具有抗拉强度反常温度效应的Mg-Gd-Y-Sm-Zr系合金高温蠕变机理研究

Creep resistance is an important mechanical property of high temperature structural materials. It is an important mechanical property index relating to whether the alloy is suitable for high temperature application. The present study focuses on the high temperature creep mechanism of heat resistant Mg-Gd-Y-Sm-Zr system alloys with independent intellectual property rights developed by our research team, which has the tensile strength of abnormal temperature effect and excellent high temperature tensile properties. The tensile strength of the alloys does not decrease but increase with increasing stretching temperature at the range of room temperature to 250℃ (individual to 300℃), which is the abnormal temperature effect. This phenomenon is completely different with the normal magnesium alloy of decreasing of stretching temperature with the improvement of the stretching temperature. The tensile strength of anomalous temperature effects mechanism of this alloy has been researched and obtained a number of national patents. High temperature creep properties of the alloys are excellent. However, due to the tensile strength of anomalous temperature effects, the tensile strength of anomalous temperature effects has a significant effect on the high-temperature creep mechanism of this alloy, which has not been understood now. This project intends to explore high-temperature creep mechanism of the Mg-Gd-Y-Sm-Zr system alloys, which has the tensile strength abnormal temperature effect. This project will provide a new theoretical foundation for the development of high-strength creep resistant magnesium alloys at high temperature.

抗蠕变性能是高温镁合金材料的一项重要力学性能，是关系到镁合金是否适合于高温应用的一项重要力学性能指标。本项目组开发了具有自主知识产权的、高温抗拉性能优良的Mg-Gd-Y-Sm-Zr系耐热镁合金。该系镁合金在室温到250℃（个别到300℃）范围内，出现抗拉强度随着拉伸温度的提高不降低反而提高的现象（即“反常温度效应”），与其他镁合金抗拉强度随着拉伸温度的提高而降低具有完全不同的特点。该系镁合金的研究已获得多项国家发明专利，并开展了抗拉强度反常温度效应的机理研究。该系镁合金的抗高温蠕变性能也十分优良，但由于抗拉强度具有反常温度效应，对高温蠕变机理产生重大影响，目前该合金高温蠕变机理尚不清楚。本项目拟探索具有抗拉强度反常温度效应的Mg-Gd-Y-Sm-Zr系合金高温下的蠕变机理，为开发高温高强抗蠕变耐热镁合金提供理论基础。

本项目以自主开发的具有抗拉强度反常温度效应的Mg-Gd-Y(Sm)-Zr系镁合金为研究对象，系统研究了合金的组织和性能，对蠕变200h过程中析出相和晶界形态的演变进行了详细的动态观察，分析了合金的蠕变机制。结果表明：. 所设计的13%Gd时效态合金的抗拉强度随着拉伸温度的升高先升高后降低，在250℃时达到最大值，具有明显的抗拉强度反常温度效应和优异高低温强度。该合金在200-250℃/110-150MPa和270℃/110MPa的高温高应力下仍表现出优异的抗蠕变性能。. 对250℃/150MPa蠕变过程中析出相的连续动态观察表明，析出相演变序列是β'相—β'+β1相—β'+β1+β+(18R-LSPO)相。蠕变初期基体中的花瓣状纳米β'相缓慢长大，随后β'相的中间部分颈缩并转变为细小片状β1相，而β'相长轴方向开始收缩并形成椭球形，且两者交替呈串状均匀分布，椭球形β'间呈120°角分布，合金长时间能保持相对稳定。当蠕变时间长达200h时，串状析出依然为主要形态，但出现少量针状18R-LSPO相和细小片状且纵横交错的β相，此时合金仍处于稳态蠕变阶段。由于椭球形β'相120°角分布形成的稠密三角形网格小模块对位错运动产生的巨大阻力、β'相和18R-LSPO相本身具有优异的热稳定性且与基体共格，以及β相的良好分布，使合金在高温下仍能够保持高的强度和优异抗蠕变性能。. 对合金在250℃/150MPa蠕变过程中晶界形态的动态观察表明，合金晶界能在长时间内保持相对稳定。随着蠕变时间的增加，蠕变前平直的晶界出现弯曲和宽化，晶界析出相逐渐长大，并在晶界出现单侧和双侧两种类型的晶界无析出带。原子扩散和位错滑移是引起双侧晶界无析出带的主要原因，而单侧晶界无析出带形成的主要原因则是晶界滑移。所以合金的蠕变机制主要为原子扩散、位错滑移和晶界滑移。