Conference Paper: DGM Deutsche Gesellschaft fuer Materialkunde, 19. Symposium Verbundwerkstoffe und Werkstoffverbunde, 03.-05. July 2013, Editors: A. Wanner and K. A. Weidenmann, p. 144-148 The Origin of Crack Formation in SiC Fibre reinforced Multi Metal Matrix Composites investigated by Synchrotron Radiation Reinhard, Christina Diamond Light Source, Didcot, United Kingdom Gussone, Joachim; Kasperovich, Galina; Merzouk, Tarik; Gherekhloo, Human; Hausmann, Joachim Institut fuer Werkstoff-Forschung, Deutsches Zentrum fuer Luft-und Raumfahrt, Koeln Korrespondenzadresse: christina.reinhard@diamond.ac.uk Abstract The use of synchrotron radiation has become an essential tool to study the microstructure in multiphase materials. The present work focuses on using synchrotron tomography to study multi metal matrix composites (3MC) during in-situ loading. 3MCs were produced via a process in which SiC fibres are coated with a primary matrix of Ti and then infiltrated with a low melting point filler material as secondary matrix. Two different Ag- or Zr-based filler materials were used as secondary matrix. During the consolidation process, intermetallic phases form in the matrix. These intermetallic phases are expected to critically influence the mechanical properties of 3MCs. Beamline I12 at the Diamond Light Source (UK) provides the capability to conduct high resolution tomography (CT) during in-situ loading. CT was used to investigate the microstructure, to locate the origin of newly appearing cracks and to follow their dissemination during loading. The CT measurements reveal that cracks occur in the brittle zones of the matrix far below the ultimate tensile strength of the composite material. In Ag-based 3MCs, cracks appear in the brittle intermetallic reaction zone between primary matrix and the secondary matrix whereas in case of the Zr-based system, in contrast, cracks are located mainly in the secondary matrix. 1. Motivation Titanium metal matrix composites with unidirectional continuous SiC fibre reinforcement are attractive candidate materials for aerospace applications where high specific strength in combination with heat resistance is required [1]. The commonly used processing route of consolidating a Ti-matrix coated SiC-fibre by hot isostatic pressing is very costly and can lead to shrinkage, distortion and, in worst case, fibre breakage. To overcome these limitations, an alternative production route aims to produce composites by melt infiltration without applying pressure [2-3]. Here, low melting point alloys are used to consolidate the composite materials by infiltrating the matrix coated fibres. The resulting composite is referred to as multi metal matrix composite (3MC). A drawback with this technique, however, is that depending on the material combination chosen for primary matrix (PM) and secondary matrix (SM), a variety of complex intermetallic phases can form during consolidation in a reaction zone (RZ) between primary and secondary matrix, e.g. TiCu and Ti 2 Cu in a Ti/AgCu system [2]. Some of these phases are known to be brittle and therefore detrimental for mechanical properties. In order to improve the material properties, it is necessary to gain a deeper understanding of the influence of these critical intermetallic phases on crack initiation.