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Suppression of Ni 4 Ti 3 Precipitation by Grain Size Refinement in Ni‐Rich NiTi Shape Memory Alloys
Author(s) -
Prokofiev Egor A.,
Burow Juri A.,
Payton Eric J.,
Zarnetta Robert,
Frenzel Jan,
Gunderov Dmitry V.,
Valiev Ruslan Z.,
Eggeler Gunther
Publication year - 2010
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201000101
Subject(s) - materials science , nanocrystalline material , grain size , nucleation , precipitation , metallurgy , transmission electron microscopy , selected area diffraction , microstructure , annealing (glass) , severe plastic deformation , alloy , nickel titanium , crystallography , shape memory alloy , nanotechnology , thermodynamics , physics , chemistry , meteorology
Severe plastic deformation (SPD) processes, such as equal channel angular pressing (ECAP) and high pressure torsion (HPT), are successfully employed to produce ultra fine grain (UFG) and nanocrystalline (NC) microstructures in a Ti–50.7 at% Ni shape memory alloy. The effect of grain size on subsequent Ni‐rich particle precipitation during annealing is investigated by transmission electron microscopy (TEM), selected area electron diffraction (SAD, SAED), and X‐ray diffraction (XRD). It is observed that Ni 4 Ti 3 precipitation is suppressed in grains of cross‐sectional equivalent diameter below approximately 150 nm, and that particle coarsening is inhibited by very fine grain sizes. The results suggest that fine grain sizes impede precipitation processes by disrupting the formation of self‐accommodating particle arrays and that the arrays locally compensate for coherency strains during nucleation and growth.