Calculation And Simulation Of CoCrNi_x(X=0.5?1)and CoCrNiTi_x(x=0.1?1)Medium Entropy Alloys

As a new kind of metallic materials,the medium entropy alloy(MEA)is generally formed by three or more main elements by the isoatomic ratio or near the atomic ratio,and it broke through the design limitation of the traditional alloys with excellent performances,such as high strength,high hardness,high corrosion resistance,etc.,which have caused widespread concerns.However,due to the large variety of MEAs,if people want to study it one by one,the time and energy to be spent would be very large.Conversely some of the properties of the alloys can be predicted by numerical simulation method to reduce human labor,and now more reports on the MEAs are about experimental aspects,and the number of reports on simulations is very small.The types of MEAs studied are limited up to now.The study of the MEAs through simulation and calculation can avoid some instability factors(e.g.temperature,oxygen,etc.)during the experimental process,and the alloys react in an ideal state.In this study,A hybrid first-principles/Monte Carlo(MC)simulation combinated with experiments to study the structure and elastic properties of CoCrNi_x(x=1?0.5)and CoCrNi Ti_x(x=0.1?1)MEAs.For the CoCrNi_x(x=1?0.5)MEAs,the alloys gradually changes from a single face-centered cubic(FCC)phase to a co-existing structure of FCC and hexagonal close-packed(HCP)when x=0.7?0.5 as the Ni content decreases.Through the calculation of the mixing energy,it is found that FCC is the most stable structure,but the difference of the mixing energy between HCP and FCC structures is very small(within 4%),and the difference gradually decreases as the Ni content decreases.Therefore,it may be that when the difference between the two is small enough,HCP structures may appear from the FCC matrix.The plasticity of the alloys decrease with the decrease of Ni contents.And it is consistent with the experimental results.By investigating the electronic structure and magnetic moment of the alloys,it is predicted that the antiferromagnetism of Cr can suppress the magnetic moments of the alloys.CoCrNi Ti_x(x=0.1?1)MEAs have a single FCC phase when the Ti content is 0.1,0.2,and 0.3.As the Ti content increases,Cr-rich phases are gradually precipitated,and the CoCrNi Ti alloy has a single-phase BCC structure.The plasticity of the alloys gradually decrease with the increase of Ti contents,which is consistent with the experimental results,and the plasticity of the CoCrNi Ti_0.1MEA is only about half that of the CoCrNi alloy.The simulation results indicate that when Ti is added to the CoCrNi alloy,the elastic constants of the alloys decrease,and as the Ti content increases,the elastic modulus decreases monotonically,which is in agreement with the experimental results.The study of electronic structure and magnetic properties predicts that the addition of Ti can reduce the magnetic moment of the developed MEAs.