Comparison of Hot Cracking Susceptibility of TIG and Laser Beam Welded Alloy 718 by Varestraint Testing

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.

Welding Metallurgy and Weldability of Superalloys

“…Researchers were invited to submit innovative research papers in the areas of welding metallurgy, weldability, and associated topics of superalloys. In total, six research papers were published in this Special Issue of Metals, entitled "Welding Metallurgy and Weldability of Superalloys", which presents some of the research trends in the field [1][2][3][4][5][6]. All six research papers were related to weld cracking in some aspect, with the strongest focus on hot cracking [1][2][3][4]6], followed by strain age cracking [5].…”

“…In total, six research papers were published in this Special Issue of Metals, entitled "Welding Metallurgy and Weldability of Superalloys", which presents some of the research trends in the field [1][2][3][4][5][6]. All six research papers were related to weld cracking in some aspect, with the strongest focus on hot cracking [1][2][3][4]6], followed by strain age cracking [5]. The major part of the submission in terms of material was associated with Alloy 718, the "work horse" within the group of superalloys in the aero-engine industry [2][3][4].…”

“…All six research papers were related to weld cracking in some aspect, with the strongest focus on hot cracking [1][2][3][4]6], followed by strain age cracking [5]. The major part of the submission in terms of material was associated with Alloy 718, the "work horse" within the group of superalloys in the aero-engine industry [2][3][4]. In addition, Haynes ® 282 ® , a superalloy that falls into the same class of superalloys (i.e.…”

“…precipitation hardening Ni-or Ni-Fe based superalloys) as Alloy 718 was covered in two papers that were investigated [5,6]. Varestraint weldability testing [3,4,6] was the major testing method addressed within the field of weldability testing, followed by Gleeble thermomechanical testing [5]. Raza et.…”

“…al. [3] investigated susceptibility toward hot cracking of wrought and investment cast Alloy 718 by the Varestraint weldability testing method.…”