HAZ Liquation Cracking Mechanism of IN-738LC Superalloy Prepared by Laser Solid Forming
The heat-affected zone (HAZ) liquation cracking mechanism of nickel-based superalloys with high (Al+Ti) content during the laser solid forming (LSF) process was investigated via laser remelting of an as-deposited IN-738LC superalloy. Microstructural HAZ analysis revealed that cracks consistently pro...
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Veröffentlicht in: | Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2018-10, Vol.49 (10), p.5118-5136 |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | The heat-affected zone (HAZ) liquation cracking mechanism of nickel-based superalloys with high (Al+Ti) content during the laser solid forming (LSF) process was investigated
via
laser remelting of an as-deposited IN-738LC superalloy. Microstructural HAZ analysis revealed that cracks consistently propagated from the HAZ to the remelting zone along the grain boundary (GB). The formation of a liquid film during GB liquation was mainly owing to localized melting of the semicontinuous
γ
-
γ
′ eutectic distributed along the GB. The solute segregation behavior of the IN-738LC alloy during LSF was analyzed using the Giovanola–Kurz model and Scheil models, revealing that a significant enrichment of
γ
-
γ
′ eutectic-forming elements in the residual liquid at the final stage of solidification (solid fraction ~ 0.87) in the molten pool was the main cause of semicontinuous
γ
-
γ
′ eutectic formation along the GB. Further, a B enrichment at the GB was identified in LSF-fabricated IN-738LC, which promoted cracking by lowering the GB liquation temperature and promoting wetting of the GB by the liquid film. Unlike the phenomenon observed in the welding of cast IN-738LC, the coherence between the
γ
′ phases and the
γ
matrix in LSF-fabricated IN-738LC can suppress the occurrence of constitutional liquation of the
γ
′ phase. To understand the interaction between the thermal stress and the liquid film in the LSF process, thermal stress as a cracking driving force was also estimated based on the measurement of the residual stress from the substrate to the remelting zone of the IN-738LC deposit by the Vickers micro-indentation method. |
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ISSN: | 1073-5623 1543-1940 |
DOI: | 10.1007/s11661-018-4826-6 |