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用99.95%的多晶纯铁作了从350°-525℃的扭转微蠕变及应力弛豫试验,所得结果的概貌与以前用多晶纯铝所得的基本上相同。从蠕变曲线上可以看出这蠕变是由两部分组成的:第一部分是在较低温度或较短时间内发生的,第二部分是在较高温度或较长时间内发生的。第一部分的蠕变是有限的,是由于晶粒间界的粘滞性滑移所引起。根据微蠕变及应力弛豫测量的结果,这一部分蠕变所包含的激活能是78,000±4,000卡/克分子。这个激活能(晶粒间界滑移激活能)的数值与纯铁自扩散的激活能很相近,表示晶粒间界与晶粒内部对于原子迁移的基本过程而言并没有显著的差异。加碳于纯铁中对于这两部分的蠕变都有显著的影响。最值得注意的结果是含碳量少到0.0004%时已经使晶粒间界的粘滞性滑移受到显著的阻碍。这些发现在控制金属高温蠕变的问题上指出一个一般性的原则,对于以前所提出来的晶粒间界空穴模型也提供了一些新的实验证据。根据加碳的实验结果,对于第二部分高温蠕变的机构也提出了一个初步的看法,这蠕变所包括的基本过程可能是晶粒内部的空穴中的原子重新排列。Creep under very small torsional stress has been investigated for 99.95% polycrystalline iron in the temperature range of 350°-525℃. The general features of the creep curves obtained are essentially the same as those previously reported for 99.991% aluminum. The creep is shown to be consisted of two parts, one occurring at lower temperatures or shorter times and the other at higher temperatures or longer times. The first part of the creep is limited in extent and is associated with the viscous behavior of grain boundaries. The activation energy for this grain-boundary creep is 78,000 ± 4,000 calories per mole according to the present creep and stress relaxation measurements. This value is close to the activation energy for self-diffusion of iron, a correlation which indicates that, in so far as to the mechanism of atomic migration is concerned, grain boundaries may not be very different from the interior of the grains.Both parts of the creep are noticably lessened by the addition of carbon in the iron specimen. A striking feature is that the viscous slip along grain boundaries appears to be hindered by carbon at a concentration as low as 0.0004%. These observations provide a guiding clue as to the problem of controlling high-temperature creep of metals and render further experimental support on the hole model previously suggested for the grain boundaries.With regard to the second part of the creep, it is tentatively suggested that its mechanism may be connected with atomic rearrangements of holes inside the grains.
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