Transformation Mechanism of Preprecipitation NiMn Nanostructures |
| |
Authors: | Mohamad Reza Movaghar Garabagh Syamak Hossein Nedjad Habib Hamed Zargari Mahmoud Nili Ahmadabadi |
| |
Affiliation: | 1. Advanced Materials Research Center, Department of Materials Engineering, Sahand University of Technology, P. O. Box 51335-1996, Tabriz, Iran 2. Center of Excellence for High Performance Materials, School of Metallurgy and Materials Engineering, University of Tehran, P. O. Box 14395-731, Tehran, Iran
|
| |
Abstract: | The transformation mechanism of constrained b.c.c NiMn (β phase) clusters coherently precipitated during isothermal aging of Fe-Ni-Mn maraging alloy at 753 K (480 °C) has been studied. Preprecipitation of β-NiMn phase was demonstrated using conventional and high-resolution transmission electron microscopy and confirmed by flanking of electron diffraction spots, X-ray diffraction sidebands, and the invariance of lattice parameter and peak breadths in the earlier stages of age hardening. The β-NiMn clusters were recognized with interfacial dislocation dipoles lying on {011} α planes and Burgers vectors of a 0 $ leftlangle {01overline{1} } rightrangle_{alpha } $ type. During further aging, the β-NiMn clusters transformed martensitically into fct NiMn (θ phase) precipitates as envisaged by the characteristic microtwinning texture. Considering the anomalous elastic softness of β-NiMn alloy, the transformation was plausibly assumed to take place by the localized soft-mode mechanism in which the structural instability of clusters is stimulated by the strain field of the interfacial dislocations. Computerized calculations in accordance with the phenomenological theory of martensite crystallography indicated that microtwinning of martensitic θ precipitates occurs in a self-accommodating manner. Transformation of very small β clusters at earlier stages of aging is thermodynamically hampered by the interfacial energy barrier. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|