Ladislav Čelko

Diffusion in Al-Ni and Al-NiCr Interfaces at Moderate Temperatures

The diffusion couples for experimental study were prepared by HVOF spraying of nickel and nickel with 20 wt.% of chromium powders onto an aluminium sheet surface. The interfaces with sharp gradients of chemical concentration of these elements were prepared. Annealing at temperatures of 600°C and 630°C, close to the Al + Al3Ni eutectic melting point (639.9°C), with different dwell times were used. During annealing, the reactants diffuse and form layers of Al3Ni2 and Al3Ni intermediate phase compositions. Moreover, nickel without the assistance of chromium diffuses preferably along the grain boundaries into aluminium substrate and produces the strengthening of the substrate by stable Al3Ni and metastable Al9Ni2 particles. The microstructures were obtained by scanning electron microscopy. Layer thickness measurements were realized by means of image analyses. Chemical composition was estimated by energy dispersive microanalysis measurements. According to the results of the analyses performed the average chemical interdiffusion coefficients and Wagner’s integral interdiffusion coefficients were calculated.

Estimating the grade of Mg corrosion using laser-induced breakdown spectroscopy

We present a report on the potential use of the Laser-Induced Breakdown Spectroscopy (LIBS) technique for direct investigation of Mg corrosion and related optimization of the table-top LIBS system. Moreover, the preliminary study to prove the capability of this LIBS technique for the estimation of corrosion grade is given. In order to simulate the real corrosive environment, Mg samples were prepared in a constant climate chamber. We show that the corrosive layer on the sample surface significantly affects the properties of laser–matter interactions, i.e. among other parameters causing the matrix effect. Consequently, the properties and persistence of laser-induced plasmas (LIPs) and their composition, generated on such degraded surfaces, essentially differ. Collected radiation of LIP is then analysed and ratios of ionic to atomic Mg spectral lines are correlated with the grade of magnesium corrosion, i.e. content of Mg(OH)2 on the sample surface. The content of Mg(OH)2 is also correlated with plasma temperature as well as with the electron number density of LIP. Additionally, X-ray diffraction (XRD) analysis and optical profilometry were utilized to obtain more comprehensive information about the degradation grade of high purity Mg samples.

Effect of Thermal Barrier Coating on Low Cycle Fatigue Behavior of Cast Inconel 713LC at 900 °C

The effect of thermal barrier coating (TBC) on low cycle fatigue behavior of cast superalloy Inconel 713 LC has been studied at 900 °C. The TBC consisting of a CoNiCrAlY bond coat and a zirconia (ZrO2) top coat stabilized by 8% yttria (Y2O3) was deposited on the gauge section of cylindrical specimens using the atmospheric plasma spray technique. Cylindrical specimens of Inconel 713LC in as-received condition and with surface treatment were cyclically strained under strain control with constant total strain amplitude in symmetrical cycle at 900 °C in air. Hardening/softening curves, cyclic stress-strain curve and fatigue life data of coated and uncoated material were obtained. The stress response of the TBC coated specimens is lower in comparison with the uncoated specimens. Detrimental effect of surface treatment on the Basquin curve is documented. Specimen sectioning and fracture surface observations revealed fatigue damage mechanisms and help to discuss differences in fatigue behavior of the coated and uncoated superalloy.

Degradation of TBC Coating during Low-Cycle Fatigue Tests at High Temperature

The work is focused on the study of degradation of ZrO2 stabilized by Y2O3 (YSZ) thermal barrier-coating system with CoNiCrAlY bond coat applied on cast polycrystalline nickel-based superalloy Inconel 713LC. Cylindrical specimens in as-coated conditions were cyclically strained under strain control with constant total strain amplitude in symmetrical cycle at high temperature (900 °C) in air. Coating system YSZ with CoNiCrAlY bond coat were prepared by APS method on blasted surface. The microstructure of TBC was characterized with scanning electron microscopy and energy dispersion X-ray analysis. The coating thickness and hardness profile was measured. Fracture surface, surface relief and polished sections parallel to the specimen axis were examined to study damage mechanisms in coatings under cyclic loading at high temperature. It was find that initiation of the fatigue crack usually occurs on interface YSZ-CoNiCrAlY and the trajectory of the further crack propagation was documented.

High Temperature Low Cycle Fatigue Characteristics of Grit Blasted Polycrystalline Ni-Base Superalloy

The present work is focused on the study of low cycle fatigue behavior of grit blasted nickel-base superalloy Inconel 713LC (IN 713LC). Grit blasting parameters are obtained. Button end specimens of IN 713LC in as-received condition and with grit blasted surface were fatigued under strain control with constant total strain amplitude in symmetrical cycle at 900 °C in air. Hardening/softening curves, cyclic stress-strain curve and fatigue life data of both materials were obtained. Both materials exhibit the same stress-strain response. It has not been observed any improvement or reduction of low cycle fatigue life in representation of total strain amplitude versus number of cycles to failure of grit blasted material in comparison with as-received material. Surface relief and fracture surface were observed in SEM. The little effect of surface treatment on fatigue characteristics is discussed.

Detection of fluorine using laser-induced breakdown spectroscopy and Raman spectroscopy

In general, the detection of F and other halogens is challenging through conventional techniques. In this paper, various approaches for the qualitative and quantitative analysis of F using the laser-induced breakdown spectroscopy (LIBS) technique were demonstrated. In LIBS, fluorine detection can be realized by means of atomic lines and molecular bands. For the purposes of our experiment, two sets of pellets with various contents of CaF2, CaCO3 and cellulose were analyzed using a lab-based LIBS system under a He atmosphere. The fluorine atomic line at 685.60 nm was correlated with CaF signals proving their close relationship. Consequently, the limits of detection were determined for both analytical signals. Moreover, conditions necessary for the quantification of F via CaF band signals were estimated. The dependence of the CaF signal on the varying ratio of Ca and F contents was investigated. Finally, a chip of a real CaF2 crystal was prepared and its surface was mapped with Raman and LIBS systems. The obtained elemental and molecular maps showed good numerical correlations. Thus, the yielded results validated the possibility to substitute the fluorine atomic line by non-conventional CaF molecular bands in the qualitative and quantitative LIBS analysis of fluorine.

Use of the Powder Liquid Method for Aluminide Diffusion Coatings Formation on Inconel 713LC Nickel-Based Superalloy

Powder liquid method was used for aluminides diffusion coatings formation on the Inconel 713LC nickel-based superalloy. Two different powder mixtures (Al and Al + Si) in organic binder solution were prepared. Coatings deposition onto the substrate surface was realized by spraying. Two-stage heat treatment under the argon-flow atmosphere was designed. First stage at 200°C was used to decompose organic binder. In the second stage at 1000°C the elements from the coating interact with the substrate. Protective intermetallic layer and an interaction zone between the layer and substrate start to form. Elements interaction and phase transformations during annealing at 1000°C up to 600 min were studied. For this study the light microscopy, scanning electron microscopy, energy dispersive microanalysis, x-ray diffraction phase analysis, microhardness measurement, and image analysis methods were used.

Degradation of YSZ/EUCOR TBC Coating System during High Temperature Low Cycle Fatigue Tests

Thermal barrier coatings are widely used to protect the substrate from high temperature and extremely aggressive environments in gas engines. In the present article, authors have been studied degradation of complex thermal barrier coating system deposited on polycrystalline nickel superalloy IN 713LC. The substrate material was grit blasted with alumina (Al2O3) particles prior to air plasma deposition of CoNiCrAlY bond coat. Top coat consists of conventional zirconia (ZrO2) stabilized by yttria (Y2O3) -YSZ ceramic in combination with a eutectic nanocrystalline ceramic Eucor made of zirconia (ZrO2), alumina (Al2O3) and silicia (SiO2) –in the ratio of 50/50 in wt. %. The top coat was deposited using water stabilized plasma. Test specimens with the TBC coating system were fatigued under strain control condition in fully reversed symmetrical push-pull cycles at 900°C in air. The microstructure of TBC was characterized with scanning electron microscopy and energy dispersion X-ray analysis. The coating hardness and thickness were measured. Fracture surface and polished sections parallel to the specimen axis were examined to study damage mechanisms in coatings under cyclic loading at high temperature. TBC delamination was observed at the top coat/bond coat interface after cyclic loading at high temperature. Fatigue crack initiation sites are documented. Majority of fatigue cracks start from the surface and top coat/bond coat interface.

Tricalcium Phosphate - Magnesium Interface: Microstructure and Properties

The fabrication of a composite material based on magnesium (Mg) and tricalcium phosphate is reported in this work. Rods of β-tricalcium phosphate (β-TCP) were processed and consolidated together with pure Mg powder through spark plasma sintering (SPS). The microstructure at the interface, the chemical composition and transformation of the components and the microhardness were analysed. The microstructure of the composite shows two zones with well-defined and continuous interface between them: a ceramic zone composed by β-TCP filled with Mg and the metallic zone constituted by Mg and Mg rich eutectic. Vickers hardness shows the excellent mechanical interaction between the two zones.

Comparative Study of Microstructure and High Temperature Low Cycle Fatigue Behaviour of Nickel Base Superalloys Inconel 713LC and MAR-M247

The present work is focused on the study of microstructure and low cycle fatigue behavior of the first generation nickel-base superalloy IN 713LC (low carbon) and its promising second generation successor MAR-M247 HIP (hot isostatic pressing) at 900 °C. Microstructure of both alloys was studied by means of scanning electron microscopy (SEM). The microstructure of both materials is characterized by dendritic grains, carbides and casting defects. Size and morphology of precipitates and casting defects were evaluated. Fractographic observations have been made with the aim to reveal the fatigue crack initiation place and relation to the casting defects and material microstructure. Low cycle fatigue tests were conducted on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 900 °C in air. Hardening/softening curves, cyclic stress-strain curve and fatigue life data of both materials were obtained. Cyclic stress-strain curve of MAR M247 is shifted approximately to 120 MPa higher stress amplitudes in comparison with IN 713LC. Significantly higher fatigue life of MAR-M247 has been observed in Basquin representation. On the other hand IN 713LC shows prolonged lifetime compared with MAR-M247 in the Coffin-Manson representation. Results obtained from high temperature low cycle fatigue tests are discussed.