Microstructure Investigations of the Phase Boundaries in the Bridgman TRIP Steel Crystal

Abstract

Formation of microstructure defects at the phase boundaries in TRIP steels was investigated with the aid of microstructure analysis on a TRIP steel crystal, which was grown by the Bridgman technique. The microstructure studies comprised scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and transmission electron microscopy with high resolution (HRTEM). Initial XRD measurements revealed that the crystals under study consist of austenite and ferrite with extremely strong preferred orientations. Subsequent XRD pole figure measurements and EBSD scans have shown that the orientation relationship between austenite and ferrite can be described by the Nishiyama-Wassermann model. For a detailed description of the microstructure of the Bridgman crystal, the orientation distribution of crystallites within the individual phases was investigated using the XRD reciprocal space mapping and the rocking curve measurements. These experiments have shown that the density of microstructure defects is much lower in ferrite than in austenite. The direct information about the defect structures at the phase boundaries between austenite and ferrite was obtained from the TEM micrographs, which revealed complicated micro-twin structures at the boundaries between the neighbouring phases. HRTEM discovered very narrow stripes of ferrite embedded in austenite that were regarded as a source of the microstructure defects in austenite.

Design of novel materials for additive manufacturing - Isotropic microstructure and high defect tolerance

“…In previous investigations Borisova et al . 67 verified a distinct orientation relationship (OR) between bcc ferrite and fcc austenite for a 17.2 wt.% Cr, 5.5 wt.% Ni and 5.8 wt.% Mn containing TRIP steel produced by the Bridgman technique. By means of EBSD and XRD the Nishiyama-Wassermann OR with {111} fcc || {011} bcc as parallel lattice planes and 〈-211〉 fcc ||〈111〉 bcc as parallel directions has been determined.…”

Control of microstructure and shape memory properties of a Fe-Mn-Si-based shape memory alloy during laser powder bed fusion

“…The formation of columnar grains with preferential crystallographic orientation, which normally results in strong anisotropy in the mechanical properties of LPBF fabricated parts, can be suppressed by reducing the scan speed. Interestingly, an opposite trend than what is typically observed during LPBF is found, considering that the use of lower scan speeds normally results in grain growth and strong texture along the BD [42] .…”