碳在面心铁-镍合金中扩散峰的机构

固溶在面心铁—镍合金中的碳原子,能引起一个应力感生的扩散内耗峰。当振动频率约为1.4周/秒时,峰的位置在500°K附近。固溶的碳原子可以跳入点阵空位中而成为代位式碳原子,此碳原子舆另一个最近邻的间隙碳原子相结合后即形成一组碳原子对。在外加应力的作用下,这类碳原子对轴的择尤旋转便引起了内耗。根据这个机构并结合内耗测量过程中试样内部碳原子重新分布的情况,可以推导出碳浓度和内耗峰高度之间的定量关系,并从而求出合金的点阵空位形成能和构成碳原子对时所放出的能量。铁—镍合金中碳扩散峰的特徵是:峰的二边内耗曲线不对称,在高温的一边,内耗反而比低温的一边为低。峰的位置T′随淬火温度或碳浓度之增加而渐向低温移动;峰愈出现在低的温度,T′Q_max^-1相乘积就愈大。根据本文所提出的理论,对这些特徵作了解释。

MECHANISM OF CARBON DIFFUSION PEAK IN F. C. C. IRON-NICKEL ALLOYS

An internal friction peak induced by carbon diffusion has been observed in f. c. c. iron-nickel alloys. At a vibrational frequency of 1.4 cycles per sec., the peak occurs at about 500°K. This peak arises from the preferential rotation of the axes of carbon pairs existed in the specimen under the influence of an alternating load. These carbon pairs were formed by the interaction between the substitutional carbon atoms and their neighboring interstitial carbon atoms. Based upon this mechanism and considering the possible redistribution of the carbon atoms amongst the frozen-in vacancies in the specimen during the course of internal friction measurement, an equation bearing the quantitative relationship between the peak height and the carbon concentration has been derived. The energy of vacancy formation as well as the binding energy of the carbon pairs have been determined.The characteristics of the carbon diffusion peak in f. c. c. metals are: (1) The internal friction curve is not symmetric with respect to the peak position, the internal friction on the high temperature side being smaller than on the low temperature side. (2) The T′Q_max^-1 product varies with the peak temperature T′; the lower the peak temperature, the higher the T′Q_max^-1 product. (3) The peak temperature T′ drifts with the carbon concentration as well as the quench temperature of the specimen. Either an increase of the carbon concentration or a raise of the quench temperature tends to shift the peak position toward a lower temperature. These characteristics are interpreted in terms of the carbon pair theory as given in the text.