挤压态Mg-8Gd-1Er-0.5Zr合金的蠕变性能研究

Creep behavior of as-extruded Mg-8Gd-1Er-0.5Zr alloy

摘要:

本文研究了挤压态Mg-8Gd-1Er-0.5Zr合金在不同温度(150-200 ℃)和应力(50-70 MPa)条件下100 h的蠕变行为,利用OM、TEM等手段观察了蠕变过程中的组织演变规律,并对蠕变机理进行了分析。研究结果表明,在本文试验条件下,合金表现出优异的蠕变性能,所有的蠕变曲线均呈现出减速蠕变和稳态蠕变两个阶段；在150 ℃/50 MPa时稳态蠕变速率仅为6.48×10-11s-1 ,蠕变量为0.007%；在200 ℃/50 MPa时稳态蠕变速率为4.26×10-9s-1,蠕变量为0.226%；温度较低时(150 ℃)主要为扩散蠕变控制机制,温度较高时(175 ℃、200 ℃)蠕变机制以位错蠕变为主。蠕变过程中晶内析出的β′相与镁基体具有一定的位相关系：(020)_β′∥_Mg,[001] _β′∥[0001]_Mg,阻碍位错运动,而晶界析出的β相可以钉扎晶界。二者协同作用,促进合金高温蠕变性能的提高。

Abstract:

The creep behavior of the as-extruded Mg-8Gd-1Er-0.5Zr alloy was studied in the present paper under various temperatures (150-200 ℃) and stresses (50-70 MPa) for 100 h. The microstructure evolution during creep was investigated by optical microscopy (OM) and transmission electron microscopy (TEM), and the creep mechanism was analyzed. The results show that the alloy exhibited good creep properties under the experimental conditions. The creep curves can divide into two stages: the deceleration creep stage and the steady creep stage. The steady-state creep rate is 6.48×10_-11 s_-1, and the creep strain is 0.007% at the temperature of 150℃ and the stress of 50 MPa; The steady-state creep rate is 4.26×10_-9 s_-1, and the creep strain is 0.226% at the temperature of 200 ℃ and the stress of 50 MPa. In the case of lower temperature (150 ℃), diffusion mechanism acts as the main control mechanism, whereas dislocation mechanism controls the creep behavior at the higher temperature(175 ℃, 200 ℃). Furthermore, the precipitates of β′ phase in grains and the β phase at grain boundaries are formed during the creep process. The orientation relationship between the β′ phase and α-Mg matrix is (020)_β′∥_Mg, [001] _β′∥[0001]_Mg. The β′ phase can effectively inhibit the dislocation gliding, and the β phase can pin gain boundaries, both of them play an important role in improving the high temperature creep performance of the alloy.