查看更多>>摘要：In the present work, a hydrophobic Zirconium nitride (ZrN) nanoflowers [ZrNNF] surface was successfully developed on mild steel (MS) substrate via an industrial PVD technique. The developed hierarchical surface was characterized using FE-SEM (field emission scanning electron microscopy), EDS (energy-dispersive X-ray spectroscopy), XPS (X-ray photoelectron spectroscopy) and AFM (atomic force microscopy). The electrochemical characteristics of ZrNNF coating were investigated using potentiodynamic and EIS measurements in saline media [3.5 wt% NaCl solution]. The influence of hierarchical surface on corrosion parameters has also been examined. The experimental results reveal that the corrosion potential (Ecorr) of the coated substrate was shifted towards a more noble value (~- 55 mV) with a lower current density (Icorr) (0.0027 mu A/cm2) as compared to the bare (10.9 mu A/cm2) specimen. Similarly, EIS parameters also revealed a similar behavior of coated sample, resultant low corrosion rate than the bare sample. The anti-corrosion mechanism of the ZrNNF coating is also presented in detailed. Based on the presents' results, the ZrNNF@MS coating shows excellent wetting and corrosion resistant properties under the saline environment.
查看更多>>摘要：Superior surface characteristics, tribological performance and adhesion strength are critical for DLC coated surface in hip implant. Incorporating laser surface texturing and heat treatment before DLC deposition can improve surface properties by inducing oxygen diffusion and phase formation. Therefore, oriented crosshatch textures were fabricated over Ti6Al4V surface using Nd:YAG laser. Textured surface was heat treated followed by DLC coating deposition with Cr interlayer. Effect of heat treatment over DLC coating morphology, adhesion strength and surface characteristics was analyzed. Phase formation and bonding behavior at the coating inter layer were characterized and correlated with adhesion strength. Bio-tribological performance of modified surface was evaluated under elliptical sliding contact to replicate hip implant articulation. Increased surface roughness, better wettability and enhanced graphitic characteristics were associated with DLC coating with prior heat treatment. With heat treatment, Cr2O3 and TiO2 phase formation with superior bonding at interlayer demonstrated improved adhesion strength including deformation resistance. Textured, heat treated and DLC coated surface showed relatively increased compressive residual stress with HF1 quality adhesion. The synergic effect of surface texturing and DLC coating achieved lowest friction. Qualitative wear analysis using Raman spectroscopy reveals beneficial effect of heat treatment before DLC coating for long term hip implant application.
查看更多>>摘要：A series of CoCrNiAlTi coatings were deposited, via direct current (DC) magnetron sputtering, onto M2 steel substrates employing a range of substrate bias voltages (-20 V --120V). Dual phase (fcc and hcp) micro-structures, with high compositional homogeneity, were observed for all as-deposited coatings. Highly refined columnar grains, with a high density of twin boundaries that were oriented perpendicular to the coating growth direction, were identified. As the bias voltage increased, elements in the high entropy alloy exhibited different sputtering yields that led to different degrees of re-sputtering in the deposited films. This, in turn, played a critical role in determining the coating composition and hence stacking fault energy. Accordingly, the ratio between the hcp and fcc phases varied, with a maximum fraction of the hcp phase observed at a bias voltage of-80 V. The fraction of the hcp phase then decreased as the voltage increased to-120 V. An exceptional hardness of value of-9.5 GPa, along with appreciable damage-tolerance, was exhibited in the coating deposited at-80 V. It is suggested that the presence of nanotwins, as well as the dual-phase microstructure, contributed to this excellent strength-ductility unity.
查看更多>>摘要：Ti(Al/Pt)N films prepared on Ti6Al4V (TC4) plates were soaked in a simulated proton exchange membrane fuel cell (PEMFC) anode environment for three weeks. The dense Ti(Al/Pt)N films exhibited various preferred orientations: TiN and TiAlN films with (111) and TiAl(Pt)N film with (200) orientations. The inner stresses of the Ti (Al/Pt)N films changed from -13 MPa for TiN, -115 MPa for TiAlN, and -66 MPa for TiAl(Pt)N. The corrosion current densities of TiN, TiAlN, and TiAl(Pt)N were of the order of 10-8, 10-7 and 10-6 A center dot cm- 2, respectively. Their corresponding contact resistance values decreased sequentially from 29.85, 15.25 and 9.85 m omega cm2. The appearance of second EIS impedance circles after soaking the films in the simulated PEMFC environment for 3 weeks was indicative of the corrosion failure of the Ti(Al/Pt)N films. The relatively high inner stress in the TiN film led to the formation of oxides and corrosion pits. Peeling of the TiAlN film off the TC4 occurred owing to the high inner stress. The micro-potential difference between the TiAlN columns and Pt particles that were distributed along the column boundary led to the formation of crack networks in the TiAl(Pt)N film. Al/Pt in TiN deteriorated the durability of the films, although it enhanced their conductivity.
查看更多>>摘要：Plasma electrolytic oxidation (PEO) is a promising surface treatment method to improve the surface properties of light alloys. However, the high operating voltages led to significant power consumption and a burden on the grid, which limited its application. In this work, we employ a relatively low voltage (~100 V) in an organic-inorganic mixed electrolyte solution, and successfully achieve aa low energy plasma electrolysis oxidation (LEPEO) coating, enabling the reduction of the energy consumption of PEO on Mg-Li alloy. The energy consumption per unit volume (ECPUV) of the LEPEO process is 8.3 kJ.(dm(2).mu m)(-1), which is approximate 57.0% energy consumption savings compared with the PEO process (19.3 kJ.(dm(2).mu m)(-1), NaOH-Na2SiO3 electrolyte). Results show no remarkable difference between the two coatings in terms of morphologies, thickness, element type and distribution. The fracture process and corrosion protection performance of the coatings were evaluated by in-situ SEM tensile test and electrochemical impedance spectroscopy (EIS). The LEPEO coating only consists of MgO and amorphous SiOx, showing higher tensile strength, deformation displacement and better corrosion resistance compared with the PEO coating. The improved surface properties and lower energy consumption of LEPEO coatings will facilitate the application and development of PEO technology.
查看更多>>摘要：Exploring tritium permeation barriers with high permeation reduction factor (PRF) by an industrial scale process is crucial for tritium systems in fusion reactors. Herein, we fabricated a dense Fe-Al/Al2O3 coating by a simple hot-dipping aluminizing (HDA) method and optimized oxidation strategy. The microstructure, chemical composition, and crystallographic characteristic of obtained samples were investigated. And the permeation of deuterium through the sample was determined by gas-driven permeation (GDP) experiments. The results show that the obtained oxide coating mainly consisted of gamma-Al2O3 layer and Fe-Al gradient transition layer. Notably, the Al2O3 layer formed by the oxidation of FeAl alloy coating possessed a high PRF value of 2394 at 550 degrees C. Compared with the direct oxidation of HDA sample, the oxide coating prepared by the alloy topcoat oxidation strategy was denser and had less defects. Meanwhile, the effect of Al topcoat and different Fe-Al alloy topcoats on the microstructure and performance of the oxide coating were investigated, respectively. And the formation mechanisms of oxide coatings prepared by different oxidation strategies were also analyzed.
查看更多>>摘要：In this study, Ni35/WC coatings with different Ti contents were prepared by laser melting coating in two environments (oxygen-free and ordinary atmospheric environments). Effects of Ti addition on microstructure characteristics and dilution rate of the composite coating in an oxygen-free environment were investigated. Corresponding tribological properties and microhardness of the coating were evaluated. It is shown that the laser cladding in the oxygen-free environment reduced the splash phenomenon during the preparation of the Ticontaining coating, thereby reducing the number of defects in the coating. After adding Ti, the dilution rate of the coating increased significantly. The oxygen-free environment during coating preparation could effectively decrease the dilution rate, which made the microhardness distribution of the coating smoother with significantly improved friction stability. By analyzing the worn surface of the coating, it was found that the addition of Ti could effectively decrease adhesive wear and oxidation wear of the Ni35/WC coating. An oxygen-free environment can keep more actual Ti content in the coating, leading to lowered wear rate.
查看更多>>摘要：Chromic oxide (Cr2O3) exhibits outstanding behavior for applications such as glasses, paints, and biomedical applications. Various approaches have been employed in the construction of nanocomposites to meet the application's; requirements. Hydroxyapatite (HAP)/chromium oxide/graphene oxide (GO) composites are characterized by several techniques. The biological applicability carried out by antibacterial performance evaluation. TEM approves that the merge between GO and Cr2O3 into HAP is important in reducing grains agglomerations and raising the introduced surface area. The HAP/Cr2O3/GO has a grain size that varies from 7.3 to 15.6 nm. Additionally, FESEM imaging confirms that adding Cr2O3 composition to HAP/GO to form the ternary composite leads to size reduction and macro-porous structure formation with reducing grain agglomeration. Further, the prepared composites are used as antibacterial agents against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). It was noticed that (HAP/Cr2O3/GO) attained an antibacterial efficiency of 16.4 +/- 0.4 mm for E. coli and 16.8 +/- 0.4 mm for S. aureus, besides showing the viability of 97.9 +/- 0.6% in vitro. Furthermore, the nanocomposite of HAP/Cr2O3/GO represents the highest microhardness with 3.7 +/- 0.3 GPa. Obviously, GO addition forms good interfacial bonding with other ingredients allowing an efficient load transfer mechanism. The surface topography, biocompatibility, and antibacterial activity indicate the ability of HAP/Cr2O3/GO to be utilized as an implant in biomedical utilizations.
查看更多>>摘要：Thermal barrier coatings (TBCs) are suffering from severe degradations by the melted Ca-Mg-Al-silicates (CMAS) deposits during high-temperature operation. The present study evaluated the CAMS-induced degradation to the sintered gadolinium magnesium hexaaluminate (GdMgAl11O19, GdMA) ceramic bulk at 1260-1500 degrees C for 48 h to 100 h, and compared its CMAS resistance with the air plasma sprayed GdMA coating counterpart at 1350 degrees C. Results indicate that the well crystallized GdMA ceramic bulk suffered from more and more serious infiltration of the melted CMAS and microstructure destructions with extended exposure time and enhanced temperature. No barrier layer consisted of corrosion products formed to prevent the melted CMAS penetration during such a process. While, the APS GdMA coating with more amorphous phase as a chemical active component seemed much better to behave as a barrier layer to stop the melted CMAS penetration and corrosion degradation by sacrificing a thin surface layer of the GdMA coating.
查看更多>>摘要：The effect of inhomogeneous composition of Cr and Fe on morphology and formation mechanism of passive film was investigated. A bi-layer structure passive film with a Cr2O3 inner layer and a Fe(2)O3 outer layer obtained on EHLA coating. The passive film is heterogeneous (thickness, compactness) between inter-dendrite and dendrite core due to the element segregation and dislocation. Aspects of the passive film formation mechanism are discussed according to the thermodynamics. It indicates the prior oxidation of chromium resulting in the formation of inner Cr-rich layer, while higher diffusion rate of Fe3+ is the main reason for the formation of outer Fe-rich layer. This provides a new sight on the formation of multilayer oxide films.
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Elsevier