【摘要】 采用螺旋选晶法制备Ni₃Al基单晶合金IC6SX试棒,研究了不同拉晶速率对凝固组织和高温持久性能的影响.结果表明,Ni₃Al基单晶合金IC6SX凝固组织为树枝状,随着拉晶速率从1.5 mm/min增加到6 mm/min,一次枝晶间距逐渐减小.与普通镍基高温合金不同,位于枝晶干处的次生γ′相尺寸比枝晶间处的大.随着拉晶速率的增加,枝晶干和枝晶间处的γ′相尺寸都逐渐减小,由不规则形状逐渐立方化,枝晶间处的初生γ′相的数量逐渐增多.一次枝晶间距和γ′相尺寸对高温持久性能影响显著,随着拉晶速率的增加,组织细化,铸态IC6SX单晶合金的高温持久寿命增加.更多还原

【Abstract】 As high-temperature structural materials,Ni₃Al possesses excellent comprehensive properties,such as good strength at high temperature,low density,excellent ductility,superior oxidation resistance and so on.A high performance Ni₃Al-based alloys IC6 has been developed by authors and successfully applied for aero-engine vanes.It has been found that the high temperature mechanical properties of the single crystal IC6 alloy are superior to both equiaxial crystal and directional columnar IC6 alloys.A lot of research work for IC6 alloys has been carried out on the equiaxial crystal and directional columnar IC6 alloys during the last two decades.In order to further improve the mechanical properties and meet the requirement of turbine blade materials,the single crystal Ni₃Al-based alloy IC6SX has been developed and the research work on single crystal processing has been carried out recently.In the present investigation,the influence of withdrawal rate on the microstructure and stress rupture properties of a Ni₃Al-based single crystal superalloy IC6SX were studied.The single crystal specimens were prepared by screw selection crystal method.The microstructure analysis by SEM and OM reveals that the microstructure of specimens is dendrite structure,and the primary dendrite arm spacing decreases from 480μm to 390μm with withdrawal rate increasing from 1.5 mm/min to 6.0 mm/min.Different with the common Ni-based superalloys,the size of theγ’ phase in the dendritic core is larger than that in the interdendritic area.As withdrawal rate increases the size of theγ’ phase decreases.The average size of theγ’ phase in the dendritic core decreases from 3μm to 1.3μm and the average size of theγ’ phase in the interdendritic area decreases from 1.6μm to 0.8μm with withdrawal rate increasing.Meanwhile,the shape ofγ’ phase tends to regular,and more primary eutecticγ’ phase precipitates form in the interdendrite region.The volume fractions of primary eutecticγ’ phase precipitates are 0.07%,0.18%,0.36%and 0.77%,respectively at the withdrawal rates 1.5,3.0,4.5 and 6.0 mm/min.It has been found that the stress rupture properties are affected by primary dendrite arm spacing and size ofγ’ phase significantly,i.e.,the rupture lives of as-cast specimens increase with increasing withdrawal rate,which may be attributed to the refining microstructure.The above results can be used to optimize the process design for both single crystal specimen preparation and component fabrication of the present alloy IC6SX and may be used as a reference for other Ni-based single crystal alloys.更多还原