Physical chemistry and mechanical imaging of ceramic-®bre- reinforced ceramic- or metal-matrix composites G. Gouadec a,b, *, S. Karlin c , J. Wu a , M. Parlier b , Ph. Colomban a,b a Laboratoire Dynamique, Interaction et Re Âactivite  (LADIR), UPR CNRS 1580 2 rue Henri Dunant, 94320 Thiais, France b De Âpartement Mate Âriaux et Syste Ámes Composites (DMSC), Oce National d'Etudes et de Recherches Ae Ârospatiales (ONERA), BP 72, 92322 Cha Ãtillon, France c RENISHAW, 15 rue Albert Einstein, 77437 Marne la Valle Âe, Cedex 02, France Received 30 May 1999; received in revised form 12 October 1999; accepted 18 April 2000 Abstract Raman (micro)spectrometry allows the study of the non-metallic phases of ceramic- or metal-matrix composites at the micro- meter scale. The three examples that are given concern a mullite-matrix composite reinforced by the Nippon Carbon NLM-202 TM SiC ®bre, an alumina-matrix composite reinforced by a Saphikon TM monocrystalline a-Al 2 O 3 ®bre and a Textron SCS-6 TM ®bre- reinforced Ti6242 matrix composite. Physical and chemical evolution of the SCS-6 ®bre within the matrix is discussed. A compar- ison is made between residual thermal stresses estimated from the thermal expansion coecients of the ®bres and matrices and the values obtained from Raman wavenumber shifts. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: A. CMC's; A. MMC's; B. Stress/strain curve; C. Residual stress; D. Raman spectroscopy 1. Introduction Ceramic- and metal-matrix composites are manu- factured and used at high and even very high tempera- tures. Both the residual thermal stresses induced by the thermal expansion mismatch of the constitutive phases and the presence of interfaces Ð which dissipate cracks energy to accommodate local strains Ð modify the overall mechanical properties. The modelling of these composites requires accurate knowledge of the con- stituents and of their reciprocal interactions. Raman microspectroscopy is one of the very few methods that allow topological analysis of the mechanical state in inhomogeneous solids, down to the micron level. Indeed, the strain, ", generated in a stressed phase cau- ses the stretching modes wavenumbers to shift. This behaviour, which is directly related to chemical bond anharmonicity, is described by a simple linear law [1]: J " 1 Thus, precise measurement of the wavenumber shifts, , according to the topology, in principle, allows stress levels in solids to be mapped. It should be noted that J generally takes a negative value, which indicates a wavenumber increase under compressive stress (the contrary for tensile stress). The two main advantages of Raman spectroscopy, when compared to other stress- determination methods, are (i) that it applies whatever the structure of the samples being studied (including amorphous structures) and (ii) that it provides addi- tional information on the physical and chemical state of the constituents (nature of the bonds, symmetry, structure, disorder...), through spectral changes (bandwidths, wavenumbers, intensity...). Furthermore, Raman spectro- scopy is a non destructive method requiring no more than making sure, especially for coloured materials the visible absorption of which is high, that laser-induced thermal eects are avoided. In this paper, we illustrate the application of Raman microspectrometry to the study of some typical carbon and ceramic ®bres, in ceramic- or metal-matrix compo- sites. The spectra of ®bres recorded on composites cross sections [2] being consistent with those recorded through the matrix, analysis of the ceramic ®bres in their metal matrix will be performed on cross-sectional 0266-3538/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0266-3538(00)00112-3 Composites Science and Technology 61 (2001) 383±388 www.elsevier.com/locate/compscitech * Corresonding author. E-mail address: gwenael.gouadec@glvt- cnrs.fr (G. Gouadec).