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：Ternary surface hardening layers were prepared on the Q235 low-carbon steel by plasma electrolytic borocarbonitriding(PEB/C/N) under constant voltage of 260-300 V for 30 min. The microstructure, phase components and hardness depth profiles of the B + C + N ternary hardening layers were examined. The ternary hardening layers were composed of a boride layer with single Fe2B phase and a transition layer. The thickness of modified boride layers on the PEB/C/N samples was about 10 um, 15 um and 22 um at 260 V, 280 V and 300 V, respectively. The maximum hardness of boride layer was 2400 HV for the 300 V PEB/C/N sample. The surface free energy of bare Q235 steel and PEB/C/N samples at 260, 280 and 300 V were 41.084, 32.039, 26.906 and 25.726 mJ/m(2), which were calculated on the basis of their contact angles for water and n-hexadecane. Furthermore, the hardening layers exhibited excellent corrosion behavior due to the improved hydrophobicity for the dense boride layer. The lowest wear rate of PEB/C/N sample at 300 V is about 2.0375 x 10(-6) mm(3)/N center dot m, which is only 1/15 of the bare Q235 steel, the ternary hardening treatment shows a better wear resistance than the bare Q235 steel.
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.
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：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：The application of multilayer coatings in the field of nuclear-grade zirconium alloy protection has attracted much attention. However, the phenomenon of element diffusion between layers at high temperature has not been systematically studied. In this work, by selecting specific elements X (Cr, Ni, Si), the stability and oxygen barrier properties of the multilayer film coupled with Zr layer were investigated. The key characteristic indicators were clarified, including grain boundary effect, oxygen diffusion coefficient and Zr/X inter-diffusion ability. Zr/Si multilayer system outstripped others with excellent oxidation resistance, and only the surface Zr layer was completely oxidized at both 400 degrees C and 700 degrees C in air. At hot steam environment of 400 degrees C/10.3 MPa, the formation of a thin amorphous Zr-Si-O layer and an amorphous silicon oxide layer guarantee good oxygen barrier effect and greatly reduce the oxygen partial pressure at oxidation front.
查看更多>>摘要：In the present study, 7YSZ/gadolinium zirconate (GZ) and 7YSZ/2.3 wt.% yttria doped gadolinium zirconate (YGZ) bi-layers were deposited onto the plasma sprayed bond coated Inconel-718 substrates by EB-PVD technique. Structural analysis revealed that GZ and yttria doped GZ has thermally stable pyrochlore structure and no phase transformation was observed even after thermal cycling test at 1523 K up to 75 cycles. Vicker's microhardness measurements of the coatings indicated that yttria doped GZ had improved mechanical properties than that of GZ. Hot corrosion behaviour of 7YSZ/GZ and 7YSZ/Y-GZ were evaluated with the mixture content of 45 wt.% of Na2SO4 and 55 wt.% V2O5 at 1273 K. Failure analysis of these TBCs was investigated by isothermal oxidation test (1273 K) and thermal cyclic test (1523 K). The results revealed that bi-layered 7YSZ/yttria doped GZ showed improved performance than that of the bi-layered 7YSZ/GZ TBC.
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：Shot peening is often reported as being beneficial to stress corrosion cracking resistance; however, the increased surface roughness induced by shot peening may promote localized corrosion pitting. Here, AA 7075-T6 aluminum alloys were treated by different shot peening processes, and the surface characteristic, including refined microstructure, residual stress and surface roughness, were characterized, then its effect on localized corrosion pitting and stress crack propagation behavior were investigated. Compared with single shot peening, the microstructure refinement was not further enhanced by dual shot peening with adding a subsequent low intensity of micro-shot peening. The surface residual stress distribution become more uniform, and the average surface residual stress value was increased from -158 MPa to -175 MPa. The maximum residual stress was synchronously increased from -302 MPa to -319 MPa. Meanwhile, the surface roughness (Ra) value was decreased from 4.05 mu m to 2.05 mu m. Compared with single shot peening, the degree of surface localized corrosion pitting was alleviated after dual shot peening due to its low surface roughness and more uniform compressive residual stress distribution. The depth of stress corrosion cracking for dual shot peening was decreased with a minimum value of 33 mu m, which may be ascribed to the high maximum compressive residual stress at the subsurface.
查看更多>>摘要：Understanding of laser shock peening (LSP)-generated microstructural characteristics at the interfaces between hexagonal close-packed (HCP) and body-centered cubic (BCC) crystals and dislocation patterns could provide useful insights into designing the interface between both phases of dual- or multi- phase metallic materials, which is a key information for higher properties. Herein, with a severe plastic deformation process of LSP, a systematic work of the mechanism behind misfit dislocations at different grain size has been carried out. It demonstrates that, as the grain gradually is refined, extrusion and torsion of the lattice are important contributions to the modified d-spacing and quantity of misfit dislocation. Hence, the growth orientation and the style of bicrystal interface between HCP and BCC crystals are affected. Furthermore, the size effect of the LSP-generated dislocation pattern has a significant attribution to the stress of misfit dislocation originating from neighboring interfaces.
NSTL
Elsevier