Interaction of tungsten with iron–copper and iron–tin melts

Abstract

The solubility of tungsten in Fe-Cu and Fe-Sn melts and the growth kinetics of W 6 Fe 7 layer at the tungsten-melt interface at 1200°C are examined. The solubility of tungsten in these melts is well described by the following equations: lgX W = -4.3864 + 8.529X Fe (Fe-Cu melt) and lgX W = = -4.544 + 14.293 X Fe -23.583 2 Fe X (Fe-Sn melt). The melt composition in the three-phase equilibrium W-W 6 Co 7 melt is established: X Fe = 4.1 ⋅ 10 -3 , X W = 4.5 ⋅ 10 -5 , the rest is copper (Fe-Cu melt), X Fe = 0.111, X W =5.6 ⋅ 10 -4 , and the rest is tin (Fe-Sn melt). The substantial difference in k Fe-Sn > k Fe-Cu at the same iron activity a Fe is attributed to the impact of admixtures (Cu and Sn) on the growth of the W 6 Fe 7 layer.

Fe-Sn-W (Iron-Tin-Tungsten)

“…The Fe-Sn phase diagram [1993Oka] depicts a liquid miscibility gap that closes at 1495°C, followed by a monotectic reaction at 1130°C. …”

“…With starting metals of 99.99% Fe, 99.999% Sn and 99.95% W, [2009Sko] inserted W rods in the Fe-Sn melts of pre-determined composition at 1200°C, till W saturation in the melt occurred. The solubility of W was found to be a function of the Fe content in the melt.…”

“…This composition of the melt is in threephase equilibrium with (W) and Fe 7 W 6 . A tentative isothermal section at 1200°C constructed by [2009Sko] is shown in Fig. 1.…”