Abstract
Monotectic Al-17.5 mass%In alloys were solidified unidirectionally at various growth rates from 2.8×10−7 to 1.11×10−2 m/s and temperature gradients from 500 to 8500 K/m. When a temperature gradient is constant, the microstructure changes in the sequence with increasing growth rates; fibrous composite structure→periodical and regular array of L2(In) droplets→random dispersion of L2 droplets in the aluminum matrix. 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 is obtained at G⁄R more than 109 K·s/m2. The inter-fiber spacing λ of L2 is related to growth rates R; λ=KR−1⁄2, K being 2.8×10−8 m1.5 s−0.5.
