COMPOSITES SCIENCE AND TECHNOLOGY ELSEVIER Composites Science and Technology 59(1999)813-819 Thermal stability of the low-oxygen-content silicon carbide fiber Hi-Nicalon TM Michio takeda Jun-ichi sakamoto. Yoshikazu imai. Hiroshi ichikawa Research Laboratory, Nippon Carbon Company Ltd, 1-1-1 Shin-ttrashina-cho, Kanagawa-ku, Yokohama 221-0031, Japan Received 8 September 1997; received in revised form 3 August 1998; accepted 7 January 1999 Abstract The low-oxygen SiC fiber, Hi-Nicalon M, was prepared by the pyrolysis of polycarbosilane fibers cured with electron-beam irradiation. This SiC fiber is continuous, in multi-filament form, and consists of Si-1. 39C-0010 by atomic ratio. Hi-Nicalon fiber has a high tensile strength and an elastic modulus of 2.8 and 270 GPa, respectively. This Sic fiber retains high strength and modulus even after exposure for 10 h at 1873 K in argon. It exhibits outstanding thermal stability as compared to other commercially available polymer-derived ceramic fibers. C 1999 Elsevier Science Ltd. All rights reserved Keywords: SiC; Ceramic fiber: Hi-NicalonTM: Thermal stability 1. ntroduction highly crystalline SiC fibers such as SylramicTM of Dow Corning[14], sintered SiC fiber of Ube Industries [15]. High-performance ceramic materials are needed in and Hi-NicalonTM Type S of Nippon Carbon [16] have advanced high-temperature technologies. In particular, been developed. Although these new Sic fibers were ceramic-matrix composites are the most promising mate- also reported to have high heat-resistance, these are still rials in these applications. The performance of a ceramic- of limited distribution or unavailable matrix composite(CMC) is highly dependent upon the In this work, the structural and mechanical chang properties of the reinforcement. A reinforcing fiber must of Hi-NicalonTM after thermal exposure tests have have thermal stability and sufficient mechanical properties been investigated by comparison with other (some even at elevated temperature. SiC fibers produced by commercially-available) ceramic fibers polymer pyrolysis have high tensile strength, high tensile modulus, and good thermal stability [l]. One highly com- mercialized polymer-derived SiC fiber, Nicalon TM, has 2. Experimental procedure been widely applied in many high-temperature structural materials[2, 3]. However, it is well known that the prop- 2.1. Fabrication of SiC fibers, Nicalon M and Hi- erties of SiC fibers containing oxygen are degraded as a Nicalon M result of carbothermal reduction reaction at high tem perature [4-6]. At elevated temperatures, decreases in the Fig. I shows the fabrication process for SiC fibers, tensile strength and creep resistance of SiC fibers are Nicalon M and Hi-NicalonM. Preceramic polymer observed [7-10]. As a reinforcement for CMCs, these polycarbosilane(PCS), was synthesized from dimethyl- characteristics will often allow only limited use dichlorosilane via polydimethylsilane. SiC fibers were It was reported that a SiC fiber with reduced oxygen prepared by the spinning of PCs, followed by curing content and improved thermal stability is obtained by and pyrolysis. PCS fibers with diameters of about 20 um using an irradiation-curing method [11-13]. This low- were obtained by the melt-spinning method. Two curing oxygen SiC fiber, Hi-Nicalon M, has now been success- processes for making fibers infusible, following pyr fully industrialized. More recently, stoichiometric, olysis, were available. One was by thermal oxidation curing at 473 K in air and the other was by irradiation 4604 rresponding author: Tel :+81-45.459.4692: fax: +81-45 curing with an electron beam Nicalon TM was obtained by the former process and Hi-Nicalon M by the latter 0266-353899/S-see atter c 1999 Elsevier Science Ltd. All rights reserved. PlI:S0266-3538(99)00012-3Thermal stability of the low-oxygen-content silicon carbide ®ber, Hi-NicalonTM Michio Takeda*, Jun-ichi Sakamoto, Yoshikazu Imai, Hiroshi Ichikawa Research Laboratory, Nippon Carbon Company Ltd, 1-1-1 Shin-urashima-cho, Kanagawa-ku, Yokohama 221-0031, Japan Received 8 September 1997; received in revised form 3 August 1998; accepted 7 January 1999 Abstract The low-oxygen SiC ®ber, Hi-NicalonTM, was prepared by the pyrolysis of polycarbosilane ®bers cured with electron-beam irradiation. This SiC ®ber is continuous, in multi-®lament form, and consists of Si-1.39C-0.010 by atomic ratio. Hi-NicalonTM ®ber has a high tensile strength and an elastic modulus of 2.8 and 270 GPa, respectively. This SiC ®ber retains high strength and modulus even after exposure for 10 h at 1873 K in argon. It exhibits outstanding thermal stability as compared to other commercially available polymer-derived ceramic ®bers. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: SiC; Ceramic ®ber; Hi-NicalonTM; Thermal stability 1. Introduction High-performance ceramic materials are needed in advanced high-temperature technologies. In particular, ceramic-matrix composites are the most promising mate￾rials in these applications. The performance of a ceramic￾matrix composite (CMC) is highly dependent upon the properties of the reinforcement. A reinforcing ®ber must have thermal stability and sucient mechanical properties even at elevated temperature. SiC ®bers produced by polymer pyrolysis have high tensile strength, high tensile modulus, and good thermal stability [1]. One highly com￾mercialized polymer-derived SiC ®ber, NicalonTM, has been widely applied in many high-temperature structural materials [2,3]. However, it is well known that the prop￾erties of SiC ®bers containing oxygen are degraded as a result of carbothermal reduction reaction at high tem￾perature [4±6]. At elevated temperatures, decreases in the tensile strength and creep resistance of SiC ®bers are observed [7±10]. As a reinforcement for CMCs, these characteristics will often allow only limited use. It was reported that a SiC ®ber with reduced oxygen content and improved thermal stability is obtained by using an irradiation-curing method [11±13]. This low￾oxygen SiC ®ber, Hi-NicalonTM, has now been success￾fully industrialized. More recently, stoichiometric, highly crystalline SiC ®bers such as SylramicTM of Dow Corning [14], sintered SiC ®ber of Ube Industries [15], and Hi-NicalonTM Type S of Nippon Carbon [16] have been developed. Although these new SiC ®bers were also reported to have high heat-resistance, these are still of limited distribution or unavailable. In this work, the structural and mechanical changes of Hi-NicalonTM after thermal exposure tests have been investigated by comparison with other (some commercially-available) ceramic ®bers. 2. Experimental procedure 2.1. Fabrication of SiC ®bers, NicalonTM and Hi￾NicalonTM Fig. 1 shows the fabrication process for SiC ®bers, NicalonTM and Hi-NicalonTM. Preceramic polymer, polycarbosilane (PCS), was synthesized from dimethyl￾dichlorosilane via polydimethylsilane. SiC ®bers were prepared by the spinning of PCS, followed by curing, and pyrolysis. PCS ®bers with diameters of about 20 mm were obtained by the melt-spinning method. Two curing processes for making ®bers infusible, following pyr￾olysis, were available. One was by thermal oxidation￾curing at 473 K in air and the other was by irradiation￾curing with an electron beam. NicalonTM was obtained by the former process and Hi-NicalonTM by the latter. Composites Science and Technology 59 (1999) 813±819 0266-3538/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0266-3538(99)00012-3 * Corresponding author: Tel.: +81-45-459-4692; fax: +81-45-459- 4604