在疲劳载荷下含铜4%的铝合金中的位错钉扎和解脱

【摘　要】用Al-4％Cu合金进行了恆应变扭转疲劳试验,观察到ΔE在起始阶段下降直至接近零值,经过一定的疲劳循环数以后又重新上升。金相观测的结果指出,ΔE的重新上升对应着滑移区的突然变得集中。这有力地证明了我们以前所作的假设,即局部化滑移区的出现是引起ΔE的一种基本过程。在疲劳载荷下的T_m在超始阶段上升,但上升至最高值并保持此值经过一定的疲劳循环数以后,出现骤然的下降,这正对应着ΔE的重新上升。这种现象的出现可能是反映着在前期疲劳载荷下被钉紥的位错得到了骤然的解脱。初步认为,位错的被钉紥和随后得到解脱的过程,是由于在疲劳初期所形成的溶质铜原子气团沿着位错线的某些有利地段富集成核,同时使位错线上的另一些地段从溶质原子中解脱出来。随着富集核的逐惭增大,和其间的得到了解脱的位错段的长度的逐渐增加到某一临界值,便在疲劳载荷下出现了位错“雪崩”的现象,产生了大量的新位错,这使T_m骤然降低,并且导致局部滑移地区的形成,从而使ΔE重新增加。

THE PINNING AND UN-PINNING OF DISLOCATIONS IN Al-4% CU ALLOY UNDER FATIGUE LOADING

Fatigue experiments under constant torsional strain were carried out with an Al-4% Cu alloy. The energy loss △E was found to decrease to about zero in the initial stage of experiment, and to rise again after a certain number of cyclic loading. Results of metallographic observation showed that corresponding to the up-rise of △E, the slip regions became suddenly localized. These observations confirmed our previous assumption that the appearance of localized coarse slip regions is one of the basic processes giving rise to △E. Under fatigue loading, the maximum torque T_m was found to rise in the initial stage of experiment. It reached a maximum value and maintained there for a certain number of cyclic loading, after which a sudden drop occurred, and this drop corresponded to the up-rise of △E. Such an occurrence seems to be an indication of the sudden un-pinning of those dislocations which were pinned during the initial stage of fatigue loading. It is contemplated that the process of pinning of dislocations may be due to the nucleation of clusters of copper solute atoms drawn from the Cottrell atmosphere formed during the initial stage of experiment, along certain favorable sections of the dislocations, in consequence of which other sections of the dislocations were subsequently unpinned from copper solute atoms. As the clusters grow up in size, the length of the un-pinned dislocation segments increases until a certain critical value is reached, at which an avalanche occurs and numerous dislocations are produced. Such a happening results in a sudden drop of T_m and leads to the formation of localized slip regions which give rise to an up-rise of △E.