查看更多>>摘要：Waterjet peening has emerged as a potential surface treatment technology, which is gradually being used to improve the surface integrity and mechanical behavior of metal materials. Submerged abrasive waterjet peening, which combines cavitation peening and abrasive waterjet peening and called cavitation abrasive integrated waterjet peening (CAI-WJP), is proposed in this paper and was studied experimentally. The principle of CAI-WJP is first introduced. The effect of the CAI-WJP parameters (i.e., water pressure, standoff distance, traverse speed, path interval, and peening angle) on the surface integrity of TA19 titanium alloy was systematically investigated. Results show that the specimen treated with CAI-WJP using different process parameters formed a plastic deformation layer with a depth of 5-45 mu m. The minimum surface roughness of Ra obtained by CAI-WJP was 0.348 mu m, which is 28.5% lower than the as-received surface. The maximum surface microhardness increased by up to 21.1%, with a maximum work hardening depth of 150 mu m. The surface compressive residual stress (CRS) increased to approximately 640-800 MPa compared with the original CRS of 50-80 MPa on the as-received specimen, and a maximum CRS depth of 360 mu m was obtained. The microstructure evolution on the topmost surface and subsurface of the specimen treated with CAI-WJP with a water pressure of 100 MPa was observed by transmission electron microscopy, which showed that nanocrystallization with amorphization occurred, and nanocrystals with an average size of 6.9 nm formed on the topmost surface. In addition, many dislocation cells and tangles formed on the subsurface with a depth of 15 mu m, and a number of dislocation loops, walls, and pinning were found at the depth of 150 mu m. This work verifies the effectiveness of the proposed CAI-WJP and provides a favorable reference for how to pick up optimized CAI-WJP process parameters.
查看更多>>摘要：To improve the surface properties of ductile cast iron, nickel-based superalloy was deposited on QT500-7 ductile iron by cold metal transition welding process. Effects of heat input on microstructure and interfacial characteristics of Inconel 625 deposit layers were investigated. Results showed that a good metallurgical bonding between Inconel 625 deposit layer and ductile iron could be achieved. Crystalline morphology of the deposited layer from fusion line to upper was cellular crystal, columnar dendrite, and equiaxed crystal in sequence. As dilution rate increased, carbon content of deposited layers was significantly higher than that of Inconel 625 alloy, and large amount of (Mo, Nb)-rich carbides embedded in Ni-rich solid solution dendrites. Graphite in the fusion zone was completely dissolved, and its microstructure was mainly gamma-(Fe, Ni) and net carbides, while partial melted zone (PMZ) was ledeburite, martensite and incompletely dissolved graphite. Microhardness of deposited layer was higher than that of ductile iron. The shearing specimen were all fractured in the PMZ, and the interfacial bonding strength was higher than 400 MPa with a brittle-ductile mixed rupture.
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：Titanium (Ti) alloys show excellent fatigue and corrosion resistance, high strength to weight ratio, and no toxicity; however, poor osseointegration ability of Ti may lead to implant loosening in vivo. Plasma spraying of hydroxyapatite [HA, Ca-10(PO4)(6)(OH)(2)] coating on Ti surfaces is commercially used to enhance osseointegration and the long-term stability of these implants. The biological properties of HA can be improved with the addition of both cationic and anionic dopants, such as zinc ions (Zn2+) and fluoride (F-). However, the hygroscopic nature of fluoride restricts its utilization in the radiofrequency (RF) plasma spray process. In addition, the amount of doping needs to be optimized to ensure cytocompatibility. We have fabricated zinc and fluoride doped HA-coated Ti6A14V (Ti64) to mitigate these challenges using compositional and parametric optimizations. The RF induction plasma spraying method is utilized to prepare the coatings. Multiple parametric optimizations with amplitude and frequency during the processing result in coating thicknesses between 80 and 145 um. No adverse effects on the adhesion properties of the coating are noticed because of doping. The antibacterial efficacy of each composition is tested against S. aureus for 24, 48, and 72 h, and showed that the addition of zinc oxide and calcium fluoride to HA leads to nearly 70 % higher antibacterial efficacy than pure HA-coated samples. The addition of osteogenic Zn2+ and F- leads to 1.5 times higher osteoblast viability for the doped samples than pure HA-coated samples after 7-days of cell culture. Zn2+ and F- doped HA-coated Ti64 with simultaneous improvements in anti-bacterial efficacy and in vitro biocompatibility can find application in load-bearing implants, particularly in revision surgeries and immune-compromised patients.
查看更多>>摘要：The dense and smooth W-ZrO2 coating was prepared by electrodeposition on a copper substrate in Na2WO4-WO3ZrO2 melt at 1173 K. The coatings composition are alpha-W and monoclinic ZrO2, and the content of ZrO2 increased with the increase of current density. The effect of cathode current density on the morphology, microstructure and performance of the coating was investigated in this paper. The microstructure of the coating was a field-oriented texture type, including an equiaxed grain nucleation layer and a columnar grain growth layer. The roughness has the minimum value of 4.783 mu m at 30 mA/cm2, and the maximum value of 8.586 mu m at 60 mA/cm2. Then, the surface roughness dropped to 6.479 mu m at 80 mA/cm2. The surface micro-hardness increased with the current density increasing, and reached the maximum value of 482 HV at 60 mA/cm2. W-ZrO2 coated copper has excellent electrical conductivity and high temperature oxidation resistance at 30 mA/cm2, 40 mA/cm2, and 80 mA/cm2. The electrical conductivity of coatings prepared at 50 mA/cm2 and 60 mA/cm2 is slightly poorer due to their rough surface and strong preferred orientation. Overall, the texture of the composite material is the most influential factor for electrical conductivity. In summary, as the current density increases, the composition, morphology and microstructure of the coatings changes regularly, which further leads to a predictable change in performance.
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.
Tousch, C. Da SilvaMartin, J.Marcos, G.Czerwiec, T....
13页
查看更多>>摘要：Incorporation of carbon nanotubes (CNTs) into ceramic layers during plasma electrolytic oxidation (PEO) is promising for direct synthesis of composite protective coating on lightweight metallic alloys. In the present study, complementary characterization techniques were used in order to definitively assess the presence of CNTs through the thickness of a PEO alumina coating formed in a silicate-based electrolyte containing dispersed multiwalled carbon nanotubes (MWCNTs). Cross-checked results helped in evidencing that MWCNTs are partially incorporated in the thickness of the PEO alumina coating, and more precisely through the porous outer sublayer. They were mainly found in the form of scaffolds that line the interior walls of pores. To a lesser extent, some individual MWCNTs were found interlocked in the fine grain structure of alumina. The analysis of the specific Raman bands of MWCNTs also highlighted that incorporation is associated with an alteration of the structural integrity of the MWCNTs. It was also established that the increase in the amount of dispersed MWCNTs results in a thicker but more porous CNTs-enriched PEO coating. Based on the collected results, some precisions regarding the incorporation mechanisms were proposed.
查看更多>>摘要：The NiCrAlY, NiCoCrAlY and NiCoCrAlYTa coatings were prepared on a Ni16Cr13Co4Mo alloy by the D-gun spray technique. The hot corrosion behaviors of the coatings were investigated in molten NaCl-Na2SO4 at 800 degrees C through electrochemical measurements including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky plots. The corrosion layers of the coatings were characterized by electron probe micro-analysis (EPMA), auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results showed that all the corrosion layers of the three coatings displayed the electronic structure of n-p heterojunction. However, the NiCoCrAlY coating had the slowest corrosion rate because Co reduced the carrier density of the corrosion layer and improved the corrosion layer resistance (Rl). The Co sulfides effectively inhibited the internal sulfidation. Ta ion could occupy the Al2O3 lattice and increase the carrier density of the corrosion layer. The hot corrosion of NiCrAlY coating was the most severe since the (Cr, Al) sulfides along the Al2O3 stringers promoted the formation of black bumps on the coating.
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：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.
NSTL
Elsevier