Research On Microstructure And Properties Of Near-eutectic AlCoCrFeNi_2.2 High Entropy Alloy

Multi-principal element high-entropy alloy was firstly proposed by Ye Junwei and other scholars in 2004,and then has quickly become the research hotsp ot.Different from the traditional metallurgy theory,high-entropy alloys generally have 5 to 13 main elements,and the atomic ratio of each principal element is between 5%and 35%.According to different actual industrial applications,high-entropy alloys with different compositions can be designed to meet production requirements,so that they can exhibit excellent mechanical properties,corrosion resistance,thermal stability and radiation resistance.In order to improve both the strength-plasticity matching and casting performance of high-entropy alloys,Lu Yiping and some other scholars proposed the design concept of eutectic high-entropy alloys in 2014.Compared with ordinary high-entropy alloys,eutectic high-entropy alloys achieve a good balance between strength and plasticity,they also have good casting fluidity.Since then,many research teams at home and abroad have conducted a lot of research in the field of eutectic high-entropy alloys.Earlier studies found that AlCoCrFeNi_2.1 alloy exhibited a complete eutectic structure and excellent mechanical properties;AlCoCrFeNi_2.2(Ni_2.2)alloy exhibited a hypoeutectic structure,containing a certain amount of primary phases,and its mechanical properties were better.Therefore,this article chooses Ni_2.2 hypoeutectic alloy as the research object,and further optimizes mechanical properties through processing techniques such as solid solution homogenization treatment,cold rolling and annealing treatment on Ni _2.2 alloy.The study of this paper found:（1）AlCoCrFeNi_2.2 hypereutectic high-entropy alloy was composed of primary L1₂phase and eutectic L1₂/B2 phase.The as-cast alloy exhibited excellent mechanical properties and achieved a good balance between strength and plasticity.（2）The Ni_2.2 EHEA had many precipitation phases in its primary phases after homogenization and solid-solution treatment,while the ordered L1₂ phases in the eutectic structure transformed into disordered FCC phases.After the homogenization treatment,the strength and hardness of the alloy decreased and the plasticity was significantly improved.（3）After solid solution homogenization treatment at 950°C and cold rolled,there was no new phase found in AlCoCrFeNi_2.2 EHEA.The mechanical behavior of the alloy showed typical work hardening characteristics.（4）Compared with the unannealed EHEA,the AlCoCrFeNi_2.2 EHEAs which processed solid solution treatment at 950°C+75%cold-rolled+reduction-annealing at different temperatures had reduced strength and improved plasticity.The alloy annealed at 750°C showed the best tensile properties,while the strength and plasticity of the alloy decreased after annealed at a higher temperature.（5）Compared with the as-cast Ni_2.2 EHEA,the EHEA after solution treatment showed better corrosion resistance to salt water（3.5wt%/0.9wt%Na Cl solution）,and the alloys treated with homogenization and solution treatment at 1100℃showed the best corrosion resistance.The preferential dissolution of B2 phases in AlCoCrFeNi _2.2 EHEA was the main corrosion initiation mechanism and the main corrosion method was local pitting.