The Nitrogen-doped TiO2 (N-TiO2) coatings were fabricated on 304 austenitic stainless steel (SS) substrates by oxidation of titanium nitride coatings,which were prepared by plasma surface alloying technique.Microstructural investigation,corrosion tests and antibacterial tests were conducted to study the properties of N-TiO2 coatings.Composition analysis shows that the SS substrates were shielded by the N-TiO2 coatings entirely.The N-TiO2 coatings are anatase in structure as characterized by X-ray diffraction.The corrosion properties of N-TiO2 coated SS samples in Hanks' solution were investigated by a series of tests.The electrochemical measurements indicate that the corrosion potential positively shifts from 0.275 V for untrated SS to 0.267 V for N-TiO2,while the corrosion current density decreases from 1.3×105 A/cm to 4.1×10 6 A/cm2.The corrosion resistance obtained by fitting the impedance spectra also reveals that the N-TiO2 coatings provide good protection for SS substrate against corrosion in Hanks' solution.Electrochemistry noise tests indicate that the N-TiO2 coatings effectively retard the local pitting and crevice corrosion of the SS substrate.The results of the antibacterial test reveal that N-TiO2 coatings give 304 austenitic SS an excellent antibacterial property.
Cr-Cu-N coatings with copper content from 0 at%to 6.8 at%were deposited on silicon and M2 steel by ion beam assisted magnetron sputtering.The microstructure and composition of the coatings were characterized using SEM,GDOES,XRD and XPS.The mechanical properties of the coatings were tested on a standard hardness tester.The tribological behavior of the coatings in dry wear condition was studied by means of ball-on-disc wear test.The experimental results show that addition of copper can restrict the columnar crystal growing to a certain degree.XRD and XPS analysis indicate that coatings are mainly composed of Cr and CrN phase.Cu is mainly existed in a free state in the coatings.Copper adding has no obvious effects on the hardness of the coatings.However,the coatings fracture toughness can be improved by doped copper.The coefficient of friction of the coatings against bearing steel is in the range of 0.25-0.6 changing with the copper content.The coating with 2.6 at%copper shows the lowest coefficient of friction about 0.25 and wear rate which is about one tenth of that of the coating with 6.8 at%copper.The higher coefficient of friction and wear rate of the coating with 6.8at%copper may be attributed to its lower bonding strength.
Tian LinhaiZhang YangYang YaojunZhu XiaodongTang Bin
N-doped TiO2(N-TiO2)coatings were obtained by oxidation of titanium nitride coatings,which were prepared by the plasma surface alloying technique on stainless steel(SS).The microstructure of N-TiO2 coatings was characterized by X-ray diffraction(XRD),glow discharge optical emission spectrometry(GDOES),X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy(SEM),respectively.Ball-on-disc sliding wear was applied to test and compare the tribological behaviors of the coatings and substrate.XRD patterns showed that anatase type TiO2 existed in the coatings after oxidation.GDOES showed that the resultant coatings had a layered structure,comprising of N-TiO2 layer at the top and a diffusion-type interface.Such a hybrid coatings system showed good adhesion with the substrate.According to XPS,residual N atoms partially occupied O atom sites in the TiO2 lattice.Uniform,continuous and compact coatings were observed by SEM images of coatings after oxidation.Under a load of 7.6 N,the coefficient of friction was in the range of 0.27-0.38 for the N-TiO2/Al2O3 systems and the wear rate of the coatings was only one-fourteenth of that for untreated 316L SS.N-TiO2 coatings displayed much better wear resistance and antifriction performance than SS substrate.
