Abstract
The causes of liquation cracking in the heat-affected zone (HAZ) of a cast Mar-M004 superalloy weld were investigated. X-ray diffraction (XRD), electron probe microanalyzer (EPMA), and electron backscatter diffraction (EBSD) were applied to identify the final microconstituents at the solidification boundaries of the cast alloy. Fine borides and lamellar eutectics were present in front of some γ-γ′ colonies, which were expected to be liquefied prematurely during welding. The metal carbide (MC) enriched in Nb, Hf; M3B2 and M5B3 borides enriched in Cr and Mo; and lamellar Ni-Hf intermetallics were mainly responsible for the induced liquation cracking of the Mar-M004 weld, especially the MC carbides. Scanning electron microscope (SEM) fractographs showed that the fracture features of those liquation cracks were associated with the interdendritic constituents in the cast superalloy.
Highlights
Commercial Ni-based superalloys are widely applied for making critical components in gas turbine engines, which require excellent mechanical and anti-corrosion properties at elevated temperature [1,2,3,4]
For the phase contrast inspection by scanning electron microscope (SEM) with backscatter electron (BSE), the image brightness was strongly related to the solidification products
Liquation cracking in the heat-affected zone (HAZ) of a cast Mar-M004 weld was investigated in this study
Summary
Commercial Ni-based superalloys are widely applied for making critical components in gas turbine engines, which require excellent mechanical and anti-corrosion properties at elevated temperature [1,2,3,4]. Mar-M004, a cast Ni-based superalloy, is strengthened primarily by Ni3 (Al, Ti) γ0 precipitates, which are responsible for the stable mechanical properties during long-term applications at elevated temperature [5]. Preweld heat treatments [10,14,15,22,23,24] have been conducted to modify the microstructures of precipitate-strengthened Ni-based superalloys to decrease the sensitivity of liquidation cracking in the HAZ. The effects of inherent microconstituents at the solidified boundaries of cast Mar-M004 superalloy on the HAZ liquation cracking were investigated. The relationship between microstructural features and hot cracking sensitivity of the Mar-M004 superalloy weld was correlated in this study
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