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Surface & Coatings Technology
Elsevier Sequoia
Surface & Coatings Technology

Elsevier Sequoia

0257-8972

Surface & Coatings Technology/Journal Surface & Coatings TechnologySCIISTP
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    Microstructure and phase composition evolution of dual-phase ytterbium silicate coatings plasma sprayed from stoichiometric Yb2Si2O7 feedstock powder

    Wang H.Zhang J.Sun L.Wang J....
    5页
    查看更多>>摘要：© 2022The main challenges of atmospheric plasma spraying (APS) when dealing with rare earth silicate are the amorphous phase formation and silica volatilization in as-sprayed coatings. In this study, the microstructure and phase composition evolution of dual-phase ytterbium silicate environmental barrier coatings (EBCs) plasma sprayed from stoichiometric Yb2Si2O7 feedstock powder are investigated. The unavoidable silica volatilization leads to the coating composition deviate from stoichiometry of disilicate composition and result in the presence of Yb2SiO5 in coatings. By controlling the phase fraction of Yb2SiO5 through modulation of plasma character allows minimizing the effects of thermal residual stress on the coating durability in thermal cycling. The high crystallinity and crack-free coatings were achieved through optimized crystallization heat treatment. The presence of dislocation and deformation twins endow the dual-phase coating with intrinsic quasi plasticity and improvement in reliability. The present study provides useful inspirations on the optimization of spraying parameters and design of advanced EBC systems.
      原文链接:
    • NSTL

    A novel reverse-polarity plasma torch with extended hot-wall nozzle for atmospheric plasma spraying of dense yttria-stabilized zirconia coatings

    Yu D.Yao J.Chen Y.Duan B....
    14页
    查看更多>>摘要：? 2022 Elsevier B.V.Due to the high heating temperature and low cost, atmospheric plasma spraying (APS) has been widely used in the preparation of ceramic coatings, but its coatings are normally formed by the stacked splats from fully or partially melted feedstock particles, which inevitably leads to some pores, unbonded interfaces or cracks. Thus, in this paper, a novel atmospheric plasma spraying technique using a reverse-polarity plasma torch (RPT) with extended hot-wall nozzle was proposed to fully melt and accelerate feedstock particles for the preparation of dense YSZ ceramic coatings. Firstly, the RPT spray system was designed in detail, and its main electro-thermal characteristics were experimentally studied. The results showed that the RPT exhibited higher arc voltage, thermal efficiency and lower arc voltage fluctuation than that of traditional rod-cathode/normal-polarity plasma torches (NPT) at the similar output power. Secondly, a numerical simulate was carried out to reveal the effect of the extended hot-wall nozzle on the temperature and velocity distributions of the plasma jet. The results showed that the extended hot-wall nozzle remarkably extended the high-temperature and high-velocity region of the plasma jet from the RPT exit to the downstream. Finally, the dense and uniform YSZ coatings with a porosity of about 5.3% were successfully prepared by the RPT with extended hot-wall nozzle. The results showed that the YSZ coating exhibited denser microstructure and fewer defects than that of the coating prepared by traditional APS process. Meanwhile, the hardness and Young's modulus of the YSZ coating were 11.9 ± 1.4 GPa and 197.9 ± 29.4 GPa, respectively, which were relatively higher than that of the coating prepared by traditional APS process, and were very close to that of the coating prepared by very low-pressure plasma spraying (VLPPS) process.
      原文链接:
    • NSTL

    Mechanical and biological properties of atmospheric plasma-sprayed carbon nanotube-reinforced tantalum pentoxide composite coatings on Ti6Al4V alloy

    Chung Y.L.Chang C.P.Ibrahim M.Z.Lee H.T....
    5页
    查看更多>>摘要：© 2022 Elsevier B.V.Ta2O5 coatings containing 0, 3, 5 and 7 vol% multi-walled carbon nanotubes (CNTs) were deposited on Ti6Al4V substrates by atmospheric plasma spraying (APS). The addition of CNTs had no obvious effect on the surface morphology and roughness of the coatings, but increased the coating porosity. The coatings consisted primarily of β-Ta2O5 phase, a small amount of α-Ta2O5, and minor C peaks corresponding to the CNTs. As the CNT content increased, the elastic modulus (E) and indentation fracture toughness also increased. However, the higher CNT content increased the coating porosity and reduced the microhardness. Following immersion in simulated body fluid (SBF) for 14 days, the surfaces of all the coatings were completely covered with hemispherical bone-like apatite. Furthermore, after incubation in osteoblast-like osteosarcoma MG-63 cell culture for 7 days, all of the coatings showed excellent cell attachment, growth and spreading. Overall, the present results show that the addition of CNTs to Ta2O5 raw powder improves the indentation fracture toughness of the resulting coatings without degrading their biological properties.
      原文链接:
    • NSTL

    Comparison of the hot corrosion behavior of the LZ, CSZ and LZ/CSZ composite thermal barrier coating

    Mousavi B.Farvizi M.Rahimipour M.R.Pan W....
    5页
    查看更多>>摘要：© 2022 Elsevier B.V.In the present study, the hot corrosion behavior of Air Plasma Spray (APS)-deposited Ceria Stabilized Zirconia-Lanthanum Zirconate (CSZ-LZ) composite thermal barrier coatings (TBCs) was investigated and compared with CSZ and LZ coatings. The hot corrosion tests were conducted at 950 °C in a cyclic mode in the presence of V2O5 + Na2SO4 molten salt mixture. The microstructural aspects were evaluated by energy dispersive spectroscopy (EDS) equipped scanning electron microscopy (SEM) and x-ray diffraction (XRD) methods. The results showed that CSZ, 75CSZ-25LZ, 50CSZ-50LZ, 25CSZ-75LZ and LZ coating systems lasted for 28–30 h, 24–26 h, 22–24 h, 20–22 h, and 18–20 h, respectively. The results revealed an improvement in the hot corrosion resistance of composite coating compared with LZ coating which can be attributed to better coefficient of thermal expansion (CTE) compatibility of composite coatings. The formation of hot corrosion products such as CeVO4, LaVO4, and also tetragonal to monoclinic transformation are the main reasons for the failure of these coatings.
      原文链接:
    • NSTL

    Effect of water in oil emulsion on the surface quality of Inconel 718 alloy during coupling electrical pulse and ultrasonic treatment

    Wang B.Ji R.Gong Z.Zhao Q....
    5页
    查看更多>>摘要：© 2022 Elsevier B.V.A new kind of water in oil (W/O) emulsion with 40 wt% of water content is developed and applied to the coupling electrical pulse and ultrasonic treatment (CEPUT) of Inconel 718 alloy. After treatment, a strengthening layer of about 450 μm is produced on the surface, the surface hardness reaches 503.8 HV, and the surface roughness Ra is reduced to 0.042 μm, reaching a mirror surface. The role of the W/O emulsion in CEPUT is analyzed, and it is found that 40% (wt% of water content) W/O emulsion can suppress the discharge between carbon brush and the sample surface, and effectively reduce the surface discharge pits. At the same time, it can provide an excellent lubrication effect, reducing the “harmful” tangential plastic deformation caused by friction, and a better surface effect can be obtained. In addition, compared with water, 40% W/O emulsion weakens the impact damage of cavitation on the sample surface and reduces the pits caused by impact. After CEPUT with 40% W/O emulsion, the average friction coefficient of the sample surface is reduced by 22.3%, and the wear amount is reduced by 43.2%.
      原文链接:
    • NSTL

    Application of crosswise repetitive ultrasonic nanocrystal surface modification treatment to Inconel 690 alloy: Efficiency of single-path and multi-paths

    Amanov A.Ahn S.-H.
    5页
    查看更多>>摘要：© 2022 Elsevier B.V.In this study, the efficiency of crosswise repetitive ultrasonic nanocrystal surface modification (CR-UNSM) treatment on surface characteristics, tribological and fatigue properties of single and multi (double, triple, quadruple and quintuple) treated Inconel 690 alloy was investigated. All the CR-UNSM-treated specimens demonstrated better tribological and fatigue performance in comparison with the untreated specimen. Quintuple CR-UNSM-treated specimen demonstrated the lowest coefficient of friction (COF) and specific wear rate (SWR) among untreated and other CR-UNSM-treated specimens, while triple CR-UNSM-treated specimen was found to be the most effective in terms of fatigue performance. The surface roughness of Inconel 690 alloy was significantly reduced after single CR-UNSM treatment, afterwards it was gradually roughened with increasing the number of CR-UNSM treatment. The surface hardness along with hardened surface layer and also compressive residual stress (CRS) were increased with increasing the number of CR-UNSM treatment. Every CR-UNSM treatment was capable of refining coarse grains into nano-scale grains, where the higher number of CR-UNSM treatment the thicker nanostructured surface layer (NSL) and the finer grain size.
      原文链接:
    • NSTL

    On the origin of micro-cracking in zinc-coated press hardened steels

    McDermid J.R.Bassim N.D.Maleki K.Pallisco D.M....
    5页
    查看更多>>摘要：© 2022 Elsevier B.V.Zn-coated press hardened steels (PHS) are in high demand for automotive mass reduction and enhanced passenger safety applications while the Zn coating supplies robust cathodic corrosion protection. However, the mechanism of micro-crack formation during direct hot-press forming (DHPF) has not been adequately described. Thus, the objective of this work was to determine the mechanism for micro-crack formation in Zn-coated DHPF PHS that addressed the relationship between micro-cracking and the coating microstructure created during substrate austenitization. Zn-coated 22MnB5 steel sheets were annealed at 900 °C for annealing times ranging from 30 to 780 s and DHPF at 75 °C s−1 to obtain a fully martensitic substrate microstructure. The inward diffusion between the Zn coating and the substrate during annealing resulted in a dual phase coating microstructure initially comprising Γ-Fe3Zn10 + α-Fe(Zn), transitioning to a single phase α-Fe(Zn) coating after annealing for 240–420 s. Coincident coating α-Fe(Zn) and substrate Zn-enriched austenite (γ-Fe(Zn)) grain boundaries became Zn-enriched, forming a thin layer of α-Fe(Zn) along the γ-Fe(Zn) grain boundaries. It is proposed that coincident coating α-Fe(Zn) and substrate prior austenite grain boundaries (PAGBs) were weakened by this grain boundary α-Fe(Zn) layer. Upon the application of tensile stress, intergranular fracture occurred along the coincident coating α-Fe(Zn) and Zn-enriched PAGBs in the Zn-enriched martensite (M(Zn)) layer. It was further determined that crack propagation ceased and the crack tip was blunted when Zn-enrichment along the PAGBs in the M(Zn) layer was exhausted.
      原文链接:
    • NSTL

    Epitaxial growth of TiN on (0001) semi-insulating 4H-SiC substrate by reactive sputtering

    Wu P.-H.Chang L.Chen C.-H.Ko C.-J....
    5页
    查看更多>>摘要：© 2022Growth of epitaxial TiN film on a semi-insulating single crystal (0001) SiC substrate has been achieved by DC magnetron reactive sputtering deposition. The effects of growth temperature and N2 flow ratio in Ar on film quality and growth rate were investigated. X-ray diffraction (XRD) characterization shows that all the deposited TiN films at 550 and 700 °C are heteroepitaxially grown on SiC with the epitaxial relationship between TiN and 4H-SiC in (111)TiN//(0001)SiC and [11¯0]TiN//[112¯0]4H-SiC. Increasing the N2 flow ratio from 4 to 8% results in improvement of the film quality and a decrease in the growth rate. The width of the X-ray rocking curve of TiN (111) reflection can reach a value as small as 249 arcsec and the resistivity of TiN film can be 21 μΩ·cm for deposition at 700 °C with 8% N2 flow ratio. Measurements by atomic force microscopy show that the surface roughness of the TiN film can be 1.1 nm. X-ray photoelectron spectroscopy reveals that TiN composition is nearly in stoichiometry for all the grown TiN films. Examinations by cross-sectional transmission electron microscopy show that TiN is directly grown on SiC and verify the epitaxial relationship from XRD.
      原文链接:
    • NSTL

    Erosion performance of suspension plasma spray thermal barrier coatings — A comparison with state of art coatings

    Mahade S.Joshi S.Venkat A.Curry N....
    5页
    查看更多>>摘要：© 2022 Elsevier B.V.Suspension plasma spray (SPS) thermal barrier coatings are currently at an early stage of industrial adoption. There remain questions about the performance of SPS columnar coatings under different engine environmental conditions as it may influence which established engine coatings can be replaced by SPS coatings. One particular area of concern has been the erosion resistance of SPS coatings. In this study a columnar SPS coating has been evaluated against three types of state of art air plasma spray coatings: conventional porous coating, high porosity coating and dense vertically cracked coating. Air-jet erosion testing was performed on coatings at a glancing angle of 30 degrees and with direct impact at 90 degrees. Coatings have been ranked according to their mass loss per unit erodent mass. Coatings were also evaluated for their microstructure, porosity content, hardness, and fracture toughness. The erosion damage created during testing has also been investigated using electron microscopy to observe the damage mechanism. The results of this study demonstrate that SPS coatings can outperform porous APS coatings in erosion resistance and could be considered a match for dense vertically cracked coatings. The SPS columnar coatings have shown a decreasing erosion rate with exposure time that suggest the influence of surface roughness on initial erosion behaviour.
      原文链接:
    • NSTL

    Nanoindentation in alumina coated Al: Molecular dynamics simulations and experiments

    Luu H.-T.Merkert N.Raumel S.Dencker F....
    5页
    查看更多>>摘要：© 2022 Elsevier B.V.Oxygen is often a significant disruptive factor in many production engineering processes and efforts have been made to limit or remove these oxide layers during manufacturing. However, the mechanical properties of oxide layers and their relationship to the raw material are not yet fully understood. In this work, we examine the nanoindentation process on Al surfaces covered with a native oxide layer of various thicknesses using molecular dynamics (MD) models and experiments. For MD simulations, the most advanced interatomic potentials, COMB3 and ReaxFF, are employed to model the interaction between Al and O elements. The two potentials were thoroughly tested and compared with the Embedded Atom Method (EAM). According to our findings, the oxide layer has a significant impact on defect emission in the substrate. However, the behavior of the oxide layer during the indentation process is different for the two potentials. In agreement with experiments, the COMB3 potential shows crack initiation and propagation. The ReaxFF potential displays a pile-up of atoms surrounding the indenter, but no cracks are visible.
      原文链接:
    • NSTL