Welding the Inconel 718 Superalloy, Manikandan, SGK

Alloy 718 is a high strength Ni-Fe base superalloy and is one of the indispensable superalloys in the aerospace, oil and gas, and nuclear industries. It is extensively used in the high temperature systems of cryogenic and semi-cryogenic rocket engines. Alloy 718 was welded in the solution treated condition and subsequently age hardened, since it has excellent strain age cracking resistance. The weldability of this alloy was extensively studied considering the aspects of strain age cracking and/or HAZ microfissuring. Use of Nb as an age hardener in place of Al/Ti in alloy 718 eliminated the problem of strain age cracking but resulted in the formation of brittle Laves phase in the interdendritic region of fusion zone by segregation during solidification. Hence response of fusion zone for age hardening is poor. These laves phases are the favorable sites for easy crack initiation and propagation which affects the mechanical properties of the welded components

Laves Phase in Alloy 718 Fusion Zone explores the day-to-day welding business in Alloy 718 and presents solutions to avoid or minimise the micro-segregation. It considers the limitations of changing from lab scale models to actual production model. It presents new technologies with proven experimental background. Various case studies are presented within the text, as well as proposed solutions backed by experimental evidence. Items previewed in this edition include: enhanced cooling rate in GTA welding process with cryogenic cooling and enhanced dendrite refinement using modified pulse waveform in GTA welding. This work will be useful to researchers from the aerospace, space, power generation, nuclear, and chemical industries, as well as students interested in superalloys and welding.

• Resolves the industrial limitations in reducing the formation of laves phases in welding of alloy 718
• Presents case studies in industrial applications
• Discusses new technologies with proven experimental background
• Includes a comparison of Laves size and distribution between GTAW, EBW, LBW and FW