Effect of substrate cooling on the epitaxial growth of Ni-based single-crystal superalloy fabricated by direct energy deposition
来源期刊：JOURNAL OF MATERIALS SCIENCE TECHNOLOG2021年第3期
论文作者：Jianwen Nie Chaoyue Chen Longtao Liu Xiaodong Wang Ruixin Zhao Sansan Shuai Jiang Wang Zhongming Ren
文章页码：148 - 161
摘 要：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 Rene 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 from55.81 % 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 tempe rature gradient in [0011 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.
Jianwen Nie，Chaoyue Chen，Longtao Liu，Xiaodong Wang，Ruixin Zhao，Sansan Shuai，Jiang Wang，Zhongming Ren
State Key Laboratory of Advanced Special Steels, School of Materials Science and Engineering, Shanghai University
摘 要：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 Rene 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 from55.81 % 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 tempe rature gradient in [0011 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.
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