In-Situ Reaction Processing Using Friction Stir Processing

Friction stir processing (FSP) is an innovative microstructural modification process developed initially for achieving superplasticity in commercial Al alloys. It adapts the concepts of friction stir welding (FSW), which has gained wide acceptance over the last decade for joining Al alloys.  In this work the use of FSW has been further modified to include processing involving chemical reactions between the substrate and materials introduced into the stirred zone. This process is termed friction stir reaction processing (FSRP).  It may be applied to a wide range of substrates. This investigation is focused primarily on aluminum substrates. In the present paper, an attempt has been made to determine if in-situ chemical reactions can occur between selected compounds introduced into a friction stir process and the metal substrate being processed. Particulate CuO, SiO₂, TiO₂, NiO, and BN powders were stirred into Al and NiO into Fe. Reaction driving forces include Gibbs energy, mechanical energy, and surface energy changes, however, the mechanical and surface energies are likely small compared to Gibbs energy. Exposing the particles to unoxidized Al within the nugget zone should make reaction more likely compared to reaction with the normally oxidized Al surface. Reaction in Al was observed with CuO, SiO₂, TiO₂ and NiO to produce Cu, Al-Si, Al-Ti, and Ni-Al. Reaction in Fe was observed with NiO to produce Fe-Al and Fe-Ni.