ニューコンポジット材料　　ＳｉＣウィスカー／Ｓｉ３Ｎ４複合セラミックスの室温機械的性質

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  • Room Temperature Mechanical Properties of SiC Whisker/Si3N4 Ceramic Composites.
  • SiC ウィスカー Si3N4 フクゴウ セラミックス ノ シツオン キカイテ

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This manuscript is the summary of the results of our studies on the effects of the kind and amount of sintering aids, orientation of silicon carbide whisker {SiC(w)} and evaluation method on the room temperature mechanical properties of SiC(w)/Si3N4 hot-pressed composite ceramics, which was talked in the memorial presentation assigned for the winner of “JSPM Award for Research Advancement”. The main results are as follows: I. Effect of Sintering Aids;(1)The effective sintering aids and the amount for the enhancement of fracture toughness (KIC) of the composite are the ones such that needle-like Si3N4 grains with large size or large axial ratio develop during sintering, in the same way as the Si3N4 monolithic ceramics.(2)The transverse-rupture strength (TRS) was considerably affected by the size of fracture source such as SiC(w) aggregate as well as KIC, although the value of TRS of our specimens was higher than those in the other researchers' reports. (3) Er2O3 is an effective sintering aid in a similar way to Y2O3 for obtaining higher KIC and TRS. II. Effect of Arrangement of SiC(w); (1) The unidirectional arrangement of SiC(w) to the axis of the specimen sharply increases KIC from 6.0MPa⋅m1/2 to 9.4MPa⋅m1/2. (2) The enhancements of KIC by the arrangement of SiC(w) as well as the addition are not explained by the conventional theory, i.e., “crack deflection effect”, but mainly by “load transfer effect”. III. Effect of Evaluation Method; (1) The KIC measured by CSF method (the shape of pre-crack is semi-ellipse) are nearly the same for VV and PV specimens (the characteristics are shown in Fig.6 in the text). The KIC measured by SEPB method where the shape of pre-crack is rectangle, however, was higher for VV specimen; the anisotropy of KIC was detected only by SEPB method. These results are explained by the difference of three-dimensional average angle (θ3) of the intersection of the pre-crack or propagating crack to the longer axes of SiC(w) and needle-like Si3N4 grains among the kinds of specimen and method, although these can not be explained by the difference of two-dimensional angle on the tensile surface. (2) This indicates that the method for evaluating KIC should be selected, taking into consideration the value of θ3 as well as two-dimensional angle or the microstructure of the composites.

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