激光增材制造DD98M高温合金组织及稳定性研究

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 microstructure 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 γ matrix with the sizes distribution fitting the LSW model. During the long-term aging of 500 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%.