Quantitative phase analysis by X-ray diffraction of martensite and austenite in strongly oriented orthodontic stainless steel wires

A method is described for measuring the volume fractions and textures of ma rtensite and austenite in strongly textured stainless steel orthodontic wir es using a conventional X-ray diffractometer. These wires display a classic fibre texture with the [111] of the FCC austenite phase and the [110] of t he BCC martensite phase aligned parallel to the wire axis. The samples anal ysed consisted of wire cross-sections bundled together and chemically polis hed in an epoxy disc. In this form the dominant lines in the XRD patterns a re the austenite (111) and the martensite (110). On the basis of X-ray diff raction results from these two lines only, procedures are described for, (a ) correcting the X-ray intensity data for both the finite size and irregula r cross-sectional shape of the specimens in relation to the X-ray beam foot print, (b) separately measuring the texture of the austenite and martensite phases and, (c) correcting the 111 and 110 integrated intensities for text ure. These procedures are illustrated using X-ray data from four different orthodontic wires. The factors limiting the accuracy of the phase analysis are discussed. (C) 2000 Kluwer Academic Publishers.