K4750合金重力铸造和离心铸造凝固组织及室温力学性能研究

Solidification Microstructure and Room-Temperature Mechanical Properties of K4750 Superalloy Prepared by Gravity Casting and Centrifugal Casting

摘要:

研究了K4750高温合金重力铸造和离心铸造的凝固组织及室温力学性能，对比分析了两种工艺条件下实验合金的第二相分布、晶粒尺寸、元素偏析、缩松缺陷分布、室温力学性能及其断口形貌。发现两种铸造工艺条件下铸态K4750合金均由γ基体相、晶内MC碳化物、细小弥散分布的晶内γ'相以及晶界MC和M₂₃C₆碳化物组成，离心铸造工艺下析出相的尺寸减小。离心铸造铸态K4750合金的平均晶粒尺寸从重力铸造下的4.52 mm减小到2.22 mm，缩松缺陷面积分数由重力铸造的1.75%减少至0.27%；重力铸造铸态K4750合金组织枝晶排列整齐，离心铸造铸态K4750合金组织枝晶发生破碎，元素微观偏析程度减轻；离心铸造制备的铸态K4750合金展现出优异的室温力学性能，其屈服强度、抗拉强度和断裂延伸率分别为632 MPa、938 MPa和11.2%。相比于重力铸造试样，其抗拉强度提高了20.6%，这主要归因于晶粒细化、析出相尺寸减小以及铸造缺陷减少的共同作用。

Abstract:

The solidification microstructure and room-temperature mechanical properties of K4750 superalloys prepared by gravity casting and centrifugal casting were investigated. Their second phase distribution, grain size, element segregation, distribution of shrinkage defects, room-temperature mechanical properties and fracture morphology were analyzed comparatively. Results show that the as-cast K4750 superalloys prepared by both casting processes consist of γ matrix phase, intragranular MC-type carbide, fine and dispersed intragranular γ' phase, as well as MC-type and M₂₃C₆-type carbides at grain boundary. However, the precipitate size is found to be more refined in the centrifugal casting process. The average grain size of as-cast K4750 superalloy decreases from 4.52 mm (gravity casting) to 2.22 mm (centrifugal casting). Furthermore, the area fraction of shrinkage defects is reduced from 1.75% (gravity casting) to 0.27% (centrifugal casting). The K4750 superalloy prepared by gravity casting exhibits well-aligned dendritic structures, whereas centrifugal-cast superalloy shows fragmented dendrites and a reduced degree of elemental segregation. The K4750 superalloy samples prepared by centrifugal casting exhibit excellent room-temperature mechanical properties, with yield strength, ultimate tensile strength and elongation of 632 MPa, 938 MPa and 11.2%, respectively. Compared to the gravity-casting counterpart, its ultimate tensile strength is increased by 20.6%, which can be attributed to the combined effects of grain refinement, γ' phase refinement and a reduction in casting defects.