Effect of Al, Ti and C additions on Widmanstatten microstructures and mechanical properties of cast Al0.6CoCrFeNi compositionally complex alloys

The cast microstructure of the Al0.6CoCrFeNi compositionally complex alloy was successfully refined with small additions of Al, Ti and C and its mechanical properties were optimized. In the as-cast state, this alloy has a Widmanstatten microstructure with coarse grains (similar to 110 mu m) of a strong BCC/B2 matrix and soft FCC plates (similar to 65 vol.%) with large widths (similar to 1.3 mu m). The addition of 0.25 at.% C to Al0.6CoCrFeNi stabilizes the FCC phase and favors the formation of a coarse dendritic microstructure making this alloy unsuitable for structural applications. In contrast, alloying of either 3 at.% Al, Ti, or 3% Ti and 0.25% C to Al0.6CoCrFeNi refined its Widmanstatten microstructure, i.e. the thickness of the FCC plates and/or the size of the prior BCC/B2 grains were significantly reduced. As a result of these microstructural changes, Al and Ti containing alloys show an outstanding strength (twice higher than that of Al0.6CoCrFeNi) and ductilities <= 5% at 20 degrees C. These properties are retained at 400 degrees C but at 700 degrees C, the strength and ductility of almost all alloys decrease. However, Ti containing alloys exhibit much larger ductilities (similar to 50%) at 700 degrees C due to their high density of grain boundaries which accommodate plastic deformation through grain boundary sliding. (C) 2019 The Authors. Published by Elsevier Ltd.