Failure analysis of thermally cycled columnar thermal barrier coatings produced by high-velocity-air fuel and axial-suspension-plasma spraying: A design perspective

Axial-suspension-plasma spraying (ASPS) is a fairly recent thermal spray technology which enables production of ceramic top coats in TBCs, incorporating simultaneously the properties of both the conventional-plasma sprayed (highly insulating porous structures) and electron-beam-physical-vapor-deposited (strain-tolerant columnar structures) top coats. TBCs are required to insulate the hot components in a gas turbine engine against high temperature and harsh operating conditions. Periodic heating and cooling of turbine engines during operation can create severe thermal cyclic fatigue conditions which can degrade the performance of these coatings eventually leading to the failure. An in-depth experimental investigation was performed to understand the failure behavior of columnar TBCs subjected to thermal cyclic fatigue (TCF) test at 1100?C. The study revealed that the TCF performance was influenced to an extent, by the top coat microstructure, but was primarily affected by the severity of thermally grown oxide (TGO) growth at the bond coat-top coat interface. Mixed failure modes comprising crack propagation through the bond coat-TGO interface, through TGO and within the top coat were identified. Based on the analysis of the experimental results and thorough discussion a novel design of microstructure for the high TCF performance columnar TBC is proposed.     

Laser Clad and HVOF-Sprayed Stellite 6 Coating in Chlorine-Rich Environment with KCl at 700 °C

Laser clads and HVOF coatings from a stellite 6 alloy (Co–Cr–W–C alloy) on 304 stainless steel substrates were exposed both bare and with KCl deposits in 500 ppm HCl with 5% O₂ for 250 h at 700 °C. SEM/EDX and PXRD analyses with Rietveld refinement were used for assessment of the attack and for analysis of the scales. The bare samples suffered from scale spallation and the scale was mostly composed of Cr₂O₃, CoCr₂O₄ and CoO, although due to dilution haematite (Fe₂O₃) was detected in the scale formed on the laser clad sample. A small amount of hydrated HCl was detected in bare samples. While the corrosion of the bare surfaces was limited to comparatively shallow depths and manifested by η and M₇C₃ carbide formation, the presence of KCl on the surface led to severe Cr depletion from the HVOF coating (to 1 wt%). Both inward and outward diffusion of elements occurred in the HVOF coating resulting in Kirdendall voids at the coating–steel interface. The laser clad sample performed significantly better in conditions of the KCl-deposit-induced corrosion. In addition to the oxides, CoCl₂ was detected in the HVOF sample and K₃CrO₄ was detected in the laser clad sample. Thermodynamic calculations and kinetic simulations were carried out to interpret the oxidation and diffusion behaviours of coatings.     

Adaptive video filtering framework

We present a new 3D adaptive filtering approach capable of detecting and removing impulsive noise in image/video sequences. The proposed method takes advantage of switching median schemes and robust lower‐upper‐middle (LUM) smoothing characteristics. Simulation studies reported in this article indicate that the proposed filtering scheme achieves an excellent trade‐off between noise attenuation and detail preserving characteristics, and clearly outperforms previously introduced approaches in terms of subjective and objective image quality measures. Besides the filter analysis and the testing of its performance, an important part of this article discusses the filter implementation in Altera field programmable logic devices (FPLD). Simulation studies indicate that the proposed method can be efficiently implemented in hardware and is suitable for real‐time image/video processing applications. © 2005 Wiley Periodicals, Inc. J Imaging Syst Technol 14, 223–237, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20027     

Temperature and gain dynamics in flashlamp-pumped Er:YAG

A novel optical transmission method was used for measuring transient temperature dynamics inside an Er:YAG laser crystal during optical pumping with flashlamp pulses of different duration and spectral composition. Time-resolved measurements of the crystal gain at 2.94 μm were also performed for the same set of pumping conditions. The results are compared with predictions of a theoretical model for gain and temperature dynamics during optical pumping of Er:YAG. A good spatial resolution of the implemented temperature measurement method was utilized also to determine the lateral temperature profiles inside the laser rod under various pumping conditions     

Silver-Doped Hydroxyapatite Coatings Deposited by Suspension Plasma Spraying

Pure hydroxyapatite suspension was produced by wet chemical synthesis. Using a hybrid water-stabilized torch, a series of HA coatings were produced on SS304 and Ti6Al4V substrates and their properties were characterized by SEM, EDX and XRD techniques. After deposition, the amorphous phase content reached 6-10% and the coatings retained 75-82% of crystalline HA phase. Their thickness reached 145 μm. To understand the wear behavior of the coatings, pin-on-disc tribology evaluation was performed. Additionally, a set of HA coatings was prepared with pure metallic Ag content. This formed by in situ chemical decomposition of AgNO₃ added into the HA suspension. The Ag was dispersed evenly within the coatings in the form of submicron-sized particles situated predominantly along the HA splats boundaries with a total Ag content of 8 wt.%. Given the antibacterial properties of Ag, such result presents a promising step forward in the hard tissue replacement research.     

cDNA microarray image segmentation using root signals

A vector processing based framework suitable for cDNA microarray image segmentation is introduced and analyzed in this paper. By using nonlinear, generalized selection vector filters the framework proposed here classifies the cDNA image data as either microarray spots or image background. The solution converges to a root signal that represents the segmented cDNA microarray image with the regular spots ideally separated from the background and with their coloration uniquely described by dominant color vectors. It will be demonstrated that the framework readily unifies image denoising, enhancement, data normalization, irregular spot rejection, and spot segmentation in one processing step delivering excellent performance at reasonable computational cost. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 16, 51–64, 2006     

Wave reworking of reservoir banks composed of flysch in Slovakia

Conclusion A wave regime on reservoirs leads to erosion of their banks, to wave scour. The total length of the shoreline of reservoirs in Slovakia is more than 300 km, of which about 50% is accounted for by those which are characterized by a large storage capacity and intense wave action (Orava, Bolsaja Domasa, Liptovská Mara, Vihorlat). Wave scour in combination with landslides develops rapidly where the banks are composed of thick accumulations of loose deposits. On the basis of the data of long-term investigations on the Orava and Bolsaja Domasa reservoirs it was established that a prediction of the development of reworking of the banks of reservoirs with time under the engineering-geologic conditions of the Carpathian flysh by the methods of Soviet authors E. G. Kachugin and B. A. Pyshkin is found to be reliable. The works of other authors (B. A. Pyshkin, S. V. Rusakov, V. L. Maksimchuk, Yu. N. Sokol'nikov, V. S. Shaitan, et al.) served as the basis for planning protective measures to limit the development of wave abrasion on the indicated reservoirs. These measures were developed in 1974–1975 at the department of geotechnics of SVST in Bratislava [14]. Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 5, pp. 46–50, May, 1979.     

Replication in cultured C2C12 muscle cells correlates with the neuroinvasiveness of California serogroup bunyaviruses

The neuroinvasiveness of California serogroup bunyaviruses is determined by the ability of the virus to replicate in striated muscle after peripheral inoculation of mice. Neuroinvasiveness was mapped to the medium (M) RNA segment of the virus, which encodes the viral glycoproteins, when reassortants were made between La Crosse/original virus, a neuroinvasive isolate, and Tahyna-181/57 virus, a nonneuroinvasive clone. We have tested the murine muscle cell line C2C12 as a surrogate for myotropism and have found that there is a slight, but reproducible difference in the replication of virus clones bearing the M RNA segment of La Crosse/original virus compared to clones bearing the M RNA segment of Tahyna-181/57 virus, as determined by viral titer, antigen expression, and plaque formation.     

Flip-flop polarization effect in cube-corner-flat cavity Nd:YAGlaser

A polarization effect in Nd:YAG leading to mutually orthogonal polarizations of two successive passive Q-switch laser pulses in a flashlamp pumped cube-corner-flat-cavity laser is reported. The polarization memory in optically isotropic Nd:YAG crystal is attributed to local Nd³⁺ site symmetry selection rules