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

• Main Authors: Tai-Cheng Chen, Yi-Hsin Cheng, Leu-Wen Tsay, Ren-Kae Shiue
• Format: Article
• Language: English
• Published: MDPI AG 2018-03-01
• Series: Metals
• Subjects: gas tungsten arc welding; liquation crack; MC carbide; intermetallic compound; boride; Mar-M004 superalloy
• Online Access: http://www.mdpi.com/2075-4701/8/4/201

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.