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Improvement in Laser Weldability of INCONEL 738 Superalloy through Microstructural Modification

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Abstract

Microstructural study of laser-beam-welded IN 738 superalloy was carefully performed to better understand the causes of heat-affected zone (HAZ) cracking and to determine an improved approach of alleviating the weldability problem. The HAZ cracks in the alloy were intergranular liquation cracks that resulted from the liquation reaction of both secondary solidification products (MC carbides and γ-γ′ eutectic) and solid-state reaction products (γ′ particles) present in the preweld material. In contrast to the expectation based on Chadwick’s equation, a reduction of grain boundary liquid film thickness did not produce a decrease in HAZ cracking owing to increased base alloy hardness that accompanied a preweld heat treatment designed to reduce the intergranular liquation. Moreover, a major factor limiting the effectiveness of an existing preweld heat treatment with low base alloy hardness in reducing HAZ cracking was found to be the formation of intergranular M5B3 boride particles during the heat treatment. These borides can widen the HAZ brittle temperature range (BTR) during weld cooling and increase the propensity for cracking. Based on the results, a new preweld heat treatment that induces a moderate hardness and precludes grain boundary boride formation was found and was shown to produce a significant reduction in HAZ cracking in the welded alloy compared to the most effective pre-existing preweld heat treatment.

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Notes

  1. INCONEL and IN are trademarks of INCO Alloys International, Huntington, WV.

  2. JEOL is a trademark of Japan Electron Optics Ltd., Tokyo.

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Acknowledgments

The authors appreciate the financial support provided by Standard Aero Ltd. (Winnipeg, MB, Canada) and NSERC. One of the authors (ATE) is grateful to the Government of Manitoba for the award of a Manitoba Graduate Scholarship.

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Author notes

  1. A.T. Egbewande (Graduate Student)

    Present address: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB, Canada, T6G 2V4

Authors and Affiliations

  1. Department of Mechanical and Manufacturing Engineering, University of Manitoba, Winnipeg, MB, Canada, R3T 5V6

    A.T. Egbewande (Graduate Student), H.R. Zhang (Postdoctoral Research Fellow), R.K. Sidhu (Electron Microprobe and SEM Manager) & O.A. Ojo (Associate Professor)

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  1. A.T. Egbewande
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  2. H.R. Zhang
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  3. R.K. Sidhu
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  4. O.A. Ojo
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Corresponding author

Correspondence to O.A. Ojo.

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Manuscript submitted October 1, 2008.

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Egbewande, A., Zhang, H., Sidhu, R. et al. Improvement in Laser Weldability of INCONEL 738 Superalloy through Microstructural Modification. Metall Mater Trans A 40, 2694–2704 (2009). https://doi.org/10.1007/s11661-009-9962-6

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