Institute Advanced Ceramics

Ceramic matrix composites (CMCs) have attracted lots of attention for thermomechanical applications due to their damage tolerant fracture behavior. This is the result of toughening mechanisms, particularly crack deflection into fiber-matrix interface as well as subsequent fiber pullout and bridging. Among the different categories of CMCs, all-oxide systems have recently been in the focus of research because of their inherent high oxidation resistance compared to their non-oxide counterparts. This is interesting particularly at high temperature applications in oxidizing environments such as gas turbines. However, despite the considerable interest in oxide-oxide CMCs over the past decades, there are still barely production concepts which meet requirements in view of cost and performance. Up to now, production of all-oxide CMCs is dominated by a few small companies and research institutes in Germany and USA. Long manufacturing times, high material costs and multiple infiltration steps, in case of the most common CMC production routes, are some factors that lead to high prices and prevent a wider industrial application of these materials. Therefore, it is of vital importance to reduce production costs and to make all-oxide CMC manufacturing more flexible. In this project, routes and performance have been investigated in order to achieve this objective by using a combination of conventional powder metallurgy routes and well-known production concepts existent for manufacturing polymer matrix composites, e.g. a prepreg technology based approach. The manufacturing comprise the integration of commercially available techniques for the production of polymer composites with well-known powder metallurgy routes typical for ceramics. As schematically shown in Figure 1, the proposed route consists of the following steps: (a) infiltration of commercial oxide fiber fabrics with a liquid suspension of the matrix material; (b) lamination of the pre-infiltrated fiber textiles with a paraffin-based suspension for the formation of prepregs; (c) layup of prepregs; (d) warm-pressing for the consolidation of the green body; (e) burn out of the organic binders (debinding) and (f) reaction bonding and/or sintering for synthesis of the oxide matrix.

Figure 1: Schematic representation of the prepreg processing route proposed in this project for the fabrication of oxide ceramic matrix composites.

The microstructure of a Nextel 610 Satin fabric in an alumina-zirconia matrix is shown in Fig. 2. The maxtrix, resulting from the two suspensions used in the composite production (ethanol and paraffin-based) are indicated by IB (intrabundle) and IT (intertextile), is homogeneous with a very few shrinkage-related, through-thickness cracks. Additionally, no delamination was detected, indicating a very effective adhesion between adjacent prepregs during the manufacturing process.. The very small amount of matrix cracks in the composites investigated here can be attributed to the two-step impregnation process used in the novel route, which guarantees a homogenous distribution of matrix particles throughout the green composites. Moreover, the alumina-zirconia matrix used presents very low shrinkages up to 1300°C, which also avoid crack formation during sintering.

Figure 2: Microstructures of A8Z2-matrix CMCs produced by the novel prepreg lamination route IB and IT indicate the intra-bundle and inter-textile matrices, respectively

These materials exhibit a high flexural strength (~450 MPa in four-point bending) with remarkable high remaining loading capability when exceeding the max. strength, e.g. a very advanced damage tolerant behavior. Thereby, the strength degradation is stepwise due to a combination of toughening by fibers and by the layered structure; even at strains above 1 % the composites exhibit a retained strength of ~100 MPa. More details are available in an extended version of the DFG report. The document is password-protected, the password is available on request (send email to ceramic(at)tuhh(dot)de).

Publciations

D.E. Garcia, D. Hotza, R. Janssen, Building a sintering front through fast firing, International Journal of Applied Ceramic Technology ([6] 1486-1493 (2011)

S.M.Goushegir, P.O. Guglielmi, J.P.G. Silva, M Hablitzel, D Hotza, H.A. Al-Qureshi, R. Janssen, Fiber-Matrix Compatibility in an All-Oxide Ceramic Composite with RBAO Matrix, J. Am. Ceram. Soc. 95 [1], 159-164 (2012)

D. Blaese, D:E. Garcia, P. Guglielmi, D. Hotza, M. C. Fredel, R. Janssen., ZrO2 Fiber-Matrix Interfaces in Alumina Fiber-Reinforced Model Composites, J. Eur. Ceram. Soc. 35 (2015) 1593-1598

P.O. Guglielmi, D, Blaese, M.P. Hablitzel, G. Nunes, D. Hotza, H.A. Al-Qureshi, R. Janssen, Microstructure and Flexural Properties of Multilayered Fiber-Reinforced Oxide Composites fabrciated by a Novel Lamination Route, Ceramics Int 41 7836-7846 (2015)

L. Neckel, J.G.P. da Silva, P.O. Guglielmi, D. Hotza, H.A. Al-Qureshi, O.R.K. Montedo, C.P. Bergmann, R. Janssen, Mechanical tests and simulation on load sharing in alumina fiber bundles. Ceram. Int. 41 13257-13263 (2015)

P.O. Guglielmi, D.E. Garcia, M.P. Hablitzel, D. Blaese, D.P. Goulart, A. Borchert, D. Hotza, R. Janssen, Processing of All-Oxide Ceramic Matrix Composites with RBAO Matrices, J. Ceram. Sci. Tech. in print, available online at www.ceramic-science.de

Short Papers/Proceedings

J.P.G. da Silva, D. Hotza, R. Janssen, H.A. Al-Qureshi,. Modelling of load transfer between porous matrix and short fibres in ceramic matrix composites, WIT transactions on engineering sciences (Online), v. 72, p. 165-174 (2011)

R. Janssen, Reaction Formed Alumina-Alumina FRCMC, in "High Temperature Ceramic Materials and Composites", ed. by W. Krenkel & J. Lamon , 398-404 (2010)

P.O. Guglielmi, R. Janssen, G.F. Nunes, D. Hotza, A Prepreg Approach for Low Cost Oxide-Oxide Composites, in "High Temperature Ceramic Materials and Composites", ed. by W. Krenkel & J. Lamon, 420-428 (2010)

P.O. Guglielmi, G.F.Nunes, M.P. Hablitzel, D. Hotza, R. Janssen, Production of oxide ceramic matrix composites by a prepreg technique, Materials Science Forum, Vols. 727/728, 556-561(2012)

S.M. Goushegir, P.O. Guglielmi, A.P.N. Oliveira, D. Hotza, R. Janssen, "Fiber-matrix compatibility in LZSA glass-ceramic matrix composites", Materials Science Forum, Vols. 727/728, 562-567 (2012)

L. Neckel, D. Hotza, D. Stainer, R. Janssen. A.G.R. Lezana, A. Dias, H.A. Al-Qureshi, Solutions for impact over aerospace protection, Key Engineering Materials, v. 488-489, 25-28 (2012)

J.G.P, da Silva, D. Hotza, R. Janssen, H.A. Al-Qureshi, Modeling of ceramic oxide fiber bundles mechanical properties, Materials Science Forum, v. 727-728, 574-580, (2012)

L. Berti, C.R. Rambo, E. Bazzo, R. Janssen, D. Hotza, A novel route for porous matrix composites, Materials Science Forum, 727/728, 568-573 (2012)

P.O. Guglielmi, D. Blaese, M.P. Hablitzel, G. Nunes, V. Lauth, D. Garcia, H.A. Al-Qureshi, D. Hotza, R. Janssen, Multilayered fiber-reinforced oxide composites produced by lamination of thermoplastic prepregs, Advances in Science and Technology Vol. 89, 145-150 (2014)