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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。
Torsional creep and stress relaxation tests were performed from 350 ° -525 ° C with 99.95% polycrystalline pure iron and the results obtained are essentially the same as those obtained with polycrystalline pure aluminum. It can be seen from the creep curve that this creep is made up of two parts: the first part occurs at a lower temperature or a shorter time, and the second part occurs at a higher temperature or a longer time. The first part of the creep is limited due to the viscous slip of the grain boundaries. Based on the results of the creep and stress relaxation measurements, this part of the creep contains an activation energy of 78,000 ± 4,000 calories per mole. The value of this activation energy (intergranular slip activation energy) is very similar to the activation energy of pure iron self-diffusion, indicating that there is no significant difference between the grain boundaries and the interior of the grain for the basic process of atomic migration. Addition of carbon to pure iron has a significant effect on the creep of both parts. The most noteworthy result is that viscous slip of the grain boundaries has been significantly hampered with as little as 0.0004% carbon content. These findings point out a general principle in controlling the creep of metal at high temperatures and provide some new experimental evidence for the previously proposed grain boundary hole model. According to the experimental results of carbon addition, a preliminary view is also provided for the mechanism of the second part of high temperature creep. The basic process involved in this creep may be the rearrangement of the atoms in the holes inside the crystal grains.