Study On The Preparation,Microstructure And Properties Of Hf Matrix Coating On The 316L Stainless Steel

316L stainless steel（SS）has been used widely in the field of medicine,due to its excellent mechanical performance,corrosion resistance and low cost.However,it is characterized by pitting corrosion and poor biocompatibility which limit potential applications.Currently,magnetron sputtering is one of the most important physical vapor deposition（PVD）technologies,the use of which deposits layers which demonstrate high adhesion force and density.Therefore,magnetron sputtering was used to deposit bioinorganic inert coatings in this study.Three classes of coatings:Hf_xC_1-x,HfC_xN_1-x and Zr（Hf）C_xN_1-x,were deposited on the surface of 316L SS by RF magnetron sputtering.The chemical characteristics,surface profile and microstructure of the coatings were studied using XPS,SEM,AFM,XRD and TEM.The mechanical properties of the coatings were analyzed using nanoindentation techniques,a scratch test and friction coefficient test.Electrochemical performance was investigated using cyclic voltammetry and electrochemical impedance.The blood compatibility of Hf_xC_1-x and HfC_xN_1-x coatings was studied by platelet adhesion experiment and hemolysis test.A BP neural network was utilized to forecast the mechanical properties of the coatings,and their resistance to corrosion.The technical parameters of the Hf_xC_1-x coatings were optimized by adjusting bias voltage and analysis of the cross-section of the coatings demonstrated that a compact structure with homogeneous thickness had been achieved.XRD and TEM were used to demonstrate that all Hf_xC_1-x coatings had an FCC crystallographic structure.A reduction in the rate of deposition enhanced（111）face orientation,with a decrease in roughness as bias voltage was increased.At a bias voltage of-200V,crystallites of approximately 12nm to 14nm were observed,as spheroidal crystals embedded in the Hf_xC_1-x coatings.XPS results indicated that the chemical bonds at the surface were mainly HfC with a small number of HfO₂.The hardness,modulus,adhesion and wear-resistance of HfC coatings were significantly enhanced by utilizing an increased bias voltage.Coated 316L SS had corrosion resistance and blood compatibility that was improved compared to bare 316L SS substrates.Increased bias voltage improved surface corrosion resistance.This was due to enhanced adhesion of the coating to the substrate and decreased surface roughness when the bias voltage was increased.As surface roughness and the ratioγ_s^d/γ_s^pdecreased,blood compatibility improved.The doped element N had a clear influence on the microstructure of the Hf_xC_1-x coating,the technical parameters of HfC_xN_1-x coating optimizesed by adjusting the substrate temperature（T_s）.The SEM results showed that the coatings had a compact structure,and the substrate temperature had little influence on deposition rate.When T_s was 400℃,the amorphous coating transformed into Hf₂CN spheroidal crystals,whose diameters was 8nm.At higher T_s,the deposited atoms had higher diffusion energy.As a result,roughness decreased and adhesion was enhanced.The stronger adhesion strength resulted in better coating corrosion resistance.The chemical bonds of the coating were mainly HfC and HfN,with a small number of HfO₂.The coating deposited at a T_s of 400℃had the highest values of hardness and modulus compared with that of other Ts,and the friction coefficient significantly reduced when the T_s rose above 300℃.With increasing T_s,the corrosion resistance improved.This is due to a smoother surface,stronger adhesion force and better compactness under higher T_s.As surface roughness and the ratio ofγ_s^d/γ_s^p decreased,blood compatibility improved.Quaternion Zr（Hf）C_xN_1-x coatings were successfully deposited on the substrate of 316L SS by magnetron sputtering.XRD results indicate that ZrC_xN_1-x coatings transformed into an FCC structure Zr₂CN phase from amorphous conditions of T_s at 400℃.The doped Hf element has little impact on the crystal structure of the Zr（Hf）C_xN_1-x coatings.The quaternion coating consisted of spheroidal crystals whose average diameter was 5nm with a content of 7.33%Hf.With increased Hf content,the hardness,modulus and corrosion resistance were enhanced.However,the content of Hf element has little impact on the wear resistance,adhesion strength and surface roughness of the coating.Based on the favorable nonlinear forecasting capability of a three tier architecture BP neural network,the forecast results indicate that the exact mechanisms of process parameter versus mechanical properties and corrosion resistance could be built,and the error between forecast value and measurement could meet the design requirements.