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| KINETICS OF THE EVAPORATION PROCESS OF ALLOY ELEMENTS IN LIQUID Nb ALLOYS |
| Yang Kenu Sun Congxi Hogjihu (Institute of Metal Research; Academia Sinica; Shenyang) (Manuscript received 13 February; 1981) |
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Cite this article:
Yang Kenu Sun Congxi Hogjihu (Institute of Metal Research; Academia Sinica; Shenyang) (Manuscript received 13 February; 1981). KINETICS OF THE EVAPORATION PROCESS OF ALLOY ELEMENTS IN LIQUID Nb ALLOYS. Acta Metall Sin, 1982, 18(4): 411-417.
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Abstract The evaporating rates of alloy elements from melts of Nb, Nb-W or Nb-W-Zr alloy at 3000-3600℃ have been examined by“melting ingot block”method. The activation energy of evaporation of Nb from Nb-W-Zr melt was obtained to be 175.9 kcal/mol. The rate-controlling step of the evaporation of Nb from Nb-W or Nb-W-Zr alloy is the detachment of Nb atoms from the liquid alloy surface, whereas the evaporation of Zr from Nb-W-Zr alloy seems to be a complex process. The evaporating rate of W from both Nb-W and Nb-W-Zr alloys, however, is controlled mainly by diffusion. The distribution of the alloy elements in the surface diffusion layer of quenched alloy melts has been determined by EPMA. It is measured that the thickness of diffusion boundary layer of Zr in liquid Nb-W-Zr alloy is 5.5—13.5×10~(-4)cm at 3080℃, and the concentration of Zr at surface is about 20% of that in bulk; the thickness of W diffusiin boundary layer is about 7—10×10~(-4) and 4—10×10~(-4)cm at 3120 and 3080℃ respectively, and the Wconcentration at surface is only 10% of that in bulk. A tentative estimation has also been made on the activity of coefficient of Nb or Zr. At 3000—3280℃ the activity of Nb in the Nb-W alloy is roughly equal to l. However, in the case of Nb-W-Zr alloy the Nb activity is much smaller, being 0.24 at 3600℃ and 0.17 at 3350℃. The apparent activity coefficient of Zr in Nb-W-Zr alloy is 0.16—0.31 at 3350℃ and 0.16—0.22 at 3600℃.
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Received: 18 April 1982
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