Corrosion And Biological Properties Of Al_xFeCoCrCuTi_0.5 High Entropy Alloys

The corrosion and biological properties of AlxFeCoCrCuTi0.5(x=0.25,0.5,0.75,1and 1.5)high entropy alloys(HEAs)with different Al content were studied in this thesis.The effect of the addition of Al on the microstructure of the alloys has been studied.The effects of Al content on mechanical properties,corrosion and wear behaviors of the HEAs were also studied.Finally,the biocompatibility of the HEAs was explored in order to extend the potential applications of HEAs in biomedical fields.The microstructure observations of AlxFeCoCrCuTi0.5 HEAs with different Al content indicated that,as Al content increases,the structure transfers from FCC and BCC to the single BCC.The shape of crystalline phase changes fromcellular to dendrite gradually.With increasing Al content,the hardness and yield strength of the HEAs increased whereas the plasticity decreased gradually.The corrosion resistance of AlxFeCoCrCuTi0.5 HEAs in 0.9 % NaCl solution firstly increased and then decreased with increasing Al content,yielding the best corrosion resistance at x=0.75,better than those of pure Ti and Ti6Al4 V.The immersion corrosion tests of the alloys showed that when after corrosion tests the sample surface of the alloy with less Al content exhibits some small pitting holes and corrosion products in the interdendrite.With the increase in Al content,the interdendritic Cu-rich FCC phases gradually decrease,whereas the BCC phases gradually increase.The higher Cr content in the dendrite region causes the formation of a dense Cr2O3 passivation film on the surface to prevent further corrosion of the HEAs.However,with further increasing Al content,the passivation film on the sample surface containing numerous aluminum oxides becomes thicker and more dispersed,deteriorating the protective ability of the passivation film,and thus reducing the corrosion resistance of the alloys.The analysis of ion precipitation after corrosion tests of the alloys showed that as the Al content increases,the precipitation of Al ion decreased firstly and then increased,yielding the fewest precipitation of each ion at x=0.75.This further suggests that the alloy with x=0.75 has best corrosion resistance.The wear behaviors of HEAs with different Al contents were studied.The wear resistance of the alloys increased firstly and then decreased with increasing Al content.The alloy with x=0.75 has the best wear resistance,better than pure Ti and Ti6Al4 V.The blood compatibility of AlxFeCoCrCuTi0.5 HEAs with different Al contents showed that the alloy with x=0.75 has excellent anticoagulant property.Compared with pure Ti and Ti6Al4 V,all the studied HEAs have considerable anticoagulant properties of both endogenous and extrinsic coagulation pathways.The hemolytic rate of less than5% for all the HEAs accorded with the requirement of clinical medicine.Plateletadhesion test showed that it has excellent anti-thrombotic ability;The cytotoxicity tests showed,that after culture for a period of time in the high entropy alloy extract of x=0.75,the morphology of L929 cells remain fusiform.Its cytotoxicity was evaluated to be Grade I,demonstrating its excellent cell compatibility.