Corrosion And Tribological Behavior Of（TiZrNbTa）₉₀Mo₁₀High-entropy Alloy

Due to the chemically multi-constituent and equi-atomic nature,high-entropy alloys(HEAs)offer rich opportunities for the researching of new alloys with excellent properties in more broad composition space.In the meantime,it is important to explore whether this kind of alloy has unique mechanical property and performance comparing to traditional alloys.Arc-melting(TiZrNbTa)90Mo10 high-entropy alloy consisting of refractory metallic elements achieves outstanding mechanical properties,as well as excellent biocompatibility in the implanting environment.Thus,it has the potential to be used as implant bio-medical metallic material.It is necessary to learn the corrosion and tribological behavior of this alloy in simulated body environment.From the perspective of electrochemistry and tribology,this work studied the corrosion behavior and the nature of passive film,analyzed basic tribological mechanism of HEA in dry sliding condition against several ceramics.The main conclusions are as follows:(i)In Ringer’s solution with the pH range of 1-9,the OCP of HEA shifts to more electro-positive direction as the pH decreases.When the pH decreases down to 1,results of film resistance(Rp)and corrosion current density(icorr)reveal that the protectiveness of the film decreases,even though,the corrosion current density maintains as the level of 10-2 μA·cm-2,indicating that the HEA achieves excellent corrosion resistance.Comparing to the pure constituent elements,the corrosion resistance of HEA is comparable to that of Ta and Ti,better than that of Nb,Zr and Mo in neutral environment.The existence of Ti,Ta and Nb restrained the formation of pits and trans-passive dissolution.The multi-oxides passive film on the surface of HEA shows better chemical stability facing the change of pH,comparing to that of traditional implant alloys including Ti6A14V,CoCrMo and 316L stainless steel.(ii)Due to selective oxidation of constituent elements in the electrolyte,the formation of multi-oxides passive film is the main feature of HEA.Using XPS to characterize the nature of passive film on the surface of HEA,it is found that in both conditions of as-polished and immersed,the film is composed of multi-oxides including TiO2,ZrO2,MoO2,Ta2O5 and Nb2O5,along with sub-oxides of Ti,Nb and Ta.The film thickness under these two conditions are 1-2 nm and 9 nm,respectively,indicating that the film-growth process mainly happens during immersion.Comparing the nominal bulk alloy composition,Ti and Zr are enriched in the film,while Nb and Ta are depleted,this segregation phenomena is accelerated by anodic polarization.It is determined thermodynamically by the Gibbs free energy and kinetically by the migration rate of metallic ions.(iii)In the condition of dry sliding against Si3N4,ZrO2 and Al2O3,the CoF of HEA is in the range of 0.7-0.9,which is higher than that of Ti6A14V and Co28Cr6Mo alloy.When sliding against ZrO2,the CoF of Ti6A14V and Co28Cr6Mo alloy are closely,in the range of 0.4-0.6.Comparing to Ti6A14V alloy,the specific wear rate of HEA reduce by 64%and 49%when sliding against Si3N4 and ZrO2,indicating the better wear resistance of HEA under these two conditions.However,the wear resistance of HEA is still worse than that of Co28Cr6Mo alloy.The profile of wear tracks on HEA are a little bit shallower but similar to that on the surface of Ti6A14V alloy.The wear tracks on Co28Cr6Mo alloy is much shallower and narrower comparing to that on the other two alloys.Abrasive and adhesive wear are the main wear mechanism of HEA sliding against ceramics.The better wear resistance of HE A originates from the impeding effect to plastic deformation during sliding,showing grooves intercepted by patches.During dry sliding against Al2O3 the wear resistance of HEA is worse than that of the other two alloys.As a result,Al2O3 is not propriate to construct tribological system with HEA.