S.T. Mileiko Current Opinion in Solid State and Materials Science 9(2005)219-229 [7-9] and alumina-YAG-eutectics [7, 8, 10]. YAG with the 2. Coating fibres with a thin layer of various materials (100) orientation of the fibre axis [12] and single crystalline yields healing of surface defects and an essential mullite [13, 14]fibres have been produced. Crystallization of nhancement of the fibre strength. A CVd process was sapphire fibres [9] was conducted by using a seed to get used to coat the fibres to ensure an intimate contact fibres with the c-axis coinciding with the fibre axis: YAG on the interrace and mullite fibres have been crystallised without using seed, so their axis coincides with the (00 1) and c-directions, The second feature is of an obvious importance in the respectively(see Fig. 4) present context. There is a clear dependence of the fibre strength on the coating thickness presented in Fig. 6. How- 2.2.1. Strength of ICM-fibres ever, at the present time it is not clear as to the extent of the Room temperature strength of the fibres was measured maximum fibre strength that can be obtained. A maximum by bending a fibre over rigid cylinders of decreasing diam- can be expected as the coating layer also contains defects eters and counting an average distance between fibre gh temperature strength of the fibres has been mea breaks on each step of the experiment [15]. This yields a sured by testing oxide/molybdenum composites obtained dependence of ultimate strain on the fibre length provided by ICM in either tension [7, 8] or bending. Some results the Youngs modulus of the fibre material is also known. are shown in Fig. 7 The room temperature strength of ICM-fibres(see an example in Fig. 5)are characterised by two features [9, 10]: 2. 2. High temperature creep characteristics of ICM-fibres Creep tests of ICM-fibres are normally performed by 1. The strength/scale dependence is very strong, so the bending oxide-fibre/Mo-matrix specimens. The analysis Weibull exponent varies usually between 3 and 5. A rea- of the experimental data allows obtaining tensile creep son for it is certainly an existence of sufficiently rough characteristics of the fibres. The analysis [16] is based on defects, which are located mainly on the fibre surface. the following assumptions: Molybdenum carcass Oxide/molybdenum block oxide melt the carcass Fig. 1. Schematic of the internal crystallization method (ICM)[7–9] and alumina–YAG-eutectics [7,8,10], YAG with the h100i orientation of the fibre axis [12] and single crystalline mullite [13,14] fibres have been produced. Crystallization of sapphire fibres [9] was conducted by using a seed to get fibres with the c-axis coinciding with the fibre axis; YAG and mullite fibres have been crystallised without using seed, so their axis coincides with the h001i and c-directions, respectively (see Fig. 4). 2.2.1. Strength of ICM-fibres Room temperature strength of the fibres was measured by bending a fibre over rigid cylinders of decreasing diam￾eters and counting an average distance between fibre breaks on each step of the experiment [15]. This yields a dependence of ultimate strain on the fibre length provided the Young’s modulus of the fibre material is also known. The room temperature strength of ICM-fibres (see an example in Fig. 5) are characterised by two features [9,10]: 1. The strength/scale dependence is very strong, so the Weibull exponent varies usually between 3 and 5. A rea￾son for it is certainly an existence of sufficiently rough defects, which are located mainly on the fibre surface. 2. Coating fibres with a thin layer of various materials yields healing of surface defects and an essential enhancement of the fibre strength. A CVD process was used to coat the fibres to ensure an intimate contact on the interface. The second feature is of an obvious importance in the present context. There is a clear dependence of the fibre strength on the coating thickness presented in Fig. 6. How￾ever, at the present time it is not clear as to the extent of the maximum fibre strength that can be obtained. A maximum can be expected as the coating layer also contains defects. High temperature strength of the fibres has been mea￾sured by testing oxide/molybdenum composites obtained by ICM in either tension [7,8] or bending. Some results are shown in Fig. 7. 2.2.2. High temperature creep characteristics of ICM-fibres Creep tests of ICM-fibres are normally performed by bending oxide–fibre/Mo–matrix specimens. The analysis of the experimental data allows obtaining tensile creep characteristics of the fibres. The analysis [16] is based on the following assumptions: Fig. 1. Schematic of the internal crystallization method (ICM). S.T. Mileiko / Current Opinion in Solid State and Materials Science 9 (2005) 219–229 221