Thermomechanical Properties of Arc Welds between Additively Manufactured and Wrought Ni-base Superalloys

Laser-powder bed fusion (L-PBF) additive manufacturing (AM) process is being exploited for printing of Haynes 282 and IN740H Ni superalloys for critical components in generation 3 concentrating solar plants, where corrosion resistance and thermomechanical properties at 500-750°C are critical. In the design, arc fusion welding is necessary to join a L-PBF AM part to a conventional wrought product. This work aims to identify whether welding and post heat treatment protocols established for wrought materials are applicable for this similar welding situation.

Gas tungsten arc welding (GTAW) experiments were completed on ½” thick Haynes 282 and In740H AM and wrought plates with a double-v geometry in solution annealed condition and aged condition, respectively. Tensile testing at ambient temperature, 500°C, and 720°C, aided with digital image correlation (DIC), was carried out on transverse tensile samples to determine thermomechanical properties of the arc welded specimens. Molten salt corrosion experiments were performed at 750°C for 100 hours in a ternary Mg-K-Na chloride salt environment to calculate the corrosion rates of these welded specimens.

Yield strength of both welds exceeded 80% of wrought plates. However, ductility was significantly impacted by microcracks and lack of fusion defects present within the FZ, especially FZ/HAZ boundaries near the AM side, implicating a potential weldability challenge and need for further parameter optimization in the AM-to-wrought similar joints. The Haynes 282 welds showed resistance to deformation in the L-PBF HAZ, but the L-PBF HAZ in the In740H welds experienced localized yielding first and incurred most deformation. Partition of strain in the similar welds revealed by DIC measurement corresponds well to microhardness map with failure mostly occurring in lower microhardness regions either on wrought or L-PBF side, aside from samples failing from defects. The corrosion rate in In740H similar welds almost doubles that of Haynes 282 welds.