铁锰合金在正、反马氏体型相变温度范围内出现的位错内耗峰

用扭摆法测量了含锰18.5％的铁锰合金的内耗,在正和反马氏体型相变温度范围内都观察到一个稳定的内耗峯。在降温时,正马氏体型相变区域内的内耗峯出现在100℃左右;在重新加热时,反马氏体型相变区域内的内耗峯出现在200℃左右。对于这两个变为稳定以后的内耗峯进行了系统的研究,它们的共同特征是:1.内耗峯的位置与测量内耗所用的振动频率无关;2.稳定内耗峯的高度,随着测量内耗所用的应变振幅的增大而显著地升高;3.随着对于试样的加热和冷却循环次数的增加,内耗峯的位置离相变开始点的温度越远,而且内耗峯的高度也下降。从以上的特点可以看出,内耗峯的位置与频率无关表示产生内耗的基本过程不是受热激活所控制的。此外,内耗与振幅有关这一现象进一步指出,产生内耗的机构不是一种滞弹性效应。电子衍衬金相观测已经指出,作为扩展位错的组成部分的堆垜层错可以作为马氏体型相变的核,因此,这种内耗现象可能是由于扩展位错的应力感生加宽和收缩所引起的。这种模型可以统一地解释在铁锰合金中所观察到的各种内耗现象。

DISLOCATION DAMPING PEAKS APPEARING WITHIN THE TEMPERATURE RANGE FOR THE DIRECT AND INVERSE MARTENSITIC TRANSFORMATIONS OF AN IRON-MANGANESE ALLOY

Internal friction in an iron-manganese alloy containing 18.5% Mn was measured by a torsion pendulum; a stable internal friction peak was observed within the temperature range for the direct as well as for the inverse martensitic transformation of this alloy. When measurement was taken in descending temperatures, the internal friction peak associated with the direct martensitic transformation appeared round 100℃; and that associated with the inverse martensitic transformation appeared round 200℃ when measurement was taken in ascending temperatures.Systematic studies were made on these two internal friction peaks after they became stable and they were found to have the following characteristic features:1. The position of the peak is independent of the vibration frequency used;2. The height of the peak increases appreciably with an increase of the strain amplitude used in the measurement of internal friction;3. With an increase of the number of cycles of heating and cooling given to the specimen, the position of the peak shifts to a temperature further apart from the initial transformation temperature, and the height of the peak decreases consecutively.The independence of the position of the peak on frequency indicates that the basic process giving rise to internal friction is not controlled by heat activation. The dependence of the height of the peak on strain amplitude indicates further that the mechanism of internal friction is not concerned with anelasticity. Observations by transmission electron microscopy have revealed that the stacking fault associated with an extended dislocation may serve as nuclei for martensitic transformation of the Fe-Mn alloy studied, so that the stable internal friction peaks observed may be associated with the stress-induced expansion and contraction of the extended dislocations in the specimen. Such a model can explain the internal friction phenomena observed in the Fe-Mn alloy in a unified manner.