Atomic displacements in the austenite–martensite transformation

Abstract

BONDS IN THE IROI~SILICIDE FeSi AND RELATED CRYSTALSsmall axial ratio, such as shown by AuSn (Pauling, 1947), might be assumed by FeSi. The axial ratio could adjust itself in such a way that the silicon atom would use its valence of 4 in forming four bonds with the surrounding six iron atoms, and the iron atom would use its extra valence 2 in forming two iron-iron single bonds, one with each of the iron atoms above and below it along the c axis. Similarly, the cesium chloride structure might be assumed by FeSi, each silicon atom then forming eight half-bonds with the iron atoms surrounding it in a cubic arrangement, and each iron atom forming eight half-bonds with silicon atoms, and six one-third bonds with the six adjacent iron atoms. It seems not unlikely that co-ordination number 6 (bond number ~) is more suitable for silicon in an intermetallic compound than co-ordination number 8* (bond number ½), and that, moreover, resonating iron-iron bonds, with bond number ½, are more stable than nonresonating bonds, with bond number 1. The actual FeSi structure would thus be preferred to the cesium * A substance in which the four bonds of the silicon atom show pivoting resonance among eight positions is Mg~Si, with the fluorite structure (Pauling, 1948).chloride structure for the first reason, and to the nickel arsenide structure for the second reason.We are grateful to Prof. J. H. Sturdivant for assistance with the experimental part of this investigation. The work reported in this paper is part of a series of studies of metals and alloys being carried on with the aid of a grant from the Carbide and Carbon Chemicals Corporation.References BeRliN, B. (1933) The atomic displacements in the transformation from austenite to martensite are described, and the strains involved are derived. It is shown that the tetragonality ofmartensite arises as a necessary consequence of the assumption that the iron and carbon atom displacements constitute a common homogeneous deformation. An explanation of the observed high indices of the habit plane of martensite of certain carbon contents is advanced.

Variant selection in surface martensite

“…This model is used to compare different crystallographic descriptions of the transformation. In particular, we consider the invariant plane strain and the invariant line strain based on the phenomenological theory of martensite crystallography (PTMC) (Bowles & Mackenzie, 1954), the Jaswon and Wheeler distortion (Jaswon & Wheeler, 1948), and the continuous distortion associated with the Kurdjumov-Sachs orientation relationship (Cayron, 2015). The study shows that all four descriptions of the transformation are able to predict correctly the trend of variant selection in surface martensite; however, the Jaswon and Wheeler distortion and the continuous distortion are more appropriate for accounting for other features of the transformation, such as the habit plane and accommodation by twin-related variant pairing.…”

The crystallographic mechanism of the martensite reaction in iron-carbon alloys

“…Jaswon & Wheeler have proposed that the displacements which seem most likely to occur are those which move each atom in austenite to the nearest available position in the martensite structure. For the standard variant of the Kurdjumow-Sachs relationship, the coordinate transformation matrix (r) describing these minimum displacements (Jaswon & Wheeler, 1948) is…”

“…More recently there have been two important contributions, namely, those of Greninger & Troiano (1941, and Jaswon & Wheeler (1948).…”

An interactive program for crystal orientation and martensitic transformation investigations:COATI

“…The principal axes of the pure lattice deformation may distort by 40% (Fraser & Kennedy, 1974) and rotate by as much as 15 ° . Theories manifesting these phenomena have been presented from 1948 (Jaswon & Wheeler, 1948) up to the present day (Crocker, 1982). The function of the program described here is to assist in the experimental study of the above mentioned transformation characteristics and to facilitate the intelligible comparison between experimental and theoretical data.…”