查看更多>>摘要：Multicomponent and multilayer coatings have been attracting significant research interest, and these coatings allow the deposition of graded layers with a continuous variation of the concentration of the components to fulfill specific requirements at the substrate interface or that at the surface. On the basis of the binary compounds TiN, CrN and ZrN, various deposition strategies were developed to improve or adapt the hard coatings to a specific tribological problem. In this study, a cathodic arc deposition technology was used to deposit the AlTiSi/CrV/Zr and multilayer nitride coatings of AlTiSiN/CrVN/ZrN. By controlling the rotation speed of the substrate, hierarchical gradient and multilayered structures containing periodic AlTiSiN, CrVN and ZrN layers were found in the multilayer nitride coatings. Microstructure, mechanical properties and cutting applications were discussed. The highest hardness was obtained for the multilayered AlTiSiN/CrVN/ZrN coating with modulation period of 13.5 nm. The presence of multicomponent AlTiSiN/CrVN/ZrN with nanolayer structure mainly attributed to the formation of strong metal-nitrogen bonding enhanced the hardness of the coatings. For the field test of cutting, a glass-reinforced epoxy laminate material was machined by the coated WC-Co end mills using a milling machine at high cutting spindle rotational speed of 40,000 rpm. The obtained results showed that the periodic thickness of the multilayer structure had a direct effect on the mechanical properties and cutting performance of the coatings. The design of nanostructured AlTiSiN/CrVN/ZrN hard coatings improved the overall tribological performance and showed applicability of these coatings in high speed cutting of glass-reinforced epoxy laminate materials.
查看更多>>摘要：In flexible and/or wearable electronics the thin films deposited on compliant substrates are not only subjected to straining and bending but also to tribological loading conditions. A frequently used method to assess tribological properties of materials systems is the ball-on-disc test. In the current work, Mo films were deposited by high power impulse magnetron sputtering on polyimide substrates to serve as a model system. To establish different tribological contact conditions, a series of different counterpart materials was chosen for the performed ball-on -disc tests. A detailed analysis by 3D confocal laser scanning microscopy and scanning electron microscopy revealed details about the wear mechanisms active during sliding where mainly abrasion of the softer one of the material pair was noticed. The obtained results for friction and wear together with the performed simulations of the induced stresses due to the loading conditions show that ball-on-disc tests can contribute to the under-standing of the tribological response of metallic films on compliant substrates which in turn may help to improve the lifetime of components in flexible and/or wearable electronic applications.
查看更多>>摘要：The limit of applicability of the correlation between the ratio of hardness to elastic modulus (H/E) of coating systems and their wear resistance has been explored. Experimental approaches to determine accurate H/E values by nanoindentation are discussed and best practice recommendations summarised. Small-scale tribo-testing has been used to simplify complex wear conditions, and the role of contact severity and damage tolerance studied to determine why and when coating optimisation strategies are effective. Case studies show the importance of relatively low coating elastic modulus in reducing tensile stresses in sliding/abrasive contact. This may be a key factor in why coating design for optimised H/E and resistance to plastic deformation, H-3/E-2, can be more effective than aiming for extremely high coating hardness since that is typically accompanied by high coating stiffness. The influence of substrate ductility and load support on the damage tolerance of the coating system in impact tests has been investigated by testing at different contact size. Results show that mechanical and microstructural factors should not be considered in isolation. The role of coating microstructural design and temperature on optimising coating performance in high speed machining is investigated.
Hsieh, Ping-YenChen, Ying-HungMatthews, David T. A.He, Ju-Liang...
10页
查看更多>>摘要：To prevent overheating of high-power electronic devices, effective cooling and thermal management is a key issue. Owing to the extraordinarily high thermal conductivity of graphene structure in nature, an approach for growth of carbon nano-coating with multiplex layer architecture on copper foil by using high power impulse magnetron sputtering (HiPIMS), as an alternative to the conventional chemical vapor deposition process, is reported for heat-spreading purposes. For successful deposition, a high peak current of 600 A with a short pulse of 30 mu s at a relatively low substrate temperature of 600 C was applied. Moreover, growth mechanisms without and with applying copper for Cu/carbon (Cu/C) nano-coating periodic deposition are revealed and discussed. Based on the measurement results using Angstrom's method, under optimum deposition time, the HiPIMS pre -pared carbon nano-coating with multiplex layer architecture, which contains in-plane-oriented multilayer gra-phene structure and the following out-of-plane-oriented turbostratic graphene structure, can enhance the heat spreading ability of the copper foil, reaching a thermal diffusivity value of 1.05 cm2/s. For Cu/C nano-coating periodic deposition, copper can act as catalyzing ingredient to inhibit amorphous carbon formation and pro -mote the crystalline graphene-like structure growth, resulting in a further increase in the thermal diffusivity up to 1.21 cm2/s, twice that of the bare copper foil.
查看更多>>摘要：In this study, we investigated the microstructural evolution, surface hardening and general corrosion properties of a precipitation-strengthened Inconel 718 Ni-superalloy after triode-plasma nitriding (TPN) at low treatment temperatures of 400-450 degrees C (i.e. thermodynamic paraequilibrium conditions) and a high treatment temperature of 700 degrees C. At low treatment temperatures, apart from the formation of nitrogen-expanded austenite (gamma N) from the high-Cr gamma matrix, the pre-existing gamma' and gamma '' intermetallic nano-precipitates appear to exhibit different nitriding responses. The spheroidal N-modified gamma' (or gamma'(N)) precipitates were 'slightly-expanded', leading to slightly shifted XRD peaks, i.e. 2-theta angles of similar to 0.2 degrees from gamma(substrate)(111) and similar to 0.5 from gamma(substrate)(200). In contrast, N-modified gamma '' (or gamma ''(N)) could experience substantial lattice expansion close to that of the gamma(N) matrix. With increasing treatment temperature, nitride formation started as additional nano-sized precipitates (e.g.-3-6 nm diameter as observed at 450 degrees C) and grew into laths (e.g.-5-10 nm thick and-15-30 nm wide as observed at 700 degrees C). Without changing core microstructure/properties, surface nitrogen modification and hardening were obtained on alloy 718 after TPN (e.g. from-486 HV0.025 to-1212 HV0.025 after TPN at 400 degrees C). No degradation of corrosion performance was observed for the nitrogen-supersaturated surface after TPN at 400 degrees C. However, the 450 degrees C TPN-treated surface showed a slightly increased current density in the anodic region, which can be associated with early-stage nitride formation. The significantly deteriorated corrosion performance after TPN treatment at 700 degrees C is due to pronounced nitride formation and segregation of substitutional alloying elements.
查看更多>>摘要：The soft sparking regime of Plasma Electrolytic Oxidation (PEO) of valve metals attracts increasing attention as it enables a better process control with improved energy efficiency and coatings with enhanced performance to be obtained. Here, the discharges softening phenomenon was characterised by evaluation of changes in electrical signal, composition of gaseous products and morphology of the metal-oxide interface in PEO coatings on Al. The coatings were formed using two electrical regimes retarding or promoting soft sparking conditions. Harmonic analysis of PEO process has been performed using independent evaluation of the positive and negative half waves of polarisation signal. The composition of gas evolved during the PEO process was evaluated by a quantitative gas analyser. Coatings were characterised by scanning and transmission electron microscopy with energy dispersive spectroscopy and small area electron diffraction. It was found that discharge softening is accompanied with a decrease in oxygen evolution rate, an increase in equivalent capacitance of anodic process as well as structural and compositional changes near the metal-oxide interface. The experimental findings provide further support to the explanation of discharge softening phenomenon by narrowing the active zone at the metal oxide interface due to intercalation of hydrogen species into anodic alumina under cathodic polarisation. Such mechanistic understanding allows rational regime selection, in-situ process control and optimisation of the coating properties to be performed that paves the way to intellectual manufacturing approach based on careful process monitoring in operando.
查看更多>>摘要：Multicomponent alloy thin films including high entropy alloy (HEA) and medium entropy alloy (MEA) thin films have drawn lots of attention from researchers and industries because of their outstanding properties, such as high hardness, good wear and corrosion resistance. Among several kinds of multicomponent alloy systems, the refractory HEA and MEA are characterized by their high temperature strength and stable thermal properties. In this work, the W-Nb-Ta-Ti and W-Nb-Ta-Ti-N refractory MEA thin films were fabricated by a magnetron co-sputtering system. The structure of W-Nb-Ta-Ti-N coatings changed from BCC to B1 FCC nitride phase when the nitrogen concentration reached 42.6 at.%. The microstructure of BCC structured W-Nb-Ta-Ti-N thin films changed from a coarse columnar to a dense feature as the nitrogen content increased from 0 to 16.2 at.%. A maximum hardness of 24.4 GPa was obtained for the BCC structured W34.3Nb21.7Ta26.4Ti1.4N16.2 thin film. The best adhesion property and the lowest coefficient of friction were found for the FCC W31.1Nb9.6Ta13.1Ti3.6N42.6 nitride thin film. The corrosion resistance of 304SS substrate in 5 wt% NaCl aqueous solution was greatly enhanced by the deposition of the W-Nb-Ta-Ti and W-Nb-Ta-Ti-N refractory MEA thin films. The best corrosion resistance can be seen for the nitrogen-free W37.9Nb25.8Ta28.8Ti7.5 thin film due to its dense microstructure, highest Ta and Nb contents, high configurational entropy and sluggish diffusion effects.
Delgado, A.Garcia-Zarco, O.Restrepo, J.Rodil, S. E....
10页
查看更多>>摘要：AlCrN coatings have long been used to endure the lifetime of cutting tools due to their high hardness and good mechanical qualities. Vanadium (V) additions to AlCrN coatings were studied for their mechanical and tribological properties against Al2O3 counterparts using the linear reciprocating sliding test. The AlCrN and AlCrVN coatings were deposited using cathodic multi-arc evaporation to steel substrates. We evaluated the effect of a high fraction of V into equimolar Al and Cr coatings, which is different from those reported in previous works. X-ray diffraction patterns and Raman spectroscopy demonstrated that the structure remained as the metastable face center cubic. Microidentation tests demonstrated that AlCrVN coating has a higher hardness than AlCrN coating, probably due to an improved microstructure and larger nitrogen incorporation. The wear resistance of the hard steel substrate was significantly increased using both hard coatings. However, no significant changes were observed in the coefficient of friction and wear rate. The results show that V addition significantly improved the mechanical and adhesive capabilities of the AlCrN coating without compromising the oxidation resistance at moderate temperatures (< 500 C).
Hans, MarcusCzigany, ZsoltNeuss, DeborahSaelker, Janis A....
12页
查看更多>>摘要：Single-phase metastable cubic (V,Al)N thin films with columnar microstructure were grown by high power pulsed magnetron sputtering at 440 ? and the thermal decomposition mechanisms were systematically investigated by post-deposition vacuum annealing from 600 to 900 ?. The onset of spinodal decomposition into isostructural V-and Al-rich cubic nitride phases is demonstrated after cyclic vacuum annealing at 700 ?. Moreover, at this temperature, evidence for aluminum diffusion to grain boundaries and triple junctions is provided by correlation of transmission electron microscopy and atom probe tomography data. The formation of Al-rich regions can be understood by the more than 25% lower activation energy for bulk diffusion of aluminum compared to vanadium as obtained from ab initio calculations. It is reasonable to assume that these Al-rich regions are precursors for the formation of wurtzite AlN, which is unambiguously identified after annealing at 800 ? by microscopy and tomography. The significantly larger equilibrium volume of wurtzite AlN compared to the cubic phase explains its initial formation exclusively at triple junctions and grain boundaries. In contrast, twin boundaries are enriched in vanadium. Interestingly, the formation of the wurtzite phase at grain boundaries and triple junctions can be tracked by resistivity measurements, while X-ray diffraction and nanoindentation data do not support an unambiguous wurtzite phase formation claim for annealing temperatures < 900 ?. Hence, it is evident that previously reported formation temperatures of wurtzite AlN in transition metal aluminum nitrides, determined by other characterization techniques than chemical and structural characterization at the nanometer scale and/or resistivity measurements, are overestimated.
NSTL
Elsevier