual stress characterization would be available for other materials, such as ceramics and composites. Thus it will be an appropriate nondestructive technology for the characterization of materials, especially in micro scales.更多还原