The Effect of Optimizing Repair Welding Parameters an‎d Filler Metal on the Microstructure an‎d Mechanical Properties in Gas Tungsten Arc Welding of FSX-414 Cobalt-Based Superalloy

10/8/2026 12:00:00 AM

The cobalt-based superalloy FSX-414 is widely used in the first-stage stationary vanes of Frame 9 gas turbines due to its mechanical properties an‎d high-temperature stability. However, this alloy often undergoes degradation during service as a result of thermal fatigue an‎d oxidation. In addition, primary MC an‎d M23C6 carbides in FSX-414 decompose at elevated turbine operating temperatures an‎d transform into fine secondary M23C6 carbides. These carbides, which are chromium-rich an‎d highly strong, exhibit poor toughness an‎d are therefore prone to damage under cyclic thermal stresses caused by contraction an‎d expansion. In this study, gas tungsten arc welding (GTAW) with four different filler metals—FSX-414, HS25, HS188, an‎d Mar-M918—was employed to investigate the influence of repair welding on the microstructure an‎d mechanical properties of repaired specimens. Tensile tests were carried out at room temperature an‎d at 650 °C in accordance with ASTM E8 an‎d ASTM E21 stan‎dards. The results revealed that, in most cases, fracture occurred within the heat-affected zone (HAZ), while only the samples welded with HS188 exhibited fracture in the weld metal. Moreover, qualitative tensile results indicated that specimens welded with Mar-M918 demonstrated the highest tensile strength (793 MPa), whereas those welded with FSX-414 exhibited the lowest tensile strength (711 MPa) at room temperature. In addition, microstructural changes an‎d carbide phase transformations were examined to eva‎luate the effects of welding an‎d heat input on mechanical properties. Repair welding of this alloy presents significant challenges due to the susceptibility to solidification cracking, microstructural alterations, an‎d the formation of undesirable phases. The aim of this research is to optimize repair welding parameters— including welding current an‎d filler metal selec‎tion—in order to enhance component durability an‎d reduce maintenance costs. The findings of this study can contribute to extending vane service life, minimizing unexpected failures, an‎d improving gas turbine efficiency. This research is scientifically novel as it represents the first comprehensive eva‎luation of the simultaneous effects of multiple filler metals on the mechanical an‎d microstructural behavior of FSX-414 under operating conditions, providing valuable insights for the development of advanced repair strategies an‎d improved reliability of gas turbines.

سوپرآلياژ , FSX-414 , GTAW , جوشكاري تعميري , فلز پركننده , پارامترهاي جوشكاري

FSX-414 Superalloy , GTAW , Repair Welding , Filler Metal , Welding Parameters

Mohammad Reza Sheikh Mohseni

Dr. Seyed Mohammad Ali Boutorabi