Undercooling Heredity of Cu_(70)Ni_(30) Alloy Melts in Non catalytic Crystal Coating Mould
A SiO 2 glassy film coating was prepared by dip coating process on the inner surface of investment casting molds that had SiO 2 glass lined coating using sol gel principle.When the gel film was analyzed by using FTIR and TGA methods,it was found that its crack property was sensitive to heating process parameters.The analytical results also show that cracking in glass converting heating occurs in the range of ambient temperature to 400℃.The expansion of the film coating,caused by rapid evaporation of water and alcohol that absorb between the networks and form during progress polymerization of the gel,plays a key role in cracking.During this evaporation,the losing weight is amount to 89.5% of the total one.For the purpose of solving the cracking,an effective step heating treatment is adopted to prepare the sound B F composite coating with SiO 2 glass structure proved by X ray diffraction.198K undercooling was achieved that means the undercooling heredity was 0.76 when the undercooled Cu 70 Ni 30 melts was poured into the mold.