Inﬂuence of ﬁber orientation and matrix processing on the tensile and creep performance of Nextel 610 reinforced polymer derived ceramic matrix composites E. Volkmann a , K. Tushtev a,n , D. Koch b , C. Wilhelmi c , G. Grathwohl a , K. Rezwan a a Advanced Ceramics, University of Bremen, Am Biologischen Garten 2, 28359 Bremen, Germany b Ceramic Composite Structures, Institute of Structures and Design, German Aerospace Center, Stuttgart, Germany c EADS Deutschland GmbH, Airbus Group Innovations, Munich, Germany article info Article history: Received 6 May 2014 Received in revised form 9 July 2014 Accepted 10 July 2014 Available online 18 July 2014 Keywords: Ceramic-matrix composites (CMCs) Oxides Creep High-temperature properties abstract The tensile and creep performance of two Nextel s 610 (N610) reinforced polymer derived ceramic composites (UMOX™, OXIPOL) is studied up to 1200 1C. Independent of the ﬁber orientation ( 7451 or 01/901) all samples exhibit a segment where the strain rate was constant. The creep performance in 7451 is matrix dominated and shows a more pronounced primary creep regime, due to changes within the matrix. The following creep regime with a constant strain rate might be attributed to viscous ﬂow of the SiOC within the matrix based on activation energy (283 kJ/mol) and stress exponent (0.6). In 01/901 orientation the creep and tensile performance is independent of oxidation, but directly inﬂuenced by grain structure of the ﬁber. The coarser and non-uniform microstructure of the ﬁbers in UMOX™ decreases the stationary creep rates and changes the diffusional creep mechanism. The possibility to modify the microstructure of the ﬁber during the manufacturing process might be used to adjust e.g. the strength and creep stability of these materials related to the desired applications. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Ceramic matrix composites (CMCs) resulting of polymer inﬁl- tration and pyrolysis (PIP) have been proven to be promising candidates for application in oxidizing atmospheres, like in hot structures of re-entry vehicles [1], thermal protection systems [2] or gas turbines [3–5]. The PIP process is one of the most versatile and cost-effective manufacturing routes [6,7], due to the possible application of knowledge gained from the polymer composite ﬁeld [8]. However, the commonly used polysiloxane precursors result in a SiOC matrix containing residual amounts of carbon. Therefore, compared to all-oxide composites these materials are not inherently oxidation resistant, and application of these com- posites in oxidative atmospheres will lead to the formation of silica [9]. In combination with often used fugitive coatings [10] this can cause an increase of the interfacial adhesion accompanied by a decrease of toughness, due to a bridging of the interfacial gap [11– 13]. Besides the effects on the matrix, also the often used polycrystalline Nextel 610 ﬁber (N610) is inﬂuenced by an expo- sure to high temperatures. Schmücker et al. showed that in the case of WHIPOX™ based on pure alumina matrices an outwards diffusion of the grain growth inhibiting silica in the ﬁbers leads to a pronounced grain growth in the peripheral regions of the N610 ﬁbers [14,15]. This effect could be reduced by the addition of an appropriate amount of silica to the matrix system [16]. An inverse behavior was found for CMCs based on SiOC, mullite or zirconia/ alumina matrices. Here, a tendency to smaller grains in the peripheral zone can be observed [17]. The different grain structures might inﬂuence the ﬁber dominated CMC properties, as the performance of the ﬁber is based on its microstructure. Investigations on single ﬁlaments after thermal exposure showed a decrease of strength due to grain coarsening [15,18–20]. In contrast, an increasing grain size improves the creep resistance of the ﬁbers [21]. While numerous studies were conducted on the creep performance of all-oxide CMCs [22–31], only few works were published regarding polymer derived composites. An elaborate overview regarding CMCs for gas turbine applications including a PIP manufactured SiC/SiCNO composite with a BN interface was published by Lara-Curzio [5]. It was shown, that in comparison to metallic alloys superior high temperature stabilities could be achieved. Regarding composites with oxide reinforcements, Gonczy and Sikonia [32] investigated the creep performance of a 01/901 Nextel s 312 reinforced Blackglas™ (SiOC) composite using a BN interface at 566 1C in air atmosphere. The loads in the study ranged from 55 to 96 MPa leading to creep rates between 5.5  10 10 and 1.1  10 8 s 1 . In 2004, Casas and Martinez-Esnaola [33] tested a N610 reinforced polymer derived Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A http://dx.doi.org/10.1016/j.msea.2014.07.027 0921-5093/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ49 421 218 64947; fax: þ49 421 218 64932. E-mail address: tushtev@uni-bremen.de (K. Tushtev). Materials Science & Engineering A 614 (2014) 171–179