HIGH UNDERCOOLING AND HEREDITY OF Cu-Ni-Fe ALLOYS IN SPECIAL COATING MATERIALS
Cu—Ni—Fe合金在特殊涂层中的深过冷及其遗传性

By using glass flux and thermal cycling technologies, the undercooling ability and undercooling heredity of Cu-39%Ni-6%Fe and Ni-30%Cu-5%Fe alloys were investigated in the crucible coatings and shell mold coatings. .The experimental results indicated that the bed coating material of sintered crucible consists of (80%silica sand+20%fused silica powder) and 3%H3BO3. With the coating material and high purity graphite as heater, a fine glass layer (>3mm) without any crack has been obtained under 1923K sintering temperature in an induction furnace. In the glass layer crucible, Cu-39%Ni-6%Fe and Ni-30%Cu-5%Fe alloys have substantially undercooled tO 190K and 210K,respectively. The undercoolings have exceeded their critical undercooling limits at which the mictostructures of alloys will change abruptly from dendrite to fine spherical grains. Shell mold with the special coating can prevent premature nucleation. By pouring Ni-30%Cu-5%Fe alloy melt fray the sintered crucible under 1923K to the coated mold,substantial undercooling up to 100K has been achieved. This undercooling surpasses the critical undercooling limit at which the autonomous directional solidification can be realized under negative temperature gradient.