Proposition and research progress of the third-type strain aging

The traditional knowledge of plastic flow behavior of metal, dislocation activation theory, and thermoviscoplastic constitutive model of metal needs a further perfection due to the occurrence of third-type strain aging. Third-type strain aging leads to a bell-shaped flow stress-temperature curve, that is, the flow stress first increases as temperature increases, and after a peak value is reached, it decreases with further increase of temperature. Third-type strain aging occurs at both low and high strain rates. The bell-shaped segment induced by third-type strain aging on the flow stress-temperature curve shifts to higher temperature region as strain rate increases. In order to develop a systematic understanding of the third-type strain aging, firstly, macro characteristics of third-type stain aging effect that was distinguished from static strain aging effect and Portevin-Le Chatelier dynamic strain aging effect were introduced. Then, the micro mechanism of third-type strain aging and correlation of third-type strain aging, Portevin-Le Chatelier dynamic strain aging, blue brittleness phenomenon, and internal friction were systematically concluded. Third-type strain aging, Portevin-Le Chatelier dynamic strain aging, blue brittleness phenomenon, and mechanical spectroscopy are all resulted from the interaction of mobile dislocations with diffusion atoms. Third-type strain aging, Portevin-Le Chatelier dynamic strain aging, and blue brittleness phenomenon are different manifestations of dynamic strain aging. Third-type strain aging can be considered as another mode of mechanical spectroscopy. The common constitutive models are able to capture the plastic behavior of many metals under the coupling influence of strain rate and temperature in some cases. However, these thermoviscoplastic constitutive models do not take the effect of third-type strain aging into consideration, and they cannot describe the thermoviscoplastic behavior including the third-type strain aging effect. To accurately describe the plastic behavior of metals, some constitutive models including the effect of third type strain aging were proposed. The development of the thermoviscoplastic constitutive model of metal considering the effect of third type strain aging was finally introduced.