Effects Of Heat Treatment On Microstructure And Properties Of Al_xFeCrCoNi High-entropy Alloys

High-entropy alloys generally consist of five or more elements,and multi-principal alloying makes the alloys characterized by atomic hysteresis diffusion,high lattice distortion,and single structure.In the case of constant composition,heat treatment usually affects the microstructure and mechanical properties of the materials.However,the above characteristics of the high-entropy alloys make the ratio and morphology between the phases after heat treatment different from ordinary alloys,thus affecting the final mechanical property.In this paper,Al_0.4FeCrCoNi?FCC?,Al_0.6FeCrCoNi?FCC+BCC?and Al_1.0FeCrCoNi high-entropy alloys?BCC?were prepared by non-consumable vacuum arc melting furnace.Two heat treatments were carried out for the alloy,the holding time?24h,48h and 96h?and cooling rate?furnace cooling,air cooling and water cooling?,respectively.The microstructure and crystal structure of the high-entropy alloys were analyzed by OM,XRD and SEM-EDS,and the hardness,compression and tensile tests were performed.The main findings are as follows:1)The Al_0.4FeCrCoNi?FCC?alloy was heat treated:as the holding time increases,the rich-Al phase precipitates between the dendrites.The strength and plasticity of the alloy can change better with prolonging the holding time and increasing the size and number of the rich-Al phase.After changing the cooling rate,a white continuous strip is precipitated from the furnace cold alloy at the grain boundary,and yield strength?475MPa?and tensile strength?737MPa?of the alloy reach the largest,which are higher 267MPa and 258MPa comparing with the as-cast alloys.With the increase of cooling rate,the white continuous strip disappears,and the rich-Al phaseis precipitated on the matrix.The tensile strength and elongation of the alloy increase,and the elongation of the alloy after air cooling?64.51%?is the best.2)The Al_0.6FeCrCoNi?FCC+BCC?alloy was heat treated:as the holding time increases,the FCC phase volume fractions gradually increases.The hardness and strength decrease,but the plasticity increases.After 96 hours heat retention,the elongation reachs 27.6%,and the elongation increases by 2.2 times compared with the as-cast alloy.As the cooling rate increases,the BCC volume fraction,yield strength,tensile strength,and elongation increase.3)The Al_1.0FeCrCoNi?BCC?alloy was heat treated:as the holding time increases,the size of the particle phase precipitated at the grain boundary decreases,and the fracture strength and plasticity of the alloy increase.After 96 hours heat preservation,the compression rate reaches30.2%,and the plasticity increased by 9.5%compared with the as-cast alloy.With the increase of cooling rate,the size of precipitated particles around the grain boundary decreases,and the yield strength of furnace cold alloy is the highest?1775MPa?,which is higher 335Mpa compared with the as-cast alloy.As the cooling rate increases,the number of massive particles increases and the plasticity is improved.