Abstract:

Effects of cold rolling with 75% reduction and different cooling methods (air cooling and furnace cooling) after heat treatment at 1073 K for 1 h on the microstructure and mechanical properties of Al_0.3CoCrFeNi high entropy alloy were studied by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and tensile test. The results show that, all the as-cast and cold-rolled Al_0.3CoCrFrNi alloy samples are FCC single-phase structure. After holding at 1073 K for 1 h, both the furnace-cooled and the air-cooled samples are FCC+BCC dual-phase structure. Compared with the as-cast state, the strength of the alloy after cold-rolling increases significantly, but the plasticity decreases greatly. After the heat treatment, the furnace cooling sample has excellent mechanical properties due to fine grain strengthening, twinning and precipitation strengthening. The tensile strength of the furnace cooling sample is 1289 MPa, which is about twice as much as that of as-cast specimen(719 MPa), and the maximum elongation is 28.7%. Because of the increase of the precipitated phase and twin size, the strength of the furnace-cooled sample increases without loss of plasticity compared with that of the air-cooled sample.

Key words: high entropy alloy, cold rolling, heat treatment, microstructure, mechanical properties