1484 M. Drissi-Habti, K. Nakano was prepared under the same experimental conditions virgin and BN-coated fibers were provided The microstructure of the as-processed material was ivestigated by scanning electron microscopy (SEM) and transmission electron microscopy(TEM)(Hitachi H9000 NAR). The TEM specimens were prepared by mechanical and ion thinning of a slice cut perpen dicular to the fiber axis of the composite. The topographies of both virgin and coated fibers were investigated by means of atomic force microscopy 季 (AFM) Mechanical characterization of the composite was carried out in an Instron testing machine( model 4204) Fig. 2. TEM micrograph of a fiber/BN-interphase/matrix with a 5 kN load cell. Three-and four-point bend tests region in a Hi-Nicalon(BN)/Si N4 composite material( scale wert rformed both unnotched and notched bar is 0-1 um) specimens. The configuration of both flexural tests, together with the dimensions of the specimens, are close to 2-9%. With the aid of an optical microscope, llustrated in Fig. I Tests were displacement-controlled the fiber volume fraction was estimated as being 0.48 and conducted at a crosshead speed of 0 5 mm min Figure 2 shows a TEM micrograph of the interfacial Micro-indentation tests were performed on a force- fiber/matrix region in the composite. It is conjectured driven, static, measuring ultra micro-indentation that the BN interphase has a layer crystal structure by instrument(UMIS 2000). The force system was varied its electron diffraction patterns shown in the inserts. between 50 and 1000 mN, since the depth measure- The Sic fiber had a structure consisting of fine B Sic ment system had a maximum value of 40 um with 20 crystallites. 2 The lattice image around a boundary nm resolution. The system was equipped with a video region between the BN interphase and the matrix, microscope and a positioning stage with a field of Fig. 3, shows that the (0001) planes of the BN travel of 20 mm and a minimum step size under motor interphase are aligned nearly parallel to the boundary, ontrol of 2: 5 um. A spherical diamond indenter wa which suggests that these planes form concentric indenter was equipped with a personal computer with circles around the fiber two spare 8-and 16-bit expansion slots. Tests were 3.2 Mechanical characterization conducted on a fine polished surface of the specimens 3.2.1 Notched specimens (up to 1 um diamond paste)which was previously Figure 4 shows a four-point notch bend test for two embedded in a resin specimens: monolithic silicon nitride and the icalon/BN/silicon-nitride composite with the same 3 RESULTS AND DISCUSSION notch depth of 1 mm. As noticed, the conjunction of the fibers with the Si3N4 leads to a significant non 3.1 Microstructure linear behavior, thus suggesting that the load is The first results obtained were related to the sintering characteristics and microstructure of the as-fabricated 0.01 um composite. The composite was sintered at 1550.C.It showed a bulk density of 2 81 g cm(corresponding to 94. 3% of theoretical density) and an open porosity №⊥LN4】 一一一一 Fig. 1. Configuration of the tests with the corre sponding parameters. L is the of the specimen, h is Fig 3. Lattice image around a region located between the the notch depth, /, and /2 are th ances between the inner n interphase and matrix in the composite(scale bar is and oute 001m)1484 M. Drissi-Habti, K. Nakano was prepared under the same experimental conditions as those used for the composite. In addition, both virgin and BN-coated fibers were provided. The microstructure of the as-processed material was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (Hitachi, H 9000 NAR). The TEM specimens were prepared by mechanical and ion thinning of a slice cut perpen￾dicular to the fiber axis of the composite. The topographies of both virgin and coated fibers were investigated by means of atomic force microscopy (AFM). Mechanical characterization of the composite was carried out in an Instron testing machine (model 4204) with a 5 kN load cell. Three- and four-point bend tests were performed on both unnotched and notched specimens. The configuration of both flexural tests, together with the dimensions of the specimens, are illustrated in Fig. 1. Tests were displacement-controlled and conducted at a crosshead speed of 0.5 mm min-‘. Micro-indentation tests were performed on a force￾driven, static, measuring ultra micro-indentation instrument (UMIS 2000). The force system was varied between 50 and 1000 mN, since the depth measure￾ment system had a maximum value of 40 pm with 20 nm resolution. The system was equipped with a video microscope and a positioning stage with a field of travel of 20 mm and a minimum step size under motor control of 2.5 pm. A spherical diamond indenter was used for this study. For data analysis, the micro￾indenter was equipped with a personal computer with two spare 8- and 16-bit expansion slots. Tests were conducted on a fine polished surface of the specimens (up to 1 ,um diamond paste) which was previously embedded in a resin. 3 RESULTS AND DISCUSSION 3.1 Microstructure The first results obtained were related to the sintering characteristics and microstructure of the as-fabricated composite. The composite was sintered at 1550°C. It showed a bulk density of 2.81 g cmP3 (corresponding to 94.3% of theoretical density) and an open porosity B w c, /L_--_-_ ,1=30lWl f--b L=50mm,B=4mm,W=3mm L I2=10mm 4-w B h=llIlm w rt” J-- --- l1=30mm f---b .=50mm,B=3mm,W=4mm Fig. 1. Configuration of the flexure tests with the corre￾sponding parameters. L is the length of the specimen, h is the notch depth, 1, and I2 are the distances between the inner and outer spans. Fig. 2. TEM micrograph of a fiber/BN-interphase/matrix region in a Hi-Nicalon (BN)/S&N, composite material (scale bar is 0.1 pm). close to 2.9%. With the aid of an optical microscope, the fiber volume fraction was estimated as being 0.48. Figure 2 shows a TEM micrograph of the interfacial fiber/matrix region in the composite. It is conjectured that the BN interphase has a layer crystal structure by its electron diffraction patterns shown in the inserts. The SIC fiber had a structure consisting of fine p SIC crystallites.2 The lattice image around a boundary region between the BN interphase and the matrix, Fig. 3, shows that the (0001) planes of the BN interphase are aligned nearly parallel to the boundary, which suggests that these planes form concentric circles around the fiber.’ 3.2 Mechanical characterization 3.2.1 Notched specimens Figure 4 shows a four-point notch bend test for two specimens: monolithic silicon nitride and the Hi￾Nicalon/BN/silicon-nitride composite with the same notch depth of 1 mm. As noticed, the conjunction of the fibers with the Si3N4 leads to a significant non￾linear behavior, thus suggesting that the load is Fig. 3. Lattice image around a region located between the BN interphase and matrix in the composite (scale bar is 0.01 pm)