Chemical and mechanical stabilization of martensite

An algorithm of quantitative analysis of two basic contributions to the stabilization of martensite - atomic reordering (chemical stabilization component) and pinning of interfaces (mechanical contribution) - has been developed. The algorithm uses data obtained by routine calorimetry measurements. The possibility to quantitatively separate contributions of chemical and mechanical stabilization components stems from the fact that they affect the first reverse transformation of stabilized martensite through thermodynamically reversible and irreversible factors, respectively. Analysis of the thermodynamics of the thermoelastic martensitic transformations allowed us to conclude that stabilization of martensite should be described in terms of pure shift and broadening of the reverse transformation. These parameters are shown to have a clear physical meaning. Namely, pure shift of the reverse transformation as a result of martensite stabilization provides an upper estimate for the atomic reordering or chemical contribution to the stabilization, whereas broadening of the reverse transformation represents a lower limit for pinning-induced or mechanical stabilization component. Experimental data on stabilization of a Cu-Zn-Al alloy are analyzed, indicating that contributions of chemical and mechanical stabilization components are comparable but depend on martensite ageing period and details of the initial heat treatment of samples. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.