On the reaction between Fe-Ti and Fe-C liquids under microgravity
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I.
INTRODUCTION
TITANIUM carbide precipitation in iron-base alloys is important for both in situ formation of composites reinforced by titanium carbide and for inoculation of steel. In situ formation of titanium carbide by reaction between liquid Fe-Ti alloys and graphite or Fe-C alloys has been studied under normal gravity conditions,tl] It has been shown that convection may be induced by the density differences in the system during the reaction between graphite and FeTi alloys.tt] The reaction between two liquid alloys on the ground also showed significant effects due to melt convection. Within the alloys studied, Fe-C and Fe-Ti alloys have different densities. The density of the carbide particle precipitation layer is also different from those of the two alloys. The two liquid alloys can never remain in equilibrium in any relative position due to the reaction in a gravity field. Convection always occurs in the melt. This makes the shape of the reaction interface very complicated even in a very short reaction time. tl] It is impossible to evaluate the kinetics of the carbide precipitation when convection is involved. To minimize the convection, a microgravity environment can be used during the experiments. By the method of parabolic flights, a microgravity of 10 -2 g can be repeatedly achieved for a period of 20 seconds. It is most convenient to study nucleation and growth of dispersed crystals in a solution at their early stage by performing experiments using this method. The microgravity experiments on the dual-liquid reaction were performed together with the experiments on graphite/Fe-Ti alloy reaction. The results and the theoretical analyses of the reaction process between graphite and Fe-Ti alloys were presented in separate articles. I2,3j An analytic model has been derived to calculate the growth rate of the
Z. LIU, Researcher, Postdoctoral Student, Department of Materials Processing, Royal Institute of Technology, is with Volvo AB, S-361 80 Sk6vde, Sweden. H. FREDRIKSSON, Professor and Head, is with the Department of Materials Processing, Royal Institute of Technology, S-100 44 Stockholm, Sweden. Manuscript submitted February 21, 1994. METALLURGICAL AND MATERIALS TRANSACTIONS A
precipitation zone. Assuming that the diffusion of carbon controlled the reaction at high titanium concentrations and diffusion of titanium controlled the reaction at low concentrations, a good agreement was obtained between measured and calculated thicknesses of the carbide precipitation zone for the high titanium alloys53] In the present dual-alloy reaction, a diffusion controlled method was used to calculate the growth rate of the precipitation layer at short reaction times. The calculated results were compared with the experimental results obtained under microgravity. II.
EXPERIMENTS
The experimental configuration, as shown in Figure 1, has been used to study the reaction between Fe-C and FeTi alloys. The sample consists of two pieces. One piece is an Fe-C alloy with a length of 2.5 mm, and the other piece is an Fe-Ti all
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