S Guo, Y. Kagawa/Journal of the European Ceramic Society 22(2002)2349-2356 stress and matrix cracking stress, can be determined by The polycarbosilane had a melting point of 514 K,an a tensile test and fractographic analysis and measure- average molecular weight of 2410, and its chemical ments. 0,I Thus, it is possible to evaluate correlation of composition was: 60 mass% Si, 40 mass% C,<l e mechanical behavior to in situ constituent proper- mass%O. The five infiltrated pre-preg sheets were ties. Although the correlation of tensile fracture beha- stacked and pressed, and the stacked sheets were then vior to in situ constituent properties has been rep for precursor. The composite precursor was pyrolyzed at in CVI-processed composites, 3. 2 this correlation PIP-processed composites is not well known. In the 1273K in a high purity N2 atmosphere. Approximately present study, tensile testing of the two PIP-processed 40 vol. of pores existed in the pyrolyzed composite SiC fiber-reinforced SiC matrix composites was carried due to the low yield weight of the polycarbosilane. To out at room and elevated temperatures. The matrix further reduce the porosity of the composite, a multiple racking stress, in situ fiber strength and interface shear PIP process was applied. After 10 PIP cycles, the total stress were obtained. The correlation of the tensile frac- fiber volume fraction, f, and the total porosity of the ture behavior of the composites to in situ constituent composite were 0.28 and s0.09, respectively. Here- properties was discusse after. the NicalonTM Sic fiber and Hi-Nicalon M Sic fiber-reinforced SiC matrix composites fabricated are denoted as Nicalon/ C/SiC and Hi-Nicalon/BN/ SiC 2. Experimental procedure respectively 2. 1. Composite materials 2. 2. Tensile test The composite materials used in the present study The composite panels were cut into a dog-bone type were 2D plain-woven fabric SiC fiber-SiC matrix com- tensile test specimen with the long axis parallel to one of posites fabricated by the Pip process. To compare the the fiber axis directions. The shape and dimensions of effect of fiber strength and interface properties on the the specimen for monotonic tension testing are shown in tensile fracture behavior of the composites, NicalonM Fig. 1. Quasi-static monotonic tensile testing was car- and Hi-NicalonM SiC fibers(Nippon Carbon Co Ltd ried out using a servo-hydraulic MTs 808 testing system Tokyo, Japan)in which the surfaces were respectively (MTS System Co., MI, USA)with a constant crosshead coated with 0.04 um amorphous carbon and 0.4 um displacement rate of 0.5 mm/ min in ambient air at room bn by chemical vapor deposition(CVD) were used as temperature (298 K), 800, 1200 and 1400 K. Three reinforcements. The typical properties and chemical composite specimens were used for each measurement composition of the two fibers are listed in Table 1. The An electric furnace attached to the mts testing system coated SiC fibers were formed a plain-woven fabric provided the heating Axial strain was measured directly sheet, with 16x 16 numbers of fiber per inch. The fabric from the gauge length of the specimen by using a con- sheets averaging 150x 150 mm in size were cut from the tact extensometer (MTS Model 632.59, MTS System formed plane-woven sheet. The cut fabric sheets were Co., MI). Before the loading, the specimen was heated infiltrated with a polycarbosilane solution containing a fine B-SiC powder. The fine B-Sic powder had an aver- age diameter of N4 um and its addition effectively (A)Top View 90° Bundle reduced pore content in the SiC matrix after pyrolysis 4.5 0° Bundle Copper T able i Typical properties and chemical composition of the two fibers Fibres Nicalon Hi. Nicalon TM 25 25 Fibre properties Tensile strength (GPa) Youngs modulus (GPa) Elongation (B) Side View Average fibre radius Number of fibres Copper Tab Chemical compositions Si (wt%)56.6 (wt.%)31.7 (wt%) Fig. 1. Shape and dimensions of the specimen for monotonic tension testing.stress and matrix cracking stress, can be determined by a tensile test and fractographic analysis and measure￾ments.10,11 Thus, it is possible to evaluate correlation of the mechanical behavior to in situ constituent proper￾ties. Although the correlation of tensile fracture beha￾vior to in situ constituent properties has been reported in CVI-processed composites,3,12 this correlation for PIP-processed composites is not well known. In the present study, tensile testing of the two PIP-processed SiC fiber-reinforced SiC matrix composites was carried out at room and elevated temperatures. The matrix cracking stress, in situ fiber strength and interface shear stress were obtained. The correlation of the tensile frac￾ture behavior of the composites to in situ constituent properties was discussed. 2. Experimental procedure 2.1. Composite materials The composite materials used in the present study were 2D plain-woven fabric SiC fiber–SiC matrix com￾posites fabricated by the PIP process. To compare the effect of fiber strength and interface properties on the tensile fracture behavior of the composites, NicalonTM and Hi-NicalonTM SiC fibers (Nippon Carbon Co. Ltd., Tokyo, Japan) in which the surfaces were respectively coated with 0.04 mm amorphous carbon and 0.4 mm BN by chemical vapor deposition (CVD) were used as reinforcements. The typical properties and chemical composition of the two fibers are listed in Table 1.13 The coated SiC fibers were formed a plain-woven fabric sheet, with 1616 numbers of fiber per inch. The fabric sheets averaging 150150 mm in size were cut from the formed plane-woven sheet. The cut fabric sheets were infiltrated with a polycarbosilane solution containing a fine b-SiC powder. The fine b-SiC powder had an aver￾age diameter of 4 mm and its addition effectively reduced pore content in the SiC matrix after pyrolysis.4,5 The polycarbosilane had a melting point of 514 K, an average molecular weight of 2410, and its chemical composition was: 60 mass% Si, 40 mass% C, <1 mass% O. The five infiltrated pre-preg sheets were stacked and pressed, and the stacked sheets were then cured at 523 Kin ambient air to obtain the composite precursor. The composite precursor was pyrolyzed at 1273 Kin a high purity N2 atmosphere. Approximately 40 vol.% of pores existed in the pyrolyzed composite due to the low yield weight of the polycarbosilane. To further reduce the porosity of the composite, a multiple PIP process was applied. After 10 PIP cycles, the total fiber volume fraction, f, and the total porosity of the composite were 0.28 and 0.09, respectively. Here￾after, the NicalonTM SiC fiber and Hi-NicalonTM SiC fiber-reinforced SiC matrix composites fabricated are denoted as Nicalon/C/SiC and Hi-Nicalon/BN/SiC, respectively. 2.2. Tensile test The composite panels were cut into a dog-bone type tensile test specimen with the long axis parallel to one of the fiber axis directions. The shape and dimensions of the specimen for monotonic tension testing are shown in Fig. 1. Quasi-static monotonic tensile testing was car￾ried out using a servo-hydraulic MTS 808 testing system (MTS System Co., MI, USA) with a constant crosshead displacement rate of 0.5 mm/min in ambient air at room temperature (298 K), 800, 1200 and 1400 K. Three composite specimens were used for each measurement. An electric furnace attached to the MTS testing system provided the heating. Axial strain was measured directly from the gauge length of the specimen by using a con￾tact extensometer (MTS Model 632.59, MTS System Co., MI). Before the loading, the specimen was heated Table 1 Typical properties and chemical composition of the two fibers Fibres NicalonTM SiC Hi-NicalonTM SiC Fibre properties Tensile strength (GPa) 3.0 2.8 Young’s modulus (GPa) 220 270 Elongation (%) 1.4 1.0 Average fibre radius (mm) 7 7 Number of fibres per bundles 500 500 Chemical compositions Si (wt.%) 56.6 62.4 C (wt.%) 31.7 37.1 O (wt%) 11.7 0.5 Fig. 1. Shape and dimensions of the specimen for monotonic tension testing. 2350 S. Guo, Y. Kagawa / Journal of the European Ceramic Society 22 (2002) 2349–2356