日本金属学会誌

J. Japan Inst. Metals, Vol. 59, No. 1 (1995),
pp. 57-64

Sintering Mechanism of Y2O3 Dispersed W Compositeand Its High Temperature Strength

Yutaka Ishiwata1, Yoshiyasu Itoh1,Takahiro Okuhata2 and Ryuzo Watanabe3

1Heavy Apparatus Engineering Laboratory, Toshiba Corporation, Yokohama
2Material and Component Division, Toshiba Corporation, Yokohama

3Department of Materials Processing, Faculty of Engineering, Tohoku University, Sendai

Abstract:

Sintering behavior and bending strength of the Y2O3 dispersed W composite were investigated, and the sintering mechanism has been discussed. W powders with 10 vol% and 20 vol%Y2O3 were compacted by cold isostatic pressing (CIP), and sintered at 1673-2273 K for 28.8 ks in vacuum (<6.7{×}10-4 Pa). The relative density of the Y2O3/W compacts were remarkably increased after sintering at 1773 K, and in the relative density over 99% was obtained at 2073 K, which is to be compared with the relative density of 84% for elemental W powder attained under the same sintering condition. This observation shows that Y2O3 addition has remarkable effect to enhance the sintering densification of W powder.
The reaction phase, identified as Y2(WO4)3 by X-ray diffraction, was observed between W grains in the Y2O3/W compacts. The melting point of Y2(WO4)3, 1713 K, is almost equal to the sintering temperature at which densification enhancement was observed. Thus, the sintering mechanism of the Y2O3/W composite is considered to be a liquid phase sintering with Y2(WO4)3 liquid.

From AES (Auger electron spectroscopy) analyses, an appreciable amount of phoshorus (P) was detected at the interface between W matrix and Y2O3 particle in the Y2O3/W compact. It is reported that the melting point of YP5O14, which is formed by the reaction between Y2O3 and P2O5, is 1130 K. It may be considered that Y2(WO4)3 is formed through the reaction with the YP5O14 glassy phase during sintering.

The bending strength of the Y2O3/W composite is 680 MPa at 973 K and 510 MPa at 1573 K, which are about three and five times higher than those of pure W, respectively.


(Received June 29, 1994)

Keywords:

composite material, tungsten, yttrium oxide, complex oxide, densification enhancement, liquid phase sintering, high temperature strength


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