The Microstructure And Performance Of High-Entropy Alloys Al_x CoCrFeNiTi_0.5

Conventionally, alloys have been designed following the principle that there is only one or two major element as their main component, and then strengthen the properties by adding minor elements. Against this background, a new alloy design principle is developed by Yeh with the name of high entropy alloys(HEAs).In this concept, alloys usually have at least five elements whose concentration is higher than5at.%and less than35at.%. Compared with traditional alloys, HEAs have many different characteristic (high entropy effects, sluggish effect, lattice distortion effect, and cocktail effect) coming from the special way of formation, so they have many excellent performance such as high strength, excellent corrosion, good temperature stability and high wear resistance and so on. At the same time, the HEAs make it possible to find novel materials unlimited, as a result, it is worth more future work on theoretical study and industrial application.Previous studies have discovered that alloy system composed of CoCrFeNi usually show good performance in different ways. So in this paper this system also be used, then add Ti and Al two elements which have good corrosion property according to mole ratio. The change of structure and property has been researched as a function of the content of Al element. The alloys are prepared by well-developed arc melting method. Their microstructure, mechanical properties and corrosion properties is studied in this study to assess the practical value of this kind of high-entropy alloys.Typical cast dendrite and interdendrite structures are observed in the alloy system. However, the morphology of dendrite and interdendrite is diverse in AlxCoCrFeNiTio.5alloy system which suggests different Al contents could have an effect on the growth behavior of dendrites. The chemical composition of dendrite and interdendrite in atom percentage are nonuniform. The crystal structure of the AloCoCrFeNiTi0.5alloy is FCC phase. BCC structure appears along with the adding of Al. While x=1FCC structure has gone, BCC becomes the only phase composition. The alloys have high microhardness. And increasing Al contents making the hardness higher suggests BCC phase has a higher hardness than FCC phase, result from the crystal structure transforming from FCC structure to BCC structure so as the increasing Al contents. The value reaches maximum Hv617, when x=1. In this study,different compression strain rates has been used as5×10-3/s and1×10-3/s. The results show that AlCoCrFeNiTi0.5alloy has the highest fracture strength2429MPa,2249MPa at different strain rate, respectively. In contrast, AloCoCrFeNiTi0.5alloy has the best plasticity whose deformation rate can reach21%and22%. Summing up the above, the alloys have a good performance in terms of mechanical properties.Because of the existing of Al, Ni, Cr elements, The AlxCoCrFeNiTi0.5high-entropy alloys are easy to generate passive film which is stable to protect the alloys from continues corrosion in0.5M H2SO4solution. SEM images of AlxCoCrFeNiTi0.5show that, general corrosion take place during the corrosion processes of alloys (x=0.2,0.5,1.0). Obviously, along with the adding of Al, the Econ-increase while the icorr decrease. The AlCoCrFeNiTio.5alloy has the best corrosion property of that Ecorr=·0.10V, icorr=5.69×10-7A/cm2. But because of a mass of Cl-, alloys couldn’t form a stable passivation film in1M NaCl solution. At last equivalent circuits of the corrosion processes have also been worked out through the method of EIS in this study to grasp the reaction mechanism.