Friction Stir Processing (FSP) is an emerging technique used to enhance the superplastic performance of a wide range of materials. The selective nature of the process allows it to be used to either modify the microstructure of bulk materials, or selectively modify only a part of an assembly that requires enhanced performance during forming. When used as a joining process, Friction Stir Joining produces bonded regions that can have the same superplastic performance as the parent sheet. This allows for the fabrication of complex built-up structures (such as multisheet panels) or large welded structures that can be formed in single forming events into final shape. Friction Stir Processing is easily achieved in aluminum and magnesium materials, but in other material systems of interest to superplastic manufacturing (specifically Titanium and Steel) the process can bring some significant challenges. The primary challenges result from the very demanding processing conditions placed on the FSP tooling, and from the high loads and temperatures seen in the parts during processing. Tool and part forge loads and temperatures for sheet materials are routinely in the 8000 lbs to 13000 lbs of normal load, and 900°C to 1200°C range in the weld nuggets and tool tips. Numerous strategies have been employed to deal with these challenging conditions including new tool materials, new tool designs, new FSP machine requirements, alternate or supplemental heating or cooling control, and other processing strategies. This presentation will outline several of the new strategies for dealing with the challenges of high temperature FSP in steel and titanium used in SPF manufacturing. In addition, to those listed above, a new technique is emerging in which hydrogenation prior to FSP is being used to lower process loads and allow FSP to be accomplished in altered, hydride-rich material. After FSP the base material is dehydrided in simple elevated temperature vacuum environments. These hydride/FSP/dehydride sequences may be an enabler for using FSP to enhance the SPF performance in some applications.
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