Research On Its Mechanical And Corrosion Resistance Properties And Mechanism Of Hot-Rolled Cobalt-Based High-Entropy Alloy

High-entropy alloy is a new type of alloy proposed in recent years.It has the characteristics of corrosion resistance,high specific strength and specific rigdity,and excellent mechanical properties under high temperature service.It has a wide range of uses in aviation,automotive,medicine and other fields.The corrosion resistance of conventional equal-ratio high-entropy alloys is usually not as good as that of stainless steels such as SS304 and SS316L.At the same time,strength and plasticity also have mutual constraints,and they still fail to meet performance requirements when used in some areas,for example,turbine blades.By adjusting the atomic ratio of different elements in the high-entropy alloy,the entropy value of the alloy is reduced,and the phase stability is reduced.At the same time,through further thermal deformation means,a high-strength alloy with excellent properties such as high strength,high plasticity and corrosion resistance can be obtained.Therefore,this paper takes Co,M,Fe,Ni and Mn as the main elements.Firstly,according to the thermodynamic phase diagram,the proportion of Co,M in the alloy was designed,and1.5Mo was added to the x=0.39M alloy to prepare（Mx Co1-x）77.5（Fey Mnz Ni1-y-z）22.5（x=0.19,0.26,0.32,0.39）,（Mx Co1-x）77.5（Fey Mnz Ni1-y-z）22.5Mo1.5（x=0.39）,SS316L,SS304 seven as-cast alloys.Secondly,the influence of different M content on the microstructure of the alloys was studied by a variety of characterization methods.The results show that with the increase of M content,the number of lath grains gradually increases,and the grain size is not much different.The main oxidation states that can be determined in the passivation film composition are M³⁺,Co²⁺,Fe³⁺,Mn²⁺,Mo⁶⁺.The designed as-cast high-entropy alloys are all FCC+HCP dual-phase structures,there are a large number of small-angle grain boundaries around the large-angle grain boundaries of the original FCC phase,the two phases inside the alloy satisfy the SN orientation relationship:FCC{110}//HCP{11-20}at the same time.The alloy has high strength and hardness.There are a large number of annealing twins inside the alloy,which block the corrosion along the grain boundary and has good corrosion resistance.At the same time,the alloy has a large Schmidt factor,many slip systems,and good plasticity.The electrochemical test of the as-cast alloy shows that as the M content increases,the corrosion resistance gradually increases.Among（Mx Co1-x）77.5（Fey Mnz Ni1-y-z）22.5Mo1.5（x=0.39）alloys,the corrosion resistance is the best,and it also has the best hardness.Two alloys,（Mx Co1-x）77.5（Fey Mnz Ni1-y-z）22.5（x=0.39）,（Mx Co1-x）77.5（Fey Mnz Ni1-y-z）22.5Mo1.5（x=0.39）,which have the best comprehensive properties in the as-cast state,were selected for hot rolling experiments to explore the effect of hot deformation methods on the structure and properties of the alloy,and to compare them with the as-cast alloy compared.The results show that the hot rolled（Mx Co1-x）77.5（Fey Mnz Ni1-y-z）22.5（x=0.39）and（Mx Co1-x）77.5（Fey Mnz Ni1-y-z）22.5Mo1.5（x=0.39）alloys are mainly composed of a small amount of HCP,FCC and a large amount ofσphase.The corrosion resistance of hot rolled（Mx Co1-x）77.5（Fey Mnz Ni1-y-z）22.5Mo1.5（x=0.39）is slightly lower than that of as cast,but the mechanical properties have been greatly improved with a hardness of 532 HV,a fracture strain of 79%,and a yield strength of 1735 MPa.