激光增材制造DD98M高温合金组织及稳定性研究

Microstructures and Long-Term Aging Stability of Nickel-Based Superalloy DD98M by Laser Additive Manufacturing

采用激光增材制造技术制备了DD98M镍基高温合金管状试样,研究了其沉积态、固溶时效态和长期时效态微观组织变化,对比分析了沉积态和固溶时效态试样中γ’相尺寸分布及在1000℃长期时效时γ’相的演化规律。结果表明:沉积态组织主要由外延生长的微细柱晶组成,枝晶间无γ-γ’共晶组织析出,试样中γ’相体积分数约为70%。合金中元素微偏析造成了枝晶干和枝晶间γ’相尺寸差异,其中枝晶干处为210 nm,枝晶间为560 nm。经固溶时效处理后,γ’相(约370 nm)均匀分布在γ基体上,其尺寸分布符合LSW模型。经1000℃长期时效500 h后,合金组织中无TCP相(拓扑密排相)生成,γ’相仍保持立方形貌,其尺寸几乎保持不变。固溶时效处理后,合金显微硬度从沉积态时的4420 MPa增加至4870 MPa,长期时效能降低合金硬度,降幅约5.9%。

The DD98M nickel-based superalloy tube was fabricated by laser additive manufacturing(LAM). The microstructural variations of the as-deposited, solution-aged and long-term aged superalloy were studied. The precipitate distribution of deposited and solution-aged alloys was analyzed combined with the study of γ’ precipitates evolution during 1000℃ long-term aging. The results show that the as-deposited micro structure of the alloy mainly consists of epitaxial finer columnar grains with an optimum amount of cubical γ’ precipitates around 70 vol%.No γ-γ’ eutectic is observed at interdendritic. Rapid solidification during LAM process largely eliminates the segregation of metal elements with an increase of γ’ precipitates sizes from 210 nm at dendritic arms to 560 nm at interdendritic regions. After solution-aging treatments, γ’precipitates(about 370 nm) are uniformly distributed in y matrix with the sizes distribution fitting the LSW model. During the long-term aging of500 h at 1000 ℃, no TCP(topologically close-packed) phase exists and the sizes of cubical precipitates have a slight increase. In addition, the micro-hardness of the as-deposited is 4420 MPa and it will obviously increase to 4870 MPa after solution-aging heat treatment. Long-term aging reduces the maximum micro-hardness by around 5.9%.