Journal of the American Ceramic Society-Lee and Riven Vol 84. No 4 0.3 Alumina/alumina platelet fibrous ceramic composite =119 MPa 0.25 WOF= 1.7 k/ 0.2 0.15 0.1 09885K上 0.3 Displacement (mi Fig. 8. Load-displacement curve of an alumina-alumina-platelet fibrous (a) 24 25Ky 500um Fig. 7.(a) SEM micrographs of the as-sintered fibrous ceramic compos- ite(a)cross section, viewed perpendicular to the fiber orientation, and(b) surface, viewed parallel to the fiber orientation) significant load-bearing capab the initial stepwise load 89625KV drops. The failed specimen is the SEM micrograph in Fig. 9. SEM micrograph of the fracture surface of the fibrous cerami Fig. 9. A slight curvature composite, as viewed from the fracture-surface side deformation, and a nonbrittle fracture surface with a woodlike fibrous cores"that were surrounded by the Al,Ox-platelet inter not exhibit a been at en decrease in strength after the ultimate tensile AL-O, core resulted from the fracture behavior, similar to the strength has tained. Instead, a notable WoF (the area under fiber-pullout effect in fiber-reinforced ceramic composites the curve)is obtained from such a composite. The correspondi SEM micrograph in Fig. 9 suggests a woodlike-fracture mecha- nism that also could operate at elevated temperatures IV. Discussion The measured mechanical properties indicated that, at room temperature, interphases of suitable weak debonding strength were The work presented here is essentially at a preliminary stage achieved using only platelets with only a minimal amount(1-3 and th p vol%)of matrix-powder additions. However, one could speculate comparative guide for further development of the microstructural that, at high temperatures, where transient creep may become an design. However, the concept of interphase debonding by a porous important issue, stronger and more-rigid interphases might be region that consists of nonsinterable platelets has been investi- required. Then, the addition of matrix powders to the interphase ed Optimization of the processing parameters can be improved may be beneficial to the overall long-term, high-temperature ignificantly. Improved presintering compaction of both the lam mechanical properties, to improve creep resistance. inates and the fibrous monoliths should increase the overall The purpose of using a bimodal microstructure was to mix trength of the composite. The matrix interphase ratio in both intimately, on a microstructural level, regions of high strength configurations also must be optimized (high matrix interphase ratio) with regions of lower strength but The fibrous-monolith configuration is versatile for uniform high toughness (low matrix interphase ratio). This concept is response to oncoming cracks perpendicular to the fibrous direc suggested in Fig. 4, where the strong matrix and interphase(which on. The optimum core interphase: matrix thickness ratio for each contained 20 vol% of 3Al203 2SiO2 powder) had high strength but of the Al,O, and 3Al2O3 2SiO2 systems could be determined low toughness (a lack of graceful-failure characteristics). The However, the preliminary load-displacement data(Fig. 8)does composite that contained only platelets in the interphase had lowsignificant load-bearing capability after the initial stepwise load drops. The failed specimen is shown in the SEM micrograph in Fig. 9. A slight curvature, which corresponded to permanent deformation, and a nonbrittle fracture surface with a woodlike texture were observed in the fibrous specimen. Some Al2O3 “fibrous cores” that were surrounded by the Al2O3-platelet inter￾phase were detected in the fractured specimen. The pullout of the Al2O3 core resulted from the fracture behavior, similar to the fiber-pullout effect in fiber-reinforced ceramic composites.44 IV. Discussion The work presented here is essentially at a preliminary stage, and the mechanical data are useful primarily as a qualitative, comparative guide for further development of the microstructural design. However, the concept of interphase debonding by a porous region that consists of nonsinterable platelets has been investi￾gated. Optimization of the processing parameters can be improved significantly. Improved presintering compaction of both the lam￾inates and the fibrous monoliths should increase the overall strength of the composite. The matrix:interphase ratio in both configurations also must be optimized. The fibrous-monolith configuration is versatile for uniform response to oncoming cracks perpendicular to the fibrous direc￾tion. The optimum core:interphase:matrix thickness ratio for each of the Al2O3 and 3Al2O3z2SiO2 systems could be determined. However, the preliminary load–displacement data (Fig. 8) does not exhibit a sudden decrease in strength after the ultimate tensile strength has been attained. Instead, a notable WOF (the area under the curve) is obtained from such a composite. The corresponding SEM micrograph in Fig. 9 suggests a woodlike-fracture mecha￾nism that also could operate at elevated temperatures. The measured mechanical properties indicated that, at room temperature, interphases of suitable weak debonding strength were achieved using only platelets with only a minimal amount (1–3 vol%) of matrix-powder additions. However, one could speculate that, at high temperatures, where transient creep may become an important issue, stronger and more-rigid interphases might be required. Then, the addition of matrix powders to the interphase may be beneficial to the overall long-term, high-temperature mechanical properties, to improve creep resistance. The purpose of using a bimodal microstructure was to mix intimately, on a microstructural level, regions of high strength (high matrix:interphase ratio) with regions of lower strength but high toughness (low matrix:interphase ratio). This concept is suggested in Fig. 4, where the strong matrix and interphase (which contained 20 vol% of 3Al2O3z2SiO2 powder) had high strength but low toughness (a lack of graceful-failure characteristics). The composite that contained only platelets in the interphase had low Fig. 7. (a) SEM micrographs of the as-sintered fibrous ceramic compos￾ite ((a) cross section, viewed perpendicular to the fiber orientation, and (b) surface, viewed parallel to the fiber orientation). Fig. 8. Load–displacement curve of an alumina–alumina-platelet fibrous monolithic composite. Fig. 9. SEM micrograph of the fracture surface of the fibrous ceramic composite, as viewed from the fracture-surface side. 772 Journal of the American Ceramic Society—Lee and Kriven Vol. 84, No. 4