Bonu, VenkataramanaSrinivas, G.Kumar, V. PraveenJoseph, Anjana...
8页
查看更多>>摘要：Development of H and metal dopant-free single phase thick diamond like carbon (DLC) coating on metal nitride layer for automobile applications is still a challenging task due to internal stress developed during deposition of DLC films. A simple process was followed to deposit thick Cr/CrN/DLC (0.25/0.75/6 mu m) coating on plasma nitrided steel using an un-filtered cathodic vacuum arc system without applying any high pulse bias voltage. In addition, the coating was deposited at room temperature and it showed very good adhesion on plasma nitrided steel surface and exhibited a very low coefficient of friction similar to & nbsp;0.06 +/- 0.005. Temperature dependent solid particle erosion tests were conducted according to ASTM-G-76-18 standards at an impinging angle of 45 degrees. Erosion resistance of the coating is 33, 11, 7 and 6 times better than nitrided steel substrate at test temperatures of 25, 200, 300 and 400 degrees C, respectively. Better erosion resistance performance of a coating infers the long life of the coating on automobile components. A multi-wavelength Raman study gives a better understanding of the structural properties of DLC. So, the Raman spectra of the coating were recorded using three different laser wavelengths: 405 nm, 532 nm and 633 nm. The thermal stability of the coating was studied using temperature dependent Raman spectroscopy. The coating showed good thermal stability until a temperature of 425 ?degrees C.
查看更多>>摘要：Alternating TiB2-DCMS and Cr-HiPIMS layers are used to fabricate TiB2/Cr multilayer films with varying the Cr-interlayer thickness, 2 and 5 nm, and the substrate bias during growth of Cr interlayers from floating, to -60 V and -200 V. The effects of multilayer structure on mechanical properties, static oxidation, and tribological behavior of the TiB2/Cr multilayers are investigated. The results reveal that TiB2 nanocolumns renucleate at each Cr interface maintaining smooth film surface and film density. Interlaying with Cr with thicknesses of 2-5 nm improves the resistance to oxidation at 500-600 degrees C as compared to TiB2 monolayer. The increase of the thickness of the Cr interlayers from 2 to 5 nm decreases the hardness of the multilayer slightly but deteriorates the wear rate significantly. The friction coefficients at 500 degrees C are lower than those at RT due to boric acid liquid lubrication induced by surface oxidation. The TiB2/Cr multilayer films show higher wear resistance than TiB2 monolayer. The multilayer films with 2 nm-thick Cr deposited at -60 V have the lowest recorded wear rates. Irradiation with 200 eV Cr+ leads to interface mixing, resulting in the formation of B-deficient TiBx phase (x < 2) and higher wear rates compared to multilayers grown at -60 V.
查看更多>>摘要：The study compares and deciphers the differences in tribological performance of CrN coatings after incorporation of Cu moiety, i.e. CrCuN coatings, prepared using DC magnetron sputtered physical vapor deposition (PVD), under glycerol lubrication conditions. The structures, compositions and mechanical properties of the coatings were investigated by using scanning electron microscopy (SEM), X-ray diffractometry (XRD), atomic force microscopy (AFM), and nano-indentation. CrCuN coatings present superior mechanical characteristics than CrN coatings. Reduced COF and wear rate values were observed more for the CrCuN coating than the CrN coating. The reason why glycerol exhibits better friction-reducing and wear protection performance in CrCuN coatings than CrN coatings is explained using X-ray photoelectron spectroscopy (XPS). Glycerol molecules were found to be easily degraded on the surface of the CrCuN coating during the sliding process to form a tribofilm which can greatly reduce the friction and wear.
Praveen, K.Alroy, Rahul JudeRao, D. SrinivasaSivakumar, G....
11页
查看更多>>摘要：Lanthanum zirconate (La2Zr2O7; LZ) and cerium doped lanthanum zirconate (La-2(Zr0.7Ce0.3)(2)O-7; LZC) has gained immense attention as thermal barrier coating (TBC) materials because of their superior thermophysical properties, high-temperature phase stability and chemical inertness than yttria-stabilized zirconia (YSZ). In the present study, LZ and LZC double-layered TBCs are prepared by solution precursor plasma spray process (SPPS) as a top layer over the atmospheric plasma sprayed YSZ coatings, and their hot corrosion behavior is studied. The as-deposited SPPS coatings exhibited single phases, and the microstructural morphologies reveal a hierarchically structured surface with vertically cracked microstructure. Exposure to the high temperature corrosion process results in damage of the morphology and microstructure within the SPPS layer by forming lanthanum vanadate (LaVO4) and lanthanum cerium vanadate ((LaCe)VO4) in LZ and LZC coatings, respectively, while leaching out zirconia (ZrO2). In the case of conventional YSZ, the corrosive salts infiltrate entirely through the coating and result in complete densification and associated phase changes. While combining the above aspects, the hybrid double-layered architecture of LZ/YSZ and LZC/YSZ coatings can be beneficial to protect the underlying YSZ layer against the detrimental infiltration of molten corrosive salt.
James, Brian L.Bhattiprolu, Venkata SatishCrawford, Grant A.Jasthi, Bharat K....
13页
查看更多>>摘要：Cold spray technology is commonly used to repair metallic components with limited temperature influence on the original component. However, for many commercial alloys, such as Al6061, it is still challenging to achieve dense deposits by using low-priced nitrogen gas. The objective of this work was to investigate the effect of secondary peening with zirconia (ZrO2) ceramic beads on the microstructure and mechanical properties of the Al6061 cold spray coatings. Al6061 spherical powder with an average size of 20 mu m coupled with zirconia beads of similar to 210 mu m were deposited onto Al6061-T6 substrates using N-2 as the carrier gas. The microstructure and mechanical properties of coatings were compared with coatings produced using He and N-2 process gases. Microstructural characterization was performed using optical and scanning electron microscopy. Coatings produced with He process gas resulted in lowest porosity and with better mechanical properties compared to the coatings produced using N-2 and N-2 along with ZrO2. The use of ZrO2 along with N-2 process gas resulted in similar to 15% increase in microhardness, similar to 680% increase in adhesion strength, similar to 28% reduction in porosity, and similar to 34% increase in tensile strengths in the coatings when compared with the coatings produced using N-2 process gas only. However, both coatings produced using N-2 and N-2 coupled with ZrO2 exhibited brittle behavior with no appreciable ductility. Even with this limitation, using ZrO2 as a secondary peening media could provide a cheaper alternative to using He gas for certain cold spray applications where a higher hardness and good adhesion strengths are needed.
查看更多>>摘要：Effects of current density on micro-mechanical properties of electrodeposited gold were evaluated by micro compression test. Three gold films were electrodeposited at 20 A/m(2), 50 A/m(2) and 100 A/m(2). The average grain sizes were analyzed by XRD. The specimens used in the micro-compression test were micro-pillars having a square cross-section and the long-side parallel to the Au/electrolyte interface fabricated by focused ion beam. Three sizes of the cross-section were prepared, which were 8 mu m x 8 mu m, 10 mu m x 10 mu m and 15 mu m x 15 mu m, and the height was kept at twice of one side of the cross-section. The micro-pillars all showed high yield strengths ranged from 400 MPa to 650 MPa, because of the micro-scale sample size by the sample size effect and the nano scale average grain size by the grain boundary strengthening. In addition, the largest sample size effect was observed in micro-pillars fabricated from the gold film electrodeposited at 100 A/m(2).
查看更多>>摘要：To solve corrosion problems of Al-Li alloys in marine environment, Fe-based amorphous coating was first deposited on 8090 Al-Li alloy by high velocity oxy-fuel spraying. The microstructure, interfacial bonding and corrosion behaviors of the Fe-based amorphous coating are investigated. It is found that the coating is mainly composed of amorphous splats, but a few crystalline phases can be observed in the splats or splat surfaces. Even so, the corrosion resistance of the coated 8090 alloy is 7 times higher than that of the bare 8090 alloy. Moreover, due to the partially melting and rapid cooling of substrate during metal droplet deposition, there is an amorphous transition zone at the AMC/8090 alloy interface, indicating the formation of localized metallurgical bonding. Owing to the metallurgical bonding interface and the high compactness of coating, the adhesion strength of Fe based amorphous coating can reach 58.2 MPa. In 3.5 wt% NaCl solution, a bipolar passive film can be formed on the Fe-based amorphous coating, and its compactness decreases as the polarization potential increases. Because of the aggregation of Cr element and the uneven passive film, the crystallized splats and crystallized splat surfaces are eroded preferentially, leading to the formation of corrosion channels and the corrosion failure of coating. The present work provides a guidance for the design of corrosion-resistance coatings on Al-Li alloys.
查看更多>>摘要：Tradeoff between residual stress and properties is the primary obstacle which hinder the practical application of laser cladding technology. Herein, a Fe-based SMA/PZT (shape memory alloy/lead zirconate titanate piezoelectric ceramic) composite coating was fabricated by laser cladding. To explore the optimal PZT doping amount and its performance enhancement mechanism of the composite coating, microstructure, phase composition, stacking fault probability (SFP), residual stress, microhardness and wear resistance of the coating were investigated. The results reveal that the composite coatings are composed of PZT (Pb(ZrTi)O-3) phase, gamma austenite phase and e martensite phase. Among which the coating with 1 wt% PZT doping amount possesses the highest microhardness as well as the best wear resistance. The grain size and stacking fault energy (SEF) of the coating have been reduced after doping with PZT. Ultramicroscopic structure unveils that the gamma -> epsilon & nbsp;& nbsp;phase transition occurred in the SMA/PZT composite coating during the laser cladding process, high-density dislocation accumulation zone appears around the PZT particles. PZT doping has an interesting effect on both promoting and hindering the transformation of gamma -> epsilon & nbsp;in the composite coating. Doping of PZT increases the amount of martensite in the local area of the composite coating, reduces the residual stress, and significantly improves the microhardness and wear resistance.
查看更多>>摘要：The influence of gas pressure on plasma nitriding of surface nanocrystalline TC4 titanium alloy prepared by shot peening (SP) was investigated. SP treatment under 0.3 MPa-25 min (Almen intensity is 0.32 mm) before plasma nitriding effectively refined the surface grain size of TC4 alloy to about 42 nm, which helped to sufficiently lower the nitriding temperature of TC4 to 500 degrees C . After nitriding treated under different gas pressures from 50 Pa to 300 Pa, nitriding gas pressure was found to has an optimal value at 200 Pa with which a thickest nitriding layer of 1.34 mu m and highest hardness of 1569 HV was achieved at 500 degrees C for 20 h. Furthermore, the influence of gas pressure on the formation and migration of active nitride particles was revealed to be related with their energy and efficiency. Higher nitriding pressure would produce more active nitride particles but consume more energy during collision which made active nitride particles difficult to transit through the nitriding environment to land on the specimen. Balanced between these two aspects, 200 Pa was found to form more active nitride particles as well as maintain a high level energy. Meanwhile, SPed specimen presented a thicker nitriding layer than coarse grained specimen. So in this study, we combine the promotion effect of surface nanocrystalline and the optimization of nitriding pressure to comprehensively improve the plasma nitriding efficiency.
查看更多>>摘要：Oriented reduced graphene oxide-MgAl layered double hydroxides (rGO-LDH) films were prepared on Mg alloy with pre-sprayed rGO-Al coating by in-situ growth method. Characteristics of orientated LDH films were detected through field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) and Raman spectroscopy. The orientation mechanism was dicussed. Corrosion behavior of the coatings was investigated using potentiodynamic polarization curves, electrochemical impedance spectroscopy and full immersion test. Ball on disc test was carried out for measuring the anti-wear performance. Results indicate that the nanosheets in LDH film tend to parallel to the substrate under low pH value, and nanosheets in LDH film tend to perpendicular to the substrate under high pH value. Parallel oriented LDH films exhibit excellent shielding and lubrication ability. And the rGO has a strong anchoring effect on perpendicular oriented LDH film, which results in higher anti-corrosion and anti-wear performance (load capacity) for the film. The orientation mechanism of films and the relationship between orientation and performance were discussed.
NSTL
Elsevier