BC monolith BC monolith B.C/BN microcomposites 1000 Crack size, c(um) 4时BC/ BN nanocomposite Fig. 7. The fracture toughness curves) behavior of the B4 C monolith, th -29.4N(20wt% h-BN B4C/BN nanocomposites(20 wt% h-BN)and the b4c/Bn microcomposites20wt% h-BN) as the function of crack length obtained from the R-curves of Fig. 6(a-c)to see clearly the differences among the curve behavior of the B4C monolith. Fig. 6(b) shows the families of KA(c) curves and R-curve behavior of the B4C/BN nanocomposites ig. 6(c)shows the families of Ka(c)curves and R-curve behavior of the B4C/BN microcomposites. As seen in Fig. 6(a), the envelope of tangency points formed the rising r-curve behavior, this result indicated that the fracture toughness of the B4 monolith increased gradually with the increase of cracks length. As seen in Fig. 6(b), the envelope of tangency points formed the relative higher rising R- Crack size, cum) curve behavior; this result indicated that the fracture toughness of the bac/Bn nanocomposites increased gradually with the Increase of cracks length. As seen in Fig. 6(c, the envelope of tangency points formed the rising R-curve behavior; this result indicated that the 73--3eN B C/BN microcomposites. fracture toughness of the B4 C/BN microcomposites increased grad 20wt% h-BN) ually with the increase of cracks length. Fig. 6 showed that the B4C monolith, the B4c/ BN nanocomposites and the bac/Bn micro- omposites all exhibited the rising R-curves behavior The B.C/BN nanocomposites exhibited the relative higher R-curve behav ior than that of the B4C monolith and the B4 C/BN microcomposites, the bac monolith and the b4c/Bn microcomposites also exhibited the rising R-curves behavior. Fig. 6 showed that the fracture toughness(R-curves)behav- 642 ior of the B4 C monolith, the B4C/BN nanocomposites and the C/BN microcomposites all increased gradually with the increase of the crack length. For the rising R-curves behavior of these hree materials, when the cracks length increased from 40 um to 1000 um, the fracture toughness of the BC monolith increased Crack size,c(μm) from 3.99 MPam/2 to 6.75 MPa m1/2: the fracture toughness of the B4C/BN nanocomposites increased from 4.11 MPam/2 to Fig. 6. The toughness-curve diagrams for (a)the Bac monolith, (b) the BaC/ BN 7.47MPam'; the fracture toughness of the B4C/BN microcom- owt.% h-B posites increased from 3 22 MPa m/2 to 6. 29MP data from Fig 5. Shaded lines were the Tc)functions, plotted as locus of tangency nanocomposites exhibited the relative higher rising R-curve behav- pints to the K'a(c)curves. The envelope of tangency points formed the R-curves ior than that of the B4 C monolith and the B4 C/BN microcomposites. ehavior. The indentation loads in the figures were shown as the follows: 1-4.9N, ig. 7 shows the fracture resist es(R-curves) of the 2-98N,3-294N,4-49N,5-98N,6-196N,7-294N. B4Cmonolith, the B4C/BN nanocomposites (20 wt% h-BN)and the B4C/BN microcomposites(20 wt. h-BN)as the function of crack curves were constructed from the indentation-strength data in length obtained from the r-curves of Fig 6(a-c) to see clearly the Fig 5, inserting oA=of at each values of indentation load P in Eq. difference among them. Fig. 7 showed that the B4C/Bn nanocom- (1). Furthermore, according to Eq(3), the envelope of tangency posites exhibited the higher rising R-curve behavior than that of the points for three materials were constructed. Fig. 6 shows the fam- B4 monolith and the b4 c/Bn microcomposites. The B4C monolith es of KA(c)curves and the envelopes of tangency points for the and the BaC/BN microcomposites also exhibited the rising R-curves three materials. Fig. 6(a)shows the families of KA(c) curves an behaviorT. Jiang et al. / Materials Science and Engineering A 494 (2008) 203–216 207 Fig. 6. The toughness-curve diagrams for (a) the B4C monolith, (b) the B4C/BN nanocomposites (20 wt.% h-BN) and (c) the B4C/BN microcomposites (20 wt.% h￾BN). Families of solid curves were plots of K A(c) in Eq.(1) using the fracture strength data from Fig. 5. Shaded lines were the T(c) functions, plotted as locus of tangency points to the K A(c) curves. The envelope of tangency points formed the R-curves behavior. The indentation loads in the figures were shown as the follows: 1–4.9 N, 2–9.8 N, 3–29.4 N, 4–49 N, 5–98 N, 6-196 N, 7–294 N. curves were constructed from the indentation-strength data in Fig. 5, inserting A = f at each values of indentation load P in Eq. (1). Furthermore, according to Eq. (3), the envelope of tangency points for three materials were constructed. Fig. 6 shows the fam￾ilies of K A(c) curves and the envelopes of tangency points for the three materials. Fig. 6(a) shows the families of K A(c) curves and R￾Fig. 7. The fracture toughness curves (R-curves) behavior of the B4C monolith, the B4C/BN nanocomposites (20 wt.% h-BN) and the B4C/BN microcomposites (20 wt.% h-BN) as the function of crack length obtained from the R-curves of Fig. 6(a)–(c) to see clearly the differences among them. curve behavior of the B4C monolith. Fig. 6(b) shows the families of K A(c) curves and R-curve behavior of the B4C/BN nanocomposites. Fig. 6(c) shows the families of K A(c) curves and R-curve behavior of the B4C/BN microcomposites. As seen in Fig. 6(a), the envelope of tangency points formed the rising R-curve behavior, this result indicated that the fracture toughness of the B4C monolith increased gradually with the increase of cracks length. As seen in Fig. 6(b), the envelope of tangency points formed the relative higher rising R￾curve behavior; this result indicated that the fracture toughness of the B4C/BN nanocomposites increased gradually with the increase of cracks length. As seen in Fig. 6(c), the envelope of tangency points formed the rising R-curve behavior; this result indicated that the fracture toughness of the B4C/BN microcomposites increased grad￾ually with the increase of cracks length. Fig. 6 showed that the B4C monolith, the B4C/BN nanocomposites and the B4C/BN micro￾composites all exhibited the rising R-curves behavior. The B4C/BN nanocomposites exhibited the relative higher rising R-curve behav￾ior than that of the B4C monolith and the B4C/BN microcomposites, the B4C monolith and the B4C/BN microcomposites also exhibited the rising R-curves behavior. Fig. 6 showed that the fracture toughness (R-curves) behav￾ior of the B4C monolith, the B4C/BN nanocomposites and the B4C/BN microcomposites all increased gradually with the increase of the crack length. For the rising R-curves behavior of these three materials, when the cracks length increased from 40 m to 1000 m, the fracture toughness of the B4C monolith increased from 3.99 MPa m1/2 to 6.75 MPa m1/2; the fracture toughness of the B4C/BN nanocomposites increased from 4.11 MPa m1/2 to 7.47 MPa m1/2; the fracture toughness of the B4C/BN microcom￾posites increased from 3.22 MPa m1/2 to 6.29 MPa m1/2. The B4C/BN nanocomposites exhibited the relative higher rising R-curve behav￾ior than that of the B4C monolith and the B4C/BN microcomposites. Fig. 7 shows the fracture resistance curves (R-curves) of the B4C monolith, the B4C/BN nanocomposites (20 wt.% h-BN) and the B4C/BN microcomposites (20 wt.% h-BN) as the function of crack length obtained from the R-curves of Fig. 6(a)–(c) to see clearly the difference among them. Fig. 7 showed that the B4C/BN nanocom￾posites exhibited the higher rising R-curve behavior than that of the B4C monolith and the B4C/BN microcomposites. The B4C monolith and the B4C/BN microcomposites also exhibited the rising R-curves behavior.