Nanocrystalline Pd alloy films coated by electroless deposition

The structures of palladium and palladium alloys thin films deposited from organic electrolytes onto metallic substrates by electroless plating method have been investigated. The coatings are dense, pore-free 0.005-1 microm thick films with high adhesive strength to the substrate surface. EDX, XRD, SEM and TEM methods were used to determine the composition and structure of alloy coatings of the following binary systems: Pd-Au, Pd-Ag, Pd-Ni, Pd-Pb, and ternary system Pd-Au-Ni. The coatings of Pd-Au, Pd-Ag and Pd-Ni have a solid solution structure, whereas Pd-Pb is intermetallic compound. It has been found that the deposited films consist of nanocrystalline grains with sizes in the range of 11-35 nm. Scanning and transmission electron microscopy investigations reveal the existence of clusters formed by nanocrystalline grains. The origin for the formation of nanocrystalline structures of coating films is discussed.     

Influence of Ni content on the structure and properties of Cr-Ni-N coatings prepared by direct current magnetron sputtering

Cr-Ni-N coatings were deposited on 304 stainless steel substrates using a conventional direct current magnetron reactive sputtering system in nitrogen-argon reactive gas mixtures. The influence of Ni content (0 ≦ x ≦ 20 at.%) on the coating composition, microstructure, and tribological properties was investigated by glow discharge optical spectroscopy, X-ray diffraction and transmission electron microscopy, scanning electron microscopy (SEM), nano-indentation, and pin-on-disk tests. The results showed that microstructure and properties of coatings changed due to the introduction of Ni. The ternary Cr-Ni-N coatings exhibited solid solution structures in spite of the different compositions. The addition of Ni strongly favoured preferred orientation growth of <200>. This preferred orientation resulted from the formed nano-columns being composed of grains with the same crystallographic orientation, as confirmed by SEM cross-sectional observations. The mechanical properties including the nano-hardness and reduced Young's modulus decreased with increasing Ni content. Pin-on-disk tests showed that low Ni content coatings presented higher abrasion resistance than high Ni content coatings.     

Transmission electron microscopy study of Ni–Si nanocomposite films

Nickel induced crystallization of amorphous Si (a-Si) films is investigated using transmission electron microscopy. Metal-induced crystallization was achieved on layered films deposited onto thermally oxidized Si(3 1 1) substrates by electron beam evaporation of a-Si (400 nm) over Ni (50 nm). The multi-layer stack was subjected to post-deposition annealing at 200 and 600 °C for 1 h after the deposition. Microstructural studies reveal the formation of nanosized grains separated by dendritic channels of 5 nm width and 400 nm length. Electron diffraction on selected points within these nanostructured regions shows the presence of face centered cubic NiSi₂ and diamond cubic structured Si. Z-contrast scanning transmission electron microscopy images reveal that the crystallization of Si occurs at the interface between the grains of NiSi₂ and a-Si. X-ray absorption fine structure spectroscopy analysis has been carried out to understand the nature of Ni in the Ni–Si nanocomposite film. The results of the present study indicate that the metal induced crystallization is due to the diffusion of Ni into the a-Si matrix, which then reacts to form nickel silicide at temperatures of the order of 600 °C leading to crystallization of a-Si at the silicide–silicon interface.     

Annealing of sputter-deposited nanocrystalline Cr-Ta coatings in a low-oxygen-containing atmosphere

As a protective hard coating on glass molding dies, Cr-Ta coatings were fabricated on binderless tungsten carbide substrates with a Ti interlayer by RF magnetron sputtering. The nanocrystalline Cr-Ta coatings were deposited at 550 °C, which revealed one nanocrystalline phase for the Ta-rich coating and two nanocrystalline phases for the Cr-rich coating. Annealing treatment was conducted at 600 °C in a 12 ppm O₂-N₂ atmosphere to evaluate the coating performance in a realistic glass molding environment. Both Auger electron spectroscopy and X-ray photoelectron spectroscopy depth profiles verified the outward diffusion of Cr, which formed a protective coating for the Cr-rich coatings. A scale of Cr₂O₃ and a Cr-depleted transition zone near the surface were identified by conducting a transmission electron microscopy investigation on the annealed Cr_0.71Ta_0.29 coating. The Cr-rich coating absorbed a smaller amount of oxygen, exhibited greater hardness, and maintained nanoscale surface roughness after annealing in the glass molding atmosphere, thus making it an appropriate protective coating for the die material.     

Characterization of electrochemically deposited Cu-Ni black coatings

Electrochemically deposited Cu-Ni black coatings on molybdenum substrate from ethylenediaminetetraacetic acid (EDTA) bath solution are shown to exhibit good optical properties (α=0.94, ε = 0.09). The deposit is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Cu is present in metallic and +2 oxidation states in the as-prepared Cu-Ni black coating, whereas Ni²⁺ as well as Ni³⁺ species are observed in the same coating. Cu and Ni are observed in their metallic state after 10 and 20 min sputtering. X-ray initiated Auger electron spectroscopy (XAES) of Cu and Ni also agrees well with XPS investigations.     

Effects of A-elements (ASi, Ge or Sn) on the structure and electrical contact properties of Ti-A-C-Ag nanocomposites

Ti-A-C-Ag (A is Si, Ge or Sn) nanocomposite coatings have been deposited by dc magnetron sputtering in an ultra high vacuum chamber. Electron microscopy, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and x-ray diffraction show that all coatings contain nanocrystalline TiC and Ag grains in a matrix of mainly amorphous C. A C/Ti ratio above unity yields a homogenous distribution of Ag with a reduced grain size. From a chemical point of view, the addition of Ge and Sn to the Ti-C-Ag system should increase the conductivity of the coatings since the formation of more metallic phases than Si. We demonstrate that Si can be replaced with Ge and Sn and still yield a homogeneous distribution of Ag. The incorporation of Ge and Sn to the Ti-C-Ag system results in elemental precipitation and intermetallic phases, respectively. This gives improved electrical properties compared to Ti-Si-C-Ag coatings, and a contact resistance at loads of ~ 1 N against an Au probe (radius of 0.7 mm) that is comparable to that of Ag.     

Mechanical and microstructural characteristics of detonation gun sprayed NiCrAlY + 0.4 wt% CeO2 coatings on superalloys

The microstructure and mechanical properties of detonation gun sprayed NiCrAlY + CeO₂ alloy coatings deposited on superalloys were investigated. The morphologies of the coatings were characterized by using the techniques such as optical microscopy, X-ray diffraction and field emission scanning electron microscopy/energy-dispersive analysis. The coating depicts the formation of dendritic structure and the microstructural refinement in the coating was due to ceria. Average porosity on three substrates was less than 0.58% and surface roughness of the coatings was in the range of 6.17–6.94 μm. Average bond strength and microhardness of the coatings were found to be 58 MPa and 697–920 H_V, respectively.     

Synthesis,characterization and photoresponse study of undoped and transition metal (Co,Ni, Mn) doped ZnO thin films

The synthesis, characterization and photoresponse studies of undoped and transition metal doped zinc oxide thin films are carried out in this work, in prospect of visible light photo detection and sensor applications. The undoped and transition metal ions such as, Co, Ni and Mn doped ZnO films in this study were synthesized by chemical solution deposition, involving spin-coating. We have characterized the deposited films using X-ray diffraction, scanning electron microscopy, photoluminescence and UV–vis spectroscopy studies. The devices of the films for photoresponse study were fabricated by top Ag contacts on the film surface in metal–semiconductor–metal configuration. The current–voltage characteristics and switching measurements of these devices were studied under the illumination of an incandescent lamp. We found a high ON/OFF ratio of 8 and highest photocurrent density of 0.7 mA/cm² for Ni doped ZnO film.     

Structure and tribological properties of Ag films deposited at low temperature

The effects of substrate temperature on the structure and tribological properties of Ag films deposited at low temperatures (LT, 130-217 K) by arc ion plating (AIP) have been studied. The structure and morphology of the Ag films were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and field emission scanning electron microscope (FESEM). The results showed that there exist (1 1 1) and (2 0 0) preferred orientation transitions for decreasing temperature at different bias voltages. The tribological properties were evaluated by a ball-on-disk tribometer and wear tracks were analyzed by means of scanning electron microscopy (SEM). The results show that substrate deposition temperature significantly affected the wear of LT Ag films. For each bias voltage studied, the film showing the highest wear rate was deposited at the lowest temperature and the film with the lowest wear rate, (significantly lower than room temperature (RT) deposited Ag films), was deposited at a temperature between the highest and the lowest temperatures examined. The wear mechanism was discussed in terms of lubrication effect of film material transferred to the counterpart and its dependence on the microstructure of the original deposited film.     

Corrosion resistance of electrodeposited Ni–Al composite coatings on the aluminum substrate

Ni matrix–Al particle composite coating was adopted via sediment co-deposition (SCD) method on the zincate coated aluminum substrate. Surface morphology was investigated by scanning electron microscopy (SEM). The electrochemical behavior of the coatings was studied by polarization potentiodynamic test in 3.5 wt.% sodium chloride using a three electrode open cell. The effect of the electroplating parameters on the Al co-deposition was studied. Maximum of 22 wt.% Al particles were deposited in the coating. It was found that the zincate coating plays an important role in improving the nickel layer adherent. Furthermore, incorporation of aluminum particles in Ni matrix refined the Ni crystal coatings. However, polarization curves shifted to negative potentials and corrosion rate is decreased.     

Characterisation of nano-structured titanium and aluminium nitride coatings by indentation, transmission electron microscopy and electron energy loss spectroscopy

Titanium and aluminium nitride Ti_1 − xAl_xN films deposited by radiofrequency magnetron reactive sputtering onto steel substrate are examined by transmission electron microscopy over all the range of composition (x = 0, 0.5, 0.68, 0.86, 1). The deposition parameters are optimised in order to grow nitride films with low stress over all the composition range. Transmission electron microscopy cross-section images of Vickers indentation prints performed on that set of coatings show the evolution of their damage behaviour as increasing x Al content. Cubic Ti-rich nitrides consist of small grains clustered in rather large columns sliding along each other during indentation. Hexagonal Al-rich films grow in thinner columns which can be bent under the Vickers tip. Indentation tests carried out on TiN and AlN films are simulated using finite element modelling. Particular aspects of shear stresses and displacements in the coating/substrate are investigated. The growth mode and the nanostructure of two typical films, TiN and Ti_0.14Al_0.86N, are studied in detail by combining transmission electron microscopy cross-sections and plan views. Electron energy loss spectrum taken across Ti_0.14Al_0.86N film suggests that a part of nitrogen atoms is in cubic-like local environment though the lattice symmetry of Al-rich coatings is hexagonal. The poorly crystallised domains containing Ti and N atoms in cubic-like environment are obviously located in grain boundaries and afford protection of the coating against cracking.     

Nanostructural, electrical, and tribological properties of composite Au-MoS2 coatings

Considerable research has been done on the tribological properties of cosputtered metal/MoS₂ solid lubricant films with low metal content (< 20 at.%) because of their usefulness in applications at high Hertzian contact stress (around 1 GPa). However, cosputtered Au-MoS₂ coatings with a much higher range of metal contents up to (95 at.%) have shown surprisingly good performance at low contact stresses (as low as 0.1 MPa). In the present study, transmission electron microscopy, X-ray diffraction and electrical resistance measurements of cosputtered Au-MoS₂ coatings reveal them to be composites of nanocrystalline Au particles within an amorphous MoS₂ matrix. Electrical conductivity images of the coatings displayed metallic (Au) and semi-conducting (MoS₂) domains of nanometer dimensions. Auger Nanoprobe analyses confirmed that sliding on the coatings causes the formation of a pure MoS₂ layer about a nanometer thick on top of the bulk of the coatings. Lattice resolution atomic force microscopy revealed that this nanometer-thick MoS₂ layer is crystalline, and oriented with the basal plane (0001) parallel to the coating surface. Electrical resistance obtained during sliding and pull-off force measurements was consistent with the structure of the coatings. Sliding friction data on the coatings support previous results showing that performance at different Hertzian contact stresses correlated strongly with Au content.     

Influence of multi-interfacial structure on mechanical and tribological properties of TiSiN/Ag multilayer coatings

The TiSiN/Ag multilayer coatings with bilayer periods of ~50, 65, 80, 115, 150, and 410 nm have been deposited on Ti6Al4 V alloy by arc ion plating. In order to improve the adhesion of the TiSiN/Ag multilayer coatings, TiN buffer layer was first deposited on titanium alloy. The multi-interfacial TiSiN/Ag layers possess alternating TiSiN and Ag layers. The TiSiN layers display a typical nanocrystalline/amorphous microstructure, with nanocrystalline TiN and amorphous Si₃N₄. TiN nanocrystallites embed in amorphous Si₃N₄ matrix exhibiting a fine-grained crystalline structure. The Ag layers exhibit ductile nanocrystalline metallic silver. The coatings appear to be a strong TiN (200)-preferred orientation for fiber texture growth. Moreover, the grain size of TiN decreases with the decrease of the bilayer periods. Evidence concluded from transmission electron microscopy revealed that multi-interfacial structures effectively limit continuous growth of single (200)-preferred orientation coarse columnar TiN crystals. The hardness of the coatings increases with the decreasing bilayer periods. Multi-interface can act as a lubricant, effectively hinder the cracks propagation and prevent aggressive seawater from permeating to substrate through the micro-pores to some extent, reducing the friction coefficient and wear rates. It was found that the TiSiN/Ag multilayer coating with a bilayer period of 50 nm shows an excellent wear resistance due to the fine grain size, high hardness, and silver-lubricated transfer films formed during wear tests.     

Effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy

The effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), differential scanning calorimeter (DSC), transmission electron microscopy (TEM) and tensile test, respectively. The results show that the mechanical property increases and then decreases with increasing the solution temperature. And the residual phases are dissolved into the matrix gradually, the number fraction of the precipitation and the size of recrystallized grains increase. Compared to the solution temperature, the solution holding time has less effect on the microstructure and the mechanical properties of Al–Cu–Mg–Ag alloy. The overburnt temperature of Al–Cu–Mg–Ag alloy is 525 °C. The yield strength and the elongation get the best when the alloy is solution treated at 515 °C for 1.5 h, is 504 MPa and 12.2% respectively. The fracture mechanism of the samples is ductile fracture.     

Optical properties of nanocrystalline SnS2 thin films

Thin films of nanocrystalline SnS₂ on glass substrates were prepared from solution by dip coating and then sulfurized in H₂S (H₂S:Ar = 1:10) atmosphere. The films had an average thickness of 60 nm and were characterized by X-ray diffraction studies, scanning electron microscopy, EDAX, transmission electron microscopy, UV-vis spectroscopy, and Raman spectroscopy. The influence of annealing temperature (150-300 °C) on the crystallinity and particle size was studied. The effect of CTAB as a capping agent has been tested. X-ray diffraction analysis revealed the polycrystalline nature of the films with a preferential orientation along the c-axis. Optical transmission spectra indicated a marked blue shift of the absorption edge due to quantum confinement and optical band gap was found to vary from 3.5 to 3.0 eV with annealing temperature. Raman studies indicated a prominent broad peak at ∼314 cm⁻¹, which confirmed the presence of nanocrystalline SnS₂ phase.     

Microstructure and tribological property of nanocrystalline Co–W alloy coating produced by dual-pulse electrodeposition

The nanocrystalline Co–W alloy coatings were produced by dual-pulse electrodeposition from aqueous bath with cobalt sulfate and sodium tungstate (Na₂WO₄). Influence of the current density and Na₂WO₄ concentration in bath on the microstructure, morphology and hardness of the Co–W alloy coatings were investigated using an X-ray diffraction, a scanning electronic microscope and a Vickers hardness tester, respectively. In addition, the friction and wear properties of the Co–W alloy coating electrodeposited under different condition were evaluated with a ball-on-disk UMT-3MT tribometer. The correlation between the electrodeposition condition, the microstructure and alloy composition, and the hardness and tribological properties of the deposited Co–W alloy coatings were discussed in detail. The results showed that the microhardness of the deposited Co–W alloy coating was significantly affected by its average grain size, W content and crystal orientation. Smaller grain size, higher W content and strong hcp (1 0 0) orientation favor the improvement of the hardness for Co–W alloy coatings. The deposited Co–W alloy coating could obtain the maximum microhardness over 1000 kgf mm⁻² by careful control of the electrodeposition conditions. The tribological properties of the electrodeposited Co–W alloy coating were greatly affected by its grain size, microhardness, surface morphologies and composition, and could be significantly improved by optimizing the electrodeposition condition.     

Influence of silicon content on the microstructure and hardness of CrN coatings deposited by reactive magnetron sputtering

CrN and CrSiN films were deposited on the stainless steel and silicon substrates by DC magnetron sputtering and their microstructural features were investigated by X-ray diffraction (XRD), scanning electron microscope (FE-SEM/EDS), and atomic force microscopy (AFM). The influence of Si content along with process parameters such as power on the microstructural characteristics of Cr–Si–N and CrN films were investigated and compared between each other. The power and increasing Si contents strongly influence the microstructural and hardness of the deposited films. XRD analysis of the coatings indicates a grain refinement with increase in Si content during deposition of coatings, which is tandem with AFM and SEM results. Also, the surface roughness and particle size are decreasing with addition of Si in the films. The hardness of CrN and CrSiN was measured by microhardness tester and found that introduction of Si content in the CrN system increases its hardness from 1839 Hv to 2570 Hv.     

Preparation of CVD diamond coatings on gamma titanium aluminide using MPECVD with various interlayers

CVD diamond coatings were deposited on to γ-TiAl surfaces using a microwave plasma enhanced CVD to improve wear properties and the performance of γ-TiAl. Diamond coatings were directly deposited on to γ-TiAl substrates and deposited on to TiC, Ti₅Si₃, Al₂O₃ + TiO₂, and Si interlayers prepared on γ-TiAl substrates. The diamond coatings deposited directly on γ-TiAl suffered severe delamination and cracked. Those deposited on TiC and Ti₅Si₃ interlayers partially delaminated, whereas those deposited on Al₂O₃ + TiO₂ and Si interlayers adhered well to the underlying surfaces. The diamond films obtained were characterized using scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Raman spectra showed that polycrystalline and nanocrystalline diamond films grew on γ-TiAl. Residual internal stresses of the diamond coatings deposited on interlayered-γ-TiAl were estimated experimentally from Raman spectra. The coatings prepared on Al₂O₃ + TiO₂/γ-TiAl and Si/γ-TiAl showed lower residual stresses.     

Bias effects on microstructure, mechanical properties and corrosion resistance of arc-evaporated CrTiAlN nanocomposite films on AISI 304 stainless steel

CrTiAlN films were deposited on AISI 304 stainless steel by cathodic arc evaporation under a systematic variation of the substrate bias voltage. The effects of substrate bias on the coating morphology and mechanical properties, such as structure, composition, adhesion, hardness and Young's modulus, were studied in details using field emission scanning electron microscopy, X-ray diffraction, electron probe microanalysis and indenter. Polarization test and immersion test were also carried out to evaluate the corrosion behavior of the various films. CrTiAlN films are nanocrystalline that exhibit a CrN/TiAlN multi-layered morphology. At the optimal value of substrate bias voltage (i.e., − 150 V), the CrTiAlN film showed an increased Cr content and improved properties, such as higher adhesion, higher hardness (38 ± 2 GPa), and greater Young's modulus (319 ± 16 GPa) vs. the films deposited at other substrate bias voltages. Moreover, the optimum film has better corrosion resistance in 3.5 wt.% NaCl and 20 vol.% HCl solutions.     

On the processing-structure-property relationship of ITO layers deposited on crystalline and amorphous Si

Indium-tin-oxide (ITO) antireflection coatings were deposited on crystalline Si (c-Si), amorphous hydrogenated Si (a-Si:H) and glass substrates at room temperature (RT), 160 °C and 230 °C by magnetron sputtering. The films were characterised using atomic force microscopy, transmission electron microscopy, angle resolved X-ray photoelectron spectroscopy, combined with resistance and transmittance measurements. The conductivity and refractive index as well as the morphology of the ITO films showed a significant dependence on the processing conditions. The films deposited on the two different Si substrates at higher temperatures have rougher surfaces compared to the RT ones due to the development of crystallinity and growth of columnar grains.