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近期文章
Nanoembryonicthermoelastic equilibrium and enhanced properties of defected pretransitional materials (含缺陷预转变材料:纳米胚胎热弹性平衡与性能增强)
发布时间:2018-11-19

Nanoembryonicthermoelastic equilibrium and enhanced properties of defected pretransitional materials (含缺陷预转变材料:纳米胚胎热弹性平衡与性能增强)
Ye-Chuan XuWei-Feng RaoJohn W. Morris Jr. & Armen G. Khachaturyan
npj Computational Materials 4:58 (2018)
doi:s41524-018-0114-7
Published online:5 November 2018
Abstract| Full Text | PDF OPEN

摘要:位移型相变材料在相变温度以上经常可观察到异常的热学、力学和磁性行为。这些异常的材料性质通常是从电子/原子的本征响应的角度来解释。本文研究表明,在具有高密度缺陷的预转变材料中,这些性质也可以由非本征的热弹平衡效应产生。缺陷(位错或共格沉淀)附近的应力集中有可能在纳米尺寸的区域内发生应力诱导的相变,产生平衡态的纳米产物相胚胎。这些纳米胚胎处于一种热弹平衡状态,能够在外应力或者磁场的作用下无耗散地改变其平衡尺寸,从而使得材料具有超弹性和超磁致伸缩效应。降温过程中胚胎也有类似的响应,可以解释实验上观测的弥散相变和热膨胀系数以及有效弹性模量的改变,进而可解释受热不改变形状和弹性模量的因瓦和艾林瓦效应   

Abstract:Behaviors of displacive phase-transforming materials above the temperature of transformation, where abnormal thermal, elastic, magnetic properties are often observed, are mostly explained by intrinsic peculiarities in electronic/atomic structure. Here, we show these properties may also be attributed to extrinsic effects caused by a thermoelastic equilibrium in highly defected pretransitional materials.We demonstrate that the stress concentration near stress-generating defects such as dislocations and coherent precipitates could result in the stress-induced transformation within nanoscale regions, producing equilibrium embryos of the product phase.These nanoembryos in thermoelastic equilibrium could anhysteretically change their equilibrium size in response to changes in applied stress or magnetic fields leading to superelasticity or supermagnetostriction.Similar response to cooling may explain the observed diffuse phase transformation, changes in the coefficient of thermal expansion and effective elastic modulus, which, in turn, may explain the invar and elinvar behaviors. 

Editorial Summary

Displacive transformations: nano-embryos enhance properties(位移型相变:纳米胚胎增强材料性能) 

在金属的原子晶格中,缺陷产生的应力可导致纳米尺度区域的相变。南京信息工程大学的饶伟锋教授团队使用微弹性相场模拟研究了位移型相变材料中缺陷周围的局部应力场。研究发现,该应力场能够在相变温度以上促进稳定的纳米产物相胚胎的形成。纳米胚胎的尺寸由温度和晶格应变决定,其改变能增强材料对外应力或磁场改变的敏感性。纳米胚胎的这些行为有助于更好地理解橡胶金属中的超弹性效应、铁基形状记忆合金中的超磁致伸缩效应,以及受热不改变形状和弹性模量的因瓦和艾林瓦效应

Defects that generate stress in a metallic atomic lattice can lead to phase transformations in nanoscale regions. Research led by Wei-Feng Rao at the Nanjing University of Information Science and Technology in Chinaused phase field microelasticity simulations to examine local stress around defects (such as dislocations and nanoprecipitates) in materials that undergo displacive martensitic transformations at a certain temperature.They found that stress fields around defects promoted the formation of stable nano-embryos of the product phase even above the transformation temperature.The size of the nano-embryos depended on the strained lattice and temperature, enhancing their sensitivity to external changes in applied stress or magnetic field.The behavior of these nano-embryos can help better understand the superelastic effect in gum metals, supermagnetostriction in iron-based shape memory alloys, and the invar and elinvar effectscs.

 
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