tkatesh/Materials Science and Engineering 4268(1999)47 Table I Room-temperature properties of PRD-166 fiber and Saphikon filament Fiber Melting point Density (g/cm) Tensile strength Tensile modulus Thermal expansion(x 10-6/C) 9. 12(parallel to c-axis); 7.95(perp. to c-axis) PRD-1662045 9.0 composite. It has been shown that tin dioxide which saphikon /Sno2glass composites. The fracture has no diffusion in alumina up to 1400C in partia urfaces of AG. asc and ssg were characterized pressure of oxygen >10-/atmospheres [11, 12] and using SEM. Percent ers aligned parallel to the very little diffusion in glass [8] could be an ideal candi- fiber axis and fibers broken in as-fabricated AG and date for a barrier coating. The present work examines ASG composites were evaluated by lightly etching the the strength and toughness of alumina-fiber(PRD-166) composite surface with HF and observing under SEM lber reinforced glass matrix composites with and with- Three-point bend tests on AG, ASG, SG and SsG out a tin dioxide interphase. were conducted in the longitudinal direction, LI and transverse directions Ti and T2. The orientation of the fibers with espect to the applied load 2. Materials and experimental procedure samples Li, T and T2 is shown in Fig. 1. Bend tests were carried out on specimens having a span length(S) The PRD-166 fiber used in the present work is a breadth(B)ratio of 0.75. The three-point bed to to thickness () ratio >8 and thickness (w polycrystalline a-Al,O3 fiber, 20 um in diameter and contains 15-20 wt%Y,O were conducted on an Instron machine(model partially stabilized zirconia with a crosshead speed of 0.005 cm/min. The bend particles.The properties of PRD-166 fiber are given in strength, o is given as Table 1 [13. The zirconia particles are dispersed throughout the fiber but primarily along the grain 0,=3/2(PS/BW2) boundaries. The grain size of alumina, as determined by the linear intercept method was about 0.5 um, and where P is the maximum load the ize of zirconia particles was 0.33 Three-point bend tests were also conducted on AG Saphikon is a single crystal alumina filament. The and ASG composites at 200, 400 and 600C c-axis of the filament is oriented parallel to the fiber Fracture toughness of AG, asG, SG and SSg were surface. The mechanical and physical properties of the evaluated using chevron notch specimens. A chevron Saphikon filaments are given in Table 1 [14]. N51A, a notch specimen is as shown in Fig. 2a. A specimen borosilicate glass(Owens Illinois ) was used. Some me- geometry having a span-to-thickness ratio of 4 and chanical properties of N51A glass and SnO2 are given thickness-to-width ratio of 1.5 was used to evaluate the Table 2 fracture toughness. The three-point bend tests were Alumina fiber reinforced glass matrix composites conducted on an Instron machine(model 1102) with vere fabricated by slurry impregnation techniques[15]. crosshead speed of 0.005 cm/min. The fracture tough The slurry consisted of glass frit, 2-propanol and an ness(Kle) was evaluated by the following equation organic binder to impart green strength to the tapes Ke=(P/Bw 1/2)Yc(do 41) and facilitate their handling. For fabrication of alu (2) mina/glass composites, a continuous process was em ployed to make unidirectional tapes. For fabrication of Table 2 Properties of N51A glass and tin dioxide lumina/SnO2 glass composites, fiber tows of 5 cm in length were coated with SnO, using a CVD process by Tin dioxide Glass reaction of SnCL and H,0 at 500C. The coated fibers were then dipped in the slurry and laid on mylar tapes E(GPa) 72 to form prepeg tapes. These unidirectional tapes were VHN(GPa) 0.7-0.8 heated to 500C in air to remove the binder and then Density (g/cm) hot pressed. The hot pressing was performed in a Thermal expansion(10-C) graphite lined die in argon atmosphere at 925C and 3 Melting point(oC) MPa Annealing point (C) Optical microscopy was used to evaluate the volume Softening point (C) fraction and fiber distributions alumina/glass (AG) Boiling point (C) 1800-1900 Molecular weight alumina / SnO /glass (ASG), Saphikon/glass (SG)and48 R. Venkatesh Venkatesh / Materials Science and Engineering A Materials Science and Engineering A268 (1999) 47–54 268 (1999) 47–54 Table 1 Room-temperature properties of PRD-166 fiber and Saphikon filament Fiber Density (g Melting point /cm3 ) Tensile strength Thermal expansion (×10−6 Tensile modulus /°C) (°C) (MPa) (GPa) Saphikon 3.9 2053 3150 380 9.12 (parallel to c-axis); 7.95 (perp. to c-axis) PRD-166 4.2 2045 2070 380 9.0 composite. It has been shown that tin dioxide which has no diffusion in alumina up to 1400°C in partial pressure of oxygen \10−7 atmospheres [11,12] and very little diffusion in glass [8] could be an ideal candi￾date for a barrier coating. The present work examines the strength and toughness of alumina-fiber (PRD-166) fiber reinforced glass matrix composites with and with￾out a tin dioxide interphase. 2. Materials and experimental procedure The PRD-166 fiber used in the present work is a polycrystalline a-Al2O3 fiber, 20 mm in diameter and contains 15–20 wt.% Y2O3 partially stabilized zirconia particles. The properties of PRD-166 fiber are given in Table 1 [13]. The zirconia particles are dispersed throughout the fiber but primarily along the grain boundaries. The grain size of alumina, as determined by the linear intercept method was about 0.5 mm, and the average size of zirconia particles was 0.33 mm. Saphikon is a single crystal alumina filament. The c-axis of the filament is oriented parallel to the fiber surface. The mechanical and physical properties of the Saphikon filaments are given in Table 1 [14]. N51A, a borosilicate glass (Owens Illinois), was used. Some me￾chanical properties of N51A glass and SnO2 are given in Table 2. Alumina fiber reinforced glass matrix composites were fabricated by slurry impregnation techniques [15]. The slurry consisted of glass frit, 2-propanol and an organic binder to impart green strength to the tapes and facilitate their handling. For fabrication of alu￾mina/glass composites, a continuous process was em￾ployed to make unidirectional tapes. For fabrication of alumina/SnO2/glass composites, fiber tows of 5 cm in length were coated with SnO2 using a CVD process by reaction of SnCl4 and H2O at 500°C. The coated fibers were then dipped in the slurry and laid on mylar tapes to form prepeg tapes. These unidirectional tapes were heated to 500°C in air to remove the binder and then hot pressed. The hot pressing was performed in a graphite lined die in argon atmosphere at 925°C and 3 MPa. Optical microscopy was used to evaluate the volume fraction and fiber distributions alumina/glass (AG), alumina/SnO2/glass (ASG), Saphikon/glass (SG) and saphikon/SnO2/glass (SSG) composites. The fracture surfaces of AG, ASG, SG, and SSG were characterized using SEM. Percent of fibers aligned parallel to the fiber axis and fibers broken in as-fabricated AG and ASG composites were evaluated by lightly etching the composite surface with HF and observing under SEM. Three-point bend tests on AG, ASG, SG and SSG were conducted in the longitudinal direction, L1 and transverse directions T1 and T2. The orientation of the fibers with respect to the applied load in bend test samples L1, T1 and T2 is shown in Fig. 1. Bend tests were carried out on specimens having a span length (S) to thickness (W) ratio \8 and thickness (W) to breadth (B) ratio of 0.75. The three-point bend tests were conducted on an Instron machine (model 1102) with a crosshead speed of 0.005 cm/min. The bend strength, sb, is given as sb=3/2(PS/BW 2 ) (1) where P is the maximum load. Three-point bend tests were also conducted on AG and ASG composites at 200, 400 and 600°C. Fracture toughness of AG, ASG, SG and SSG were evaluated using chevron notch specimens. A chevron notch specimen is as shown in Fig. 2a. A specimen geometry having a span-to-thickness ratio of 4 and thickness–to-width ratio of 1.5 was used to evaluate the fracture toughness. The three-point bend tests were conducted on an Instron machine (model 1102) with a crosshead speed of 0.005 cm/min. The fracture tough￾ness (K1c) was evaluated by the following equation Klc=(P/BW 1/2 )Yc(a0, a1) (2) Table 2 Properties of N51A glass and tin dioxide Tin dioxide Glass E (GPa) 72 233 VHN (GPa) 1.13 0.63 K1c (MPa m – 0.7–0.8 1 2 ) Density (g/cm 6.95 3 ) – Thermal expansion(10−6 /°C) 5.23 7 Melting point (°C) 1630 – Annealing point (°C) 570 – Softening point (°C) – 785 Boiling point (°C) – 1800–1900 Molecular weight – 150