Effect of Heat Treatment on Liquation Cracking in Continuous Fiber and Pulsed Nd:YAG Laser Welding of HASTELLOY X Alloy
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TRODUCTION
HASTELLOY* X is a nickel-base superalloy, which *HASTELLOY is a trademark of HAYNES INTERNATIONAL, INC.
possesses relatively high elevated temperature strength combined with corrosion resistance.[1–4] The microstructure of this alloy is comprised of a solid solution austenitic matrix with some solute-rich carbides that are mainly present at the grain boundaries. However, this alloy is generally categorized as a solid solution nickel-base alloy, since only a minor part of its strength is due to formation of carbides.[3–5] Nickel-base alloys are prone to hot cracking in fusion welding.[5,6] Solidification and liquation cracks initiate and grow along grain boundary zones enriched by solutes.[7,8] The main cause of liquation cracking is believed to be the thermal stresses applied to locally melted grain boundaries in the heat-affected zone (HAZ).[9–11] It is reported that liquation of grain boundaries is due to their lower melting point, which
M. PAKNIAT and F. MALEK GHAINI are with the Department of Materials Engineering, Tarbiat Modares University, Tehran 14115111, Iran. Contact email: [email protected] M.J. TORKAMANY is with the Iranian National Laser Research Centre, Tehran 14665-576, Iran. Manuscript submitted November 16, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS A
is attributed to the concentration of alloying elements and harmful impurities such as sulfur and phosphorus.[5,8,12] Chen et al.[13] reported that a large laser input angle in laser melting deposition of INCONEL** 718 **INCONEL is a trademark of HUNTINGTON ALLOYS CORPORATION, Inco Alloys International, Inc.
alloy leads to forming interconnections among secondary dendrites in the interdendritic regions, which results in improving resistance to hot cracking in welding. Yan et al.[14] investigated liquation cracking behavior of GH 909 alloy in Nd:YAG welding and concluded that solute segregations cause lattice distortion at the grain boundaries and inhibit the binding force at the solid/liquid interface. These researchers have also reported that the presence of cracks can greatly weaken the hot ductility of the material and can result in reduction of tensile strength of welded joints.[15] Cieslaket et al.[16] evaluated hot cracking of HASTELLOY C alloys and showed that C-4 alloy has less sensitivity to hot cracking in this family of alloys. Lienert et al.[17] showed that HASTELLOY B-2 alloy has high resistance to hot cracking, which is comparable to HASTELLOY C-4 and stainless steel 304L. However, HASTELLOY W was reported to have the highest tendency for hot cracking. Montazeri and Ghaini[18] reported that preweld solution heat treatment of INCONEL 738 LC reduced the tendency for liquation cracking in pulsed Nd:YAG laser welding of this alloy. Cao et al.[19] reported that prewelding solution treatment and aging heat treatment
improve the weldability and weld zone quality in pulsed Nd:YAG laser welding of INCONEL 718 alloy. Pang et al.[20] reported that by solution heat treatment of a single-crystal nickel-base superalloy CMSX-10K,
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