S.T. Mileiko Current Opinion in Solid State and Materials Science 9(2005)219-229 Interface where nm, On, and n are constants. The value of n can be chosen arbitrary. In what follows, mn=10h, which means that on is the stress to cause 1% creep strain for 100 h. We call this value as creep resistance of a material on 100-h time base Matrix A solution of a creep problem for a beam under bending yields a dependence of the deflection rate, f, of the beam at its centre on applied load 0. For a beam of rectangula cross-section of height 2h, width b we have Fibre Q (2) in case of 3. 0.5 um b7|1q in case of 4-point bending. Here L and Li are the distances Fibre in=a, Mn=nanbh- and M is the bending moment Matrix The solution was obtained by neglecting a contribution of shear deformations to the displacement that can be essential in case of 3-point bending Creep characteristics of ICM-fibres tested up to now Fig.2.TEM images of the sapphire-fibre/molybdenum-matrix interface fibres are presented in Fig. 8. Here alo stalline mullite in an oxide/ molybdenum block [32]. for Nextel 720 fibre (a-Al2O3 mullite) evaluated from experimental data presented in Ref [17] is shown. A num- ber of important conclusions can be now drawn; here we emphasize just three points 1. In temperature interval from 1100 to 1600C, values of the creep resistance of single crystalline YAG and mull- ite as well as that of alumina-YAG-eutectic fibres obtained by using ICM are nearly the YAG fibre looks slightly better than the others. Still, their creep resistance can be certainly enhanced by crystallising them in the(111) direction 2. Surprisingly enough, single crystalline mullite fibres pro- duced by ICM do not seem to be superior to, say, YAG fibres. Their creep resistance differs essentially from the experimental value(Dokko et al. [18] 3. Polycrystalline oxide fibres, available at th Fig. 3. A view of the flat surface of a sapphire fibre; a replica of the time, obviously lose their creep resistance below a tem- molybdenum foil can be seen with a grain size of 10 um. perature of 1200C certainly due to an intrinsic behav lour of 1. A contribution of the matrix, which is fully recrystallised molybdenum, to the creep resistance of oxide/molybde t hum composites at temperatures above 1000.C is negli-3.Oxide-fibre/metal-matrix composites A composite is characterised by identical creep behav- Metal-matrix composites reinforced with ICM-fibres our under tension and compression are obtained via liquid phase route [19, 20]. Hence, the 3. The creep law of the material is fibre/ matrix interface strength depends on wettability of an oxide with a metal melt; the issue is analysed in details (1) in a review paper[21].Ti- and Ni-based alloys as matrices are of an immediate practical interest. They represent also1. A contribution of the matrix, which is fully recrystallised molybdenum, to the creep resistance of oxide/molybde￾num composites at temperatures above 1000 C is negli￾gible, less than 10 MPa [7]. 2. A composite is characterised by identical creep behav￾iour under tension and compression. 3. The creep law of the material is e_ ¼ gn r rn n ð1Þ where gn, rn, and n are constants. The value of gn can be chosen arbitrary. In what follows, gn = 104 h1 , which means that rn is the stress to cause 1% creep strain for 100 h. We call this value as creep resistance of a material on 100-h time base. A solution of a creep problem for a beam under bending yields a dependence of the deflection rate, _ f , of the beam at its centre on applied load Q. For a beam of rectangular cross-section of height 2h, width b we have: _ f ¼ gn 1 23nþ2 nnðn þ 2Þ Q rnh2 n L b n L h L ð2Þ in case of 3-point bending and _ f ¼ vn M Mn n L2 1 8 ð3Þ in case of 4-point bending. Here L and L1 are the distances between periphery and internal supports, respectively, vn ¼ gn h , Mn ¼ 2n 2nþ1 rnbh2 and M is the bending moment. The solution was obtained by neglecting a contribution of shear deformations to the displacement that can be essential in case of 3-point bending. Creep characteristics of ICM-fibres tested up to now including preliminary data for single crystalline mullite fibres are presented in Fig. 8. Here also creep resistance for Nextel 720 fibre (a-Al2O3 + mullite) evaluated from experimental data presented in Ref. [17] is shown. A num￾ber of important conclusions can be now drawn; here we emphasize just three points: 1. In temperature interval from 1100 to 1600 C, values of the creep resistance of single crystalline YAG and mull￾ite as well as that of alumina–YAG-eutectic fibres obtained by using ICM are nearly the same. YAG fibre looks slightly better than the others. Still, their creep resistance can be certainly enhanced by crystallising them in the h111i direction. 2. Surprisingly enough, single crystalline mullite fibres pro￾duced by ICM do not seem to be superior to, say, YAG fibres. Their creep resistance differs essentially from the experimental value (Dokko et al. [18]). 3. Polycrystalline oxide fibres, available at the present time, obviously lose their creep resistance below a tem￾perature of 1200 C certainly due to an intrinsic behav￾iour of grain boundaries. 3. Oxide–fibre/metal–matrix composites Metal–matrix composites reinforced with ICM-fibres are obtained via liquid phase route [19,20]. Hence, the fibre/matrix interface strength depends on wettability of an oxide with a metal melt; the issue is analysed in details in a review paper [21]. Ti- and Ni-based alloys as matrices are of an immediate practical interest. They represent also Fig. 2. TEM images of the sapphire–fibre/molybdenum–matrix interface in an oxide/molybdenum block [32]. Fig. 3. A view of the flat surface of a sapphire fibre; a replica of the molybdenum foil can be seen with a grain size of 10 lm. 222 S.T. Mileiko / Current Opinion in Solid State and Materials Science 9 (2005) 219–229