Hot Component Research Articles

Effect of Target Coating Thickness on the Abrasive Waterjet Machining Response of 8YSZ Segmented Thermal Barrier Coatings

Segmented thermal barrier coatings (STBC) are a more strain-tolerant and erosion resistant alternative of the conventional porous thermal barrier coatings for hot gas components in gas turbines. Due to their relatively higher thermal conductivity and the ever-increasing turbine inlet temperature, there is a need for thicker STBCs. This paper presents an investigation of the microstructures and properties of STBCs with respect to coating thicknesses. Coatings with two significantly different thicknesses were fabricated under identical conditions and evaluated using standard metallographic methods. It was found that the microstructures for thin and thick coatings had subtle differences and hardness values decreased with in increasing thickness. When subjected to an abrasive waterjet machining process, the thicker STBCs showed a higher wear rate. A hypothesis is proposed to explain the observed thickness dependent changes and the microstructures and properties of STBCs.

Нове кінцеве інтегральне перетворення для рівняння Лапласа в довільній області

Reliability, survivability, as well as the optimal operating mode of operation of the supercomputer will depend on the architecture and efficiency of the cooling system of the hot components of the supercomputer. That is why the number of problems, of great theoretical and practical interest, is the problem of studying the temperature fields arising in elements of arbitrary configuration, cooling a supercomputer. To solve this class of heat conduction problems, the method of finite integral transformations turned out to be the most convenient. This article is the first to construct a new finite integral transformation for the Laplace equation in an arbitrary domain bounded by several closed piecewise-smooth contours. An inverse transformation formula is given. Finding the core of the constructed new finite integral transformation by the finite element method in the Galerkin form for simplex first-order elements reduces to solving a system of algebraic equations. To test the operability of the new integral transformation, calculations were carried out of solutions of the boundary value problem for the Laplace equation obtained using the developed new integral transformation and the well-known analytical solution. The results of comparison the calculations of the solution of the Laplace equation are presented. In the case of a square with a side length equal to one and on one side of the square, the temperature is unity, and on the other, the temperature is zero, with a well-known analytical solution and a solution obtained using the new integral transformation. These results were obtained for 228 simplex first-order elements and 135 nodes. The maximum deviation modulo of these solutions is 0,096, the mathematical expectation of deviations is 0,009, and the variance of the type is 0,001. The developed integral transformation makes it possible to obtain a solution to complex boundary value problems of mathematical physics.

Differential Emission Measure Plasma Diagnostics of a Long-Lived Coronal Hole

We use Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) data to reconstruct the plasma properties from differential emission measure (DEM) analysis for a previously studied long-lived, low-latitude coronal hole (CH) over its lifetime of ten solar rotations. We initially obtain a non-isothermal DEM distribution with a dominant component centered around 0.9 MK and a secondary smaller component at 1.5 – 2.0 MK. We find that deconvolving the data with the instrument point spread function (PSF) to account for long-range scattered light reduces the secondary hot component. Using the 2012 Venus transit and a 2013 lunar eclipse to test the efficiency of this deconvolution, significant amounts of residual stray light are found for the occulted areas. Accounting for this stray light in the error budget of the different AIA filters further reduces the secondary hot emission, yielding CH DEM distributions that are close to isothermal with the main contribution centered around 0.9 MK. Based on these DEMs, we analyze the evolution of the emission measure (EM), density, and averaged temperature during the CH’s lifetime. We find that once the CH is clearly observed in EUV images, the bulk of the CH plasma reveals a quite constant state, i.e. temperature and density reveal no major changes, whereas the total CH area and the photospheric magnetic fine structure inside the CH show a distinct evolutionary pattern. These findings suggest that CH plasma properties are mostly “set” at the CH formation or/and that all CHs have similar plasma properties.

Solar Cycle Variation of Coronal Temperature, Emission Measure, and Soft X-Ray Irradiance Observed with Yohkoh Soft X-Ray Telescope

Abstract This paper presents the solar soft X-ray irradiance (0.3–3.0 nm) obtained from the mission-long full-Sun X-ray images observed with the Soft X-ray Telescope (SXT) of the Yohkoh mission (1991–2001). The irradiance was calculated using filter-ratio temperatures and emission measures (EMs) from the full-Sun integrated X-ray signals employing a coronal spectrum synthesized with CHIANTI atomic database version 8.0. Dependence of the results on the assumption of elemental abundances is investigated. The SXT irradiance for a shorter wavelength range was also calculated and compared with the low energy flux (0.1–0.8 nm) of the X-Ray Sensor on board the GOES satellite. To incorporate the spatial information of the observed corona, we tried the alternative method to derive irradiance by applying the filter-ratio method to the images of northern hemispheric corona instead of spatially integrated signals from there. The EM weighted average of the spatially resolved temperatures turned out to be generally 20%–30% lower than those derived from the integrated signals, while the total of spatially resolved EMs are accordingly 1.5–2 times higher. This trend is enhanced when solar activity is the lowest in early 1996. The irradiance obtained from the alternative method does not significantly vary from the result from the integrated signals. This provides some validation for the simpler full-Sun integrated method. The temporal variation of the EMs of cool (<1.5 MK), medium, and hot (>2.5 MK) components indicates that the ratio of the hot component relative to the medium component is higher in the ascending phase (mid 1998–2001) than in the descending phase (1992–1995) of the solar activity cycle.

Galaxy And Mass Assembly (GAMA): Defining passive galaxy samples and searching for the UV upturn

ABSTRACT We use data from the GAMA and GALEX surveys to demonstrate that the UV upturn, an unexpected excess of ultraviolet flux from a hot stellar component, seen in the spectra of many early-type galaxies, arises from processes internal to individual galaxies with no measurable influence from the galaxies’ larger environment. We first define a clean sample of passive galaxies without a significant contribution to their UV flux from low-level star formation. We confirm that galaxies with the optical colours of red sequence galaxies often have signs of residual star formation, which, without other information, would prevent a convincing demonstration of the presence of UV upturns. However, by including (NUV−u) and WISE (W2–W3) colours, and FUV data where it exists, we can convincingly constrain samples to be composed of non-star-forming objects. Using such a sample, we examine GALEX photometry of low-redshift GAMA galaxies in a range of low-density environments, from groups to the general field, searching for UV upturns. We find a wide range of (NUV−r) colours, entirely consistent with the range seen – and attributed to the UV upturn – in low-redshift red sequence cluster galaxies. The range of colours is independent of group multiplicity or velocity dispersion, with isolated passive galaxies just as likely to have blue UV-to-optical colours, implying significant upturn components, as those in richer groups and in the previous data on clusters. This is supported by equivalent results for (FUV−r) colours which are clear indicators of upturn components.

Conjugate heat transfer analysis for composite cooling structure using a decoupled method

Composite cooling is a promising cooling technique in modern gas turbines. Quantifying the contributions of its internal and external cooling will help improve the cooling design and increase the cooling effectiveness. In this paper, a conjugate heat transfer (CHT) decoupled method is established firstly to decouple the complex interaction between internal and external cooling for a composite cooling structure. And then the rationality of the decoupled method is verified by comparing the flow and heat transfer characteristics of the decoupled model and the original composite cooling model. Using the decoupled model, the contributions of the internal and external cooling on overall cooling effectiveness are quantitatively evaluated, and the external cooling is found to encumber the overall cooling effectiveness when the film flow badly lifts off from the external surface. The detailed contributions of external cooling, impingement cooling, and film hole convective cooling on overall cooling effectiveness of the research model are additionally illustrated. Moreover, a prediction method is presented to estimate the overall cooling effectiveness based on the decoupled model, and a small prediction error is verified. The methods presented in this paper could be used in the preliminary and optimization stages of the hot end component design for gas turbines.

Evaluation of service conditions of high pressure turbine blades made of DS Ni-base superalloy by artificial neural networks

Evaluating the service conditions of high pressure turbine blades in areoengine, which is the key point for component design and remaining life prediction, has always been a great challenge. In this study, we report a method, which is developed by back propagation artificial neural networks (BPANN), for service condition evaluation of turbine blades by establishing a quantitative correlation between the microstructural evolution and the temperature, stress and time. This method was successfully applied to a directionally solidified superalloy DZ125 based on microstructural datasets obtained from temperature-stress-time (T-σ-t) simulations. As an example, the service condition of a turbine blade made of DZ125 superalloy were evaluated by the BPANN model using the microstructural descriptors, including γ′ volume fraction (Vf), γ′ rafting degree (Ω) and thickness of the rafted γ′ precipitates (D), and service time. This study shows great potential in accurately assessing the degradation and predicting the remaining life for hot section components made from directionally-solidified and single crystal nickel-based superalloys.

Simultaneous detection of an intrinsic absorber and a compact jet emission in the X-ray binary IGR J17091−3624 during a hard accretion state

ABSTRACTWe present a detailed analysis of three XMM–Newton observations of the black hole low-mass X-ray binary IGR J17091−3624 taken during its 2016 outburst. Radio observations obtained with the Australia Telescope Compact Array indicate the presence of a compact jet during all observations. From the best X-ray data fit results, we concluded that the observations were taken during a transition from a hard accretion state to a hard-intermediate accretion state. For Observations 1 and 2, a local absorber can be identified in the EPIC-pn spectra but not in the RGS spectra, preventing us from distinguishing between absorption local to the source and that from the hot ISM component. For Observation 3, on the other hand, we have identified an intrinsic ionized static absorber in both EPIC-pn and RGS spectra. The absorber, observed simultaneously with a compact jet emission, is characterized by an ionization parameter of 1.96 < log ξ < 2.05 and traced mainly by Ne x, Mg xii, Si xiii, and Fe xviii.

Assessment of the grindability of Inconel 718 under different coolant delivery techniques

Nickel-based Inconel 718 stands out from other materials due to its peculiar combination of properties such as high mechanical strength, high hardness, high chemical inertia and low thermal expansion, as well as its ability to operate at high temperatures and in cryogenic conditions. These properties make this material suitable for aeronautic applications, especially for hot structural components, such as blades and discs of aircraft engines in which a high dimensional accuracy and low surface roughness are required. Such manufacturing requirements in general can be achieved through the grinding process. However, due to low thermal conductivity of both the Inconel 718 alloy and the conventional abrasive grinding wheels, most of heat generated during machining concentrates on the workpiece–grinding wheel interface. The usual practice for the removal of heat from grinding zone is by the application of high volume of coolants, but such technique can cause injury to the operator and harm to the environment, if special care with its use and disposal is not taken, which, in turn, increases the cost of the process. Furthermore, due to the poor machinability of Inconel 718, cutting conditions need to be different from those generally employed when grinding steels and cast irons, especially the depth of cut. Within this context, this study presents an approach for determining the grindability of Inconel 718 under different coolant delivery techniques (conventional and minimum quantity lubrication—MQL) and cutting conditions. Grinding tests were also carried out on a grey cast iron material for comparison purposes. Surface roughness, microhardness and surface texture of machined surfaces were the output parameters used to access the grindability of Inconel 718. Results showed that higher values of surface roughness were recorded after grinding the Inconel 718, compared to grey cast iron, thereby indicating the lower grindability of Inconel 718. No evidence of reduction in hardness due to thermal damage was observed after grinding both materials under the established cutting conditions.

Analysis of Quiescent Corona X-ray Spectra from SphinX During the 2009 Solar Minimum

The SphinX X-ray spectrophotometer on the {\em CORONAS-PHOTON}\/ mission observed the 1~--~15\,keV X-ray spectrum of the spatially integrated solar corona during the deep minimum of 2009, when solar activity was exceptionally low. Its sensitivity for energies $> 1.2$\,keV was higher than that of any other solar X-ray spectrometer in orbit at the time, including the detectors on GOES. Using much improved instrumental data than was used previously, we analyzed SphinX spectra in 576 intervals for which there was no discernible activity (NA), 40 intervals when there were X-ray brightenings (B), and sixteen intervals when there were micro-flares with peak emission less than GOES A1 (F). An instrumental background spectrum, formed over 34 hours of spacecraft night-time periods and including electronic noise and particle radiation, was subtracted from the solar spectra. Theoretical spectra were used to deduce temperatures on an isothermal assumption for the NA, B, and F intervals (1.69, 1.81, and 1.86\,MK respectively). Differential emission measure (DEM) analysis for the same spectra revealed a "cooler" component (log\,$T = 6.2$ or $T \approx 1.6$\,MK) in each case, but with a second hotter component having a less well-defined peak temperature varying from $\approx 2.5$ to $\approx 3.5$\,MK (log\,$T = 6.4$ and 6.55) and an emission measure between two and three orders smaller than that of the cooler component. These results are similar to those obtained at times just after solar minimum with the EVE instrument. A very hot component that might indicate the signature of nano-flare heating of the corona is not evident in SphinX data.

Global Radiation Magnetohydrodynamic Simulations of sub-Eddington Accretion Disks around Supermassive Black Holes

Abstract We conduct global three-dimensional radiation magnetohydrodynamic simulations of the inner regions of accretion flows around a 5 × 108 M ⊙ black hole, with mass accretion rates reaching 7% and 20% of the Eddington value. We choose initial field topologies that result in an inner disk supported by magnetic pressure, with surface density significantly smaller than the values predicted by the standard thin-disk model as well as a much larger disk scale height. The disks do not show any sign of thermal instability over many thermal timescales. More than half of the accretion is driven by radiation viscosity in the optically thin coronal region for the case of the lower accretion rate, while accretion in the optically thick part of the disk is driven by the Maxwell and Reynolds stresses from turbulence caused by magnetorotational instability. Optically thin plasma with gas temperatures ≳108 K is generated only in the inner ≈10 gravitational radii in both simulations, and is more compact in the case of the higher accretion rate. Such plasma does not form at larger radii because the surface density increases outward with radius, causing less dissipation outside the photosphere. In contrast to standard thin-disk models, the surface density in our simulations increases with increasing mass accretion rate at each radius. This causes a relatively weaker hot plasma component for the simulation with a higher accretion rate. We suggest that these results may provide a physical mechanism for understanding some of the observed properties of coronae and spectra of active galactic nuclei.

Research Progress of Continuous Fiber Reinforced Ceramic Matrix Composite in Hot Section Components of Aero engine

Continuous fiber reinforced ceramic matrix composite (CFRC CMC) possessed low density, high temperature resistance, high strength and high toughness, which have been identified as a key and promising military material for replacing the traditional super alloy. CFRC CMC had been used in some hot section components, such as nozzle, combustor and turbine stator on M88-2, F100-PW-229, CFM56-5B, F-135, GEnx, LEAP-X and other aeroengines. Manufacturing technologies of CFRC CMC were thought as the commanding elevation for hot section components of aeroengines, and therefore much attention was given in Europe, America, Russia and other developed countries and regions. The evaluation and application of CFRC CMC were introduced in detail. Further, the challenge and tendency in the future were also put forward in this study.

The ALMA-PILS survey: propyne (CH3CCH) in IRAS 16293–2422

Context. Propyne (CH3CCH), also known as methyl acetylene, has been detected in a variety of environments, from Galactic star-forming regions to extragalactic sources. These molecules are excellent tracers of the physical conditions in star-forming regions, allowing the temperature and density conditions surrounding a forming star to be determined. Aims. This study explores the emission of CH3CCH in the low-mass protostellar binary, IRAS 16293–2422, and examines the spatial scales traced by this molecule, as well as its formation and destruction pathways. Methods. Atacama Large Millimeter/submillimeter Array (ALMA) observations from the Protostellar Interferometric Line Survey (PILS) were used to determine the abundances and excitation temperatures of CH3CCH towards both protostars. This data allows us to explore spatial scales from 70 to 2400 au. This data is also compared with the three-phase chemical kinetics model MAGICKAL, to explore the chemical reactions of this molecule. Results. CH3CCH is detected towards both IRAS 16293A and IRAS 16293B, and is found the hot corino components, one around each source, in the PILS dataset. Eighteen transitions above 3σ are detected, enabling robust excitation temperatures and column densities to be determined in each source. In IRAS 16293A, an excitation temperature of 90 K and a column density of 7.8 × 1015 cm−2 best fits the spectra. In IRAS 16293B, an excitation temperature of 100 K and 6.8 × 1015 cm−2 best fits the spectra. The chemical modelling finds that in order to reproduce the observed abundances, both gas-phase and grain-surface reactions are needed. The gas-phase reactions are particularly sensitive to the temperature at which CH4 desorbs from the grains. Conclusions. CH3CCH is a molecule whose brightness and abundance in many different regions can be utilised to provide a benchmark of molecular variation with the physical properties of star-forming regions. It is essential when making such comparisons, that the abundances are determined with a good understanding of the spatial scale of the emitting region, to ensure that accurate abundances are derived.

Effect of Intrinsic Structure on Stability of Domestic SiC Fiber

The morphology, structure and composition of three different SiC fibers were studied by SEM, XRD and elemental analysis techniques in this paper. The high temperature stability of SiC fiber bundles was also characterized. The results show that the intrinsic structure of domestic first, second, and third generation silicon carbide fibers possesses large differences. The above three fibers can be classified into high oxygen high carbon, low oxygen high carbon and near stoichiometric ratio according to the composition, and classified into amorphous, low crystallinity and high crystallinity according to the structure. The difference in composition and structural characteristics of the above fibers has a great influence on the comprehensive properties of SiC fibers, especially the oxidation resistance. The high temperature oxidation resistance of the first, second and third generation SiC fibers increases gradually, which provides material basis and technical support for the preparation of ceramic matrix composites suitable for hot end components of aero-engines with different thrust-weight ratios.

Investigation of the influence of forming parameters on the springback of hot-stamped hat-shaped parts

The application of hot stamping parts has become a dominant approach to achieve lightweight design and increase crashworthiness performance in the automotive industry. Compared to the cold stamping parts, the main feature of the hot stamped component is its high strength and good size stability. However, recent studies have shown that the springback or size deviation of hot stamped parts caused some assembly problems. This paper aims to investigate the influence of forming parameters on the part’s springback via a hot stamping hat-shaped die. Three different forming parameters with the same blank heating temperature (930°C) were conducted in the study: (1) transfer time 8 sec/die quenching 15 sec (2) transfer time 8 sec/die quenching 8 sec and (3) transfer time 18 sec/die quenching 15 sec. The selected forming parameters are used to evaluate the effect of the before-forming blank temperature and die-opening blank temperature on the springback of the hot stamping parts. The results show that the case 3 with a prolonged transfer time causes a small portion of ferrite phase formation in the hot-stamped part, resulting in the decrease of the tensile strength and a more significant springback is observed.

Suzaku observation of diffuse X-ray emission from a southwest region of the Carina Nebula

Abstract A southwest region of the Carina Nebula was observed with the Suzaku observatory for $47\:$ks in 2010 December. This region shows distinctively soft X-ray emission in the Chandra campaign observations. Suzaku clearly detects the diffuse emission above known foreground and background components between 0.4–$5\:$keV at the surface brightness of $3.3\times 10^{-14}\:$erg$\:$s$^{-1}\:$arcmin$^{-2}$. The spectrum requires two plasma emission components with $kT \sim 0.2$ and $0.5\:$keV, which suffer interstellar absorption of $N_{\,\rm H} \sim 1.9 \times 10^{21}\:$cm$^{-2}$. Multiple absorption models assuming two-temperature plasmas at ionization equilibrium or non-equilibrium are tested but there is no significant difference in terms of $\chi ^{2}/$d.o.f. These plasma temperatures are similar to those of the central and eastern parts of the Carina Nebula measured in earlier Suzaku observations, but the surface brightness of the hot component is significantly lower than those of the other regions. This means that these two plasma components are physically separated and have different origins. The elemental abundances of O, Ne, and Mg with respect to Fe favor that the diffuse plasma originates from core-collapsed supernovae or massive stellar winds.

The addition of zirconium to aluminide coatings: The effect of the aluminide growth mode

Alumina-former coatings such as nickel aluminides have been the essential approach to combating the aggressive service environment of gas turbine hot section components. The positive effects of zirconium on the cyclic oxidation lifetime of aluminide coatings have been reported. The current paper has reported the effect of the growth mode of the aluminide coating on the microstructure of the Zr-modified aluminide coating. The aluminization process was carried out using the halide activated pack cementation process in the powder mixtures of aluminum, ammonium chloride, zirconium oxide, and alumina at 760 and 1040 °C for the inward and outward growth, respectively. The microstructures of the coatings were studied using FESEM, EDS and XRD. The results showed that the outward coatings contain a high level of Zr mainly incorporating it in the second phases such as AlNi2Zr in a matrix of NiAl. In contrast, the Zr concentration in the inwardly grown aluminide coatings did not exceed the 1 atomic percentage and the typical microstructure of the high activity aluminide coatings was observed. The chemical reactions involved in the pack cementation process and the mechanism of the coating formation were discussed.

High temperature oxidation behavior and mechanism of high-velocity arc sprayed FeCrNiAlBSi/Cr3C2 coating

High temperature oxidation is mainly responsible for the damage of hot components in boiler tubes, and the application of protective coatings is the most effective solution. In the present study, FeCrNiAlBSi/Cr3C2 coating was deposited on AISI 1020 steel substrate via high-velocity arc spraying (HVAS) process. The high temperature oxidation performance of the coating was investigated at 550, 650, and 750 °C in the atmospheric environment. The phase composition, microstructure, surface and cross-sectional morphology of the coating were characterized by means of x-ray diffraction (XRD), optical microscope (OM) as well as scanning electron microscopy (SEM) which equipped with energy-dispersive spectroscope (EDS), respectively. Oxidation kinetic curves that established by thermo-gravimetric technique were used to evaluate high temperature oxidation mechanism. The results showed that the kinetic curves of the coatings oxidized at different temperatures conformed to the classic parabolic law, and the coatings exhibited much better high temperature oxidation resistance as compared with bare AISI 1020 steel. The coating oxidized at 750 °C showed the largest values for mass gain/area and parabolic rate constant (kp) of 2.86 mg cm−2 and 8.11 × 10–12 g2·cm−4·s−1. As testing temperature increased from 550/650 °C to 750 °C, the oxidation products for the coating transformed from Fe2O3 and Cr2O3 to FeCr2O4. The formation of Cr2O3 and FeCr2O4 may well explained why the FeCrNiAlBSi/Cr3C2 coating exhibited excellent high temperature oxidation resistance.

Qualitative phenomenological investigation of the transient temperature gradient during gas turbine's hot section component cooling

In this study, the temporal variation of temperature gradient in the gas turbine hot section components in the transient process is raised, and according to its impact on life expectancy computations, the accuracy of the usual methods is investigated qualitatively. It is worth noting that in such two-phase problems, existing different time-scales prevent some common simplifications that are usually used for unsteady investigations like a quasi-steady assumption, and so there is no choice but to conduct coupled transient studies despite their high time-consuming manner. Hence, the phenomenological and qualitative model is introduced to analyze the cooling problem and show the transient behavior. The results show that during unsteady operations, if the time rate of changes is high, some considerable overshoots (more than 30%) of temperature gradients in hot sections may be ignored in common quasi-steady predictions, which must be predicted only by using the unsteady and coupled simulations.

Experimental study and a damage model approach to determine the effect of hot forming deformation on the service performance of 22MnB5 steel

Forming damage affects the service performance of hot stamped components such as A-pillars, B-pillars and anti-collision beams. Existing constitutive models are not suitable for predicting this problem. This research aimed to experimentally and numerically study the effect of forming damage caused by hot stamping on the service performance of quenched 22MnB5 steel. The pre-forming defects were introduced into samples at 850 °C, and then the samples were quenched, cut, and stretched to fracture to ascertain the relationship between the forming strain, ultimate stress and failure strain. X-ray diffraction (XRD) tests and microstructure tests were conducted to investigate the phase composition and microdefects, respectively. A Damage-Coupled Pre-forming Constitutive Model (DCPCM) was proposed and embedded into ABAQUS by the VUMAT interface to simulate the service performance of quenched 22MnB5 steel. The results showed that the main reason for the reduced mechanical properties of the quenched 22MnB5 steel with pre-strain was increases in the number of microvoids and microcracks rather than changes in phase composition. The prediction by the proposed constitutive model agreed with the experimental results. These predictions are important for the performance design of hot stamped components.