The Diffusion Behavior In LaCe-based Glass Forming Melts

The diffusion coefficient is not only a key parameter of liquid metal but also important to material design and forming. In this paper, we use the sliding cell method to measurer the inter-diffusion coefficients in binary Ce80Cu20 liquid metal and pseudo-ternary (La1-xCex)65Al10Cu25(x=0,0.3,0.5,0.7,1) glass forming metal. The results indicate that the inter-diffusion coefficients in these metals are smaller than ordinary alloy metal. In the binary Ce8oCu2o liquid alloys, combined with the self-diffusion coefficients measured by our group, we found that the activation energy of self-diffusion is equal with the inter-diffusion in the error range and the absolute value of inter-diffusion coefficients are about 1.5 times larger than the self-diffusion coefficients of copper atom. According to the data of Gibbs free energy, we calculate the thermal dynamic driving force (i.e. the thermal dynamic factor) for inter-diffusion of this alloy. The relation between self-diffusion and inter-diffusion in the present liquid alloy is not well described by darken equation, when we introduce a dynamic factor S, the inter-diffusion can expressed by self-diffusion and thermal dynamic factor and S is between 1.1±0.2～1.3±0.2. This result is different with the Al-based and Zr-based alloys. In the experiment of pseudo-ternary (LaxCe1-x)65Al10Cu25(x=0,0.3, 0.5,0.7,1) glass forming metal, we keep the total content of La、Ce with on change and measured the Al-Cu inter-diffusion coefficients, all the experiment are carried out under 773k. We found that all the inter-diffusion coefficients of Al-Cu, with Lanthanum and Cerium ratio change, are similar in the error range, and this result is contrary to glass forming ability of this alloys. This tendency may be related to the mixing enthalpy of La-Ce-Al-Cu system.