HfO_(x)N_(1-x)涂层的制备、组织及性能研究

Preparation,Microstructure and Performance Evaluation of HfO_(x)N_(1-x)Coating

医用316L不锈钢以其良好的力学性能和耐腐蚀性能及较低的成本,广泛应用于医疗领域。但是,在生物环境中,医用316L不锈钢存在易腐蚀、析出有害离子以及生物相容性差等问题。目前,磁控溅射是主流的物理气相沉积(PVD)表面处理技术之一,其制备的涂层具有结合性能强和致密度高等优点。因此,采用射频磁控溅射技术在316L不锈钢表面成功制备HfO_(x)N_(1-x)涂层并探究涂层中氧(O)含量对HfO_(x)N_(1-x)涂层微观结构、力学性能和电化学性能的影响,并最终评价了涂层的血液相容性。微观结构测试结果表明,涂层中O含量对涂层晶体结构有显著影响,随着O含量的降低,涂层晶体结构由HfO_(2)相转变为Hf_(2)ON_(2)相并最终转变为非晶相。力学性能和电化学性能测试结果表明当涂层中O含量占比(f_(O))为0.14(HfON-3)时所制备涂层的力学性能及耐腐蚀性能最佳。血液相容性测试结果表明涂层的血液相容性与其表面粗糙度及涂层成分有关。以上研究结果表明HfO_(x)N_(1-x)涂层的性能较316L不锈钢更为优异,具备作为医用植入体表面涂层的应用潜力。

316L stainless steel(316L SS)is widely utilized in implant materials due to the corresponding mechanical properties similarity to the human skeleton,the good corrosion resistance,the good biocompatibility and lower costs.In contrast,the localized pitting corrosion poor resistance restricts the corresponding application.Furthermore,certain researchers discovered that tAISI 316L released Ni,Cr and Mo ions,which could cause local immunoreactions and inflammatory response,or stimulate the platelet-activation,which in turn might induce an intimal hyperplasia and an in-stent restenosis.Therefore,it was necessary to research the surface modification technology for 316L SS performance improvement.The transition-metals Ti,Zr,Ta,Nb and Hf were widely utilized in biocompatible materials due to the corresponding excellent properties.As a promising element among transition metals,hafnium(Hf)displayed higher mechanical properties,improved corrosion resistance and biocompatibility than other elements.From our previous works,HfC coating and HfCN coating which possessed good mechanical properties similarity to the human skeleton,good corrosion resistance in PBS powdered(as simulated body fluid)and good biocompatibility included a little of platelets adhered on the surface of 316L SS and low hemolysis ratio.At present,magnetron sputtering was one of the most important physical phase depositions(PVD)technologies,and the deposited layer demonstrated high adhesion force and density.HfO_(x)N_(1-x)coatings were deposited on 316L SS by magnetron sputtering with a base pressure of 8.0×10^(-5)Pa.The deposition of HfO_(x)N_(1-x)coatings was prepared with the pure Hf target at the sputtering pressure of 0.35 Pa under an Ar-O_(2)-N_(2)mixture atmosphere,where the negative bias voltage was-100 V.The applied radio frequency magnetron sputtering power for Hf target was 150 W.The distance between the substrate and the target was 70 mm.The pure Hf target was sputter cleaned for 10 min under an Ar-N_(2)mixture atmosphere and the target surface impurities to be removed firstly.HfO_(x)N_(1-x)coatings was prepared at various Ar∶N_(2)∶O_(2)(10∶5∶5,10∶7∶3,10∶9∶1 and 10∶9.5∶0.5)and the deposition duration was 150 min.The surface of 316L SS was successfully coated with HfO_(x)N_(1-x)by radio frequency magnetron sputtering,and the influence of oxygen(O)content on the microstructure,mechanical properties and electrochemical properties of the coating was investigated.In addition,the blood compatibility of the coating was evaluated.The phase composition and microstructure of the HfO_(x)N_(1-x)coatings were characterized by Xray photoelectron spectroscopy(XPS),X-ray diffraction(XRD)and transmission electron microscopy(TEM),respectively.The cross-sectional topography and thickness of HfO_(x)N_(1-x)coatings were observed by scanning electron microscopy(SEM).The thickness of HfO_(x)N_(1-x)coating was obtained from three samples;five tests were performed for each specimen and the errors were calculated as the standard deviation.The rootmean-square(S_(q))roughness of HfO_(x)N_(1-x)coating was studied by atomic force microscopy(AFM)with a triangular microfabricated cantilever with a length of 100 mm,a Si pyramidal tip,and a spring constant of 48 N·m^(-1).The surface roughness of HfO_(x)N_(1-x)coating was measured from three samples at six different positions for one sample and the average value was used and the errors were calculated as the standard deviation in this paper.Nanoindentation experiments were carried out using a Nanoindentor to obtain the nanohardness and Young's modulus.An echelon load function was used in all tests,with the loading,holding and unloading time of 5 s each.Nanoindentation tests were carried out for three samples;10 indentations were performed for each specimen and the errors were calculated as the standard deviation.The friction coefficient and adhesion strength of HfO_(x)N_(1-x)coatings were respectively measured by a Friction Teste and the Scratch test.During scratching acoustic emission signal intensity was continuously monitored to determine the critical load(L_(c))to evaluate the adhesive strength,and the results were then verified by SEM.Three specimens were used in the adhesion test and average value and standard deviation was then calculated.The corrosion resistance of HfO_(x)N_(1-x)coatings was tested by electrochemical workstation.Potentiodynamic polarization experiments were conducted in phosphate buffered saline(PBS)which was mainly used to evaluate the drug release profile of the drugeluting stents.The hemocompatibility of HfO_(x)N_(1-x)coated 316L SS was identified by measurement of hemolysis ratio and the platelet adhesion test.The results of the test on microstructure showed that the O content in the coating had a significant influence on its crystal structure.As O content decreased,the crystal structure of the coating changed from HfO_(2)phase to Hf_(2)ON_(2)phase and finally to amorphous phase.The results of the tests on the mechanical and electrochemical properties showed that the mechanical properties and corrosion resistance of the coating were the best when O content was 0.14(HfON-3 coating).The results of the tests on blood compatibility showed that the blood compatibility of the coating was related to its roughness and composition.In conclusion,the results indicated that HfO_(x)N_(1-x)coating had better performance than 316L SS and had a potential application value for medical implants as protective coating.