抄録
Al-17.5 mass%In alloys of monotectic composition were solidified unidirectionally at various growth rates and temperature gradients, and monotectic solidification structures were observed. Solidification conditions of alloys were measured by the use of 3-4 sets of C. A. thermocouples which were inserted into a mold cavity. In the present work, growth rates and temperature gradients changed over ranges from 2.8×10−7-1.11×10−2 m/s and from 500-8500 K/m, respectively.
When a temperature gradient was constant, the microstructure changed in the sequence, fibrous composite structure→periodical and regular array of L2(In) droplets→random dispersion of L2 droplets, in the aluminum matrix with increasing growth rate. The critical growth rate to form regular composite structures increases as the temperature gradient increases. The monotectic composite structure, i.e., the regular arrangement of L2 fibers or L2 droplets in the aluminum matrix was obtained at the G⁄R values more than 109 K·s/m2. The inter-fiber spacing (λ) of L2 was related to growth rates (R) by λ=KR−1⁄2 which was a common relationship among many lamella or rod eutectic composite structures, K being 2.8×10−8 m1.5 s−0.5.
