WELDING AND WELDABILITY OF NICKEL-IRON ALUMINIDES.

A study was undertaken to investigate the weldability of the boron-doped (500 ppm by weight) ductile aluminides by gas tungsten arc (GTA) and electron beam (EB) welding processes. Autogenous GTA welding of boron-containing nickel-iron aluminides produced severe cracking within the weld metal and the heat-affected zone (HAZ). A series of EB welds with welding speeds ranging from 13 to 64 mm/s (30 to 150 ipm) with varying beam focus conditions gave successful complete joint pentration welds only in a narrow range of speeds and focus conditions. The cracks were predominantly intergranular in the HAZ and interdendritic in the fusion zone. Transmission electron microscopy (TEM) revealed tetragonal distortions of the ordered B2 (NiAl type) phase with a martensitic appearance. Microprobe analysis revealed extensive solute redistribution in the fusion zone and the HAZ as a result of the weld thermal cycle.