MATERIALS IENGE& EGEERIG Materials Science and Engineering A 412(2005)146-152 www.elsevier.com/locate/msea Si3N4/BN fibrous monoliths: Mechanical properties and tribological responses K C. Goretta,*D. Singha. T.A. Cruse a. A. Erdemir a. J. L. Routbort a F. Gutierrez-Morab, A.R. de Arellano-Lopez b, T.S. Orlova", B I Smirnov c Energy Technology Division, Argonne National Laboratory Argonne, IL 60439-4838 USA b Departamento de Fisica de la Materia Condensada, Universidad de Sevilla, 41080 Sevilla, spain e loffe Physico-Technical Institute, Politekhnicheskaya ul. 26, St. Petersburg 194021, Russia Received in revised form 21 April 2005 Ceramic fibrous monoliths ( FMs)consist of fiber-like cells that surround a weaker matrix phase called the cell boundary. FMs based on Si, N4/BN exhibit many excellent mechanical properties, and much work has been done to characterize and understand the relations among their processing, microstructure,and properties. The following body of data and understanding for Si3 N4/BN FMs are discussed in this paper: processing, elastic onstants,in-plane fracture and modeling of fracture, thermal stresses, interfacial shear strength and tailoring of gross interface structure, creep, impact erosion resistance, and sliding wear resistance. Possibilities to improve their properties are also presented C 2005 Elsevier B V. All rights reserved Keywords: Fibrous monolith; Ceramic composite; Mechanical properties 1. Introduction Tucson, AZ). Substantial work continues on them to improve processing methods, lower fabrication costs, incorporate new Powder-derived fibrous monoliths(FMs) generally consist compositions, and produce new forms. The properties of exist- of strong cells, typically 100-500 um wide, that are surrounded ing ceramic FMs have been studied in detail for nearly a decade by a weaker cell boundary[1-8]. FMs are produced most often [3-8, 11-21]. This paper will summarize current knowledge and by extrusion of duplex filaments, followed by lay-up of the understanding of Si3 NA/BN FMs filaments into laminates. The extruded filaments consist of a cell phase surrounded by a sheath that forms a continuous cell boundary [2-8 2. Manufacture of Si3 Ng/BN fibrous monoliths FMs exhibit graceful failure in flexure. Energy dissipation arises from substantial sliding of the cells, and branching and All current ceramic FMs are based on a duplex microstructure deflection of cracks [8]. FMs constitute in some applications that consists of dense cells separated by a continuous cell bound lower cost alternatives to conventional continuous-fiber ceramic ary. The cells provide most of the strength of the FM. The cell omposites, and many ceramic FMs are available commercially boundary provides toughness by isolating the cells from each 9]. Cermet FMs are also produced; they have exhibited excep- other and promoting dissipation of fracture energy by mecha- nal performance drill bits nisms such as pullout of the cells [18] or deflection of a crack through the cell boundary [7, 18 Ceramic FMs based on Si3N4 cells and a Bn boundary Hexagonal BN [2-8, 11-20] is an effective cell boundary [2-8, 11-21] offer excellent mechanical performance, and they because it forms a dense, highly textured matrix that bonds only are a commercial product(Advanced Ceramics Research of weakly to the strong Si3N4 cells [13, 20]. Oxide sintering aids in the Si3N4 (generally Al2O3 and Y203)that leach into the BN cell boundary during hot pressing impart most of the bond Corresponding author. Tel: +1 630 2527761; fax: +1 630 252 3604 ing [20]- BN would be an ideal cell-boundary material, except Iress: gretta @anl. gov(K C. Coretta) for the fact that it can oxidize severely at elevated temperatures 0921-5093/S-see front matter o 2005 Elsevier B V. All rights reservedMaterials Science and Engineering A 412 (2005) 146–152 Si3N4/BN fibrous monoliths: Mechanical properties and tribological responses K.C. Goretta a,∗, D. Singh a, T.A. Cruse a, A. Erdemir a, J.L. Routbort a, F. Gutierrez-Mora b, A.R. de Arellano-Lopez b, T.S. Orlova c, B.I. Smirnov c a Energy Technology Division, Argonne National Laboratory, Argonne, IL 60439-4838, USA b Departamento de Fisica de la Materia Condensada, Universidad de Sevilla, 41080 Sevilla, Spain c Ioffe Physico-Technical Institute, Politekhnicheskaya ul. 26, St. Petersburg 194021, Russia Received in revised form 21 April 2005 Abstract Ceramic fibrous monoliths (FMs) consist of fiber-like cells that surround a weaker matrix phase called the cell boundary. FMs based on Si3N4/BN exhibit many excellent mechanical properties, and much work has been done to characterize and understand the relations among their processing, microstructure, and properties. The following body of data and understanding for Si3N4/BN FMs are discussed in this paper: processing, elastic constants, in-plane fracture and modeling of fracture, thermal stresses, interfacial shear strength and tailoring of gross interface structure, creep, impact erosion resistance, and sliding wear resistance. Possibilities to improve their properties are also presented. © 2005 Elsevier B.V. All rights reserved. Keywords: Fibrous monolith; Ceramic composite; Mechanical properties 1. Introduction Powder-derived fibrous monoliths (FMs) generally consist of strong cells, typically 100–500
m wide, that are surrounded by a weaker cell boundary [1–8]. FMs are produced most often by extrusion of duplex filaments, followed by lay-up of the filaments into laminates. The extruded filaments consist of a cell phase surrounded by a sheath that forms a continuous cell boundary [2–8]. FMs exhibit graceful failure in flexure. Energy dissipation arises from substantial sliding of the cells, and branching and deflection of cracks [8]. FMs constitute in some applications lower cost alternatives to conventional continuous-fiber ceramic composites, and many ceramic FMs are available commercially [9]. Cermet FMs are also produced; they have exhibited excep￾tional performance as, for example, inserts for mining drill bits [10]. Ceramic FMs based on Si3N4 cells and a BN boundary [2–8,11–21] offer excellent mechanical performance, and they are a commercial product (Advanced Ceramics Research of ∗ Corresponding author. Tel.: +1 630 252 7761; fax: +1 630 252 3604. E-mail address: goretta@anl.gov (K.C. Goretta). Tucson, AZ). Substantial work continues on them to improve processing methods, lower fabrication costs, incorporate new compositions, and produce new forms. The properties of exist￾ing ceramic FMs have been studied in detail for nearly a decade [3–8,11–21]. This paper will summarize current knowledge and understanding of Si3N4/BN FMs. 2. Manufacture of Si3N4/BN fibrous monoliths All current ceramic FMs are based on a duplex microstructure that consists of dense cells separated by a continuous cell bound￾ary. The cells provide most of the strength of the FM. The cell boundary provides toughness by isolating the cells from each other and promoting dissipation of fracture energy by mecha￾nisms such as pullout of the cells [18] or deflection of a crack through the cell boundary [7,18]. Hexagonal BN [2–8,11–20] is an effective cell boundary because it forms a dense, highly textured matrix that bonds only weakly to the strong Si3N4 cells [13,20]. Oxide sintering aids in the Si3N4 (generally Al2O3 and Y2O3) that leach into the BN cell boundary during hot pressing impart most of the bond￾ing [20]. BN would be an ideal cell-boundary material, except for the fact that it can oxidize severely at elevated temperatures 0921-5093/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2005.08.042