O.N. Grigoriev et aL./Composites: Part B 37(2006)530-541 Table 3 Compositions and mechanical properties of laminated composites Compositions of layers in composite(vol%) hess HV of composite Bending strength Fluctuation s(MPa) (SD, MPa) factor(%) 2)TiB2+42%B4C 24(7) 2)TB2+42%BC 1)阝-SiC 2)TiB2+42%B4C 324 1)B-SiC+10%B4C+4%TO2 41034) ②2)TiB2+42%B4C 324 Layers TiB2 are of double thickness, interlayer TiO2 on phase boundaries. Three samples are tested, in brackets is shown minim The tensile stresses in TiB, layers form cellular structur The structure and properties of composites obtained using with microcracks(Fig. 5b). In such layers the transverse cracks B-Sic powders(composites 3 and 4, Table 3)are essentially approaching a boundary propagate either into the near- different from others. SiC layers are coarse grained due to boundary volumes in the case of strong inter-layer boundaries the high recrystallization activity of these powders during or into boundaries in case of weak inter-layer bonds. It was hot pressing. The porosity of these layers is exceptionally found, that the boundary strength is reduced with a formation high-up to 40%. The prismatic columnar SiC crystals with of TiO, inter-layers. The delamination cracks were observed at a size about thickness of a layer (100 um)form composite butt-ends because of the redistribution of thermal 'engineered arch structure binding together the dense stresses at the edges and in the volume of the material. strong TiB 2 layers(Fig. 6) Considerable damage of structure results in low bending The microscopic studies of composites have not revealed strength of composites(20-100 MPa). any microcracking. The measured bending strength is high TiB2 TiB2 过 50μm TiB2 I TiB2 Fig. 5. Structure and crack formation in composites with low strength (<100 MPa)(a) microphoto of composite in the field of phase boundaries of layers a SiC/TiB2; (b)cracks in(TiB2) layer with tension stresses; (c)cracks on the weak phase boundaries: (d) longitudinal cracks along the pivotal zone of compressed SicThe tensile stresses in TiB2 layers form cellular structure with microcracks (Fig. 5b). In such layers the transverse cracks approaching a boundary propagate either into the near￾boundary volumes in the case of strong inter-layer boundaries or into boundaries in case of weak inter-layer bonds. It was found, that the boundary strength is reduced with a formation of TiO2 inter-layers. The delamination cracks were observed at composite butt-ends because of the redistribution of thermal stresses at the edges and in the volume of the material. Considerable damage of structure results in low bending strength of composites (20–100 MPa). The structure and properties of composites obtained using b-SiC powders (composites 3 and 4, Table 3) are essentially different from others. SiC layers are coarse grained due to the high recrystallization activity of these powders during hot pressing. The porosity of these layers is exceptionally high—up to 40%. The prismatic columnar SiC crystals with a size about thickness of a layer (w100 mm) form ‘engineered’ arch structure binding together the dense strong TiB2 layers (Fig. 6). The microscopic studies of composites have not revealed any microcracking. The measured bending strength is high Table 3 Compositions and mechanical properties of laminated composites No. Compositions of layers in composite (vol%) Hardness HV of composite layers (MPa) Bending strength (SD, MPa) Fluctuation factor (%) 1 (1) a-SiCM5C10% B4C 28 100(14) 14 (2) TiB2C42% B4C 33 2a (1) a-SiCM5C10% B4C 32 24(7) 29 (2) TiB2C42% B4C 33.5 3 (1) b-SiC 4 584(560–601)b 3 (2) TiB2C42% B4C 32.4 4 (1) b-SiCC10% B4CC4% TiO2 11 410(34) 8 (2) TiB2C42% B4C 32.4 a Layers TiB2 are of double thickness, interlayer TiO2 on phase boundaries. b Three samples are tested, in brackets is shown minimum maximum significances of strength. Fig. 5. Structure and crack formation in composites with low strength (%100 MPa) (a) microphoto of composite in the field of phase boundaries of layers a￾SiC/TiB2; (b) cracks in (TiB2) layer with tension stresses; (c) cracks on the weak phase boundaries; (d) longitudinal cracks along the pivotal zone of compressed SiC layers. O.N. Grigoriev et al. / Composites: Part B 37 (2006) 530–541 535