Al-Al₂O₃系合金のクリープ挙動と転位組織

抄録

Creep tests at high temperatures have been carried out in an Al-Al₂O₃ binary alloy and an Al-Al₂O₃-Si ternary alloy with different grain sizes. Dislocation structures after the steady-state creep have been observed in the temperature range from about 473 K to 873 K. The creep behaviour and the contribution of grain boundary sliding in a low stress range at temperatures above 773 K have been examined in details in the Al-Al₂O₃ alloy.
Dislocations were generally distributed rather uniformly, being pinned to the dispersed particles when crept at temperatures below 673 K, though incomplete subboundaries were occasionally observed in a high stress range. On the other hand, when crept at temperatures above 773 K, sharp subboundaries, which appeared to be formed associated with the grain boundary sliding, were often observed with the uniform distribution of dislocations.
At temperatures above 773 K, the Al-Al₂O₃ alloy was deformed at relatively large creep rates under stress lower than the threshold value which was estimated at temperatures below 673 K, that is, the temperature compensated creep rate \dotε_s⁄D in the low stress range deviated upwards from the \dotε_s⁄D vs. σ⁄E relation obtained at temperatures below 673 K, where \dotε_s was the steady state creep rate, D the self-diffusion coefficient of aluminium, σ the applied stress and E the Young’s modulus. The deviation increased with increasing testing temperature and with decreasing grain size. The contribution of grain boundary sliding to the total creep strain ranged from about 10 to 30% when crept at temperatures above 773 K, and the mechanism of creep deformation occurring in this temperature range was discussed.