Strain Glass and Its Detection by Mechanical Spectroscopy

Reference Speaker Authors
Xiaobing Ren Ren, X.(National Institute for Materials Science); For more than a century, martensite - a micron-sized microstructure, has played a central role in both structural materials (e.g., steels and Ti-alloys) and functional materials (e.g., shape memory alloys). The mechanical and functional properties of these materials arise from the micron-sized martensite and martensitic transformation, and the manipulation of which by temperature, stress, and magnetic field can lead to effects of technologically importance, such as shape memory effect and superelasticity. Contrasting with such martensite materials, over the past decade a class of martensite-derived materials called “strain glass” have been reported, which are characterized by nano-sized martensite domains and a sluggish strain glass transition. Strain glass is a frozen disordered ferroelastic state with short-range strain order only. It is a conjugate state to the long-range ordered ferroelastic state or martensite. Strain glass bears all the features of a glass, being parallel to other types of glasses such as relaxor ferroelectrics and cluster spin glasses. The origin of strain glass is discussed in terms of local frustration caused by point defects/alloying atoms. It is found that mechanical spectroscopy, in particular multi-frequency dynamical mechanical analysis (DMA), can provide most important information revealing the glassy dynamics of the strain glass transition and thus becomes the most effective probe for the detection of strain glass and strain glass transition. Novel properties of strain glass arising from nano-sized strain glass domains responding to stress, temperature, and magnetic field are demonstrated, such as nearly hysteresis-free superelasticity over wide temperature range, Invar (zero thermal expansion), Elinvar (constant elastic modulus) effect, and large magnetostriction with small hysteresis. These properties may enable strain glass materials to become a new class of smart/structural materials.
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