流态床冷却定向凝固技术研究进展

Due to the excellent high-temperature mechanical performance, nickel-based single-crystal superalloys have developed indispensable mate-rials in the preparation of advanced aero-engines. The high rate solidification (HRS) method is a Bridgman directional solidification technology, which moves the mold filled with molten metal out of the heating zone for cooling. Because of its simple equipment and stable solidification structure, it has been the most common technology for the preparation of aero-engine blades. However, in the process of preparing large-sized single-crystal superalloy turbine blades, the low thermal gradient of HRS method restricts the increasing of withdrawal rate, which leads to increase the tendency of defects formation, resulting in low yield of the blades. The lower withdrawal rate would also increase the production cycle and energy consumption. The gas cooling casting (GCC) method and liquid metal cooling (LMC) method developed later also have many problems, such as high cost, pollution of Sn, and the difficulties in equipment maintenance. Therefore, it is necessary to develop advanced directional solidification technology with high thermal gradient, clean cooling medium, simple equipment structure, and low cost. The fluidized bed quenching (FBQ) method is a Bridgman directional solidification technology that uses solid particles and inert gas for cooling. The FBQ method can provide a higher thermal gradient due to the excellent cooling capacity and the existence of a dynamic baffle. The dynamic baffle effectively prevents heat transfer from the hot zone to the cold zone. Additionally, the fluidized bed does not contaminate the castings and it has the advantages of simple structure, low cost, short production cycle, and easy maintenance. Therefore, the FBQ method has a good application prospect in the process of large-sized nickel-based single-crystal superalloy turbine blades. In this paper, the principles and characteristics of fluidized bed quenching are clarified, the structure of directional solidification technology with fluidized bed quenching are introduced, the research progress of dynamic baffles in directional solidification equipment with fluidized bed quen-ching are summarized, the influencing factors of the fluidized bed quenching capacity are analyzed, such as gas velocity and particle size, and the future research aspects of directional solidification technology with fluidized bed quenching are also prospected.