Abstract: A composite, 98.56%SiO2-1.44%B2O3(in molar pct) (for short B-F3), glass – lined coating was prepared by mold preparing method of investment casting and sol – gel process. Crystallization of the coating was studied as a function of the temperature by means of X – ray diffraction. It was evident that the coating had no crystallization, therefore is stable, when treated at 1173 ± 5K ×30min + 1773 ± 5K × 60min. Purified melt of Cu50 Ni50 was poured and solidified in the s – coated mould, its undercooling heredity amounted to 236 K. The observation results, with optical microscopy and EPMA, show that the solidification microstructure evolution at different undercoolings can be compartmentalized into three kinds by two, 71K and 192k, critical undercoolings. When Cu50Ni50 melt solidified under 71K undercoolings, a gradual change occurred from common dendrite to first class granular grain by increasing the underccooling. When the melt solidified between 71K and 192K, high undercooling dendritic grains appeared. Second class granular grain was obtained by undercooling the melt over 192K. The calculated results by BCT model validated these results.

Key words: Composite glass-lined coating, Cu50Ni50 alloy, High undercooling, Solidification microstructure