Abstract
Reduced hot cracking susceptibility is essential to ensure the flawless manufacturing of nickel superalloys typically employed in welded aircraft engine structures. The hot cracking of precipitation strengthened alloy 718 mainly depends on chemical composition and microstructure resulting from the thermal story. Alloy 718 is usually welded in a solution annealed state. However, even with this thermal treatment, cracks can be induced during standard industrial manufacturing conditions, leading to costly and time-consuming reworking. In this work, the cracking susceptibility of wrought and investment casting alloy 718 is studied by the Varestraint test. The test is performed while applying different welding conditions, i.e., continuous tungsten inert gas (TIG), low frequency pulsed TIG, continuous laser beam welding (LBW) and pulsed LBW. Welding parameters are selected for each welding technology in order to meet the welding quality criteria requested for targeted aeronautical applications, that is, full penetration, minimum cross-sectional welding width and reduced overhang and underfill. Results show that the hot cracking susceptibility of LBW samples determined by the Varestraint test is enhanced due to extended center line hot cracking, resulting in a fish-bone like cracking pattern. On the contrary, the minor effect of material source (wrought or casting), grain size and pulsation is observed. In fact, casting samples with a 30 times coarser grain size have shown better performance than wrought material.
Highlights
High temperature Ni-base superalloys are broadly employed for the manufacturing of high responsibility hot section parts of aircraft turbines
150 mm × 50 mm × 3.2 mm samples of wrought and investment were casted at ALFA INVESTIGACIÓN, DESARROLLO E INNOVACIÓN facilities under vacuum casting alloy 718 alloy were employed to carry out the Varestraint tests
The results show that for both welding technologies, pulsation has a reduced but beneficial effect on the drop of total crack length (TCL) measured for every ε and on cracking susceptibility
Summary
High temperature Ni-base superalloys are broadly employed for the manufacturing of high responsibility hot section parts of aircraft turbines. Precipitation-strengthened Ni superalloys are suitable to work at high temperatures (above 700 ◦ C), under high structural loads and corrosive conditions due to their outstanding tensile, fatigue, creep and oxidation resistant properties [1]. The earliest Ni superalloys were strengthened by the precipitation of γ’ (Ni3Al, Ni3Ti and Ni3(Ti, Al)) but they underwent severe strain age cracking (SAC) after welding. The post weld heat treatment limited their manufacturability. In 1963, Inconel 718 alloy was developed, which added. Nb into the matrix which forms metastable γ” precipitates of Ni3 Nb. The precipitation kinetics of γ” are slower compared to γ’ which contributes to the improvement of weldability and resistance to SAC [1]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
