Journal of the American Ceramic Sociery-Cinibulk et al Vol 87. No 5 Table L. Composition of Composite Matrice Il. Results Composition(vols, solids basis) (1) Processing and Microstructure Alumina YAG Composite powder Binder phase YAG with mean grain sizes of.2 um and uniform porosity distribu- 10 alumina tion, as shown in Figs. I and 2. The alumina-based-matrix Y0.1 3000 ppm yttrium 0. composites contained residual matrix porosity levels of 35-50 nitrate vol%. The microstructure and porosity of the matrix in composite AY50 50 10 alumina Y100 was much coarser than that of the alumina-containing YY50 IO YAG matrices. due to the much larger -I-Hm particle size(Fig. I(c)) Y100 90 IO YAG 000 Incorporation of YAG powder into the alumina matrix was found Assuming complete reaction of 3Y.0,+ 5AL01-2YAl to produce a microstructure of poorly sintered, equiaxed alumina particles containing inclusions of the much larger YAG particles as shown in Figs. I(d)and 2(b)and(e). There was little difference under controlled humidity and then sintered at 1 100 or 1200 for in microstructure when solution-derived YAG or sol-derived either 5 or 100 h in air alumina was used as the binder phase. The purpose of the YAG Scanning and transmission electron microscopies(SEM, Model binder was to form a fine-grained refractory film on all alumina 360FE. Leica. Cambridge, U. K, and TEM. Model CM2OOFEC articles to resist sintering. Figure 3(a) shows the distribution of Philips, Eindhoven, Netherlands, respectively) were used to char- the yag binder in the matrix, where the actual distribution of acterize the microstructures of the composites, Energy-dispersive YAG was discontinuous, with some of the interparticle porosity X-ray spectroscopy(EDS)was used for elemental analysis. TEM filled with YAG. EDS of surfaces of alumina particles and grain specimens were prepared by impregnating the porous samples with boundaries in the matrix detected the presence of Y as either a epoxy and thinning to electron transparency with diamond lapping segregant or as a thin YAG film( Figs. 3(b) and (c), EDS of films, followed by low-angle ion-beam milling, as described in alumina grain boundaries in the fiber near the fiber surface detail elsewhere indicated the presence of trace Y also. in addition to the presence The composites were cut into straight-sided tensile specimens, of trace amounts of Fe and Si(Fig 3(d). The Y is believed to have of -07-cm width and with a 5. 1-cm gauge length, tabbed, and diffused into the fiber from the matrices of all YAG-containing then tested in a universal testing frame. Six specimens were composites during sintering, whereas both Si and Fe were found to obtained for testing from each composite for each heat treatment. be present in the as-received fiber. The microstructure of the Stresses and strains(via digital imaging. VicGauge, Correlated Solutions) were measured to specimen failure. The strengths were the sintering time at 1200'C from 5 to 100 h. ompared by normalizing all composites to a fiber volume fraction Nextel 610 fibers in composites exhibited noticeable grain of 0. 2. assuming the load is carried completely by the fibers. growth after heating at 1200.C for 100 h Grains in the as-received (b) 之 (d)a 10 um Fig. 1. SEM images of polished cross sections of composites(a) A.(b) YO. 1. (c) Y100. and (d) AY50 sintered for 5 h at 1200.C.(a-c)are ondary-electron images, while (d) is a backscattered electron image to highlight YAG in the matrix (bright contrast)