The last few decades have witnessed an increasing emphasis on the development of strain-based ap- proach for predicting the creep life or damage of components operating at elevated temperatures. Creep ductility, as a ...The last few decades have witnessed an increasing emphasis on the development of strain-based ap- proach for predicting the creep life or damage of components operating at elevated temperatures. Creep ductility, as a key parameter in this approach, may vary with a number of factors including strain rate, state of stress, operating temperature, material microstructure, etc. The present paper, however, is focused on reviewing the state-of-the-art understanding of the effects of stress level and stress state on the creep ductility. Mechanisms involving the void growth and coalescence are presented to describe the role of stress level in the variation of uniaxial creep ductility. The prediction capacity of existing empirical duc- tility models is also assessed in light of uniaxial test data. On the other hand, a vast body of multiaxial creep test data, collected from open literature, is utilized to examine the influence of the state of stress on the creep ductility. Then, a variety of multiaxial ductility factor models are introduced and evaluated with the available experimental data. Finally, a brief discussion on the dependence of creep ductility on the stress triaxiality and Lode parameter, predicted by numerical methods, is provided.展开更多
The microstructure, mechanical properties and compression creep resistance of as-cast Mg-5Sn-2Ce-xZn（x=0, 2 wt.%, 4 wt.%） alloys were investigated in this paper. The results showed that the Ce-containing compounds w...The microstructure, mechanical properties and compression creep resistance of as-cast Mg-5Sn-2Ce-xZn（x=0, 2 wt.%, 4 wt.%） alloys were investigated in this paper. The results showed that the Ce-containing compounds were MgS nC e phase and an unknown phase, and they were the dominant intermetallics in as-cast Mg-5Sn-2Ce-xZn alloys. At x=0 wt.%, the Ce-containing compounds formed in interdendritic regions with the shape of rod. As the Zn content was increased to 2 wt.%, the Ce-containing compounds partly changed from rod-like to sheet-like. However, there were few further changes in the Ce-containing compounds with further increase in Zn content to 4 wt.%. Compared with Mg-5Sn-2Ce alloy, the tensile strength and elongation of the alloy containing 4 wt.% Zn increased by 39% and 112%, respectively, and the secondary creep rate（175 °C/55 MPa） decreased at least by an order of magnitude. These improvement could be attributed to the combined effects of the high content of Zn dissolving in a-Mg matrix and the modification of Ce-containing compounds by Zn addition.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 11472105 and 51505149)the "111 project"The first author wishes to thank the financial support provided by Shanghai Sailing Program (Grant No. 15YF1402900)
文摘The last few decades have witnessed an increasing emphasis on the development of strain-based ap- proach for predicting the creep life or damage of components operating at elevated temperatures. Creep ductility, as a key parameter in this approach, may vary with a number of factors including strain rate, state of stress, operating temperature, material microstructure, etc. The present paper, however, is focused on reviewing the state-of-the-art understanding of the effects of stress level and stress state on the creep ductility. Mechanisms involving the void growth and coalescence are presented to describe the role of stress level in the variation of uniaxial creep ductility. The prediction capacity of existing empirical duc- tility models is also assessed in light of uniaxial test data. On the other hand, a vast body of multiaxial creep test data, collected from open literature, is utilized to examine the influence of the state of stress on the creep ductility. Then, a variety of multiaxial ductility factor models are introduced and evaluated with the available experimental data. Finally, a brief discussion on the dependence of creep ductility on the stress triaxiality and Lode parameter, predicted by numerical methods, is provided.
基金Project supported by Science and Technology Support Program of Sichuan province(CN)(2009GZ0010)
文摘The microstructure, mechanical properties and compression creep resistance of as-cast Mg-5Sn-2Ce-xZn（x=0, 2 wt.%, 4 wt.%） alloys were investigated in this paper. The results showed that the Ce-containing compounds were MgS nC e phase and an unknown phase, and they were the dominant intermetallics in as-cast Mg-5Sn-2Ce-xZn alloys. At x=0 wt.%, the Ce-containing compounds formed in interdendritic regions with the shape of rod. As the Zn content was increased to 2 wt.%, the Ce-containing compounds partly changed from rod-like to sheet-like. However, there were few further changes in the Ce-containing compounds with further increase in Zn content to 4 wt.%. Compared with Mg-5Sn-2Ce alloy, the tensile strength and elongation of the alloy containing 4 wt.% Zn increased by 39% and 112%, respectively, and the secondary creep rate（175 °C/55 MPa） decreased at least by an order of magnitude. These improvement could be attributed to the combined effects of the high content of Zn dissolving in a-Mg matrix and the modification of Ce-containing compounds by Zn addition.
