用正电子湮没技术研究纯镍多晶体疲劳过程中的晶体缺陷

对充分退火纯镍多晶体样品分组进行了恒应变幅拉-压疲劳试验和冷轧形变后,测量了正电子湮没参数;并选少数疲劳试样进行了电子显微镜薄膜衍射象观察。用多指数拟合方法从疲劳试样的正电子湮没寿命谱中分解出与正电子在小空位团中湮没相应的成份。这些寿命值在不同疲劳阶段分别平均为209,255和>300ps。其相对强度的变化与小空位团浓度增加然后尺寸增大的趋势相符合。从而,本文根据正电子湮没技术提供了纯镍多晶体疲劳过程中除大量位错外空位聚集的实验证据。利用简单三态正电子捕获模型估算了上述缺陷浓度。本工作还提供了用多指数拟合方法分解复杂寿命谱和用于简单三态捕获模型的例证。关键词：

POSITRON ANNIHILATION STUDY OF CRYSTAL DEFECTS DEVELOPED DURING FATIGUE PROCESS OF PURE POLYCRYSTALLINE Ni

Positron annihilation lifetime spectra and Doppler broadening linesliapes of positron annihilation radiation energy were measured for the tension-compression fatigued Ni specimens under constant strain amplitude and for the cold rolled ones which were used for comparison. A few of the formers were selected for TEM observation. A lifetime component that can be associated with e⁺ lifetime in vacancy clusters developed during fatigue process was resolved by using a multi-exponential fitting method. It is 209, 255 and >300 ps on average in diferent ranges of fatigue respectively. The change of its relative intensity seems associated with increase of the concentration of the small vacancy clusters at early stage and growth of its dimension afterwards.Hence, this work provides a experimental evidence for the formation and clustering of vacancies as well as the development of a great number of jogged dislocations in fatigued Ni. The concentration of these defects were estimated by using a simple three state e⁺ trapping model. This work also provides a illustration of the utility of multi-exponential fitting method to complex lifetime spectra and to the above mentioned trapping model.