R Venkatesh/Ceramics International 28 (2002)565-573 1. Chemical compatibility with the matrix The alumina(Prd-166) fibres were coated with SnO 2. Refractoriness by a chemical vapor deposition technique. The alumina 3. Stability in oxidising, water vapor and corrosive fibre tows were placed in the central hot zone of the environments reactor and heated to the deposition temperature of 4. Providing a relatively weak fibre-coating inter- 500C. Dry nitrogen was the carrier gas for SnCl4. The phase allowing for fibre debonding and pullout. flow rate of nitrogen was I I/min. A second bubbler contained water heated to 80C through which oxygen In oxide fibre/oxide matrix composite systems, reac- was passed at a rate of 0.6 I/min. The deposition occur tions at the fibre/matrix interface, e.g. Al_O3/SiO2, red via the chemical reaction [38]. mullite/mullite leads to a strong interfacial bonding with the consequence of brittle behaviour of the composite. SnCl4(g)+ 2H20(g)+ SnO2(S)+4HCI(g) Various interphase coatings have been applied in oxide fibre/oxide matrix composites including, SnO2, TiO2, The microstructures of as-received fibres heat treated ZrO2, HfO2, monazite, magnetoplumbite, perouskite at 500, 600 and 900C for 90 minutes and SnO2 coated structures like BaTiO3, etc. [26-33]. In the present work, fibres were characterised using SEM and XRD. SEM the effect of fibre and coating properties on the bending was used to determine uniformity, morphology and strength and toughness of alumina fibre/glass matrix thickness of the coating. The fracture surfaces of the as- composites have been investigated SnO2 was chosen as received and SnO2 coated fibres were also characterised a coating since it has no reaction with alumina up to by SEM 1400 oC in a partial pressure of oxygen >10-7atm Single fibre tensile tests were carried out on as- [34, 35]. The strength of alumina-zirconia fibres as- received, heat treated and SnO, coated PRD-166 fibres received, heat treated and SnO2 coated were deter- A random selection of single fibres was made from the mined. Glass matrix composites fabricated using slurry impregnation technique and reinforced with two ypes of fibres, namely PrD-166(alumina-20 wt zir- conia) fibres and relatively smooth saphikon fibres were tested to investigate how the properties of the fibres can nfluence the bending strength and toughness of CMCs Experimental procedure The PRD-166 fiber used in the present work is a polycrystalline a-Al2O3 fiber, 20 um in diameter and containing 15-20 wt %Y2O3 partially stabilized zirco- nia particles. The properties of PRD-166 fiber are given in Table 1 [36]. The zirconia particles are dispersed throughout the fiber but primarily along the grain boundaries. Saphikon is a single crystal alumina fila- ment. The c-axis of the filament is oriented parallel to the fibre surface. The mechanical and physical proper ies of the saphikon filaments are given in Table 1 [37] N 5lA, a borosilicate glass, obtained from Owens Illinois Inc, was used as a matrix in the present study. Table Room-temperature properties of PRD-166 fiber and Saphikon fila- ment [ 36,37 Fibre Melting Density Tensile Tensile Thermal ao point(C)(g/cm)strength modulus expansion Mpa)(GPa)(×10-°/°C Saphikon 2053 3931503809.12∥/toc-axis) PRD-1662045 2070380 Fig. I.(a)Chevron notch specimen;(b) geometry of chevron notch.1. Chemical compatibility with the matrix. 2. Refractoriness. 3. Stability in oxidising, water vapor and corrosive environments. 4. Providing a relatively weak fibre-coating inter￾phase allowing for fibre debonding and pullout. In oxide fibre/oxide matrix composite systems, reac￾tions at the fibre/matrix interface, e.g. Al2O3/SiO2, mullite/mullite leads to a strong interfacial bonding with the consequence of brittle behaviour of the composite. Various interphase coatings have been applied in oxide fibre/oxide matrix composites including, SnO2, TiO2, ZrO2, HfO2, monazite, magnetoplumbite, perouskite structures like BaTiO3, etc. [26–33]. In the present work, the effect of fibre and coating properties on the bending strength and toughness of alumina fibre/glass matrix composites have been investigated. SnO2 was chosen as a coating since it has no reaction with alumina up to 1400
C in a partial pressure of oxygen >107 atm. [34,35]. The strength of alumina-zirconia fibres as￾received, heat treated and SnO2 coated were deter￾mined. Glass matrix composites fabricated using a slurry impregnation technique and reinforced with two types of fibres, namely PRD-166 (alumina–20 wt.% zir￾conia) fibres and relatively smooth saphikon fibres were tested to investigate how the properties of the fibres can influence the bending strength and toughness of CMCs. Experimental procedure The PRD-166 fiber used in the present work is a polycrystalline a-Al2O3 fiber, 20 mm in diameter and containing 1520 wt.% Y2O3 partially stabilized zirco￾nia particles. The properties of PRD-166 fiber are given in Table 1[36]. The zirconia particles are dispersed throughout the fiber but primarily along the grain boundaries. Saphikon is a single crystal alumina fila￾ment. The c-axis of the filament is oriented parallel to the fibre surface. The mechanical and physical proper￾ties of the saphikon filaments are given in Table 1[37]. N 51A, a borosilicate glass, obtained from Owens Illinois Inc., was used as a matrix in the present study. The alumina (PRD-166) fibres were coated with SnO2 by a chemical vapor deposition technique. The alumina fibre tows were placed in the central hot zone of the reactor and heated to the deposition temperature of 500
C. Dry nitrogen was the carrier gas for SnCl4. The flow rate of nitrogen was 1l/min. A second bubbler contained water heated to 80
C through which oxygen was passed at a rate of 0.6 l/min. The deposition occur￾red via the chemical reaction [38], SnCl4ðgÞ þ 2H2OðgÞ ! SnO2ðsÞ þ 4HClðgÞ ð1Þ The microstructures of as-received fibres heat treated at 500, 600 and 900
C for 90 minutes and SnO2 coated fibres were characterised using SEM and XRD. SEM was used to determine uniformity, morphology and thickness of the coating. The fracture surfaces of the as￾received and SnO2 coated fibres were also characterised by SEM. Single fibre tensile tests were carried out on as￾received, heat treated and SnO2 coated PRD-166 fibres. A random selection of single fibres was made from the Table 1 Room-temperature properties of PRD-166 fiber and Saphikon fila￾ment [36,37] Fibre Melting point (
C) Density (g/cm3 ) Tensile strength (Mpa) Tensile modulus (GPa) Thermal expansion (106 /
C) Saphikon 2053 3.9 3150 380 9.12 (// to c-axis) 7.95 (to c-axis) PRD-166 2045 4.2 2070 380 9.0 Fig. 1. (a) Chevron notch specimen; (b) geometry of chevron notch. 566 R. Venkatesh / Ceramics International 28 (2002) 565–573