Abstract
[001] tilt artificial grain boundaries of Ni-based single crystal superalloys CMSX-4 and DD10 have been prepared by self-diffusion bonding. The microstructural stability of 0 ∼ 30∘ artificial grain boundaries have been investigated after heat treatment at 1100 ∘ C for 0 ∼ 300 h. TCP phases and cellular colony developed on boundaries are related to misorientation angle of the bonded boundaries of DD10 and DD10 alloys as well as the bonded boundaries of CMSX-4 and DD10 alloys. The heterogeneous nucleation of TCP phase, enveloped by γ′ film, occurred along 15∘ and 20∘ boundaries. Discontinuous Precipitation (DP) reaction occurred along high misorientation angle (20∘ ∼ 30∘ ) boundaries. However, no TCP phase formation existed along grain boundaries with different misorientation angles in CMSX-4/CMSX-4 bonded alloys as well as for a 0∘ boundary in DD10/DD10 and CMSX-4/DD10 bonded alloys. The current study clearly suggests that grain boundary precipitation and its morphology were influenced by the misorientation angle of grain boundary and the content of refractory elements in alloy.
Highlights
Ni-based single crystal superalloys are primary materials for high pressure turbine blades in advanced aircraft engines
Heterogeneous nucleation of TCP phases was observed at 8◦ grain boundary in a 3rd generation single crystal superalloy containing 6.3 wt.% Re in a previous study [14], while the growth of cellular colony was detected on grain boundaries that were misoriented by 14◦
A series of artificial grain boundaries in Re-containing CMSX-4 (2nd generation single crystal superalloys) and DD10 (3rd generation single crystal superalloys) alloys with certain misorientation angles were investigated for microstructural stability of boundaries after heat treatment at 1100 ◦C for 0 ∼ 300 h
Summary
Ni-based single crystal superalloys are primary materials for high pressure turbine blades in advanced aircraft engines. The welding boundary with misorientation angle is similar to grain boundaries [4]. These boundaries are preferential heterogeneous nucleation sites for precipitates due to their high diffusion mobility, and the corresponding mechanical properties of materials and components would be affected [5,6,7]. The present study is to investigate microstructural stability of diffusion bonded boundaries in 2nd and 3rd generation single crystal superalloys. The current study will be helpful for understanding the microstructural stability of single crystal blades containing low angle boundary and the stability of boundary between mutimaterial blades
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