DOI: 10.1002/adem.201000039 Global Techniques for Characterizing Phase Transformations – A Tutorial Review By Michel Perez * , Olivier Lame and Alexis Deschamps 1. Introduction In order to characterize phase transformations and their kinetics, one needs to know (i) the nature (crystallography, chemistry, morphology) of each phase, and, (ii) their distribution and volume fraction. Phase transformations can involve very small volume fractions (e.g. fine precipitation) as well as the whole sample (e.g. ferrite to austenite transforma- tion). Presently, no experimental technique can, alone, measure accurately these two types of information. The nature of phases is indeed a local data (nano or micrometer scale) whereas their distribution, or volume fraction are more easily accessible with global measurements (micrometer to meter scale). From a local point of view, the most wildly used technique is electron microscopy (see Fig. 1, the introductory book of Murphy [2] and a more specific paper dedicated to precipita- tion [3] ). Another rising technique is the tomographic atom probe (TAP), which gives access to the nature and position of REVIEW Fig. 1. High resolution TEM image of Al 3 Zr x Sc 1–x precipitate showing core-shell structure with Zr rich shell (from Cloue´et al. [1] ). [*] Prof. M. Perez, O. Lame Universite´de Lyon, INSA Lyon MATEIS, UMR CNRS 5510, France E-mail: michel.Perez@insa-lyon.fr Prof. A. Deschamps Universite´de Grenoble, Grenoble INP SIMAP, France To characterize phase transformations, it is necessary to get both local and global information. No experimental technique alone is capable of providing these two types of information. Local techniques are very useful to get information on morphology and chemistry but fail to deal with global information like phase fraction and size distribution since the analyzed volume is very limited. This is why, it is important to use, in parallel, global experimental techniques, that investigate the response of the whole sample to a stimulus (electrical, thermal, mechanical...). The aim of this paper is not to give an exhaustive list of all global experimental techniques, but to focus on a few examples of recent studies dealing with the characterization of phase transformations, namely (i) the measurement of the solubility limit of copper in iron, (ii) the tempering of martensite, (iii) the control of the crystallinity degree of a ultra high molecular weight polyethylene and (iii) a precipitation sequence in aluminum alloys. Along these examples, it will be emphasized that any global technique requires a calibration stage and some modeling to connect the measured signal with the investigated information. ADVANCED ENGINEERING MATERIALS 2010, 12, No. 6 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 433