Effect of C on microstructure and strength of AlxCu0.14CrFeMnNi-Towards producing a recycled high entropy alloy

The present study examines the effect of C and Al addition on a low-Cu containing multi-principal element alloy (MPEA) which has been shown to have high ductility. AlxCu0.14CyCrFeMnNi (x = 0, 0.15 and y = 0, 0.01, 0.04) alloys were arc cast and homogenized at 1150 °C followed by water quenching. Irrespective of Al content, the microstructures of C-free alloys consisted of an FCC A1 and a Cr-rich BCC A2 phase. Adding a small amount of C (AlxCu0.14C0.01) led to a decrease in volume fraction of BCC while higher C addition (AlxCu0.14C0.04) resulted in formation of Cr carbides. These microstructural changes led to first a decrease and then an increase in strength in both alloy groups. By considering the Zener pinning effect and nano-hardness of secondary phases, it is proposed that BCC particles are more efficient in grain refining than carbides, while carbides contribute more to strengthening. Electron Back Scatter Diffraction suggests TWIP and TRIP mechanisms are more prevalent in Al- and C-containing alloys where increased FCC lattice parameter implies the lattice strain and phase hardness are enhanced. Controlling Al and C levels will be critical to modulating strength and ductility if HEAs are to be made with high levels of recycled content.