G. Moskal

Structure and resistance to oxidation of an Al-Si diffusion coating deposited by Arc-PVD on a TiAlCrNb alloy

Abstract This article presents research results of isothermal and cyclic oxidation of TiAlNbCr intermetallic with and without an Al–Si coating. The coating was deposited by the arc-PVD method in two steps. Firstly, the AlSi layer was deposited then the samples were heated in a vacuum chamber to form a diffusion TiAlSi coating. After coating deposition the samples were heat-treated in vacuum at a temperature of 950 °C for a period of 2 h. Cyclic oxidation tests were carried out at 950 °C. The heating and cooling time was 5 min (3 °C/s). Mass changes of the specimen were recorded every 100 cycles. A total of 2400 cycles were performed. An analysis of the results obtained from cyclic oxidation was performed. The analysis of the Si effect on the structure of the layers and on the oxidation mechanism of the TiAlNbCr alloy was performed. Phase composition, morphology and the distribution of elements were defined by EDX, XRD and SEM in AlSi layers as well as in the scale. The results showed that Al–Si coatings (thickness approx. 40 μm) were effective in reducing the oxidation rate of γ-TiAl. The oxide formed on the surface of the Ti–48Al–2Cr–2Nb coating after oxidation is composed of a mixture of a large portion of Al 2 O 3 and a small portion of TiO 2 .

Microstructure and Thermal Diffusivity of Gd2Zr2O7 Powders

The selection of new TBC materials is restricted by few basic requirements such as: high melting point, no phase transformation between room and the operation temperatures, low thermal conductivity, chemical inertness to the combustion gases and environment, thermal expansion match with the metallic substrate, good adherence to the metallic substrate and low sintering rate of the porous microstructure. Among these properties, one of the most important is thermal diffusivity. The number of material that can be used as TBCs is limited and so far only a few materials have been found to basically satisfy these requirements. Recent research has shown that certain rare-earth zirconates, such as Gd2Zr2O7, have even lower thermal conductivities than 7YSZ, and this has spurred an intensive research in discovering alternative TBC materials. The results of microstructure tests performed on the powders intended for thermally sprayed TBCs with APS method were presented in this article. The tests of phase and chemical composition of the analysed powder were performed. The carbon, sulphur and gas nitrogen contents were, among other things, determined during those tests. The x-ray powder diffraction phase identification in as received material was determined. The tested material showed the presence of Gd2Zr2O7 compound as the predominant one and Gd2O3 and ZrO2 oxides. The surface morphology analysis of the powder was carried out and its internal structure was characterized. The tested material shows porous structure typical for agglomerated powders. The second testing area applied to analysis of the powder thermal properties. The thermal diffusivity of the compressed samples with density similar to the solid material was determined with the laser flash (LF) method. The measurement results show that requirements for the materials used for new generation TBCs are met.

Sonochemical preparation of SbSeI gel

A novel sonochemical method for direct preparation of nanocrystalline antimony selenoiodide (SbSeI) has been established. The SbSeI gel was synthesized using elemental Sb, Se, and I in the presence of ethanol under ultrasonic irradiation (35 kHz, 2W/cm(2)) at 50 degrees C for 2h. The product was characterized by using techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and optical diffuse reflection spectroscopy (DRS). The SEM and HRTEM investigations exhibit that the as-prepared samples are made up of large quantity nanowires with lateral dimensions of about 20-50 nm and lengths reaching up to several micrometers and single crystalline in nature.

Influence of the solvent on ultrasonically produced SbSI nanowires

The influence of the substitution of methanol in place of ethanol during the ultrasonic production of antimony sulfoiodide (SbSI) nanowires is presented. The new technology is faster and more efficient at temperatures greater than 314 K. The products were characterized by using techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), optical diffuse reflection spectroscopy (DRS) and IR spectroscopy. The coexistence of Pna2(1) (ferroelectric) and Pnam (paraelectric) phases at 298 K was observed in the SbSI nanowires produced in methanol. The methanol decomposes during the sonication or due to the adsorption process on SbSI nanowires.

Effect of Heat Treatment on Structure and Phase Transformation of Rare Earth (Gd) Zirconate

In the present work, zirconium gadolinium oxide (Gd2Zr2O7) ceramics were prepared by annealing in different conditions and with APS (air plasma sprayed) techniques for thermal barrier coating (TBC) application. Thermal properties, phase transformation, crystal structure and cross-sectional morphologies of these materials were investigated. The thermal behaviour of the material was investigated from room temperature to 1500°C using the differential thermal analysis (DTA). The X-ray diffraction methods were used for the qualitative phase analysis. The structure of the studied samples has been characterized by employing powerful Rietveld’s whole X-ray profile fitting technique using the DBWS 9807a program. The SEM and EDS techniques were used to in the ceramic samples morphology analysis and for their chemical composition, respectively. The research showed that further stages of annealing result in the phase transformation of the parent substances and the main phase Gd2Zr2O7. It was found out that complete phase transformation into Gd2Zr2O7 phase takes place only for the air plasma sprayed sample. The analysis of the morphology of the initial powder revealed the spherical shape of the powder particles, which have a porous internal structure.

Degradation of the TBC system during the static oxidation test

This study was done on the IN‐738 type alloy with thermal barrier coatings. On the basic surface of the NiCoCrAlY superalloy, VPS‐sprayed powder was applied as the bond‐coat. In addition, ZrO2× 8%Y2O3 powder was used for a deposition outside the top surface of a ceramic layer by the APS method. Appropriate control of the spraying process parameters permitted to obtain a gradient of porosity on the thickness of the ceramic coating. Then a static oxidation test at 1100°C and for 1100 h was performed. The basic conclusions of that testing showed that main degradation modes of the gradient thermal barrier coating system were connected with formation of porous NiAl2O4 oxides in the thermally grown oxide area and, consequently, formation of micro‐cracks, delamination of a ceramic layer and final spallation of a ceramic top‐coat.

Laser remelting of silicide coatings on Mo and TZM alloy

Characterization of top surface and microstructure of silicide coatings obtained during diffusion process of pack cementation type and laser remelting treatments was showed in this article. The basic materials were pure Mo sheet and TZM molybdenum alloy. The coatings were deposited in powder process and glazed by different types of lasers. In first step the phase’s compositions of coatings was described by XRD analysis in initial condition and after remelting process. The morphology of the coatings top surface was described as well. All types of coatings were characterized by network of cracks on top surface of the coatings. Laser treatment of the silicide top surface changed morphology of the top surface, especially their cracks network. LM and SEM analysis revealed that internal coatings morphology was very similar in all cases.

Characterization of TiAlSi Coating Deposited by Arc-PVD Method on TiAlCrNb Intermetallic Base Alloy

Results of microstructural investigations of aluminide coatings modified by Si are presented in this work. Protective coating (TiAlSi type) was deposited by Arc-PVD. Thickness of the outside layer of deposited coating was 35µm and it contained TiAl3 phase modified by Si as a main component. The second layer was found as a transition area between the TiAl3 outside layer and the surface of TiAlCrNb substrate. Thickness of the inside sublayer was 5 µm. The diffusion treatment caused the progress of coating homogenisation from the point of view of phase and chemical composition. It was found that the coating consisted of the dominant TiAl3 phase and Ti5Si3 in thick outer sublayer and only TiAl2 phase in transition thin sublayer. Below the transition area, on the surface of TiAlCrNb substrate alloy, the layer of g−TiAl was found. The amount of silicides was increased in comparison with the coating only after the Arc-PVD process and the area of its presence had been removed in the outside direction of the coating.

Characterization of Thermal Properties of Micro-Sized Ceramic Powders for APS Deposition of Ceramic Layers

The paper presents test results concerning characteristics of the selected thermal properties of ceramic powders based on rare earth zirconates with a pyrochlore structure of RE2Zr2O7 type, intended for thermal spraying of TBCs. Gadolinium, lanthanum, samarium and neodymium based powders were tested. The scope of the tests encompassed thermal diffusivity analysis of the powders in a compressed pellets form within temperature range 25-1500°C, and also tests of specific heat and thermal expansion coefficient within similar temperature range. Standard powder of 8YSZ type on the basis of zirconium oxide modified with yttrium oxide was used as a reference material. Specific heat measurements of the powders showed that the highest values within the entire test temperature range were obtained for the standard YSZ type powder. In the case of new type of powders, the results obtained are very similar and only slightly lower in comparison with YSZ powder. The lowest values were obtained for the samarium based powder (temperature range corresponding to operating temperature). Character of the curves obtained do not show course of strong reactions connected with phase changes. Dilatometric tests of materials made it possible to determine thermal expansion coefficient. Mean coefficient values are included within the range from 5.5 x 106mm/°C to 10.0 x 106mm/°C. The highest mean value of thermal expansion coefficient was obtained for Nd2Zr2O7 powder and the lowest one for La2Zr2O7 powder. The lowest thermal diffusivity value at room temperature was shown by Nd2Zr2O7 powder, and the highest one by 8YSZ powder (0.215 mm2/s).

The Influence of Heat Treatment Parameters on the Thermal Diffusivity of WE54 and Elektron 21 Magnesium Alloys

In the present study, the thermal diffusivity and conductivity of WE54 and Elektron 21 alloys were studied. The results showed the thermal diffusivity of WE54 and Elektron 21 alloys were temperature and microstructure dependent. The thermal diffusivity of both alloys was dependent on the content of the solute element in the α-Mg matrix. The solid solution of Y and Gd in Mg has a lower thermal conductivity than alloys where the intermetallic Mg3(Nd,Gd) and Mg14Y2Nd phases are present. The formation of strengthening phases during ageing caused the consumption of the solute element in the α -Mg matrix, and improved the thermal conductivity of the alloys.