| 摘要 |
The invention is related to the foundry practice. According to this invention, the method for making castings by directed solidification from a selected point of the melt toward the periphery of the casting comprises forming a casting in a mold having thermodynamic characteristics that allow uniform volume cooling of the melt to be effected to a temperature at which natural solidification processes are completed. To improve the structural isotropy of the casting formed, the cooling is effected at a rate not exceeding 0.5� C./sec. The casting is formed in a nonuniform field of force. The nonuniform field of force is set up by ultrasonic waves focused on a selected point of the melt to form therein a localized elevated pressure zone and to direct the solidification front from the zone toward the periphery of the casting. The nonuniform field of force is sustained in the mold until the cooling casting reaches a temperature at which the natural melt solidification processes are completed as the melt cools. Before the melt is poured into the mold, it is overheated to a level that, together with the thermodynamic characteristics of the mold allowing the melt therein to be cooled at a rate not exceeding 0.5 K/sec, sustains the liquid phase of the melt for a time sufficient for directed melt solidification to be effected from the selected point of the melt toward the periphery of the casting before the commencement of natural melt solidification processes as the melt cools. Subsequently, as the temperature at which natural solidification processes are completed is reached, the nonuniform field of force is removed, and casting cooling may continue at any reasonable rate. |
