In-Situ Scanning Electron Microscopy/Electron Backscattered Diffraction Observation of Microstructural Evolution during α → γ Phase Transformation in Deformed Fe-Ni Alloy

Abstract

TATSUYA FUKINO, SADAHIRO TSUREKAWA, and YASUHIRO MORIZONOThis article presents in-situ observation of ferrite (a)/austenite (c) phase transformation in an Fe-8.5 at. pct Ni alloy deformed by rolling using an automated scanning electron microscopy/ energy backscattered diffraction (SEM/EBSD) system. During heating, recrystallization in a phase and a fi c phase transformation independently occurred. The c grains nucleated in unrecrystallized a grains were most probably incorporated into the grain interior of recrystallized a grains. They did not have any specific orientation relation (OR) with recrystallized a grains and grew in an isotropic manner. On the other hand, the intragranular c grains nucleated in recrystallized a grains had a Kurdjumov-Sachs (K-S) OR with the a grains and grew in a considerably anisotropic manner. They preferentially grew along the common direction of surface traces of {110} a /{111} c . Approximately half of grain boundary (GB) allotriomorphs had either the K-S OR or the Nishiyama-Wasserman (N-W) OR with the parent a grains. The c allotriomorphs predominantly grew into the a grain having the special OR with themselves. The GB character distribution of c phase at high temperatures was measured. The fraction of CSL boundaries was as high as 63 pct, particularly that of R3 grain boundaries (GBs) was 54 pct.

Interphase boundary motion elucidated through in-situ high temperature electron back-scatter diffraction

“…This is due to the lower nucleation barrier for the formation of grains with special orientation relationships. This observation is in line with the observations of the ferrite-austenite phase transformation in Fe-Ni alloys, where both the Kurdjumov-Sachs and Nishiyama-Wasserman (111) fcc ||(110) bcc ; ½011 fcc ||[001] bcc relationships were observed [4,8] and EBSD observations of low carbon steel, where the Kurdjumov-Sachs dominated [18]. In the work presented here the growth was also observed to be mainly into ferrite grains, for which the austenite grains did not have the K-S OR.…”

“…Recent evolution of this setup on the speed of in-situ signal processing, allows us to study the dynamics of phase changes with an enhanced temporal resolution. In our work we combine a heating stage and electron-back scattering diffraction (EBSD), resulting in insitu scanning electron microscopy (SEM) observations of microstructural changes [4][5][6][7][8].…”

Continuous atomic displacements and lattice distortion during fcc–bcc martensitic transformation

“…Ohmori et al [34] report that the Widmanstätten austenite  laths are in KS OR with the ferritic  matrix and exhibit a well-defined (1 ̅ 10)  //( 1 ̅ 11)  habit plane with the growth direction parallel to [111]  //[110]  , which is completely coherent with the first solution found for ( = 1.571, = 2.356) . The same OR and the same HP were observed for the bccfcc transformation obtained by heating martensitic steels to produce reverse austenite [41] [42]. In Cu-Zn brass, Srinivasan and Heworth [38] investigated the habit planes by Laue diffraction and reported two possible different HPs indexed in the parent  bcc phase: (2, 11, 12)  and (123)  with a large scatter of the results depending on the alloy composition; but interestingly the scatter is not random and actually the HPs are aligned in the pole figure on a segment containing the <111>  dense direction and located between the two extreme (2, 11, 12)  and (123)  planes ( Fig.…”

In Situ High-Temperature EBSD and 3D Phase Field Studies of the Austenite–Ferrite Transformation in a Medium Mn Steel

“…The actual motion of real α / γ interfaces has been studied experimentally with different in situ techniques such as optical microscopy (OM) (Watanabe et al, 2004; Witusiewicz et al, 2005, 2013), laser scanning confocal microscopy (Phelan et al, 2005; Chen et al, 2013 a ; Cheng et al, 2014; Sainis et al, 2018), scanning electron microscope (SEM)/electron backscattered diffraction (EBSD) (Prior et al, 2003; Seward et al, 2006; van der Zwaag et al, 2006; Fukino & Tsurekawa, 2008; Mishra & Kubic, 2008; Fukino et al, 2011; Torres & Ramírez, 2011; Enomoto & Wan, 2017; Shirazi et al, 2018) photoemission electron microscopy (Middleton & Form, 1975; Middleton & Edmonds, 1977; Edmonds & Honeycombe, 1978), and transmission electron microscopy (Brooks et al, 1979; Moine et al, 1985; Onink et al, 1995; Mompiou et al, 2015; Guan et al, 2017; Liu et al, 2017; Du et al, 2018). Each of these techniques has its own advantages and drawbacks in accurately documenting the interface motion as a function of the imposed external parameters (such as temperature and composition) and the transient local conditions (such as triple junctions where three or more boundaries meet, neighboring interfaces and grain boundaries and overall degree of transformation).…”