ICMCTF2014 Session AP: Symposium A Poster Session

Three materials were deposited over AISI-SAE 4340 steel using the wire arc thermal spray technique. The deposited materials are the alloy Fe, Nb, Cr, W and the traditional steels AISI-SAE 1020 and 420. With the aim of evaluating the best strategy for increasing the corrosion resistance in the coating-substrate system, the coatings were deposited in three different ways: (1) homogeneous monolayers of each material, (2) bilayers composed of a monolayer of the alloy over a monolayer of either 1020 or 420, and (3) simultaneous monolayer-type coatings achieved by depositing the alloy + 1020 in the first case and the alloy + 420 in the second case. The coatings were characterized by optical microscopy and X-ray diffraction. The corrosion resistance was evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization.

It was found that the corrosion resistance in the fabricated coatings depends on the defect concentration in the microstructure and on the deposition strategy. For example, the resistance to polarization of the material deposited in bilayers was increased through the congestion of defects with corrosion products, while the simultaneous monolayers achieved increased corrosion resistance by the reduction of defects with respect to the alloy. The details and mechanisms of corrosion in the fabricated coatings are described in this study.

nc-TiN/a-SiN_x coatings were synthesized by means a hybrid deposition technique of high power impulse (HIPIMS) and pulsed-DC magnetron co-sputtering. The coatings were processed employing two targets of Ti- and Si-connected to HiPIMS and pulsed-DC generators, respectively.

The discharge current on the Si-target was increased from 0 to 0.9 A whereas the deposition parameters of titanium were fixed at 2 A. As a result, the Si-content increased progressively from 0 to 19.72 at. %. The increase in silicon content allows to favour the amorphous SiN_x phase which is responsible for embedding the metal nitride.

Since matrix grain sizes evolved from 41 to ≈ 5 nm with increasing Si content, the hardness values followed the trend up to a threshold of about 40 GPa when grain size decreased around 7 nm corresponding to ≈ 10 at. % Si content. As a consequence, this phenomenon allows obtaining different wear behaviours in the tribological tests.

Similarly, the oxidation resistance was studied by submitting the samples to thermal annealing at 700°C in air atmosphere. After annealing, the mechanical properties strongly decrease but this softening is less pronounced as Si content in the films increases. Indeed, the sample containing the maximum content ≈ 20 at.% kept the hardness at ≈ 18.5 GPa whereas TiN hardnes was about only 12 GPa. This particular sample containing 20 at.% Si presented low rutile-TiO₂ content among the others, meaning an improved resistance to oxidation.

Finally, the samples were analyzed by SEM and TEM with the aim of studying the morphology and their microstructure evolution.

The substitutional incorporation of Al into the TiN lattice to form the ternary alloy TiAlN, has been seen to improve some of the properties of the TiN thin films, such as hardness and thermal stability. In the present work TiAlN thin films have been prepared by the simultaneous laser ablation of a Ti and an Al target in an Ar/N2 atmosphere. The film properties could be controlled by adjusting the plasma parameters, which were monitored using a planar Langmuir probe at the substrate position. The amount of Al incorporated in the TiAlN films was found to be, for a fixed titanium target-plasma, directly proportional to the density of the plasma formed during the ablation of the aluminum target. This study was restricted to relatively small amounts of incorporated aluminum up to 15 at%. The structural characterization of the deposits was carried out using X-ray diffraction and it was found that the films were highly oriented in the (111) direction of TiN. Small shifts of the diffraction peaks towards higher values of 2θ were observed and were correlated to the distortion of the TiN lattice due to the incorporation of Al. The hardness reached a maximum value of 40 GPa at an aluminum concentration close to 11 at%. The thermal stability of the films was studied by micro-Raman spectroscopy, in order to detect their transformation to one of the TiO2 phases, in the temperature range from 500 to 700 ^oC. The results indicated that the inclusion of aluminum, in general, led to an improved thermal stability. We also report the variation of the improvement of the friction coefficients and wear rate of the films as a function of the aluminum content.

This work was partially supported by CONACYT under contract No. 128732.

The paper presents the results of high temperature oxidation of EB-PVD TBCs deposited on a Pt-diffused second generation single crystal Ni-based superalloy. The Pt-diffused bond coating was obtained using a novel PVD method applying a Closed Hollow Cathode (CHC) for deposition of 5µm of Pt layer and subsequent annealing at 1140 °C for 2h in vacuum. The TBC system was thermally cycled in 1h cycles at 1100 °C for 730h until delamination of 10% of YSZ (Yttria Stabilized Zirconia) top coating. A non-destructive 3D optical scanning method was applied for a macroscopic examination of the YSZ delamination which allowed predicting and revealing of the regions of YSZ buckling prior to its spallation. The microstructure of the TBC system in the as-deposited and thermally cycled conditions was studied using FEG-SEM. The growth and evolution of the TGO (Thermally Grown Oxide) scale was performed using high resolution FEG-S/TEM and FIB methods. The TGO in the as-deposited condition was found to consist of porous α-Al₂O₃ which grew to form distinctive dense and columnar grains with ionic diffusion of reactive elements (Hf and Y) through grain boundaries during high temperature exposure. Additionally the formation of high volume oxides containing Ni was found to accelerate the spallation of the YSZ top coat.

Carbon and stainless steel, as well as Fe-Nb-Cr-W nanocomposite coatings were deposited over steel substrates using electric arc spray, and the feasibility of applying such coatings in the naval industry was analyzed. To achieve this, the microstructure before and after the tests was characterized to evaluate resistance to corrosion and abrasive wear, as well as the properties of the thermal barrier on the coatings produced. Corrosion resistance was analyzed by Polarization and Electrochemical Impedance Spectroscopy (EIS) tests using a NaCl electrolyte at 3 %; abrasive wear resistance was measured using a three-component system following ASTM G-65 recommendations, while state and quality control of the thermal barriers were studied using EIS tests. The microstructure of the coatings was characterized by Scanning Electron Microscopy (SEM), optical microscopy and X-ray diffraction (XRD).

Nanocomposite coatings have been extensively studied due to their potential for achieving very high hardness, oxidation resistance and lubrication characteristics, in an effort to improve wear behavior of tools and components in several applications. Coatings containing nanoscale features may be produced by alternatively depositing nanolayers of different materials in a laminated structure or by co-depositing immiscible phases. Nanocomposite films produced by co-deposition may comprise only nanocrystalline phases (nc-nc) or nanocrystalline and amorphous phases (nc-a). The successful production of hard isotropically nanostructured films containing crystalline and amorphous phases depends on the appropriate size and distribution of these nanoscale phases. On the other hand, the oxidation resistance is a very important property for multicomponent and multiphase thin films that are especially designed for a wide variety of applications, such as high temperature protective coatings and high speed cutting tool protective coatings. The present work investigates the co-deposition of Ti-B-N-Si nanocomposite films from a composite target of TiB₂ and a pure boron doped Si target using high power impulse magnetron sputtering in an Ar/N₂ gas mixture. The microstructure for the films were investigated in various Si contents and were evaluated by X-ray diffractometer (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscope (XPS), and high-resolution transmission electron microscope (HRTEM). The oxidation resistance studied here was conducted in an effort to understand the temperature dependent structural and compositional evolution of Ti-B, Ti-B-N, and Ti-B-N-Si films in an oxidizing atmosphere. Dynamic oxidation was studied using a Netzsch model STA-409C thermal analyzer with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) in flowing air atmosphere.

In this work the laser coating of steel with aluminum powder was evaluated. A pre coating of aluminum powder was applied on samples of SAE 4340 steel by a pneumatic pistol and irradiated with a defocused CO₂ laser beam of 125W and 0.3mm diameter. The laser beam parameters (intensity and scanning speed) were adjusted to promote the solid diffusion of the aluminum powder on the steel surface. All the tests were performed using a N₂ gas to prevent the steel oxidation in the heat zone. X-ray diffraction analyses indicates the formation of a layer of iron aluminides of FexAly on the steel surface and Vickers hardness indentation in this layer presented 1100Hv_0,01 with substrate hardness near to 280Hv_0,01. The solid state diffusion in the steel surface was confirmed by EDS analysis.

High temperature coatings are used to prevent surface degradations or as thermal barriers against hot atmosphere. In this line, the present work studies the oxidation behavior of plasma sprayed titania-doped yttria stabilized zirconia (YSZ) TBC coatings. ZrO2–10% Y2O3–18% TiO2 coating and NiCoCrAlY bond coat were deposited on AISI A36 steel coupons by atmospheric plasma spraying (APS). Cyclic oxidation process in 4 h intervals was performed in an air electrical furnace at two temperatures: 800 and 1100 °C. During each cycle the specimens were cooled in the furnace. The mechanical properties of the coating were evaluated using microindentation hardness and bonding strength tests in as sprayed and after oxidation conditions. The microstructure and phase composition of the coating were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was observed that system ZrO2–10% Y2O3–18% TiO2 obtained a good performance for the temperature evaluated.

Key Words: titania- doped, YSZ, Plasma-sprayed, bond strength, microhardness.

SiC/SiC ceramic matrix composites (CMCs) systems will play a crucial role in next generation turbine engines for hot-section component applications because of their ability to significantly increase engine operating temperatures, reduce engine weight and cooling requirements. However, the environmental stability of Si-based ceramics in high pressure, high velocity turbine engine combustion environment is of major concern. The water vapor containing combustion gas leads to accelerated oxidation and corrosion of the SiC based ceramics due to the water vapor reactions with silica (SiO₂) scales forming non-protective volatile hydroxide species, resulting in recession of the ceramic components. Although environmental barrier coatings are being developed to help protect the CMC components, there is a need to better understand the fundamental recession behavior of in more realistic cooled engine component environments.

Characterization of microstructure of silicide coatings obtained during diffusion process of out-of-pack type was showed in this article. The basic materials were pure Mo, W and Nb sheets. The coatings were deposited in out of pack process with four different times of exposure. The temperature of deposition process was constant. In first step of investigations the phases compositions of coatings was described by XRD analysis. In each cases the silicide’s of Mo, W and Nb respectively was revealed on top surface of the coatings. The morphology of the top surface of coatings was very similar as well. In all cases the coatings were characterized by presents of network of cracks. Additionally there was no influence of depositions time on phases constituent and coatings topography. LM and SEM analysis revealed that internal coatings morphology was very similar in each of types of coatings (for Mo, W and Nb respectively) independently to time of exposure. Basic differences was related to the thickness of coatings. All coatings were good quality without deep cracks. EBSD analysis revealed that microstructure of coatings was single –layered and a columnar-like type without pores and voids. There was to transition zone between coatings and basic materials. Oxidation resistant of silicide coatings was characterized during isothermal oxidation test at temperature 1200°C.

This work was supported by National Centre for Research and Development, project no PBS1/B5/3/2012 realized as a part of Applied Research Programme