E噩≈S Journal of the European Ceramic Society 23(2003)309-313 www.elsevier.com/locate/jeurceramsoc Thermal shock properties of alumina reinforced with TI(C, N whiskers Pernilla pettersson Mats johnsson* Department of Inorganic Chemistry, Stockholm University, S-106 91 Stockholm, Sweden Received I March 2002; received in revised form 26 May 2002: accepted I June 2002 Abstract a Alumina composites reinforced with Ti(C, N)whiskers were produced to evaluate the thermal shock properties. The indentation acture toughness (49 N load)increased from 2.6 MPa m/ for pure alumina to 5.0 MPa m/ for the sample with 30 vol% Ti(C, N)whiskers. The hardness also increased, from 17.6 to 24.2 GPa. a clear R-curve behaviour was observed. An indentation- quench test was used to measure the thermal shock resistance. The best thermal shock resistance was observed at 30 vol. Ti(C, N C 2002 Elsevier Science Ltd. All rights reserved Keywords: Al2O3; Composites; Indentation; Thermal shock resistance; Ti(C, N); Whiskers 1. Introduction on indenting small initial cracks on a polished plate. The indented plate is heated in a vertical tube furnace Alumina is a brittle material with a poor thermal and subsequently quenched in a water bath. The crack shock resistance. However, the mechanical properties length is measured before and after quenching. The can be improved substantially by reinforcing it with a indentation-quench method gives data useful for com- phase having good thermal stability, high strength and paring the thermal shock resistance of different ceramic high elastic modulus. Sic whiskers is the preferred materials. The influence of different experimental para- reinforcing phase, especially for cutting tool applica meters on the resolution of this measurement technique tions. During the last few years a number of new whis- has recently been evaluated ker materials in the form of transition metal carbide and The aim of the present work was to evaluate the carbonitride phases have been developed, such as Tic thermal shock resistance of alumina composites rein- nd Ti(C, N ) ,2 Such whiskers have high hardness and forced with Ti(C, N) whiskers. Another aim was to test strength, and they are chemically inert to iron up to the applicability of the indentation-quench test to this high temperatures, making them interesting candidates type of materials for reinforcement of ceramic cutting tools. Many thermal-shock testing techniques use test bars of specified dimensions and geometries. After a heating 2. Experimental and quenching procedure the bars are subjected to mechanical testing by e.g. three- or four-point bending- 2.1. Starting materials and sample preparation strength tests. These techniques involve some draw backs: a new test bar is needed for each temperature The Ti(C, N) whiskers were synthesised carbother and, to improve statistics, more than one bar should be mally via a vapour-liquid-solid (VLS) growth mechan ested at each temperature. The technique used in the Ism ace cording to Ahlen et al. l, 2 The whisker product current work is an indentation-quench method based was analysed chemically for Ti, N, C and O, and the bulk composition was found to be TiCo.21 No6 g Oo. 16. The 4 Corresponding author whisker morphology was investigated both in an optical E-mail address: mats@ inorg. suse(M. Johnsson). microscope and in a scanning electron microscope 0955-2219/02/S. see front matter C 2002 Elsevier Science Ltd. All rights reserved. PII:S0955-2219(02)00177-2Thermal shock properties of alumina reinforced with Ti(C,N) whiskers Pernilla Pettersson, Mats Johnsson* Department of Inorganic Chemistry, Stockholm University, S-106 91 Stockholm, Sweden Received 1 March 2002; received in revised form 26 May 2002; accepted 1 June 2002 Abstract Alumina composites reinforced with Ti(C,N) whiskers were produced to evaluate the thermal shock properties. The indentation fracture toughness (49 N load) increased from 2.6 MPa m1=2 for pure alumina to 5.0 MPa m1=2 for the sample with 30 vol.% Ti(C,N) whiskers. The hardness also increased, from 17.6 to 24.2 GPa. A clear R-curve behaviour was observed. An indentation– quench test was used to measure the thermal shock resistance. The best thermal shock resistance was observed at 30 vol.% Ti(C,N) whiskers. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Al2O3; Composites; Indentation; Thermal shock resistance; Ti(C,N); Whiskers 1. Introduction Alumina is a brittle material with a poor thermal shock resistance. However, the mechanical properties can be improved substantially by reinforcing it with a phase having good thermal stability, high strength and high elastic modulus. SiC whiskers is the preferred reinforcing phase, especially for cutting tool applica￾tions. During the last few years a number of new whis￾ker materials in the form of transition metal carbide and carbonitride phases have been developed, such as TiC and Ti(C,N).1,2 Such whiskers have high hardness and strength, and they are chemically inert to iron up to high temperatures, making them interesting candidates for reinforcement of ceramic cutting tools. Many thermal-shock testing techniques use test bars of specified dimensions and geometries. After a heating and quenching procedure the bars are subjected to mechanical testing by e.g. three- or four-point bending￾strength tests. These techniques involve some draw￾backs: a new test bar is needed for each temperature and, to improve statistics, more than one bar should be tested at each temperature. The technique used in the current work is an indentation–quench method3 based on indenting small initial cracks on a polished plate. The indented plate is heated in a vertical tube furnace and subsequently quenched in a water bath. The crack length is measured before and after quenching. The indentation–quench method gives data useful for com￾paring the thermal shock resistance of different ceramic materials. The influence of different experimental para￾meters on the resolution of this measurement technique has recently been evaluated.4 The aim of the present work was to evaluate the thermal shock resistance of alumina composites rein￾forced with Ti(C,N) whiskers. Another aim was to test the applicability of the indentation–quench test to this type of materials. 2. Experimental 2.1. Starting materials and sample preparation The Ti(C,N) whiskers were synthesised carbother￾mally via a vapour–liquid–solid (VLS) growth mechan￾ism according to Ahle´n et al.1,2 The whisker product was analysed chemically for Ti, N, C and O, and the bulk composition was found to be TiC0.21N0.63O0.16. The whisker morphology was investigated both in an optical microscope and in a scanning electron microscope 0955-2219/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0955-2219(02)00177-2 Journal of the European Ceramic Society 23 (2003) 309–313 www.elsevier.com/locate/jeurceramsoc * Corresponding author. E-mail address: matsj@inorg.su.se (M. Johnsson)