Plasma Nitriding Under Low Temperature Of Textured Ti-6Al-4V And Its Wear Resistance And In Vitro Bioactivity

Ti-6Al-4V alloy has been regarded as an important candidate used extensively for medical implants in dental and orthopedic,due to its low density,high strength,non-toxicity,and excellent mechanical properties and biocompatibility in the physiological environment.However,as a result of the bioinert of titanium alloys,a mechanical bonding but not an osseous dystrophy will be formed after implantation.Meanwhile,the disadvantages such as low hardness,poor corrosion and wear resistance are also the important reasons of implant failure.Hence,the enhancement of hardness and improvement of corrosion and wear resistance is of great significance.In this thesis,laser texturing technology and plasma nitriding technology were used to fabricate such a nitrided surface that present special texture.The aim of this paper is to improve the in vitro bioactivity,enhance the surface hardness and corrosion and wear resistance by controlling the surface morphology together with phase constituents of the Ti-6Al-4V surface.Phase constituents,surface morphology,microstructure,element distribution and kinetics of plasma nitriding were investigated using XRD,SEM,and LSCM.The wettability,in vitro bioactivity,corrosion and wear resistance were evaluated.The main phases in the PN,LT and LT/PN samples include Ti,TiN and Ti2N.Textured morphologies were obtained after LT and LT/PN treatment.The surface roughness decreased after PN treatment,while that of LT and LT/PT samples increased compared with Ti-6Al-4V substrate.Nitriding temperature and time duration were main factors of influencing the thickness of nitride layer.The diffusion coefficient of nitrogen atoms increased with increasing of temperature.The activation energy of diffusion of nitrogen atoms was approximately 156.06 kJ/mol.The emprical formula among nitriding thickness d and temperature T and nitriding time t obtained on the basis of the present work can be expressed as d=1.99 × 10-3(?).The wettability and in vitro bioactivity of the Ti-6Al-4V surface were improved by the formation of textured morphology or nitrides layer.The textured nitrides layer obtained by LT/PN composite technology presents better hydrophilic property,wettability and excellent in vitro bioactivity.Compared to Ti-6Al-4V substrate,the surfaces processed by LT,PN,and LT/PN technologies presented lower intendancies of corrosion in SBF solution.However,the corrosion current density and corrosion rate of the surface processed by LT technology were much higher than that of Ti-6Al-4V substrate,the resistance of passivation film was similar to that of Ti-6Al-4V substrate.On the contrary,the corrosion current density and corrosion rate of the surfaces processed by PN and LT/PN were much lower than that of Ti-6Al-4V substrate.Meanwhile,the resistance of passivation film was significantly higher than that of Ti-6Al-4V.This indicated that the surface processed by LT exhibited a worse corrosion resistance to SBF solution,but the surface processed by PN,especially that processed by LT/PN presented excellent corrosion resistance to SBF solution.The results from friction and wear resistance indicated that the COF,volume wear rate and volume wear value decreased compared to that of Ti-6Al-4V substrate.The wear mechanism of Ti-6Al-4V substrate can be concluded as abrasive wear combined with adhesive wear and oxidative wear.The LT surface presented characteristics of abrasive wear and adhesive wear.For the PN and LT/PN samples,the wear mechanis can be characterized as abrasive wear.In summary,the textured nitrides layer processed by LT/PN technology presented better wettability,in vitro bioactivity,wear and corrosion resistance than the surfaces processed by LT or PN technology.Hence,the combination of laser texturing technology and plasma nitriding is an effective way to improve the combination properties of titanium alloy.It is also expected to be widely used in other materials and fields.