Effect Of Heat Treatment And Copper On The Biodegradable Behaviour And Mechanical Properties Of Fe-Mn-C Alloy

Fe-based alloys are considered as potential new biodegradable implant materials due to their biodegradable properties,excellent mechanical properties and biocompatibility.The existing results showed that the Fe-30Mn-1C alloy had a pure austenite structure,which reduced the displacement and heating problems in NMR testing.In addition,Fe-30Mn-lC alloy had excellent mechanical properties,and the degradation rate of pure iron increased obviously with the addition of Mn and C elements.However,its degradation rate was still low,which did not meet people's ideal need for degradation cycle of degradable materials.And for a specific environment,such as the urethra,alloy implantation is easy to cause inflammation,so it is necessary to give the material antibacterial properties.To solve the above problems,this paper prepared Fe-30Mn-1C-x(x=0,0.5,1.0,1.5)Cu alloy system,through the addition of Cu element,giving certain antibacterial properties of the alloy.In addition,through different heat treatment process,the microstructure of the alloy was changed,and then the degradation rate of the alloy was changed.Therefore,by changing the heat treatment process and Cu content,the effects on the microstructure,degradation properties,antibacterial properties and mechanical properties of the alloy were studied.The main conclusions are as follows:The Cu content increased from 0.5 wt.%to 1.5 wt.%,and the grain size increased from 40?m to about 70?m.After aging treatment,the grain boundaries of the alloy became more obvious,and the second phase appeared in both grain boundaries and grain interior.The second phase inside the grain was square and the second phase at the grain boundary was long strip.The carbon content of the second phase at the grain boundary was obviously higher than that of the second phase inside the grain.The structure of the second phase was the same as that of the matrix,which was austenite.The microstructure of both solid solution and aged alloys was pure austenite.After the alloy was stretched,martensite transformation occurred.The electrochemical test results showed that with the increase of Cu content,the self-corrosion potential of the alloy decreased from about-0.58 V to about-0.63 V,indicating that the introduction of Cu increased the self-corrosion tendency of the alloy.In addition,the self-corrosion current density of the aged alloy was significantly higher than that of the solid solution alloy.The analysis showed that the degradation rate of the aging alloy was increased because of the galvanic corrosion between the second phase and the matrix.The degradation rate of 1.5Cu-A24h alloy was the highest,reaching 0.19 mm/y.The results of immersion experiment showed that the degradation rate of the alloy had the same tendency with the results of electrochemical test.However,with the prolonging of immersion time,the degradation rate of the alloy decreased obviously because the surface of the alloy was covered by corrosion products.The results of antimicrobial experiments showed that the solid solution alloy had no antimicrobial properties,while the aged alloy had antimicrobial properties.With the increasing of Cu content and the prolonging of aging time,the antibacterial properties of the alloy also increased.The mechanical properties of the alloy showed that the tensile strength of the alloy decreased obviously with the increase of Cu content,while the plasticity did not change.However,the tensile strength and elongation of the aged alloy decreased obviously due to the appearance of the second intergranular phase.Moreover,the longer the aging time and the higher the Cu content caused the greater decrease of tensile strength and elongation of the alloy.However,the overall mechanical properties still met the actual needs,so the loss of mechanical properties was acceptable.The work hardening rate curve of the alloy showed that the work hardening rate of the whole alloy was higher than the true stress of the alloy.In addition,with the increase of Cu content,the work hardening rate of the alloy decreased obviously.The critical strain of dynamic strain aging of the alloy was measured.It is found that the critical strain of dynamic strain aging of the alloy increased with the increase of Cu content,which indicated that Cu element had an inhibiting effect on the dynamic strain aging of the alloy.