Wear Resistance,corrosion Resistance,and Biological Behavior Of Ta-based Modification Layer On Ti6Al4V Alloy Surface

Titanium alloys have been widely used in human hard tissue replacement and repair due to their low density,high specific strength,non-magnetism,elastic modulus close to human bone,and good biocompatibility.However,as the most widely used biomedical titanium alloy,Ti6A14V(TC4)still has shortcomings such as poor wear resistance,corrosion resistance,and biological activity.Studies have shown that the implant surface plays a crucial role in its interaction with the surrounding tissue,so many biomedical materials researchers have been working on targeted surface modification of implant materials to optimize the comprehensive performance of the implant.Metal tantalum(Ta)has better biocompatibility and corrosion resistance than Ti and is often used in the manufacture of surgical sutures and skull repair materials.Ta’s excellent corrosion resistance and biological activity are mainly caused by the spontaneously formed passive film(Ta2O5)on its surface.However,Ta’s high density and high price severely restrict its application.Depositing Ta-based modified layers on titanium alloys via surface modification technology can combine the advantages of both materials,so it is also one of the current research hotspots in the field of medical materials.Meanwhile,the biomimetic micro-and nano-structures on implant surfaces will also significantly impact the biological response of surrounding tissues.For example,TiO2 nanotube arrays(NTAs)fabricated on the surface of titanium alloys by anodization are believed to improve the biological properties of various human cells significantly.Based on plasma surface alloying technology(PSAT)and combined with the anodization process,three types of Ta-based modified layers were prepared on the surface of TC4 alloy:Ta coating,Ta/TC4 alloy layer,and Ta2O5/TiO2 NTAs.Through gradual optimization,the corrosion resistance,anti-friction and wear resistance,biocompatibility,and osteogenesis ability of TC4 alloy were improved in a targeted manner.The main contents and results of this study are as follows:(1)Ta coating was prepared on TC4 surface by PSAT process,the effects of alloying temperature(750 ℃-850 ℃)and time(10 min-120 min)on coating’s interfacial strength were explored,and a set of samples with the best interfacial strength were subjected to in-depth characterization and performance testing.The results show that Ta coating is composed of Ta deposition layer and Ta/TC4 diffusion layer(alloy layer).The effect of PSAT temperature on the interfacial strength of Ta coating is much more significant than that of time.Ta coating prepared at 800℃ has the best interfacial strength,and it increases with the prolongation of alloying time.The decrease of the Ta/TC4 alloy layer thickness in Ta coating with alloying time is the main reason for the deterioration of hardness and wear resistance of Ta coating.The corrosion resistance of Ta coating is improved compared with that of TC4 substrate.In vitro,cellular assays showed that the Ta coating had a better ability to promote osteoblast proliferation,adhesion,spreading,alkaline phosphatase(ALP)secretion,and extracellular matrix(ECM)mineralization than TC4 substrate.(2)Based on(1),the PSAT temperature was increased to 900℃ and rapidly cooled after the alloying process was completed,the Ta deposition layer was successfully removed from the surface of the Ta coating,and Ta/TC4 alloy layer with a scalelike micro/nano-textured surface was exposed.The results show that the thickness and surface roughness of the Ta/TC4 alloy layer gradually increase with the extension of alloying time(30 min-120 min).Ta/TC4 alloy layer can significantly improve the microhardness,wear resistance,and corrosion resistance of the TC4 alloy.With the increase of surface roughness,osteoblasts’ viability and spreading ability remained stable basically,and the initial adhesion was significantly enhanced.In addition,the scalelike structure also improved the osteogenic ability of osteoblasts to a certain extent possible through the synergistic effect of micro-and nano-topography.(3)Based on(2),Ta2O5/TiO2 NTAs were anodically growing on the Ta/TC4 alloy layer,and the effects of anodization voltage(1 V-90 V),time(5 s-90 min),water content(2 vol.%20 vol.%),and NH4F concentration(0 M-0.3 M)on the growth of Ta2O5/TiO2 NTAs were systematically investigated.The results show that high anodization voltage(>30 V),NH4F concentration(>0.15 M),and long oxidation time(>60 min)contribute to the transformation of nanopore arrays to NTAs.Excessive water content(>10 vol.%)accelerates the chemical dissolution of NTAs and leads to poor regularity and reduced thickness.The scalelike microstructure can only be retained in the initial stage of anodization and will be gradually chemically dissolved as the reaction continues and replaced by lamellar NTAs,which depend on the microstructure of the Ta/TC4 alloy layer.(4)Based on(3),Ta2O5/TiO2 NTAs with regular morphology and suitable size were selected as the research obj ect,TiO2 NTAs prepared under the same condition,TC4,and Ta/TC4 alloy layer were used as the control.These four groups were chosen for characterization and performance evaluation.It was found that Ta2O5/TiO2 NTAs were composed of amorphous Ta2O5 and TiO2,having higher surface roughness,hydrophilicity,and interfacial strength but slightly worse corrosion resistance than the other groups.Ta2O5/TiO2 NTAs can significantly promote the initial adhesion and spreading of endothelial cells and osteoblasts,and promote the proliferation of endothelial cells but have a slight inhibitory effect on osteoblasts.The vascular endothelial growth factor secretion level of endothelial cells and osteogenic capacity of osteoblasts on Ta2O5/TiO2 NTAs surface had also been significantly improved,mainly due to the combined effect of the lamellar distribution of NTAs and doping bioactive Ta2O5.In conclusion,using PSAT combined with the anodizing process has gradually optimized the morphology and composition of the Ta-based modified layer on the surface of the medical TC4 alloy.The samples in each group had good wear resistance on the whole,the interfacial strength first increased and then weakened,the corrosion resistance gradually weakened,and the biocompatibility and osteogenesis ability were significantly improved.This study provides a theoretical reference for the research on Ta-based modified layers and reveals the great potential of Ta-based modified layers in the field of medical metals.