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用低频扭摆进一步研究了在Al-0.5％Cu合金中观察到反常位错内耗峯的条件。结果指出,对于完全退火的试样来说,需要有适当的冷加工量,但是对于高温淬火试样则不需要冷加工。 用位错气团模型定性地解释了过去所观测到的表现反常振幅效应的时效内耗峯和温度内耗峯;同时指出,简单的气团模型在作定量的解释时,遇到了下述的困难:(i)在测量内耗所用的交变应力的作用下,位错线所能够拖着气团移动的距离太短。(ii)为了气团能够被位错拖着移动,组成气团的溶质原子必须具有比通常大很多个数量级的扩散系数。(iii)根据气团模型,从理论上计算出来的使位错拖着气团以临界速度而移动时,所需的临界应力比观测值大几百倍。 提出了溶质原子沿着位错弯结而扩散的气团模型,这个改进模型能够初步解决上述困难,并能定性地解释所观测的结果。这个模型所依据的基本假设是,要观测到反常内耗现象,位错线上必须具有一定数目的弯结。要得到这种弯结,可以对于退火试样进行适量的冷加工,或者把试样从高温淬火。带着弯结的位错线能够通过弯结的沿边运动而实现垂直于位错线方向的移动。可以假定,气团只在弯结两端的直位错段处形成,在弯结本身上并不形成气团。在弯结的沿边振动的过程中,聚集在弯结两端的溶质原子可以沿着位错管道进行来回?
The condition of anomalous dislocation internal friction peak observed in Al-0.5% Cu alloy was further studied by low frequency torsion. The results indicate that for fully annealed specimens, a suitable amount of cold working is required, but cold working is not required for the high temperature quenched specimens. The dislocation air-mass model was used to qualitatively explain the aging time-consuming internal friction peaks and temperature internal friction peaks observed in the past. At the same time, the simple air mass model encountered the following difficulties in quantitative interpretation: (i ) In the measurement of internal stress by the alternating stress, the dislocation line can drag the air mass moving the distance is too short. (ii) In order for the air mass to be able to be dislocated and dragged, the solute atoms that make up the air mass must have a diffusion coefficient that is many orders of magnitude larger than usual. (iii) According to the air mass model, the theoretical critical stress required to move a dislocation trailing air mass at a critical velocity is several hundred times greater than the observed value. An air mass model was proposed in which solute atoms diffused along the dislocations. The improved model could initially solve the above difficulties and interpret the observed results qualitatively. The basic assumption behind this model is that to observe the anomalous internal friction, the dislocation line must have a certain number of knots. To get this bend, you can anneal the sample for a suitable amount of cold work, or to quench the test specimen from a high temperature. Dislocation lines with bent knots can move perpendicular to the direction of the dislocation line by moving along the edge of the knot. It can be assumed that the air mass is formed only at the straight dislocation sections at both ends of the bend and does not form an air mass on the bend itself. During bending along the edge of the bend, the solute atoms that collect at both ends of the bend can be traversed along the dislocation pipeline.