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Effects of Grain Boundary Microconstituents on Heat-Affected Zone Cracks in a Mar-M004 Weldment

1
Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan
2
Nuclear Fuels and Materials Division, Institute of Nuclear Energy Research, Taoyuan 32546, Taiwan
3
Institute of Materials Engineering, National Taiwan Ocean University, Keelung 20224, Taiwan
*
Author to whom correspondence should be addressed.
Metals 2018, 8(4), 201; https://doi.org/10.3390/met8040201
Received: 26 February 2018 / Revised: 19 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
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Abstract

Repair-welding of a cast Mar-M004 superalloy by gas tungsten arc welding was performed. Liquation cracks of the heat-affected zone (HAZ) in a Mar-M004 weldment were closely related to the presence of low-melting constituents along the solidified boundaries in the weld. The metal carbides (MC), M3B2 and M5B3 borides, Ni7(Hf,Zr)2 intermetallic compounds, and γ-γ′colonies were found at the interdendritic boundaries. Fine boride precipitates mixed with intermetallic compounds in lamellar form were more likely to liquate during repair-welding. The melting of borides and intermetallic compounds in 1180 °C/4 h treated samples confirmed the poor weldability of the Mar-M004 superalloy due to enhanced liquation cracking. In addition to boride formation, fractographs of liquation cracks revealed strong segregation of B element in carbides and intermetallics, which might further lower the solidus temperature of the repair weld. View Full-Text
Keywords: gas tungsten arc welding; liquation crack; MC carbide; intermetallic compound; boride; Mar-M004 superalloy gas tungsten arc welding; liquation crack; MC carbide; intermetallic compound; boride; Mar-M004 superalloy
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Chen, T.-C.; Cheng, Y.-H.; Tsay, L.-W.; Shiue, R.-K. Effects of Grain Boundary Microconstituents on Heat-Affected Zone Cracks in a Mar-M004 Weldment. Metals 2018, 8, 201.

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