Autogenous Gas Tungsten Arc Weldability of Cast Alloy Ti-48A-2Cr-2Nb (Atomic Percent) versus Extruded Alloy Ti-46A-2Cr-2Nb-0.9Mo (Atomic Percent)

摘要

This study examines procedures for consistentlyproducing sound (crack and void free ) welds using theautogenous (without filler metal )gas tungsten arc (GTA)welding process. Cast alloy Ti-48A-2Cr-2Nb (at.pct) andextruded alloy Ti-46A-2Cr-2Nb-0.9Mo (at.pct) have beenexamined to determine if sound welds can be produced usingautogenous GTA welding without any preheat. Experimentationconsisted of GTA spot welding samples of gamma titaniumaluminide at weld current levels of 45,55,65, and 75 A for aduration of 3 seconds. For the cast alloy, current levels of 45,55,and 65 A for 3 seconds produced similar fusion zonemicrostructures, which consisted of a dendritic solidificationstructure. The fusion zone microstructure of the 75 A for 3seconds current level differed significantly firm the lowercurrent levels. It also consisted of a dendritic solidificationstructure; however, the morphology was quite different. For theextruded alloy, current levels of 45and 55 A for 3 secondsproduced fusion zone microstructures similar to the lowercurrent level samples of the cast γ-TiAl, which consistedof a dendritic solidification structure. The fusionzone microstructures of the 65 and 75 A samples weresimilar to each other, but they had a dendriticsolidification structure of a different morphologythan that of the 45 and 55 A samples. For both alloys at allcurrent levels, microhardness profiles showed an increase inhardness from the base metal to the fusion zone. There were nosignificant differences in the average fusion zone hardness as afunction fo increasing current level. However, nanoindintationtesting did show that certain phases and microconstituents in thefusion zone did have significant variations in hardness inrelation to the enrichment and depletion of chromium.