Preparation And Performance Evaluation Of The ZrC Coating On 316L Stainless Steel

ZrC coatings were fabricated on 316L stainless steel (316L SS) by radio-frequency (RF)magnetron sputtering at different substrate temperatures (Ts). The phase constitution,microstructures,mechanical properties, corrosion resistance and hemocompatibility of ZrC coatings were systematically investigated by X-ray diffraction (XRD), transmission electron microscope (TEN),scanning electron microscope (SEM),atomic force microscopy (AFM),nanoindentation techniques, scratch test, electrochemical measurments and platelet adhension test. The influence of substrate temperature (Ts) on the properties of ZrC coatings was inspected specially.The XRD results showed that 316L stainless steel and the ZrC coatings (Ts =25℃,200℃ and 400℃) are FCC lattice structure. When substrate temperature (Ts) increases, the diffraction peak intensity of ZrC coatings increases and half peak width of diffraction peak turns to be narrower. It indicated that ZrC grains grow bigger with the increase of substrate temperature (Ts) which gives the Zr and C atoms more energy to diffuse fully. The ZrC phase with (111) preferred orientation was formed when Ts was 400 ℃. The TEM results showed that the ZrC coatings exhibited in the form of particulates with the crystallite sizes of about 5 nm. Moreover, (111) lattice fringes with d =0.273 run and (2 0 0) lattice fringes with d=0.238 nm were most frequently observed. The same region of fast Fourier transform (FFT)pattern was indexed into diffraction spots, indicating the single crystalline nature of the nanoparticles. Selected area electron diffraction (SAED) image reveals the polycrystalline nature of the ZrC coating, which is also confirmed by X-ray diffraction (XRD). According to the camera constant value and diffraction ring radius value, ZrC coating is FCC structure. The SEM results showed that a thin ZrC coating of about 1.0 μm is clearly observed (outermost layer) over the 316L SS substrate. The coating reveals an extremely smooth, dense,homogeneous and featureless morphology. The AFM results showed that the total varying trend of the root-mean-square (Sq) values of ZrC coatings was gradually decreasing, and then increased slightly with the increasing of substrate temperature, which is due to the improving of diffusion rate with the increasing of Ts which can decrease the surface roughness of ZrC coatings. However, when Ts increased to 400℃, the diffusion of Zr and C atoms became sufficient,which promoted the rapid growth of ZrC nanocrystalline. The growth and agglomeration of nanocrystals increased surface roughness of the ZrC coating slightly.The results of nano-indentation tests indicated that the degree of plastic deformation and residual indentation depth were lower than that of 316L stainless steel, which decreased with the increasing of Ts for the ZrC coatings. The above results indicated that the higher Ts gived Zr and C atoms more energy which contributed to the increasing of diffusion rate and form a more dense and homogeneous ZrC coating.The scratch test results demonstrated that ZrC coatings deposited above 200 ℃ exhibited good adhesion performance. It is obvious that the higher Ts bright more energy to Zr and C atoms, which contributed to improve the the critical load (Lc) between 316L SS and ZrC coatings.The potentiodynamic polarization test results showed that the ZrC coatings deposited at Ts of 200 ℃ and 400 ℃ possessed better corrosion resistance than those deposited at Ts of 25℃,which was due to high adhension and low the root-mean-square (Sq) values which favor the isolation of coating and PBS in order to improve the corrosion resistance.The platelet adhesion test results showed that the blood compatibility of ZrC coating is better than that of 316L stainless steel. When Ts increased, the number and activated pattern of the platelets adherent to the ZrC coatings were in less. It is obvious that the hemocompatibility of ZrC coating was affected by Ts. Firstly,the root-mean-square (Sq)values decreased with the increasing of Ts. Secondly, wetting experimental results also showed that surface tension and polar dispersion ratio of the ZrC coating all decreases with the increasing of Ts. Both will lead to better blood compatibility of ZrC coatings with the increasing of Ts.