E ARELLANO. LOPEZ et al.: CREEP OF SIC-WHISKER-REINFORCED ALUMINA HP Axis Table 2. Average space available between the whiskers in sections with more than 10 vol% of whiskers, and equivalent three-dimen- sional diameter(defr) Sample ANLI5 ANL30 ORNLIO ORNL20 3.5 3. 2.4 measured using an image analyzer. The average values of d and di are listed in Table 2 The equivalent three-dimensional diameters of the ellipsoidal objects are calculated by means of the geometric average referential orientation of the whiskers, perpendicularly to the hot-pressing(HP)axis values are listed in the HP axis. Reflected polarized light was used to A comparison between the values in Table 2, and obtain a clear contrast of the whiskers (white) the reported NGS in Table 1, shows some corre- on the uniform gray background of the alumina lations, except for the ORNLIO sample, for which matrIX the EGs is as much as three times larger tha In order to estimate the egs for the different the NGS. Nevertheless the egs decreases as the samples, a metallographic study has been performed volume percentage of whiskers increases, consis on both types of sections for each sample. It was tent with intuition. An analytical expression for assumed that "regular-shaped"ellipsoidal objects defr=dend, ... )can be derived by a simple two- fit into the whisker network. The diameters of dimensional model that correlates d with the these"grains"will be called dhh. if it corresponds volume fraction of whiskers, o, and the whisker to the face parallel to the hP axis, and d, if it radius, r. orresponds to the face perpendicular to the hP Figure 4 shows the location of perfectly distri- axis. The objects were subsequently digitized and buted whiskers in square cells of side e. The perp ara Fig 3. Optic graphs of polished sections parallel (para)and perpedicular (perp) to the HP axis of samples (a) ORNLIO, and (b)ANL30. Reflected polarized light was used to contrast the whiskers (white) on the uniform background of the alumina matrixFigure 3 presents a set of optical micrographs taken on polished sections parallel and perpendicular to the HP axis. Re¯ected polarized light was used to obtain a clear contrast of the whiskers (white) on the uniform gray background of the alumina matrix. In order to estimate the EGS for the di€erent samples, a metallographic study has been performed on both types of sections for each sample. It was assumed that ``regular-shaped'' ellipsoidal objects ®t into the whisker network. The diameters of these ``grains'' will be called d6, if it corresponds to the face parallel to the HP axis, and d_, if it corresponds to the face perpendicular to the HP axis. The objects were subsequently digitized and measured using an image analyzer. The average values of d6and d_ are listed in Table 2. The equivalent three-dimensional diameters of the ellipsoidal objects are calculated by means of the geometric average: 4 3 p  d? 2 2 dk 2  ˆ 4 3 p  deff 2 3 ˆ)deff ˆ  d2 ?dk 3 q …2† The values are listed in Table 2. A comparison between the values in Table 2, and the reported NGS in Table 1, shows some corre￾lations, except for the ORNL10 sample, for which the EGS is as much as three times larger than the NGS. Nevertheless, the EGS decreases as the volume percentage of whiskers increases, consis￾tent with intuition. An analytical expression for de€=de€(f,...) can be derived by a simple two￾dimensional model that correlates d6 with the volume fraction of whiskers, f, and the whisker radius, r. Figure 4 shows the location of perfectly distri￾buted whiskers in square cells of side `. The Fig. 2. Schematic of the preferential orientation of the whiskers, perpendicularly to the hot-pressing (HP) axis. Fig. 3. Optical micrographs of polished sections parallel (para) and perpedicular (perp) to the HP axis of samples (a) ORNL10, and (b) ANL30. Re¯ected polarized light was used to contrast the whiskers (white) on the uniform background of the alumina matrix. Table 2. Average space available between the whiskers in sections perpendicular (d_) and parallel (d6) to the HP direction of samples with more than 10 vol.% of whiskers, and equivalent three-dimen￾sional diameter (de€) Sample ANL15 ANL30 ORNL10 ORNL20 d_ (mm) 3.5 2.5 4.0 2.8 d6(mm) 2.4 1.6 2.9 1.8 de€ (mm) 3.1 2.2 3.6 2.4 6364 DE ARELLANO-LO PEZ et al.: CREEP OF SiC-WHISKER-REINFORCED ALUMINA