742 Ph Colomban, N. lapous Table 1. Main parameters for the preparation of BAS, CAS, NAS and CNAS matrix composites and resulting physical properties Matrix nterface Open porosity Fibre volume Three-Dos x fraction flexual streng Temp.C°C)Dwel(h) (MPa) CAS TBB SiAl 1250 035 ZrSiPB 030 ZrSiPB 7CAS-3NAS ZrSiPB 1050 030 BAS TBB+ SiAl 0·30 l250 8 030 BASS %L TBB+SiAl 85 033 TBB+ SiA 3 033 BAS10%Li TBB SiAl 124 03 BAS10%LI ZrSiPB 1200 035 250 Symbols explained in the text. Hot-pressing at 20 MPa Not measured corresponding monolithic BAS ceramics. At this level chosen in preference. An electron microscope study of of densification, the observed mechanical properties the fibre matrix interface and of its ageing will be are higher than those of LAs glass-ceramic- required to determine the most suitable interface matrix/SiC-fibre composites (<180 MPa) prepared precursor. However, the evaporation of boron during with the same fabric but by the usual molten glass the hot-pressing cycle occurs more readily than that of process. The mechanical properties of CAS and NAs phosphorus and hence the use of the ZrSiPB interface matrix composites are lower, despite a rather similar precursor may lower the refractoriness of the open porosity(Table 1). composites and consequently reduce their use above he results are not very sensitive to the interface precursor used (TBB+ SiAl or ZrSiPB). However, Figure 2 shows the good impregnation of the fabric previous studies have shown that the use of ZrSiPb voids by the ceramic. Evidence for the dissipative precursor promotes the formation of a thick behaviour of the fracture is shown in Fig 3. The use the Sic Nicalon NLM202 fibre by alkali or alkaline of zirconia which recursors leads to precipitatio carbon rich interphase as a result of the attack of of ZrSiPB interface appears white on electron earth ions. The presence of a carbon-rich interphase photomicrographs(Fig. 2, composites 2 and 3). The may promote oxidation and the sial precursor may be precipitation results from the reaction between Ba matrix), 2(CAS matrix)and 3(NAS matrix)(mean fibre diameter=11 um). See Table 1 for preparation details, AS Fig. 2. Sliced sections of Sic composites of Nicalon Sic fibre in aluminosilicate Sic Nicalon matrices; composites 5(B742 Ph. Colomban, N. Lapous Table 1. Main parameters for the preparation of BAS, CAS, NAS and CNAS matrix composites and resulting physical properties Composite number Matrix” Interface precursor Sinteringb Open porosity Fibre volume Three-point (%) fraction Temp. (“C) Dwell (h) flexual strenght (MPa) 1 CAS TBB + SiAl 12.50 1 6 0.35 _c 2 CAS ZrSiPB 1200 0.5 7 o-30 -100 3 NAS ZrSiPB 1050 0.5 8 0.30 -70 4 7CAS-3NAS ZrSiPB 1050 1 6 0.30 _= 2 BAS TBB ZrSiPB + SiAl 1250175 1 5.5 8 0.30 200 0.30 120 7 BASS%Li TBB + SiAl 1150 1 8.5 0.33 180 8 BASS%Li TBB + SiAl 1250 1 3 0.33 250 9 BASlO%Li TBB + SiAl 1250 1 4 0.35 _= 10 BASlO%Li ZrSiPB 1200 1 6 0.35 250 a Symbols explained in the text, b Hot-pressing at 20 MPa. ’ Not measured. corresponding monolithic BAS ceramics. At this level of densification, the observed mechanical properties are higher than those of LAS glass-ceramic￾matrix/Sic-fibre composites ( < 180 MPa) prepared with the same fabric but by the usual molten glass process. The mechanical properties of CAS and NAS matrix composites are lower, despite a rather similar open porosity (Table 1). The results are not very sensitive to the interface precursor used (TBB + SiAl or ZrSiPB). However, previous studies have shown that the use of ZrSiPB precursor promotes the formation of a thick carbon-rich interphases,9 as a result of the attack of the Sic Nicalon NLM202 fibre by alkali or alkaline earth ions. The presence of a carbon-rich interphase may promote oxidation and the SiAl precursor may be chosen in preference. An electron microscope study of the fibre matrix interface and of its ageing will be required to determine the most suitable interface precursor. However, the evaporation of boron during the hot-pressing cycle occurs more readily than that of phosphorus and hence the use of the ZrSiPB interface precursor may lower the refractoriness of the composites and consequently reduce their use above 700°C. Figure 2 shows the good impregnation of the fabric voids by the ceramic. Evidence for the dissipative behaviour of the fracture is shown in Fig. 3. The use of ZrSiPB interface precursors leads to precipitation of zirconia which appears white on electron photomicrographs (Fig. 2, composites 2 and 3). The precipitation results from the reaction between Ba2+ Fig. 2. Sliced sections of Sic composites c )f Nicalon SIC fibre in aluminosihcate Sic Nicalon matrices; composites 1 aatrix), 2 (CAS matrix) and 3 (NAS matrix) (mean fibre diameter = 11 pm). See Table 1 for preparation detail (BAS