High-Resolution Electron Microscopic Study on Atomic Arrangements at Growing Tips of Martensite Plates and a Nucleating Martensite in Fe-Ni-Mn and Fe-Cr-C Alloys

• Published in: MATERIALS TRANSACTIONS Vol. 48; no. 4; pp. 860 - 868
• Main Authors: Ogawa, K., Kajiwara, S.
• Format: Journal Article
• Language: English
• Published: Sendai The Japan Institute of Metals and Materials 01-04-2007; Japan Science and Technology Agency
• Subjects: atomic structure; Austenite; Crystal lattices; Crystal structure; Dislocations; Ferrous alloys; growing tip; habit plane; Habits; Half planes; High resolution; High resolution electron microscopy; K-S orientational relationship; Martensite; martensitic transformation; Martensitic transformations; nucleation; Nuclei; Planes; Plates; transformation dislocations
• ISSN: 1345-9678; 1347-5320; 1347-5320
• DOI: 10.2320/matertrans.48.860

The present work aims to clarify the atomic arrangements at the austenite/martensite interfaces for the nucleating martensite and the growing tip of martensite plates. An Fe-23Ni-3.8Mn alloy and an Fe-9Cr-1.1C alloy with the K-S orientational relationship with the {112} habit plane were observed with high resolution electron microscopy. At the very tip of the wedge-shaped growing martensite, dislocations queue up on about every six (111)f layers along the interface, with their extra-half plane in the austenite. A nucleus of the martensite was observed in the Fe-9Cr-1.1C alloy. The nucleus has the K-S orientational relationship with a habit plane of (111)f(||(011)b), a wing-like shape, and remarkably expands in the direction of [\\bar101]f(||[\\bar1\\bar11]b). The crystal structure of the nucleus shows a transient lattice region from fcc to bct toward the inside, and the transformation into the final martensite structure (bct) is still incomplete even at the center of the nucleus.