火焰熔覆镍基/陶瓷涂层的耐磨性研究

研究了陶瓷WC和SiC加入量对氧乙炔火焰重熔方法制备的镍基合金涂层耐磨性的影响。试验结果表明,采用粘接手段作为预涂敷方法、氧乙炔火焰作为热源可得到致密、均匀的陶瓷复合涂层。Ni60基/WC复合层的耐磨性优于Ni21基/SiC复合层,且在一定的范围内这2种复合层均随着陶瓷含量的增多而耐磨性提高。当WC含量达到30 %时,Ni60基/WC复合层的耐磨性最好,继续增加WC含量耐磨性反而降低。当SiC含量达到4%时,Ni21基/SiC复合层的耐磨性最好,继续增加SiC含量耐磨性反而降低。

Effects of current density on microstructure and properties of plasma electrolytic oxidation ceramic coatings formed on 6063 aluminum alloy

Plasma electrolytic oxidation (PEO) ceramic coatings were fabricated in a silicate-based electrolyte with the addition of potassium fluorozirconate (K2ZrF6) on 6063 aluminum alloy, and the effects of current density on microstructure and properties of the PEO coatings were studied. It was found that pore density of the coatings decreased with increasing the current density. The tribological and hardness tests suggested that the ceramic coating produced under the current density of 15 A/dm2showed the best mechanical property, which matched well with the phase analysis. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves proved that the coating obtained under 15 A/dm2 displayed the best anti-corrosion property, which was directly connected with morphologies of coatings.

Tribological properties of nanostructured Al_2O_3-40%TiO_2 multiphase ceramic particles reinforced Ni-based alloy composite coatings

The Ni-based alloy composite coatings reinforced by nanostructured Al2O3-40%TiO2 multiphase ceramic particles were prepared on the surface of 7005 aluminum alloy by plasma spray technology. The microstructure and tribological properties of the composite coatings were researched. The results show that the composite coatings mainly consist of γ-Ni, α-Al2O3, γ-Al2O3 and rutile-TiO2 etc, and exhibit lower friction coefficients and wear losses than the Ni-based alloy coatings at different loads and speeds. The composite coating bears low contact stress at 3 N and its wear mechanism is micro-cutting wear. As loads increase to 6-12 N, the contact stress is higher than the elastic limit stress of worn surface, and the wear mechanisms change into multi-plastic deformation wear, micro-brittle fracture wear and abrasive wear. With the increase of speeds, the contact temperature of worn surface increases. The composite coating experiences multi-plastic deformation wear, fatigue wear and adhesive wear.

Interface characteristics of Al_2O_3－13%TiO_2 ceramic coatings prepared by laser cladding

Al2O3-13%TiO2 （mass fraction） coatings, prepared by laser cladding on nickel-based alloy, were heated using high frequency induction sources. The coating microstructure and the interface between bond coating and ceramic coating were characterized by SEM, XRD and EDS. The results show that two-layer substructure exists in the ceramic coating： one layer evolving from fully melted region where the sintered grains grow fully; another layer resembling the liquid-phase-sintered structure consisting of three-dimensional net where the melted Al2O3 particles are embedded in the TiO2-rich matrix. The mechanism of the two-layer substructure formation is also explained in terms of the melting and flattening behavior of the powders during laser cladding processing. The spinel compounds NiAl2O4 and acicular compounds Cr2O3 are discovered in the interface between bond coating and ceramic coating. It proves that the chemical reactions in the laser cladding process will significantly enhance the coating adhesion.

Antibacterial activities and corrosion behavior of novel PEO/nanostructured ZrO_2 coating on Mg alloy

Plasma electrolytic oxidation（PEO） was developed as a bond coat for air plasma sprayed（APS） nanostructure ZrO2 as top coat to enhance the corrosion resistance and antibacterial activity of Mg alloy. Corrosion behavior and antibacterial activities of coated and uncoated samples were assessed by electrochemical tests and agar diffusion method toward Escherichia coli（E. coli） bacterial pathogens, respectively. The lowest corrosion current density and the highest charge transfer resistance, phase angle and impedance modulus were observed for PEO/nano-ZrO2 coated sample compared with those of PEO coated and bare Mg alloys. Nano-ZrO2 top coat which has completely sealed PEO bond coat is able to considerably delay aggressive ions transportation towards Mg alloy surface and significantly enhances corrosion resistance of Mg alloy in simulated body fluid（SBF） solution. Moreover, higher antibacterial activity was also observed in PEO/nano-ZrO2 coating against bacterial strains than that of the PEO coated and bare Mg alloys. This observation was attributed to the presence of ZrO2 nanoparticles which decelerate E. coli growth as a result of E. coli membranes.

Zinc-doped hydroxyapatite-zeolite/polycaprolactone composites coating on magnesium substrate for enhancing in-vitro corrosion and antibacterial performance

This work is focused on developing zinc-doped hydroxyapatite-zeolite(Zn HA-Zeo)and polycaprolactone(PCL)composite coatings on magnesium(Mg)substrate to improve the corrosion resistance and antimicrobial properties.Dip-coating technique was used to coat Zn HA-Zeo/PCL on the Mg substrate at room temperature.The samples were subjected to field emission scanning electron microscopy(FESEM),X-ray diffraction(XRD),Fourier transform infrared(FTIR),energy dispersive X-ray spectroscopy(EDX)and antimicrobial potential.Results demonstrated that composite coatings consist of HA,scholzite,zeolite,and PCL phases.EDX spectra indicated the presence of calcium(Ca),silicon(Si),aluminum(Al),zinc(Zn),phosphorus(P)and oxygen(O).The composite surface appeared in spherical-like microstructure on coating with thickness ranging 226-260μm.Zinc-doped HA-Zeo composite coating had a high corrosion resistance and provided sufficient protection to the Mg surface against galvanic corrosion.Doped Zn HA-Zeo coating samples exhibited superior disc inhibition by confirming antimicrobial activity against the E.coli as compared to HA-Zeo sample.Altogether these results showed that the Zn HA-Zeo coatings not only improved the corrosion resistance,but also enhanced the antimicrobial property and hence they can be used as suitable candidates for implant applications.

Preparation of High-Entropy Alloy-Ceramic Coating Compos-ites on Steel Surfaces by Combined Process and Their Mechanical Properties

A combined process of molten salt electro-deoxidation and vacuum hot-pressing sintering was proposed to prepare AlCrFeNiTi_(x) high-entropy alloy(HEA)-TiN ceramic coating composites on low-carbon steel surfaces,where nitrides were introduced from BN isolater between graphite mold and HEA powders.The effect of Ti content on the microstructure,ultimate tensile strength,hardness,and wear resistance of the composites was investigated,and the bonding mechanism was elucidated.Results demonstrate that the composites have excellent hardness and wear resistance.The hardness of composites is significantly increased with the increase in Ti content.The extremely high wear resistance is attributed to the extremely high melting point and high thermal hardness of TiN,which can effectively prevent oxidation deformation of the worn surface.

Ti-based composite coatings with gradient TiC_x reinforcements on TC4 titanium alloy prepared by laser cladding

TiCx-NiTi2/Ti cermet composite coatings C1 and C2 with gradient TiCx reinforcements were prepared on TC4 titanium alloy by laser cladding method.The microstructure and phase compositions were analyzed by means of scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS)and X-ray diffraction(XRD)meter.The TiCx exhibited a dendritic microstructure,and homogeneously dispersed in the Ti-based matrix where NiTi2 was embedded.With increasing ingredient supercooling,temperature gradient and cooling temperature,the dendrites displayed a finer morphology with longer primary trunks and intensified side branches in the dilution zone.But the smoothed,coarse columnar ones became dominant in the upper clad layer due to the repeated energy input during multi-track cladding.The Vickers microhardness presented a linear change trend through the cross-sections,which well confirmed the gradient distribution of TiCx.With more TiCx,C1 presented higher hardness than C2.