Crystal growth control of Ni-based alloys by modulation of the melt pool morphology in DED

• Published in: Journal of alloys and compounds 2022-03, Vol.898, p.162976, Article 162976
• Main Authors: Shao, Jiayun, Yu, Gang, Li, Shaoxia, He, Xiuli, Tian, Chongxin, Dong, Binxin
• Format: Article
• Language: English
• Subjects: Crystal growth; Crystal structure; Crystals; Epitaxial growth; Grains; High temperature; Laser deposition; Mechanical properties; Melt pool morphology; Microstructure; Morphology; Ni-based superalloys; Nickel base alloys; Parameters; Solidification; Substrates; Texture
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.162976

In additive manufacturing especially in directed energy deposition, it is hard to control crystal growth pattern due to the high temperature gradient in AM. Essentially, the crystal grows epitaxially from the substrate and columnar crystals with strong texture are exhibited in AM components. Here, small spot diameter was used for DED-L of Ni-based alloys and various crystal growth patterns were obtained by changing power density. Samples processed under low power density were shown to exhibit wide and shallow spindle-like melt pool, along with apparently hierarchical planar-columnar-equiaxed microstructure. While samples prepared under relatively high power density were shown to exhibit narrower and deeper melt pool with two sharp turning points, exhibiting inclined columnar grains and several discontinuous central axial columnar crystals. When highest power density and small spot diameter were applied, crystal growth with weak texture was achieved. Under this deep and narrow melt pool, the crystal growth can be separated into four regions: nearly-equiaxed grains with random grain orientations; horizontally symmetrically grown crystal grains; axial columnar in the center; columnar grains grew approximately vertical to the boundary of melt pool. Correlations were investigated between melt pool shape, solidification parameters and microstructure. The transformation of melt pool morphology was mainly attributed to the change of power density. Solidification parameters were shown to be different under different melt pool morphology. Diverse crystal growth patterns were achieved under different melt pool morphology controlled by power density, showing the feasibility of site-specific of microstructure control in DED-L according to the required mechanical properties. •Crystal growth pattern in DED of Ni-based superalloys have been modulated through control of melt pool morphology.•Three dimensional EBSD characterization experiments were conducted to elucidate crystal growth evolution.•Crystal structure appearance, texture, size and aspect ratio were studied.•Relationship between power density, melt pool morphology and crystal growth was studied.