Thermal Cycling Properties Research Articles

Gradient La2Ce2O7/YSZ thermal barrier coatings tailored by synchronous dual powder feeding system

Progress in the design and fabrication of thermal barrier coating (TBC) is strongly dependent on the application of new materials and deposition methods. In this work, one novel and efficient plasma spraying method was employed to deposit a La2Ce2O7 (LC)/YSZ gradient TBC using a synchronous dual powder feeding system, in which the melting state and feeding rate of LC or YSZ feedstock powder can be precisely controlled. The experimental and simulation results suggested that the as-sprayed LC/YSZ TBC presented an obvious gradient change along the coating thickness direction. The heat insulation temperature and thermal cycling property of gradient TBC were greatly improved compared to its double-layer-structured counterpart due to the increased interfaces and deflection of fatigue cracks resulted from the gradient structure.

Negative thermal expansion property of CuMoO4

The triclinic copper (II) molybdate (α-CuMoO4) was synthesized by a solid state method and its negative thermal expansion (NTE) was systematically studied. The results show that α-CuMoO4 exhibits non-linearly NTE and the coefficient of thermal expansion (CTE) is −4.40 × 10−6/K, when the temperature ranges from room temperature (RT) to 390 K. Its negative expansion behavior may be caused by the charge transferred from O2− to Cu2+, resulting that a part of the CuO6 octahedron transferred to CuO5 hexahedron, and the CuO bond length in CuO5 hexahedron became shorter than in CuO6 octahedron. The synthetic action of d9Jahn-Teller effect of Cu2+ and small amount of pores may also contribute to the NTE of CuMoO4. CuMoO4 also has excellent photocatalytic properties, luminescent properties, dielectric properties and thermal cycling properties. The NTE and other excellent properties of CuMoO4 make the material have great prospects in application.

Effects of La2O3 content and particle size on the long-term stability and thermal cycling property of La2O3-dispersed SUS430 alloys for SOFC interconnect materials

We developed oxide-dispersed alloys as interconnect materials for a solid oxide fuel cell by adding La2O3 to SUS430 ferritic steels. For this purpose, we prepared two types of La2O3 with different particle sizes and added different amounts of La2O3 to SUS430 powder. Then, we mixed the powders using a high energy ball mill, so that nano-sized as well as micro-sized oxide particles were able to mix uniformly with the SUS430 powders. After preparing hexahedral green samples using uni-axial and cold isostatic presses, we were finally able to obtain oxide-dispersed alloys having high relative densities after firing at 1,400 °C under hydrogen atmosphere. The nano-sized La2O3 dispersed alloys showed properties superior to those of micro-sized dispersed alloys in terms of long-term stability and thermal cycling. Moreover, we determined the optimum amounts of added La2O3. Finally we were able to develop a new oxide-dispersed alloy showing excellent properties of low area specific resistance (16.23 mΩ cm2) after 1000 h at 800 °C, and no degradation after 10 iterations of thermal cycling under oxidizing atmosphere.

Preparation and thermal performance of n-octadecane/expanded graphite composite phase-change materials for thermal management

Series of n-octadecane/expanded graphite composite phase-change materials (PCMs) with different mass ratio were prepared using n-octadecane as PCMs, expanded graphite as multi-porous supporting matrix through vacuum impregnation method. Microstructure, crystallization properties, energy storage behavior, thermal cycling property and intelligent temperature-control performance of the composite PCMs were investigated. Results show that the composite PCMs have a good energy storage property. The melting enthalpy and crystallization enthalpy can reach 164.85 and 176.51 J g−1, respectively. Furthermore, the good thermal conductivity of expanded graphite reduces the super-cooling degree of n-octadecane and endows the composite PCMs with fast thermal response rate and excellent thermal cycling stability. As a result, the phase-change temperatures and phase-change enthalpy almost have no change after 50 thermal-cooling cycles. The test of intelligent temperature-control performance shows that the electronic radiator filled with the composite PCMs possesses a high intelligent temperature-control performance, and its temperature can sustain in the range of 22–27.5 °C for about 6120 s. These results indicate that the prepared composite PCMs possess good comprehensive property and can be widely used in energy storage and thermal management systems.

Thermal cycling property of supersonic atmospheric plasma sprayed thermal barrier coatings reinforced by Ni-coated YSZ fibers

Fiber reinforcement is wildly used in the metal matrix composites to restrict the initiation and propagation of cracks. In thermal barrier coatings (TBCs), the thermo-mechanical stresses lead to formation and propagation of detrimental cracks which usually cause premature failure of TBCs. In our study, the reinforcement effect of yttria-stabilized zirconia (YSZ) fibers in TBCs Ni20Al bond coat has been investigated and the wettability of YSZ fibers was taken into account. Electroless plating was conducted on the surface of YSZ fibers to enhance the interfacial compatibility between YSZ fibers and Ni20Al. TBCs with Ni20Al bond coat and YSZ top coat were deposited onto the In738LC superalloys by supersonic atmospheric plasma spraying. The microstructure and morphology of TBCs with and without YSZ fibers were estimated. The cyclic oxidation behaviour was investigated at 1050°C, and the TBCs with Ni-coated YSZ fibers show better cyclic oxidation resistance than conventional TBCs, which indicates that the addition of YSZ fibers can improve the cyclic life of TBCs. Further analysis shows that the fibers improved the thermal cycling resistance which could be attributed to the fiber bridging process.

Microstructure and oxidation protection of a MoSi2/SiO2-B2O3-Al2O3 coating for SiC-coated carbon/carbon composites

A MoSi2/SiO2-B2O3-Al2O3 double layer coating was prepared on the surface of SiC-coated carbon/carbon (C/C) composites by pulse arc discharge deposition (PADD). The phase compositions and morphology were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The oxidation resistance and thermal cycling property of the multi-layer coating were investigated. Results indicate that the multi-layer coating exhibit excellent anti-oxidation property. The MoSi2/SiO2-B2O3-Al2O3 coating can effectively protect C/C composites from oxidation in air at 1073K for 200h with negligible weight loss and 1773K for 200h with a weight loss of 0.7%. Meanwhile, the coating can endure the thermal cycling for 50cycles between 1773K and room temperature (298K). The formation of B2O3 glass phase at low temperature and borosilicate glass at high temperature are the main reasons for the good oxidation resistance of the coating.

Fabrication and characterization of cordierite-based glass-ceramic adhesives for bonding solar heat transmission pipelines

Cordierite-based glass–ceramic adhesives for bonding solar heat transmission ceramic pipelines were fabricated successfully using Suzhou kaolin, talc and commercial alumina as the main raw materials, TiO2 as nucleation agent, waste glass powder and frit 242 as high-temperature fluxes. Bonding behavior, phase transformation, microstructure, thermal shock resistance and thermal cycling properties of the adhesives were investigated, and bonding mechanism was studied. The results indicated that adhesives B4 (composed of 60wt% cordierite glass–ceramic and 40wt% frit 242) after heat treatment (nucleated at 800°C for 2h and then crystallized at 950°C for 2h) exhibited the optimal performances with a shear strength of 10.26MPa, which exceeded the industrial standard (JC/T 547-2005) of 1MPa. The analysis of bonding mechanism showed that the glass of adhesive that filled up the pores in matrix surface and penetrated inside contributed to the high shear strength. Adhesives B4 had good thermal shock resistance and thermal cycling properties, as the shear strength of samples after 30 thermal shock cycles (1100°C-room temperature, air cooling) was 8.51MPa, which increased to 26.93MPa with an increase rate of 162.48% after 100 thermal cycles (200–1100°C). During thermal shocks or thermal cycles, cordierite particles crystallized at the interfaces to form a pinning-in effect, contributing to a higher shear strength.

Thermal cycling properties of a lead-free positive temperature coefficient thermistor in the Ba0.97(Bi0.5Na0.5)0.03TiO3 system

A Pb-free PTC (positive temperature coefficient thermistor) heater was developed in the Ba0.97(Bi0.5Na0.5)0.03TiO3 system especially for automotive part applications. The reliability was verified by using a thermal cycling test designed on the basis of the result from a quality function deployment (QFD) analysis. We compared the thermal cycling test results from the newly-developed Pb-free PTC heaters with the results from PTC heaters currently on the market, namely, PTC heaters containing Pb. Life prediction and stress-strength relationships were analyzed together with a thermal diffusivity evaluation. We discuss the potential failure mechanisms during the thermal cycling test, focusing on the fact that electrical degradation in PTC materials is closely related to mechanical degradation due to the internal stress in the materials that comes from repeated phase changes. Different grain size distributions on the sintered bulks were considered to a key factor for explaining the different results of the reliability tests between the new Pb-free PTC heaters developed in this study and the commercial PTC heaters containing Pb.

Thermal cycling and oxidation resistance of B modified ZrB2–SiC coatings on SiC coated graphite

To protect graphite matrix from oxidation, B modified ZrB2–SiC coatings were prepared on SiC coated graphite by a two-step pack cementation. The microstructure, thermal cycling and oxidation resistant properties of the coatings were studied. The results show that the as-prepared coatings were mainly composed of SiC, ZrB2 and Si. ZS50-1B, ZS50-3B and ZS50-5B showed good thermal cycling resistance with 97.4%, 98.2% and 98.6% weight retention after 15 thermal cycles between 1500°C and room temperature. ZS50-7B and ZS50-9B showed good oxidation resistance with 93.5% and 97.5% weight retention after 19h oxidation at 1500°C.

Thermal cycling, microstructure and mechanical properties of 9Cr2WVTa steel welds

Samples of enlarged heat affected zones (HAZs) submitted to single and double welding thermal cycles were fabricated by a thermal-mechanical physical simulator (Gleeble 1500). Typical welding thermal cycle curves were extracted based on the measurement of the non-equilibrium phase transformation of 9Cr2WVTa steel, and the simulated and experimental thermal cycles were compared. Observation of the microstructure revealed that the blocky δ-ferrite that existed in the coarse grained heat affected zone (CGHAZ) was the main cause of the decrease in impact toughness. Each of the areas retained the δ-ferrite with different sizes and shapes after the CGHAZ underwent the second welding thermal cycle. Hardness tests, tensile tests, and instrumented impact tests were carried out to investigate the corresponding mechanical properties. When the peak temperature of the second welding thermal cycle was 1315°C, grain and structure coarsening was the main causes of the decrease in impact toughness. When the peak temperature of the second welding thermal cycle was decreased to 1100°C, the toughness increased the most due to the fine grains formed by phase transformation recrystallization.

Boron modified multi-layer MoSi2–CrSi2–SiC–Si oxidation protective coating for carbon/carbon composites

Boron modified multi-layer MoSi2–CrSi2–SiC–Si coatings were prepared on the surface of carbon/carbon (C/C) composites by three-step pack cementation in argon. The morphology and the element distribution were analyzed by scanning electron microscopy and energy dispersive spectroscopy, respectively. The oxidation resistance and thermal cycling property of the multi-layer coating were investigated. These results indicated that the coatings could protect the C/C composites from oxidation at 1173K for 200h or 1773K for 200h and endure the thermal cycling for 30 cycles between 1773K and room temperature. The oxidation resistance of the coating was improved due to the formation of compound glass during oxidation.

Tuning thermal properties of latent heat storage material through confinement in porous media: The case of (1-CnH2n+1NH3)2ZnCl4 (n=10 and 12)

In practical use, latent heat storage system always faces a lack of phase change materials (PCMs) that have ideal performance at desirable temperature and high efficiency to treat thermal effects from various outer heat sources. To solve this problem, some new latent heat storage composites were prepared by incorporating those well-performed PCMs in porous materials. In doing this, the layered perovskite-type compounds, (1-C10H21NH3)2ZnCl4 (C10Zn) and (1-C12H25NH3)2ZnCl4 (C12Zn), were embedded in controlled porous glass (CPG), which can acquire size-dependent thermal properties. Heat storage nature, morphology and crystalline structures of the materials were characterized using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and powder X-ray diffractions (XRD). Under confinement of the porous glass with nominal pore sizes of d=12–300nm, the porous CnZn compound gains a regulation window of around 10°C in relation to the bulk by its solid–solid phase transition. The transition temperature (Td), depression of the transition temperature (∆Ttrs), and enthalpy change of the transition (∆trsHd) of the confined compound show a linear relation to the reverse pore size. A same stable thermal cycling property is observed in the pore compound as the bulk, which is consistent with similar diffraction patterns among them. The supercooling of the pore form becomes larger than the bulk. The retention of the layered structure and complete crystallization in the pore CnZn is responsible for its reversible heat storage property.

Simulation and analysis of temperature field for in-service multi-pass welding of a sleeve fillet weld

Abstract The multi-pass fillet welds of sleeve were welded onto the in-service pipeline, during which the natural gas was substituted by flowing water as the cooling medium. In accordance with the practical welding process, the parameters of double ellipsoid heat source for each bead were determined by a fitting method for heat source, and the molten pool morphology simulated was coincided well with that of welded fillet bead. Using the heat source adjusted above, the processes of in-service welding were simulated by finite element method (FEM), and the temperature fields of multi-pass fillet welds were obtained. Two kinds of methane gas with different pressure and flowing rate (1.6 MPa, 10 m/s and 4 MPa, 20 m/s) were introduced to investigate the impact of cooling media on thermal cycle properties. The results show that the heat transfer condition has a significant effect on thermal cycle characteristic at the inner wall of pipelines, but a less effect on that at the outer surface of pipelines. For the different pass sequence, it is found that a faster cooling rate will appear if a fillet weld is as the first pass, compared with the situation when a surfacing bead on the pipeline is as the first one. For in-service welding of sleeve-repair, it should be concerned that the effect of pass sequence on thermal cycling characteristics.

A novel method to determine the particle–particle fracture of yttria stabilized zirconia

A novel method is presented to determine the particle–particle fracture of yttria stabilized zirconia (YSZ), which is crucial in predicting the thermal cycle properties of solid oxide fuel cells (SOFCs). The method is demonstrated by determining the Weibull and normal distribution parameters via resistivity variation of YSZ–Al2O3 composites undergoing thermal cycle processes. A straightforward approach is developed to relate YSZ mechanical property with its conductivity based on fracture statistics distributions and percolation theory. By the measurement of the conductivity change in thermal cycles, the fracture between YSZ particles caused by thermal stress can be statistically “counted”, approaching these parameters with a statistical principle, and offering a possible way to understand particle–particle fracture in microscale, and to predict the effect of microstructure change using electric signals. Finally, this method offers a potential to precisely forecast the performance degradation in the different thermal cycle processes for SOFC components such as doped ceria electrolytes and perovskite electrodes.

Characterization of ${\rm Bi}_{2}{\rm Sr}_{2}{\rm CaCu}_{2}{\rm O}_{8+\delta}$ Stacks Fabricated by Acid Treatment Process

Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8+δ</sub> (Bi-2212) stacks of intrinsic Josephson junctions were fabricated by an acid-treatment process from inside a single crystal. The surrounding acid-treated product is a transparent material, BiOCl. During the process, an optical adhesive (NOA-61) was used to fix a piece of the crystal on a glass substrate and to coat the surface of the sample. The current-voltage characteristics of the stacks at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> = 77 K exhibited large hystereses and multiple branches with voltage spacings of approximately 2-3 mV. Under an external microwave field in the frequency range of 2-18 GHz, clear Shapiro steps were observed at voltages with multiples of ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> /2 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</i> ) <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rf</sub> . In addition, the thermal cycling properties of the critical current ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) were investigated. No apparent degradation of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was observed during repeated thermal cycling between 300 and 77 K.

Effect of base metal on thermal cycle properties of heat-resistant plasma sprayed coating

Effect of base metal on thermal cycle properties of heat-resistant plasma sprayed coating

Thermal cycling failure of new LaMgAl 11O 19/YSZ double ceramic top coat thermal barrier coating systems

New LaMgAl 11O 19 (LaMA)/YSZ double ceramic top coat thermal barrier coatings (TBCs) with the potential application in advanced gas-turbines and diesel engines to realize improved efficiency and durability were prepared by plasma spraying, and their thermal cycling failure were investigated. The microstructure evolutions as well as the crystal chemistry characteristics of LaMA coating which seemed to have strong influences on the thermal cycling failure of LaMA and the new double ceramic top coat TBCs based on LaMA/YSZ system were studied. For double ceramic top coat TBC system, interface modification of LaMA/YSZ by preparing thin composite coatings seemed to be more preferred due to the formations of multiple cracks during thermal cycling making the TBC to be more strain tolerant and as well as resulting in an improved thermal cycling property. The effects of the TGO stresses on the failure behavior of the TBCs were discussed through fluorescence piezo-spectroscopy analysis.

Thermal cycle properties of plasma sprayed YSZ/Al2O3 thermal barrier coatings

In the present study, yttria partially stabilised zirconia (YSZ)/Al2O3 coatings, which are used for jet engines, gas turbines and diesel engines were coated with thermal barrier coatings to provide high thermal resistance, reduce the metal surface temperatures and increase component durability. The effect of alumina addition from 0 to 80 wt-% on the properties of plasma sprayed YSZ coatings was investigated. The coating comprised of YSZ–Al2O3 (0, 20, 50 and 80 wt- %Al2O3); NiCrAlY bond coat; and AISI 304L stainless steels substrates. Scanning electron microscopy was used to analyse the microstructures of the coated samples. Thermal shock tests were performed over the specimens, at 1000 and 1200°C for 5 min and then forced air quenching for 2 min. The microhardness was investigated depending on the alumina contents. Vickers hardness on cross-section of coatings was observed to increase with the increase in alumina mixing ratio. It was noticed that with increase in Al2O3 content the thermal shock life of the specimens decreased.

Thermo-physical and thermal cycling properties of plasma-sprayed BaLa 2Ti 3O 10 coating as potential thermal barrier materials

Increased turbine inlet temperature in advanced turbines has promoted the development of thermal barrier coating (TBC) materials with high-temperature capability. In this paper, BaLa 2Ti 3O 10 (BLT) was produced by solid-state reaction of BaCO 3, TiO 2 and La 2O 3 at 1500 °C for 48 h. BLT showed phase stability between room temperature and 1400 °C. BLT revealed a linearly increasing thermal expansion coefficient with increasing temperature up to 1200 °C and the coefficients of thermal expansion (CTEs) are in the range of 1 × 10 − 5 –12.5 × 10 − 6 K − 1 , which are comparable to those of 7YSZ. BLT coatings with stoichiometric composition were produced by atmospheric plasma spraying. The coating contained segmentation cracks and had a porosity of around 13%. The microhardness for the BLT coating is 3.9–4.5 GPa. The thermo-physical properties of the sprayed coating were investigated. The thermal conductivity at 1200 °C is about 0.7 W/mK, exhibiting a very promising potential in improving the thermal insulation property of TBC. Thermal cycling result showed that the BLT TBC had a lifetime of more than 1100 cycles of about 200 h at 1100 °C. The failure of the coating occurred by cracking at the thermally grown oxide (TGO) layer due to severe oxidation of bond coat. Based on the above merits, BLT could be considered as a promising material for TBC applications.

Cathode reaction mechanism of porous-structured Sm0.5Sr0.5CoO3− and Sm0.5Sr0.5CoO3−/Sm0.2Ce0.8O1.9 for solid oxide fuel cells

Abstract The cathode reaction mechanism of porous Sm0.5Sr0.5CoO3−δ, a mixed ionic and electronic conductor (MIEC), is studied through a comparison with the composite cathode Sm0.5Sr0.5CoO3−δ/Sm0.2Ce0.8O1.9. First, the cathodic behaviour of porous Sm0.5Sr0.5CoO3−δ and Sm0.5Sr0.5CoO3−δ/Sm0.2Ce0.8O1.9 are observed for micro-structure and impedance spectra according to Sm0.2Ce0.8O1.9 addition, thermal cycling and long-term properties. The cathode reaction mechanism is discussed in terms of frequency response, activation energy, reaction order and electrode resistance for different oxygen partial pressures p(O2) at various temperatures. Three elementary steps are considered to be involved in the cathodic reaction: (i) oxygen ion transfer at the cathode–electrolyte interface; (ii) oxygen ion conduction in the bulk cathode; (iii) gas phase diffusion of oxygen. A reaction model based on the empirical equivalent circuit is introduced and analyzed using the impedance spectra. The electrode resistance at high frequency (Rc,HF) in the impedance spectra represents reaction steps (i), due to its fast reaction rate. The electrode resistance at high frequency is independent of p(O2) at a constant temperature because the semicircle of Rc,HF in the complex plane of the impedance spectra is held constant for different values of p(O2). Reaction steps (ii) and (iii) are the dominant processes for a MIEC cathode, according to the analysis results. The proposed cathode reaction model and results for a solid oxide fuel cell (SOFC) well describe a MIEC cathode with high ionic conductivity, and assist the understanding of the MIEC cathode reaction mechanism.