Mechanisms of creep deformation in Mg-Sc-based alloys
Mechanisms of creep deformation in Mg-Sc-based alloys
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DOI：
10.1007/s11661-005-0037-z
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发表时间：
2005-07-01
影响因子：
2.8
通讯作者：
Smola, B
中科院分区：
文献类型：
--
作者：
Mordike, BL;Stulíková, I;Smola, B
由于Sc在Mg中的低扩散率，二元Mg-Sc合金仅显示出非常弱的时效硬化响应，并且与WE合金相比表现出较差的抗蠕变性。与WE合金相比，添加少量Mn（<1.5wtpet）显著改善了它们的蠕变行为，在高于300 ℃的温度下将最小蠕变速率降低了高达约两个数量级。这是由于细Mn 2SC相基底盘的沉淀，这是在基底位错的交叉滑移和非基底滑移是速率控制机制的温度下控制蠕变的非常有效的障碍。由于晶界共晶的作用，Cc的加入进一步提高了抗蠕变性。在具有低Sc含量（类似于1重量% pet）和添加稀土（RE）元素（类似于4重量% pet的Gd、Y、Cc）的合金中仍然可以看到Mn 2Sc盘的效果。含有RE和Mn的非常薄的六边形板，其平行于Mg基体的基面，增强了Mn 2SO 4沉淀物在升高的温度（类似于250 ℃）下的效果。Mg-RE系亚稳相或稳定相的棱柱板的三角形排列有效地控制了这些合金在高温或高温蠕变过程中的基底位错运动。在低Se含量合金中，基底滑移、基底位错的交叉滑移和非基底滑移的组合控制确保了在升高的和高温下的最小蠕变速率比WE合金中观察到的蠕变速率低约一个数量级。
Binary Mg-Sc alloys show only a very weak age-hardening response due to the low diffusivity of Sc in Mg and exhibit inferior creep resistance compared to WE alloys. The addition of a small amount of Mn (< 1.5 wt pet) improves their creep behavior markedly, decreasing the minimum creep rates by up to about two orders of magnitude at temperatures above 300 degrees C compared to WE alloys. This is due to the precipitation of fine Mn2SC phase basal discs, which are very effective obstacles in controlling creep at temperatures at which cross-slip of basal dislocations and nonbasal slip are the rate controlling mechanisms. The addition of Cc improves the creep resistance even more due to the effect of the grain boundary eutectic. The effect of Mn2Sc discs can still be seen in alloys with a low Sc content (similar to I wt pet) and with the addition of rare earth (RE) elements (Gd, Y, Cc similar to 4 wt pet). Very thin hexagonal plates containing RE and Mn, which lie parallel to the basal plane of the Mg matrix, augment the effect of the Mn2SC precipitates at elevated temperatures (similar to 250 degrees C). The triangular arrangement of prismatic plates of metastable or stable phases of Mg-RE systems controls effectively the motion of basal dislocations during the creep of these alloys at elevated or high temperatures. The combined control of basal slip, cross-slip of basal dislocations, and of nonbasal slip in low Se content alloys ensures minimum creep rates of about one order of magnitude lower than those observed in WE alloys, both at elevated and high temperatures.