G.A. Gogotsi/ Ceramics international 29(2003)777-784 三 Y-PSZ v月9 Y-PSZa , P__SEPB-method V-notch root radius (um) V-notch root radius(um) Fig 3. Effect of V-notch root radii on the Kls values for Si,N4(a)and Y-PSz (b)ceramics 60 z40 4 mm x 5mm cr 3mm x 4mm cross-section pecten 024681012141618 6 Deflection(um) Deflection(um) Fig 4. Load-deflection diagrams for notched Si3 N4+ 30% SiC+ 3% Mgo (a) and SiC+ 50% ZrB2+10% BC(b)specimens tested at room tem- perature(1, 3)and at 1400C(2, 4) presented in Figs 4 and 5. The results of micro-Raman racy of our test procedures. The comparison of the data analysis are given in Fig. 6. The comparative data on presented in Table 3 also points to the fact that essential SEVNB and senB results are summarized in Tables 4-6. differences between three- and four-point flexure results High-temperature test results are cited in Table 7 are absent. a similar conclusion was also made else- It is useful to start the analysis with emphasis on the where [18] for ceramic matrix composites. Conse Kle values obtained in three- and four-point flexure quently, both test methods might be considered (Table 3). The data presented in this table demonstrate identical. Moreover, four-point flexure can be more good agreement between our results and the average easily applied in practice because it does not require a results of RRFT97 [6], which confirms sufficient accu- precise placement of specimens on the bearing rollers, which is difficult to achieve without a trained operator On the other hand, three-point flexure tests can utilize small-size specimens, which is advantageous for materi- p1=20m als science research t The analysis of results(Fig. 3)shows that a decrease decrease in the Kle values for Si3 N4 and Y-PSZ ceramics (similar relation was also observed for other materials [2D. It is interesting to note that the fracture toughness- Si3N4(Fig. 3a) Deflection 8, um the vicinity of a small notch root radius as compared to Fig. 5. Load-deflection diagrams for notched SiC+50%- that of the Y-PSZ(Fig. 3b). Such an effect is probably TiB+10%BC specimens with V-notch root radiuses PI and p2 are determined by different sensitivity of these materials to qual (1 and 2)and differed (3)in values on them opposite side stress concentrations because of differences in theirpresented in Figs. 4 and 5. The results of micro-Raman analysis are given in Fig. 6. The comparative data on SEVNB and SENB results are summarized in Tables 4–6. High-temperature test results are cited in Table 7. It is useful to start the analysis with emphasis on the KIc values obtained in three- and four-point flexure (Table 3). The data presented in this table demonstrate good agreement between our results and the average results of RRFT’97 [6], which confirms sufficient accu￾racy of our test procedures. The comparison of the data presented in Table 3 also points to the fact that essential differences between three- and four-point flexure results are absent. A similar conclusion was also made else￾where [18] for ceramic matrix composites. Conse￾quently, both test methods might be considered identical. Moreover, four-point flexure can be more easily applied in practice because it does not require a precise placement of specimens on the bearing rollers, which is difficult to achieve without a trained operator. On the other hand, three-point flexure tests can utilize small-size specimens, which is advantageous for materi￾als science research. The analysis of results (Fig. 3) shows that a decrease in the V-notch radius of a specimen leads to an essential decrease in the KIc values for Si3N4 and Y-PSZ ceramics (similar relation was also observed for other materials [2]). It is interesting to note that the fracture toughness￾notch root radius curve for Si3N4 (Fig. 3a) flattens in the vicinity of a small notch root radius as compared to that of the Y-PSZ (Fig. 3b). Such an effect is probably determined by different sensitivity of these materials to stress concentrations because of differences in their Fig. 3. Effect of V-notch root radii on the KIc values for Si3N4 (a) and Y-PSZ (b) ceramics. Fig. 4. Load–deflection diagrams for notched Si3N4+30% SiC+3% MgO (a) and SiC+50% ZrB2+10% B4C (b) specimens tested at room tem￾perature (1, 3) and at 1400
C (2, 4). Fig. 5. Load–deflection diagrams for notched SiC+50%- TiB2+10%B4C specimens with V-notch root radiuses
1 and
2 are equal (1and 2) and differed (3) in values on them opposite sides. 780 G.A. Gogotsi / Ceramics International 29 (2003) 777–784