REFRACTORY METALS HARD MATERIALS ELSEVIER International Journal of Refractory Metals Hard Materials 16(1998)337-341 Fracture and creep of an Al2O3-SiC (whisker)-TiC (particle) posite A.R. de Arellano-Lopeza, B. I. Smirnov, JJ. Schuldies, E. T Park, K.C. Coretta J .L Routbort Departamento de Fisica de la Matena Condensada, Unn'erstdad de Sevilla, PO Bax 1065, 41080 Sevilla, Spain A F Ioffe Phystco-Techmcal Instttute, Russian Academy of Sciences, 194021 St Petersburg, Russia dustnal Ceramic Technology, Ann Arbor, MI 48103, USA Energy Technology Dunston, Argonne Natonal Laboratory, Argonne, IL 60439, USA Received 9 March 1998; accepted 14 July 1998 Abstract h-temperature fracture strength and compressive creep of an electrodischarge- machinable composite, AlO 30.9 vol %o SiC whiskers-23 vol TiC particles have been studied to 1200C and 1450.C, respectively, in Inert atmosphere. Microstructures of fractured and deformed specimens were examined using scanning and transmission electron microscopy. Fast fracture occurred at T<1200C Steady-state creep was achieved for T> 1350C at stresses <80 MPa, with the rate-controlling mechanism being partially unaccommodated grain-boundary sliding, with a stress exponent of x1 and an activation energy of x 470 kJ/mol. 1998 Elsevier Science Ltd. All rights reserved Keywords CeramIc-matrIx composites; Fracture, Creep, electrodischarge machInIng 1. Introduction SiC whiskers to produce an electrodischarge-machin able ceramic composite [7. These composites have Significant improvements in strength, toughness and high electrical conductivity [ 8] creep resistance of ceramic mate Laboratories in Spain, Russia and the uSa, under achieved in the past decade. This is particularly true the auspices of NAtO, have extensively characterized for ceramic-matrix composites [1, for which the microstructural and mechanical properties of this SiC-whisker-reinforced Al2Oj-based composites have new ceramic composite, with a goal of determining become a classic system and the object of extensive processing paths and microstructures, that will yield study [2-5. Although whisker-reinforced ceramic conducting composites with further improved mechan- composites are commercially available, high machining ical properties. Previous work on Al O3-SiC (whisker)- costs for complex parts have limited use of these Tic(particle) composites (AISiTi) dealt with composites and, therefore, they have not found microstructure and room-tempen echanica widespread application despite their uniquely favour- properties, such as fracture strength, fracture toug able properties, such as low density, chemical and ness, microhardness, elastic modulus and response to thermal stability, and mechanical durability [6]. A solid-particle erosion [9, 10]. Summarizing the earlier composite has recently been developed with sufficiently findings: AISiTi has an elastic modulus at room high electrical conductivity to take a step towards the temperature of 410 GPa, microhardness values that possible realization of the goal of wider commercial depend on whether the indentor is centred on a TiC usage. TiC particles are added to Al2O3 powder and particle or not and an indentation fracture toughness (Kic) of 9.6 MPa(m). As in other complex compo- of toughening mechanisms operates. In addition to debonding and bridging,ELSEVIER International Journal of Refractory Metals & Hard Materials 16 (1998) 337-341 International Journal of REFRACTORY METALS & HARD MATERIALS Fracture and creep of an A1203-SiC (whisker)-TiC (particle) composite A. R. de Arellano-L6pez a*, B. I. Smirnov b, J. J. Schuldies c, E. T. Park d, K. C. Goretta d, J. L. Routbort d aDepartamento de Ftstca de Ia Materta Condensada, Umverszdad de Sevtlla, PO Box 1065, 41080 Sevdla, Spam bA E Ioffe Phystco-Techmcal lnstttute, Russtan Academy of Sctences, 194021 St Petersburg, Russta Clndustnal Ceramtc Technology, Ann Arbor, 341 48103, USA aEnergy Technology Dtvtston, Argonne National Laboratot); Argonne, 1L 60439, USA Recewed 9 March 1998; accepted 14 July 1998 Abstract High-temperature fracture strength and compresswe creep of an electrodischarge-machinable composite, Al203-30.9 vol.% SiC whiskers-23 vol % TiC particles have been studied to 1200°C and 1450°C, respectively, in inert atmosphere. Microstructures of fractured and deformed specimens were examined using scanning and transmission electron microscopy. Fast fracture occurred at T_< 1200°C. Steady-state creep was achieved for T > 1350°C at stresses <80 MPa, with the rate-controlling mechanism being partially unaccommodated grain-boundary sliding, with a stress exponent of ~ 1 and an activation energy of ~470 kJ/mol. © 1998 Elsevier Science Ltd. All rights reserved. Keywords" Ceramic-matrix composites; Fracture, Creep, electrodischarge machining 1. Introduction Significant improvements in strength, toughness and creep resistance of ceramic materials have been achieved in the past decade. This is particularly true for ceramic-matrix composites [1], for which SiC-whisker-reinforced A1203-based composites have become a classic system and the object of extensive study [2-5]. Although whisker-reinforced ceramic composites are commercially available, high machining costs for complex parts have limited use of these composites and, therefore, they have not found widespread application despite their uniquely favour￾able properties, such as low density, chemical and thermal stability, and mechanical durability [6]. A composite has recently been developed with sufficiently high electrical conductivity to take a step towards the possible realization of the goal of wider commercial usage. TiC particles are added to A1203 powder and *Corresponding author SiC whiskers to produce an electrodischarge-machin￾able ceramic composite [7]. These composites have high electrical conductivity [8]. Laboratories in Spain, Russia and the USA, under the auspices of NATO, have extensively characterized the microstructural and mechanical properties of this new ceramic composite, with a goal of determining processing paths and microstructures, that will yield conducting composites with further improved mechan￾ical properties. Previous work on A1203-SiC (whisker)- TiC (particle) composites (A1SiTi) dealt with microstructure and room-temperature mechanical properties, such as fracture strength, fracture tough￾ness, microhardness, elastic modulus and response to solid-particle erosion [9,10]. Summarizing the earlier findings: A1SiTi has an elastic modulus at room temperature of 410 GPa, microhardness values that depend on whether the indentor is centred on a TiC particle or not and an indentation fracture toughness (Kic) of 9.6 MPa(m) °5. As in other complex compo￾sites, a combination of toughening mechanisms operates. In addition to debonding and bridging, 0263-4368/98/$ -- see front matter © 1998 Elsevier Science Ltd All rights reserved PII" S0263-4368(98)00037-7