2 N 1. Baklanova et al /Journal of the European Ceramic Sociery 28(2008)1687-1696 ed Hi-Nicalon d Hi-Nicalon S s-received 1000C · coated1000°C coated1200°c 0 12 Fig.5. Weibull probability plots for room temperature tensile strengths of the coated Tyranno-sa fiber at 1000 and 1200"C RezrO-coated Hi-Nicalon TM and Hi-Nicalon STM fibers population was small in number. Therefore we could not extract 3.3. Tensile strength measurements the Weibull parameters from the obtained data. It is well known that mechanical properties of fiber-reinforced 3.4. The oxidized Rezro2-coated SiC fibers CMC's depend not only on the interfacial stress transfer capacity but also on mechanical properties of fibers. Because of ten Dependences of the relative mass Am/mo on time for sile strength fibers can be greatly influenced by coating, it is the as-received and RezrO2-coated Tyranno-SA fibers(one very important to determine the tensile properties of the coated dipping-annealing cycle)at 1000 and 1200C are represented SiC fibers in order to evaluate their ability as reinforcement in Fig. 6. Both the as-received and coated fibers exhibit a simi- for CMCs. In this study the single filament tensile tests of the lar behavior during oxidation test at 1000C, namely, (i) first LezrO2-coated fibers were performed at room temperature. The mass loss over a short period of time(2h); (ii) a slight mass strength data for individual fibers were obtained using measured gain; and (iii) gradual mass loss for long exposition. The mass values of diameter of each filament, after that the data were ana- loss of the initial and coated fibers at the beginning of oxida- zed using two-parameter single-modal Weibull function. The tion is not more than several percents and could be attributed to In(1/Pr)vs. In o Weibull probability plots for ReZrO2-coated Hi- burnoff of carbon. The following small mass gain could be due NicalonM and Hi-Nicalon S M fibers are represented in Fig. 5. to oxidation of SiC that results in the formation of thin silica The tensile strength and the Weibull modulus were found to be layer. The exposition of the coated fibers to air at 1200C leads 2.71+0.08 GPa and 3.73, respectively, for the ReZrO2-coated to significant mass loss due to the volatilization of silicon-and Hi-Nicalon M fiber. The tensile strength is in good agreement carbon-containing with that reported in literature 4, 16 for desized fiber. The ten- the upper layer I/ com) through the cracks and pores in sile strength for the hi-Nicalon STM fiber is 3.14+0.10GPa SEM micrographs of the coated fibers after exposition to air and this value is slightly higher that those for the initial desized at 1000C(40 h) are represented in Fig. 7a-c. As a whole, the fiber. The Weibull modulus was found to be 4.20. The increase coatings conserve their integrity, uniformity and smoothness in the fiber strength appears to be related to the elimination The round shape formations were observed on the surface of of the surface flaws by the Rezroz coating. The most part of oxidized coated Hi-Nicalon $ fiber. They were present on the the RezrO2-coated Tyranno-SA filaments were broken at the surface of coated fibers(Fig 3a)and originated from the initial edge of frame during tensile strength measurements and data fiber(Fig 1b). Contrary to Hi-Nicalon STM, the new formations 10 um 2 Fig. 7. SEM images of the ReZrO2-coated Hi-NicalonTM (a), Hi-Nicalon SM()and Tyranno-SATM (c)fibers after exposition to air at 1000C for 40h.1692 N.I. Baklanova et al. / Journal of the European Ceramic Society 28 (2008) 1687–1696 Fig. 5. Weibull probability plots for room temperature tensile strengths of the ReZrO2-coated Hi-NicalonTM and Hi-Nicalon STM fibers. 3.3. Tensile strength measurements It is well known that mechanical properties of fiber-reinforced CMC’s depend not only on the interfacial stress transfer capacity but also on mechanical properties of fibers.1 Because of ten￾sile strength fibers can be greatly influenced by coating, it is very important to determine the tensile properties of the coated SiC fibers in order to evaluate their ability as reinforcement for CMC’s. In this study the single filament tensile tests of the ReZrO2-coated fibers were performed at room temperature. The strength data for individual fibers were obtained using measured values of diameter of each filament, after that the data were ana￾lyzed using two-parameter single-modal Weibull function. The ln(1/Pf) vs. ln σ Weibull probability plots for ReZrO2-coated Hi￾NicalonTM and Hi-Nicalon STM fibers are represented in Fig. 5. The tensile strength and the Weibull modulus were found to be 2.71 ± 0.08 GPa and 3.73, respectively, for the ReZrO2-coated Hi-NicalonTM fiber. The tensile strength is in good agreement with that reported in literature14,16 for desized fiber. The ten￾sile strength for the Hi-Nicalon STM fiber is 3.14 ± 0.10 GPa and this value is slightly higher that those for the initial desized fiber. The Weibull modulus was found to be 4.20. The increase in the fiber strength appears to be related to the elimination of the surface flaws by the ReZrO2 coating. The most part of the ReZrO2-coated Tyranno-SATM filaments were broken at the edge of frame during tensile strength measurements and data Fig. 6. Dependences of the relative mass m/m0 on time for the initial and coated Tyranno-SATM fiber at 1000 and 1200 ◦C. population was small in number. Therefore we could not extract the Weibull parameters from the obtained data. 3.4. The oxidized ReZrO2-coated SiC fibers Dependences of the relative mass m/m0 on time for the as-received and ReZrO2-coated Tyranno-SA fibers (one dipping–annealing cycle) at 1000 and 1200 ◦C are represented in Fig. 6. Both the as-received and coated fibers exhibit a simi￾lar behavior during oxidation test at 1000 ◦C, namely, (i) first a mass loss over a short period of time (∼2 h); (ii) a slight mass gain; and (iii) gradual mass loss for long exposition. The mass loss of the initial and coated fibers at the beginning of oxida￾tion is not more than several percents and could be attributed to burnoff of carbon. The following small mass gain could be due to oxidation of SiC that results in the formation of thin silica layer. The exposition of the coated fibers to air at 1200 ◦C leads to significant mass loss due to the volatilization of silicon- and carbon-containing compounds through the cracks and pores in the upper layer.17 SEM micrographs of the coated fibers after exposition to air at 1000 ◦C (40 h) are represented in Fig. 7a–c. As a whole, the coatings conserve their integrity, uniformity and smoothness. The round shape formations were observed on the surface of oxidized coated Hi-Nicalon STM fiber. They were present on the surface of coated fibers (Fig. 3a) and originated from the initial fiber (Fig. 1b). Contrary to Hi-Nicalon STM, the new formations Fig. 7. SEM images of the ReZrO2-coated Hi-NicalonTM (a), Hi-Nicalon STM (b) and Tyranno-SATM (c) fibers after exposition to air at 1000 ◦C for 40 h.