材料期刊网

本文介绍了用“锭块熔化法”测定液态Nb,Nb-W与Nb-w-Zr合金在3000-3600℃时合金元素的挥发速率和用电子探针测定合金液表面扩散边界层内合金元素分布的结果,给出了各合金元素的活度系数值。实验结果表明,Nb自Nb-W-Zr合金中挥发过程的激活能为175.9kcal/mol,Nb自Nb-W与Nb-W-Zr中挥发的速率控制阶段为Nb原子自合金液表面脱离的蒸发过程;Zr自Nb-W-Zr中的挥发为混合速率控制阶段;W自Nb-W与Nb-W-Zr中挥发主要为扩散所控制。

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℃.