Rotary friction welding of an Fe3Al based ODS alloy

An Fe3Al based oxide dispersion strengthened (ODS) alloy is under consideration for possible use as tubes in advanced heat exchangers, and it is necessary to investigate methods of joining the alloy to itself, and to Haynes 230 alloy. Previous experience on iron aluminides has shown them to be weldable by several processes, but it is known that fusion processes invariably lead to a loss of the Y2O3 oxide dispersion which is an essential feature of ODS alloys. Therefore, solid state processes offer a potential advantage, and in this work continuous drive rotary friction welding has been investigated as a method to join the Fe3Al ODS alloy in both the recrystallized and unrecrystallized condition. Trials were also undertaken to join both recrystallised and unrecrystallized material to Haynes 230 alloy. All welds were made in 15-mm diameter material, using a conventional continuous drive rotary friction welding machine. Welds were evaluated initially using tensile tests, and detailed metallographic observations of the grain size, and the nature of the solid state interface between the materials. It was found possible to make high quality welds containing no flaws for a variety of welding conditions. The microstructural condition of the Fe3Al ODS alloy had no apparent influence on weldability, and no difficulty was encountered in making the dissimilar metal joints. The results obtained are discussed in terms of the microstructures obtained, and are compared with other studies on joining iron aluminides and ODS alloys. (C) 2002 Published by Elsevier Science B.V.