Elevated-temperature tribological behavior of Ti–B–C–N coatings deposited by reactive magnetron sputtering

Quaternary Ti-B-C-N coatings with various carbon contents were deposited on high-speed steel(HSS)substrates by reactive magnetron sputtering(RMS) system.The elevated-temperature tribological behavior of Ti-BC-N coatings was explored using pin-on-disk tribometer,scanning electron microscopy(SEM),and energy-dispersive X-ray spectroscopy(EDX).The present results show that the steady-state friction coefficient value and the instantaneous friction coefficient fluctuation range of TiB-C-N coatings decrease as carbon content increases at100 and 300 ℃,while the steady-state friction coefficient value of all Ti-B-C-N coatings becomes higher than 0.4 at500 ℃.As ambient temperature increases,the running-in periods of all Ti-B-C-N coatings become shorter.Wear damage to Ti-B-C-N coatings during sliding at elevated temperature is mainly caused by adhesive wear,and adhesive-wear damage to Ti-B-C-N coatings increases as ambient temperature increases;however,higher carbon content is beneficial for decreasing the adhesive-wear damage to Ti-B-C-N coatings during sliding at elevated temperature.     

Corrosion behaviors of Cr-Al-N coatings deposited by reactive magnetron sputtering

CrN and Cr-Al-N coatings were deposited by reactive magnetron sputtering on the glass substrate, and their corrosion behavior was studied. The electrochemical tests using both DC （polarization curves） and AC techniques （EIS） were carried out on Potentiostal/Galvanstat （EG＆G） in 3.5% （mass fraction） NaCl solution. After immersed into NaCl solution for 1 h, the mass of the CrN coating keeps constant with the time continuing. This can be explained by the passivation of the coating. The comparison between the corrosion potential （φcom） of the Cr-Al-N coatings with different aluminum contents reveals that the corrosion potentials of the aluminum contain coatings are nobler than that of the CrN coatings. This means that the addition of aluminum shifts the corrosion potential to more positive potential value. Among these coatings, CrN in NaCl solution exhibits the worst corrosion resistance, while the corrosion resistance of Cr0.63Al0.37N in NaCl solution is the best. The polarization data and EIS data suggest that addition of aluminum can improve the corrosion resistance of CrN coating.     

Growth characteristics of MoS2 coatings prepared by unbalanced bipolar DC magnetron sputtering

MoS2 coatings were prepared by unbalanced bipolar DC magnetron sputtering under different argon pressures and for different deposition times, and the structure and morphology of MoS2 coatings were determined and observed respectively by X-ray diffractometry and scanning electron microscopy. The results show that at lower argon pressures of 0.15 Pa and 0.40 Pa, MoS2 coatings are formed with the （002） basal plane parallel to the surface, whereas the coating deposited at the argon pressure above 0.60 Pa has the （002） basal plane perpendicular to the surface. Two stages can be classified for the formation of MoS2 coating. At the initial stage of coating formation, the （002） basal plane with S-Mo-S layer structure grows on the substrate whatever the argon pressure is. And then the coating under 0.40 Pa argon pressure still grows with （002） laminate structure, but the coatings under 0.88 Pa and 1.60 Pa argon pressures turn to grow with the mixed basal and edge orientations. The morphology and structure of MoS2 coatings are highly related to their growth rate and the energy of sputtered particles.     

Investigation of Si–B–C–N coatings produced by ion sputtering of SiBC target

Using the method of ion sputtering of sintered Si–B–C targets, amorphous Si–B–C–N thin-film coatings with different nitrogen contents have been prepared. The structures of coatings are studied by the methods of X-ray phase analysis, scanning electron microscopy, glow-discharge optical-emission spectroscopy, infrared spectroscopy, and Raman spectroscopy. The mechanical properties of the obtained coatings are determined using the nanoindentation method. To evaluate the oxidation resistance of the coatings, they are annealed in air at temperatures of 1000, 1100, and 1200°C. It is established that coatings of the optimal composition show a hardness of 26 GPa, an elastic modulus of 221 GPa, and an elastic recovery of 65%. The coatings obtained in the medium consisting of Ar and 15% N₂ are oxidation-resistant at temperatures of up to 1200°C owing to the formation of a SiO₂-based protective film on their surface.     

Structural and photoelectrochemical properties of Ti1−xWxO2 thin films deposited by magnetron sputtering

W-doped titanium dioxide is a promising candidate material for applications ranging from UV–VIS light photocatalytic reactions to catalyst support in proton-exchange membrane fuel cells, depending on the doping content. The present study reports on the possibility to synthesize substitutional Ti_1?xW_xO₂ thin films with 0 ≤ x ≤ 1 by magnetron co-sputtering from Ti and W metallic targets. Two routes were investigated starting from 1) crystalline titanium tungsten alloys deposited in non-reactive (pure Ar) mode, and 2) amorphous titanium tungsten oxides deposited in reactive (Ar + O₂ atmosphere) mode. The structure and phase stability after air annealing at 550 °C has been investigated by X-ray Diffraction (XRD). X-ray Reflectivity (XRR) was used to determine the change in film mass density upon annealing. Films of the non-reactive mode series could not be successfully fully oxidized into Ti_1?xW_xO₂ form. For the reactive mode film series, ternary Ti_1?xW_xO₂ oxides were obtained after air annealing and the crystal structure was changed from anatase to rutile with increasing W content in the range 0–33 at.%. Films with higher W content (0.33< x ≤ 1) eventually crystallized in the WO₃ triclinic structure. Photo-electrodes were elaborated from the deposited thin films on FTO coated glass, and they all showed photo-response when tested in acid solution, under UV–VIS illumination. Among the doped materials, the Ti_0.92W_0.08O₂ thin film showed the highest photo-current.     

Structure and electronic properties of SiC thin-films deposited by RF magnetron sputtering

SiC thin-films were prepared by RF-magnetron sputtering technique(RMS) with the target of single crystalline SiC and then annealed. The surface morphology of thin-films was characterized by AFM. The result shows that the surface of the thin-films is smooth and compact; XRD analysis reveals that the thin-films are amorphous. The thickness, square-resistance and curves of resistance—temperature were measured. The results show that the curves of lnR versus 1/kT both before and after annealing satisfy the expression of lnR∝△W/kT, where ?W is electron excitation energy in the range of 0.014 2-0.018 5 eV, and it has a trend of increasing when the temperature is increased. After synthetical analysis we get the conclusion that the electronic mechanism of the thin-films is short distance transition between the localized states in the temperature range of 25-250 ℃. The resistivity is in the range of 2.4×10-3-4.4×10-3 Ω·cm and it has the same trend as electron excitation energy when annealing temperature is increased, which further confirms the electronic mechanism of thin-films and the trend of electron excitation energy versus annealing temperature.     

Photocatalytic degradation characteristic of amorphous TiO2-W thin films deposited by magnetron sputtering

TiO2-W films were deposited on the slides by reactive magnetron sputtering. Properties of the films were analyzed via AFM, XRD, XPS, STS, UV-Vis and ellipse polarization apparatus. The results show that TiO2-W films are amorphous. The AFM map reveals that the surface of the film is tough and porous. The experiments of decomposing methylene blue indicate that the thickness threshold on these films is 141 nm, at which the rate ofphotodegradation is 90% in 2 h. And when the thickness is over 141 ran, the rate of photodegradation does not increase any more. This result is completely different from that of crystalloid TiO2 thin film.     

Microstructure and properties of indium tin oxide thin films deposited by RF-magnetron sputtering

Tin-doped indium oxide （ITO） thin films were prepared using conventional radio frequency （RF） planar magnetron sputtering equipped with IR irradiation using a ceramic target of In2O3/SnO2 with a mass ratio of 1：1 at various IR irradiation temperatures T1 （from room temperature to 400℃）. The refractive index, deposited ratio, and resistivity are functions of the sputtering Ar gas pressure. The microstructure of ITO thin films is related to IR T1, the crystalline seeds appear at T1= 300℃, and the films are amorphous at the temperature ranging from 27℃ to 400℃. AFM investigation shows that the roughness value of peak-valley of ITO thin film （Rp-v） and the surface microstructure of rio thin films have a close relation with T1. The IR irradiation results in a widening value of band-gap energy due to Burstein-Moss effect and the maximum visible transmittance shifts toward a shorter wavelength along with a decrease in the film＇s refractive index. The plasma wavelength and the refractive index of ITO thin films are relative to the T1. XPS investigation shows that the photoelectrolytic properties can be deteriorated by the sub-oxides. The deterioration can be decreased by increasing the oxygen flow rote （fo2）, and the mole ratio of Sn/In in the samples reduces with an increase info2.     

Microstructural control of Cr–Si–N films by a hybrid arc ion plating and magnetron sputtering process

The microstructural evolution of Cr–Si–N films deposited by a hybrid arc ion plating and magnetron sputtering process was investigated by varying the sputtering power of Si target and substrate bias voltage. Detailed nanocomposite microstructures of the films were studied by high-resolution transmission electron microscopy. The results indicated that the incorporation of Si into the growing CrN films at 0 V led to the formation of a nanocomposite containing CrN nanocolumns embedded in amorphous SiN_x matrix or near-amorphous microstructure. For the films having a Si content of ～10 at.% and ～15 at.%, a negative bias voltage of ?50 V resulted in the aggregation of nanocolumns in the amorphous matrix. Further increase of negative bias voltage to ?250 V led to the formation of a three-dimensional CrN/a-SiN_x nanocomposite microstructure. The mechanism of microstructure evolution is discussed by considering the thermodynamic and kinetic factors.     

Phase and morphology evolution of TiC in the Ti–Si–C system

TiC was synthesized by reactive pyrolysis of a mixture of poly(dimethylsilaacetylide), [-MeSi(H)C≡C-]_n, Ti, and TiSi₂ particles under Ar atmosphere between 1100 °C and 1400 °C. The pyrolysis products were studied by means of X-ray diffraction (XRD), scanning electron microsphere (SEM), and Energy-Disperse Spectrometer (EDS). The results showed that TiC crystals appeared at 1200 °C accompanied by Ti₅Si₃. At 1400 °C, single crystalline phase TiC was obtained. By changing the ratio of raw materials, TiC crystals with different morphologies, including octahedron, truncated-octahedron, and polyhedral were prepared.     

Microstructure evolution of eutectic Nb–24Ti–15Si–4Cr–2Al–2Hf alloy processed by directional solidification

In this work, the near-eutectic Nb–24Ti–15Si–4Cr–2Al–2Hf(at%) alloy was directionally solidified at 1900 ℃ with withdrawal rates of 6, 18, 36, 50 mm·min~(-1) and then heat-treated at 1450 ℃ for 12 h. The microstructure evolution was investigated. The results show that the microstructure of the directionally solidified(DS) alloy is composed of Nb_(ss)+Nb_5Si_3 eutectics within the whole withdrawal rate range, while the variation of rates makes a great difference on the solidification routes,the morphology and size of Nb_(ss)+Nb_5Si_3 eutectic cells.With the increase in withdrawal rates, the petaloid Nb_(ss)+Nb_5Si_3 eutectic cells transform into granular morphology. After the heat treatment, a mesh structure Nbssis formed gradually which isolates the Nb_5Si_3, and the phase boundaries become smoother in order to reduce the interfacial energy. Moreover, two kinds of Nb_5Si_3 exist in the heat-treated(HT) samples identified by crystal form and element composition, which are supposed as α-Nb_5Si_3 and γ-Nb_5Si_3, respectively. This study exhibits significant merits in guiding the optimization of Nb–Si-based alloys' mechanical properties.     

Microstructure and properties of intermetallic composite coatings fabricated by selective laser melting of Ti–SiC powder mixtures

Transition metal silicides and carbides are attractive advanced materials possessing unique combinations of physical and mechanical properties. However, conventional synthesis of bulk intermetallics is a challenging task because of their high melting point. In the present research, titanium carbides and silicides composites were fabricated on the titanium substrate by a selective laser melting (SLM) of Ti–(20,30,40 wt.%)SiC powder mixtures by an Ytterbium fiber laser with 1.075 μm wavelength, operating at 50 W power, with the laser scanning speed of 120 mm/s. Phase analysis of the fabricated coatings showed that the initial powders remelted and new multiphase structures containing TiC_x, Ti₅Si₃C_x, TiSi₂ and SiC phases in situ formed. Investigation of the microstructure revealed two main types of inhomogeneities in the composites, (i) SiC particles at the interlayer interfaces and, (ii) chemical segregation of the elements in the central areas of the tracks. It was suggested and experimentally proven that an increase in laser power to 80 W was an efficient way to improve the laser penetration depth and the mass transport in the liquid phase, and therefore, to fabricate more homogeneous composite. The SLM Ti–(20,30,40 wt.%)SiC composites demonstrated high hardness (11–17 GPa) and high abrasive wear resistance (3.99 × 10⁻⁷–9.51 × 10⁻⁷ g/Nm) properties, promising for the applications involving abrasive wear.     

Microstructure of Al2O3–SiC nanocomposite ceramic coatings prepared by high velocity oxy–fuel flame spray process

Ion and thermal etching techniques are used to investigate the microstructure of nanocomposite Al₂O₃–SiC coatings prepared by HVOF spraying on mild steel substrate. The observed microstructural features are compared with that of coatings and bulk ceramics prepared with similar feed. The effect of SiC on the microstructure is highlighted.     

Effect of Mo content on the structure and mechanical properties of TiAlMoN films deposited on WC–Co cemented carbide substrate by magnetron sputtering

TiAlMoN films with different Mo contents were deposited by magnetron sputtering at various duty ratios of sputtering Mo target power source, after depositing a Ti interlayer. The concentrations and structure of the films were determined by energy dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffraction. The Mo content of TiAlMoN films gradually increased with increasing the duty ratio. The structure of TiAlMoN films changed from blocky to featurelessness, and ultimately changed to columnar at 12.1 at.% Mo. The TiAlMoN films exhibited the single TiN-based phase with a TiN(111) preferred orientation, and the intensity of this diffraction peak gradually increased with increasing Mo content. Nanoindentation tests indicated that the hardness of TiAlMoN films continuously increased with Mo content, while the H/E ratio reached a peak at 8.3 at.% Mo. All the films exhibited a good adhesion to WC–Co substrates because of the internal Ti interlayer. The ball-on-disk wear properties of TiAlMoN films showed that the lowest wear rate and best wear resistance were for 8.3 at.% Mo, resulting from the formation of molybdenum trioxide on the surface of wear track.     

Corrosion behavior of NiCrBSi coatings deposited by HVOF spraying

The corrosion resistance of NiCrBSi coating deposited on steel substrate by HVOF was examined using electrochemical tests and immersion tests so as to offer an experimental basis to expand a promising applied field of HVOF in aqueous medium, comparing with those of coatings deposited by oxyacetylene flame spraying and flame cladding. The results show that the general corrosion rate of HVOF sprayed coatings is quite bigger than that of clad coatings, bat it is less sensitive to local corrosion. There is less and smaller porosity in the coatings deposited by HVOF than that in flame sprayed coatinlgs. The effects of porosity on the corrosion current density was indistinctive, bat the existence of large amount of defects in the coatings damaged the cohesion of the coatings, causing the metallic particles drop off from the coatings under the influence of corrosive medium. Improving the quality and reducing the porosity of coatings is the key to get the coatings with high corrosion resistance.     

Fabrication of ZnO films by radio frequency magnetron sputtering and annealing

ZnO thin films were deposited on Si（111） substrates through a radio frequency （rf） magnetron sputtering system. Then the samples were annealed at different temperatures in air ambience and ammonia ambience respectively. The structure and composition of the ZnO films were studied by X-ray diffraction （XRD） and X-ray photoelectron spectroscopy （XPS）. The morphology of the samples was studied by scanning electron microscopy （SEM）. Measured results show that ZnO films with hexagonal wurtzite structure were grown on Si（111） substrates when annealed in the two ambiences. The volatilization process of ZnO in the ammonia ambience at high temperature was discussed and the mechanism of the reaction was analyzed.     

Microstructure and wear behaviour of pulse electrodeposited alumina nanoparticle reinforced Co–W nanocomposite coatings

Abstract

The microstructure and wear behaviour of alumina nanoparticle reinforced Co–W alloy coatings have been investigated for potential replacement of hard chrome coatings. The composite coatings were pulse electrodeposited on steel substrates using a citrate bath. The effects of current density, in the range of 1–9 A dm^?2, on the particle reinforcement, phase/microstructure, microhardness, and wear properties of the coating have been studied. The coatings codeposited with current density of 5 A dm^?2 at 333 Hz pulse frequency and 33% duty cycle exhibited microhardness comparable to hard chromium coatings.     

Structural and physical properties of permalloy thin films prepared by DC magnetron sputtering at different substrate temperature

Permalloy Ni80Fe20 films have been grown on thermal oxidized Si (111) wafers by magnetron sputtering at well-controlled substrate temperatures of 300, 500, 640 and 780 K in 0.65 Pa argon pressure. The base pressure was about 1×10-4 Pa. The deposition rate was about 5 nm/min for all the films. The structure of the films was studied using X-ray diffraction, scanning electron microscopy and atomic force microscopy. The composition of the films was analyzed using scanning Auger microprobe. The resistance and magnetoresistance of the films were measured using four-point probe technique. The results show that the content of oxygen in the films decreases gradually with raising substrate temperature. In addition, the surface morphology of the films presents notable change with the increasing of the substrate temperature; the residual gases and defects decrease and the grains have coalesced evidently, and then the grains have grown up obviously and the texture of (111) orientation develops gradually in the grow     

Effect of Zr Addition on Microstructure and Properties of Cu–Ag–Ti Alloys

Effects of small addition of Zr on the microstructures and properties of as-cast Cu₅₀Ag_46?xZr_xTi₄ alloys were investigated by differential scanning calorimeter (DSC), x-ray diffraction, microscope, and property testings. The results show that the melting point of the Cu₅₀Ag₄₆Ti₄ alloys does not change obviously with the addition of Zr at the melting points of about 779 °C. Adding Zr reduces the volume fraction and size of the board strips of Cu₃Ti phase, promotes the uniform distribution of the new phase Cu₄AgZr, and improves the Vickers hardness and shear strength of the based alloys. Moreover, increasing the Zr content can improve the high-temperature oxidation resistance of alloys.