Friction stir processing of Ni-base alloys

Friction stir processing has been conducted on both solid-solution strengthened and precipitation-strengthened nickel base alloys. All processing was conducted using a W-25Re tool material with a small cone angle. Processing depths were on the order of 2 mm. Processing windows for Alloys 625, 718 and Hastelloy X were established in terms of processing speed and spindle rotation. Process forces and processing temperatures measured using embedded thermocouples are reported. Microstructure characterization revealed a dramatic decrease in grain size as a result of processing. Additive friction stir processing was conducted by depositing a precipitation hardenable Alloy 282 filler metal on an Alloy 600 substrate and then using friction stir processing to modify the aswelded microstructure. High resolution characterization indicated that gamma-prime precipitates were present in the as-processed layer and that large increases in hardness (strength) could be achieved by an aging heat treatment relative to the welded and aged condition.