Int J. of Refractory Metals Hard Materials 15(1997)13-4 Printed in Great Britain. All rights reser ELSEVIER PII:S0263·4368(96)00046-7 Progress in Silicon-Based Non-Oxide Structural Ceramics Wolfgang Dressler*& ralf riedel Fachgebiet Disperse Feststoffe, Fachbereich Materialwissenschaft, Technische Hochschule Darmstadt, Petersenstr 23 A, D-64287 Darmstadt, Germany (Received 1 August 1996; accepted 16 August 1996) Abstract: The progress in monolithic Si,N, and SiC as well as in Si3N4/SiC composites for structural applications is reviewed. The conventional processing including the powder synthesis, densification and microstructural design is dis- cussed. The mechanical properties of the resulting silicon based non-oxide cera- mics and their industrial applications as structural components are summarized As an alternative route to fabricate Si,N /SiC composites the hybrid processing utilizing the thermal conversion or organosilicon precursors to amorphous and polycrystalline multicomponent materials is described. The hybrid processed cera- mics exhibit ultra-high temperature stability with respect to crystallization, oxida- tion and decomposition. o 1997 Elsevier Science Limited 1 INTRODUCTION oxidizing environments only up to temperatures in the range of 1200-13000C. At higher tem- high hardness and strength, excellent creep, oxi- dized. even in the bulk. This behavior is dation and corrosion resistance as well as their related to the presence of sintering promoting low density, silicon nitride(Si3N4)and silicon compounds like Mgo, Al2O3 or Y2O3 which nitride/carbide(Si, N,/SiC) based ceramics and react with SiOz formed during the oxidation ceramic composites are promising candidate reaction to give low viscous silicates, (iii)th materials for high temperature applications in use of conventionally processed secondary motor and turbine devices and are frequently phase free SiC in the high temperature field is ed as cutting tools, a typical applio limited to low strength applications, ,> du hard materials. However, these materials still the reduced flaw tolerance caused by the low mechanical performance at temperatures above uid phase sintered Sic reveals a higher sensitiv- 1200oC is required. These limitations are due to ity towards oxidation owing to the reaction of the intrinsic properties of ceramics or result the used sintering aids with the oxide product from the used processing process and basically formed on the SiC surface,(v)the conven- an be attributed to the following points: (i) tional fabrication of dense Si3N,/SiC-composites ceramics are difficult to apply with high relia- is difficult due to the distinct sintering behavior bility owing to their intrinsically brittle behavior. of the Si3 na and Sic powder particles used as In contrast to this, metals are limited by corro- the starting materials. .8 However, significant sion problems and by reduced performance at improvements of the room and high-tempera temperatures approaching their melting point, ture properties of Si3 Na- and Sic-based cera- (ii) commercial Si3N, parts can be applied in mics like strength, fracture toughness, creep and oxidation resistance have been achieved by *Present address: Robert Bosch GmbH, FVIFLW, Post- tailoring of microstructure, -I7 by generation of fach 106050, D-70049, Stuttgar Si,N,/SiC micro/micro-., 18-20 or micro/nano- 13ELSEVIER Int. J. of Refractory Metals & Hard Materials 15 (1997) 13-47 © 1997 Elsevier Science Limited Printed in Great Britain. All rights reserved 0263-4368/97/$17.00 PII: S0263-4368(96)00046-7 Progress in Silicon-Based Non-Oxide Structural Ceramics Wolfgang Dressier* & Ralf Riedel Fachgebiet Disperse Feststoffe, Fachbereich Materialwissenschaft, Technische Hochschule Darmstadt, Petersenstr. 23 A, D-64287 Darmstadt, Germany (Received 1 August 1996; accepted 16 August 1996) Abstract: The progress in monolithic Si3N4 and SiC as well as in Si3Nn/SiC￾composites for structural applications is reviewed. The conventional processing including the powder synthesis, densification and microstructural design is dis￾cussed. The mechanical properties of the resulting silicon based non-oxide cera￾mics and their industrial applications as structural components are summarized. As an alternative route to fabricate Si3N4/SiC composites the hybrid processing utilizing the thermal conversion or organosilicon precursors to amorphous and polycrystalline multicomponent materials is described. The hybrid processed cera￾mics exhibit ultra-high temperature stability with respect to crystallization, oxida￾tion and decomposition. © 1997 Elsevier Science Limited 1 INTRODUCTION Owing to their advantageous properties, like high hardness and strength, excellent creep, oxi￾dation and corrosion resistance as well as their low density, silicon nitride (Si3N4) and silicon nitride/carbide (Si3N4/SiC) based ceramics and ceramic composites are promising candidate materials for high temperature applications in motor and turbine devices and are frequently used as cutting tools, a typical application for hard materials. However, these materials still have application limits where reliability or mechanical performance at temperatures above 1200°C is required. These limitations are due to the intrinsic properties of ceramics or result from the used processing process and basically can be attributed to the following points: (i) ceramics are difficult to apply with high relia￾bility owing to their intrinsically brittle behavior. In contrast to this, metals are limited by corro￾sion problems and by reduced performance at temperatures approaching their melting point, (ii) commercial Si3N4 parts can be applied in *Present address: Robert Bosch GmbH, FVIFLW, Post￾fach 106050, D-70049, Stuttgart. 13 oxidizing environments only up to temperatures in the range of 1200-1300°C. At higher tem￾peratures, the material creeps' and is oxi￾dized 2"3 even in the bulk. This behavior is related to the presence of sintering promoting compounds like MgO, A1203 or Y203 which react with SiO2 formed during the oxidation reaction to give low viscous silicates, (iii) the use of conventionally processed secondary phase free SiC in the high temperature field is limited to low strength applications, 4"5 due to the reduced flaw tolerance caused by the low fracture toughness of additive free SiC, (iv) liq￾uid phase sintered SiC reveals a higher sensitiv￾ity towards oxidation owing to the reaction of the used sintering aids with the oxide product formed on the SiC surface, 6 (v) the conven￾tional fabrication of dense Si3Nn/SiC-composites is difficult due to the distinct sintering behavior of the Si3N 4 and SiC powder particles used as the starting materials. 7"8 However, significant improvements of the room and high-tempera￾ture properties of Si3N4- and SiC-based cera￾mics like strength, fracture toughness, creep and oxidation resistance have been achieved by tailoring of microstructure, 9-'7 by generation of Si3N4/SiC micro/micro -7'8'18-26 or micro/nano-