Corrosion of TiN, (TiAl)N and CrN hard coatings produced by magnetron sputtering

Metallic components like moulds, dies and machinery can be subjected to intensive degradation during plastic transformation processes, namely when working with fibre filler materials and plastics which release F, S or Cl during transformation. The degradation is attributed to the combined erosive and abrasive wear by the filler material and corrosive attack of agents. This degradation reduces the lifetime of the components considerably and has a direct impact on process productivity and surface finish of the final products. Nitride-based hard coatings like TiN, (TiAl)N, BN, etc. have proved their capability to increase tool lifetime when exposed to abrasive and corrosive environments found in plastic transformation processes halogenated polymers, acrylics, polyesters, fibre reinforced plastics, etc.. Within the frame of this work we produced TiN, (TiAl)N, CrN hard coatings, with and without a metallic interlayer, by dc and rf reactive magnetron sputtering, with a thickness of about 2 μm. The aqueous corrosion behaviour of the coatings was studied in saline and acidic environments by potentiodynamic and open circuit potential (OCP) measurements. The oxidation resistance during annealing in air was also studied. In saline NaCl 9% and acid HCl 3.4%environments we found that a metallic interlayer of Ti or Cr in the case of TiN– TiAl N-coated samples and CrN-coated samples, respectively, generally improve the corrosion resistance. Best results for all tested nitride coated samples were obtained for the Ti Al N coating. The OCP vs. Saturated Calomel Electrode (SCE) (60 min) measurements indicated that most samples were nobler than the un-coated substrate. The mentioned potentials depend on the deposition conditions and the film microstructure. Most of the coatings lose some of their protective capabilities after an high temperature annealing. In contrast to the Ti-based hard coatings, the corrosion resistance of CrN is improved by a 800ºC annealing treatment in air

Multi-layer solar selective absorber coatings based on W/WSiAlNx /WSiAlOyNx/SiAlOx for high temperature applications

A simulated and an experimental design of multilayer solar selective absorber coatings for high temperature applications is presented in this study. The optical tandem is composed of four layers deposited by magnetron sputtering on stainless steel substrates at room temperature. The first is a back-reflector tungsten layer, that is followed by two absorption layers based on WSiAlNx/ WSiAlOyNx structure for phase interference. The final layer is an antireflection layer of SiAlOx. The design was conducted with the help of SCOUT software creating a multilayer model based on transmittance (T) and reflectance (R) spectra of individual thin layers deposited on glass substrates. The final design shows simultaneously high solar absorptance α=96.0% and low emissivity ε=10.5% (calculated at 400 °C) together with high thermal stability at 450 °C, in air, and 600 °C in vacuum for 400 h and 300 h, respectively.FCT -Fuel Cell Technologies Program(PTDC/CTM-ENE/2882/2014)info:eu-repo/semantics/publishedVersio

Ab initio study of the properties of Ti1-x-ySixAlyN solid solution

We have studied the electronic, structural, and elastic properties of Ti1-x-ySixAlyN metastable phase, using first principles calculations based on the density functional theory. These calculations provide the lattice parameter, density of states, cohesive energy, formation energy and elastic constants, when Si and Al atoms replace Ti in the TiN lattice. The calculated values of lattice parameters and elastic constants are generally in good agreement with experiments and compare well with other theoretical results. We show that the trend followed by cohesive energy, formation energy, elastic constants is related to the electronic properties and bonding characteristics of these compounds

Young's modulus of (Ti,Si)N films by surface acoustic waves and indentation techniques

Ti1yxSixNy films with Si contents up to 17.5 at.% and N contents close to 50 at.% were prepared by r.f. reactive magnetron sputtering. Film densities are within the range 3.4–5.1 gycm3.X-Ray diffraction patterns indicated the formation of two crystalline phases.In the case of low surface mobility, a metastable (Ti, Si)N phase was formed, where Si atoms occupied Ti positions. With increasing surface mobility, a crystalline TiN phase was observed.This behaviour may be explained by the occurrence of Si3N4 segregation, leading to the formation of a nanocomposite film of the type nc-TiNync-(Ti,Si)Nya-Si3N4, although the presence of Si3N4 phase is difficult to prove.In some of the films, a mixture of the (Ti,Si)N metastable phase with the TiN phase was observed, which indicates that the segregation of both TiN and Si3N4 phases is not complete.The Young’s modulus, Ef, of each coating was evaluated using both indentation tests and the surface acoustic waves (SAW) method.For most samples, the results obtained by these two methods are in good agreement.Some differences were observed in films prepared with a bias voltage of y50 V and Si contents higher than 5.9 at.%. For these samples, indentation values of approximately 10–20% higher than those obtained from SAW were found.This discrepancy is related to the nanostructure of these coatings, and it should be pointed out that the SAW results are strongly correlated with the density of the material.Fundação para a Ciência e Tecnologia (FCT)European Community Fund (FEDER)German/Portuguese DAAD/ICCTI Institution

Microcrystalline silicon thin films prepared by RF reactive magnetron sputter deposition

Hydrogenated microcrystalline silicon (microc-Si:H) thin films with Cu as a dopant material (about 2 wt.%) were deposited by RF planar magnetron sputtering in an argon/hydrogen plasma. The composition and microstructure of the films were analysed by SEM, ERD/RBS, X-ray diffraction and Raman spectroscopy. These techniques revealed a columnar film structure, each column consisting of several small (nano) crystals with a lateral dimension up to 10nm. The crystals are oriented, generally with the (111) plane parallel to the sample surface. The hydrogen content of the thin films is about 27-33 at.%. Low deposition rates and low sputter gas pressures favour crystallisation and grain growth. The behaviour can be understood in terms of the diffusion or relaxation length of the deposited Si-atoms

Characterization of TiAlSiN/TiAlSiON/SiO2 optical stack designed by modelling calculations for solar selective applications

Preparation and characterization of TiAlSiN/TiAlSiON/SiO2 solar selective absorber is reported in this contribution. All layers were deposited in a continuous mode using a industrial equipment, the nitride and oxynitride were prepared by reactive magnetron sputtering and the SiO2 layer by Plasma Enhanced Chemical Vapour Deposition. The optical constants of individual layers were calculated by modelling of spectral transmittance and reflectance of the individual layers. The three layer stack absorber was then designed using those optical properties. The thickness of the individual layers was optimized until a solar absorptance of 96% was obtained resulting in a total thickness of about 200 nm, deposited in copper and extruded aluminium absorbers. An emissivity of 5 % for an absorber temperature of 100 ºC was obtained by analyzing the measuring data from a FTIR spectrometer with integrating sphere. After test duration of 600 h, the samples subjected to a thermal annealing at 278 ºC in air showed a performance criterion (PC) below 4% for, while the samples in the humidity tests showed a PC below 2 %.Savo Sola

Optical characterization of TiAlN/TiAlON/SiO2 absorber for solar selective applications

Characterization of a TiAlN/TiAlON/SiO2 tandem absorber is reported in this contribution. The first two layers were deposited by magnetron sputtering and the third layer was prepared by plasma enhanced chemical vapour deposition (PECVD). The optimization was performed by determining the optical constants of individual layers by first measuring spectral transmittance and reflectance of the individual layers. Subsequently the measuring spectra were fitted using the SCOUT software and dielectric function of each layer was determined. The three layer stack absorber on copper was then designed using those optical properties. The thickness of the individual layers was optimized until a solar absorptance of 95.5% was obtained resulting in a total thickness of about 215 nm (65 nm/51 nm/100 nm for the individual layers, respectively). A thermal emittance of 5% for an absorber temperature of 100 °C was obtained by analyzing the measuring data from a FTIR spectrometer with integrating sphere. During continuous thermal annealing at 278 °C for 600 h the absorptance decreased by 0.4%Savo Sola

Corrosion behaviour of substoichiometric TiNx films produced by DC magnetron sputtering

The present work describes the corrosion behaviour of substoichiometric TiNx films obtained by dc reactive magnetron sputtering. The coatings thickness ranged from 1.7 to 4.2 µm and the nitrogen content varied between 0 and 55 at. %. According to structural characterization by XRD, the films revealed a hexagonal α-Ti phase with a strong [002] orientation for low nitrogen contents. For nitrogen contents of 20% and 30%, the ε-Ti2N phase appears with a [200] orientation and further increasing of nitrogen content showed that the δ-TiN phase was dominant. Potentiodynamic polarisation and Electrochemical Impedance Spectroscopy (EIS) techniques were used to study the corrosion properties of TiNx films when immersed in artificial sweat solutions. Results of potentiodynamic polarisation tests showed that all films have a high corrosion resistance reflected by corrosion current densities values lower than 0.7µA/cm2. Also, EIS tests corroborated the results obtained in the polarisation tests, showing that films containing low percentages of nitrogen (less than 8 %) reveal the best corrosion resistance. Further increases in nitrogen content lead to a decrease in corrosion resistance. An exception to this behaviour was found for the film, with 30 % N. This sample presents an excellent corrosion resistance which increases with the immersion time. Higher nitrogen contents (52 and 55 %) promote a relative increase in the corrosion resistance when compared with 45 and 50 at % films, but never reaching values obtained for nitrogen contents lower than 30 % at.Fundação para a Ciência e a Tecnologia - (FCT

W/AlSiTiNx/SiAlTiOyNx/SiAlOx multilayered solar thermal selective absorber coating

Solar thermal energy has often been used as a renewable green energy source. Here we present a design composed of a highly selective solar thermal absorber coating that has been deposited by DC magnetron sputtering. This will consist of four layers: W/AlSiTiNx/SiAlTiOyNx/SiAlOx. The coating that was utilised revealed an excellent average solar thermal absorbance, (alpha = 95.5%) with very low emittance, (epsilon = 9.6% calculated for 500 degrees C) together with an excellent thermal stability after annealed at 500 degrees C, in air for 350 h, and at 630 degrees C in vacuum for 220 h.FCT in the framework of the Strategic Funding UID/FIS/04650/2013 and the financial support of FCT, POCI and PORL operational programs through the project POCI01-0145-FEDER-016907 (PTDC/CTM-ENE/2892/2014), co-financed by European community fund FEDER

Optimization and thermal stability of TiAlN-Mo multilayers

In this work we focus on the optimization and thermal stability of nanocomposite TiAlN/Mo multilayers that were produced by reactive magnetron sputtering on high-speed steel substrates, with modulation periods below 5 nm. These multilayers were annealed between 600– 900 ºC for 1 h in a vacuum furnace. Preliminary X-ray diffraction results reveal that these coatings are very stable up to 900 ºC, since the multilayer chemical modulation is not severely affected. At intermediate annealing temperatures the modulation period decreases due to interdiffusion at the interface, resulting in a thicker interface between metal/nitride and hence decreasing the thickness of those layers.Portuguese FCT/MCES scientific program