Effect of substrate cooling on the epitaxial growth of Ni-based single-crystal superalloy fabricated by direct energy deposition. (30th January 2021)

• Record Type: Journal Article
• Authors: Nie, Jianwen; Chen, Chaoyue; Liu, Longtao; Wang, Xiaodong; Zhao, Ruixin; Shuai, Sansan; Wang, Jiang; Ren, Zhongming
• Is Part Of: Journal of materials science & technology. Volume 62(2021)
• Page Start: 148
• Page End: 161
• Publication Date: 2021-01-30
• Subjects: Direct energy deposition -- Epitaxial growth -- Columnar-to-equiaxed transition (CET) -- Temperature gradient; Metals -- Periodicals; Materials science -- Periodicals; Materials science; Metals; Periodicals; 620.1105
• DOI: 10.1016/j.jmst.2020.05.041
• Languages: English
• ISSNs: 1005-0302

Abstract

Graphical abstract: Abstract: The columnar-to-equiaxed transition (CET) or the formation of stray grains in the laser melting deposition is the least desirable for the repair of single-crystal blades. In this work, the forced water-cooling was conducted on a single-crystal René N5 substrate during the direct energy deposition (DED). The single track remelting, one-layer, two-layer, and eight-layer depositions were investigated to explore the grain growth mechanism. The solidification conditions of the DED process, including temperature field, temperature gradient, and solidification speed, were numerically analyzed by a finite element model. The single-track remelting results showed that the fraction of columnar crystal regions increases from 55.81 % in the air-cooled sample to 77.14 % in the water-cooled one. The single-track deposits of one- and two-layer have the same trend, where the proportion of columnar crystal height was higher under the forced water-cooled condition. The electron backscattered diffraction (EBSD) grain-structure maps of an eight-layer deposit show that the epitaxial growth height increases from 1 mm in the air-cooling sample to 1.5 mm in the water-cooling one. The numerical results showed that the temperature gradient in [001] direction was significantly increased by using forced water-cooling. In conclusion, the in-situ substrate cooling can become a potential method to promote epitaxial growth during DED via the influence on CET occurrence.