Research On Microstructure And Properties Of AlCrFeNi-M High-Entropy Alloys And Its Composites

As a new focus on materials research areas and a novel alloy degin concept, high-entropy alloys has attracted great attention of many scientific and technical workers since it was proposed. High-entropy alloys overcome the stereotyped thinking pattern of the traditional concept of designing alloys, not a single principal element, using multi-principal elements to design alloys component. High-entropy alloys can obtain good thermal stability, high hardness, excellent wear resistance, high strength, peculiar electrical and magnetic properties, and many other outstanding properties.In this study, AlCrFeNi-M high-entropy alloys were prepared by vacuum non-comsumable arc-melting and copper-mold vacuum suction casting. The microstructure and porterties of AlCrFeNi-M high-entropy alloys and its composites were investigated systematically by OM, SEM, EDS, XRD, universal compression testing machine and so on.In this paper, the anaylsis reveals that the phases of all the AlCrFeNi-M high-entropy alloys are composed by simple BCC or FCC or both. It is that we have found Co element can not only change the microstructure of Al_0.5CrFeNiCo high-entropy alloys, but also soften and plasticize them apparently, and both Al_0.5CrFeNiCo_0.5 and Al_0.5CrFeNiCo_0.75 were compressed continuously into wafery pie shape. Al_0.75CrFeNiCo_0.25 high-entropy alloy which has the best property of all the button ingots in this research was prepared with increasing molar content of Al, its room temperature compressive yield strength, compressive strength, compression ratio and Vickers hardness are 1464MPa, 2959MPa, 37.2% and HV503, respectively.Al_0.25CrFeNiCoTi_0.75 and Al_0.75CrFeNiCoTi_0.5 high-entropy alloys both have a flower-like structure and have high hardness, the Vickers hardness of the former high-entropy alloy is up to 928. The plasticity of Al_0.75CrFeNiCoTi_0.25 and Al_0.5CrFeNiCoTi_0.25 are pretty good, compression ratios are 33.2% and 42.7% respectively.What deserves to be mentioned the most is irregular polygon nano-clusters are formed in Al_0.75CrFeNiCoTi_0.25 high-entropy alloy.The four alloys of Al_xCrFeNi(x=0.5, 0.8, 1) and Al_0.5CrFeNiCoTi_0.5 have excellent properties were prepared by designing component.All of the four alloys have special microstructure, Al_0.5CrFeNi precipitates spherical nano-scaled phases of about 50nm, the other three primarily precipitate non-spherical nano-phases. In AlCrFeNi and Al_0.5CrFeNiCoTi_0.5 alloys can find special flower-like structure. For the present, the compressive strength of AlCrFeNi high-entropy alloy is the best of all as-cast high-entropy alloys, up to 3618MPa, and its compression ratio is still up to 41.8%. Resecrching on Al_0.5CrFeNiCoTi_0.5 and AlCrFeNi alloys shows that the phases structure, microstructure and properties of them all will be improved significantly, in particular, compressive yield strength and compressive strength will be improved dramatically.In the three types composites of Al_0.75CrFeNiCo_0.25-TiC, the size of TiC coarsen continuously and distribute in the dendrites gradually with the TiC increasing. Adding TiC, the variation of sunflower-like tissue's volume fraction is U-shaped. When the volume fraction of TiC reaches 10%, the combination property of this composite is the best, its compression is 3212MPa, and its compression ratio increased by 11.83% than the matrix crossly.