Thermal Cycling Process Research Articles

High temperature oxidation behavior of Inc-738/NiCrAlY/LaMA thermal barrier coating system

The high temperature oxidation behavior of Inc-738/NiCrAlY/LaMgAl11O19 (LaMA) thermal barrier coating system was studied and compared with Inc-738/NiCrAlY/8YSZ coating system. The morphology of coatings, formation of TGO layer and degradation of coatings during oxidation process were investigated. The results indicated that the thermal cycling lifetime of LaMA coating was more than 8YSZ coating. The morphological evaluation of LaMA coating revealed that the recrystallization of amorphous phase was occurred. The 8YSZ ceramic top coat was sintered and microstructure was generated from columnar to equiaxed structure during thermal cycling process. Following the formation of a continuous alumina layer, undesirable oxides created at the TGO/bond coat (BC) interface in the LaMA coating system, whereas, unwanted oxides created at the TGO/top coat (TC) interface in the 8YSZ coating system and also it is believed that the oxidation of coating systems in steady-state stage was occurred under the diffusion-chemical mechanism and chemical mechanism, respectively. Therefore, the different failure mechanisms were observed in both coating systems. In the 8YSZ coating, the cracks nucleated at the TGO/TC interface, while in the LaMA coating, the cracks nucleation were occurred in TGO layer.

Microstructure and performance evolution of SnPbSb solder joint under γ-ray irradiation and thermal cycling

The requirements of miniaturization and light-weighting in the manufacture of satellite have placed much emphasis on the property of its electronic materials. To comprehend the reliability evolution of solder joint in electronic components exposed to cosmic environment, the effect of γ-ray irradiation and thermal cycling on the microstructure and performance of SnPbSb solder joints was studied. The results indicated that micro-voids and micro-cracks formed in solder matrix and the mechanical property of solder joint was decreased with the increasing irradiation time, while the thickness of intermetallic compound layer (IML) in solder joints was hardly changed. Moreover, these micro-voids and micro-cracks partly vanished during the thermal cycling process due to the migration of atoms, but the thickness of IML was greatly increased which caused the further decrease of the mechanical property of solder joint. Fracture analysis indicated that the effect of irradiation and/or thermal cycling on the fracture type of solder joint was inconspicuous, but the ductility was slightly changed in different conditions.

Numerical Simulation of Welding Process for Q235 Steel Plate

In this paper, the weld of Q235 steel pipe with diameter of 60 mm and thickness of 4 mm is simulated and analyzed by MSC. Marc software. After modeling, applying material physical properties, setting weld bead and welding path, and applying boundary conditions, the operation results are analyzed and processed by submitting the work. According to the simulation results, different joints are selected to study the thermal cycle process and temperature distribution of joints under different joints.

The Microstructure and Pitting Resistance of 2002 Lean Duplex Stainless Steel after the Simulated Welding Thermal Cycle Process.

In this paper, thermal cycles with different heat inputs and cooling rates were investigated for a novel lean duplex stainless steel 2002 using a welding simulation. The microstructure and pitting resistance of the simulated heat-affected zones were studied. With the increasing heat input, the amount and size of the austenite phase both increased, along with a transformation from rods to dendritic structures. The critical pitting temperature (CPT) and the pitting potential (Epit) both increased first and then declined as the heat input increased, indicating a strong dependence of pitting resistance on the heat input. For the different cooling rates, the amount of ferrite increased as the cooling rate increased from 0.25 °C/s to 20 °C/s. The CPT and Epit both increased with the increasing cooling rates, indicating an improved pitting resistance. The pits initiated preferentially at the boundaries of ferrite and austenite due to the precipitation of M23C6 in the specimens with different cooling rates.

Study on the fracture behavior of the planar-type solid oxide fuel cells

In this work, the commercial SUS430 ferritic stainless steel was used as the current collector to study the fracture behaviors of the planar electrolyte-supported and anode-supported solid oxide fuel cells with the size of 10 cm × 10 cm during the thermal cycle process. The anode-supported cells (ASCs) were fabricated by tape-casting, spraying, screen-printing and co-sintering. The electrolyte-supported cells (ESCs) using fully-stabilized zirconia as material were prepared by tape-casting, multilayer lamination, screen-printing and co-sintering. The output power densities at 0.7 V (P0.7V) of the anode-supported and electrolyte-supported cells could reach 0.60 W cm−2 and 0.43 W cm−2 at 850 °C, respectively. During the thermal cycle testing, the ESC sample was cracked, while the ASC sample had no obvious changes. The thermal expansion coefficient (TEC) of the different samples was studied, and the two cells were characterized by the XRD after the thermal cycle testing. In addition, the fracture behaviors of the two cells were discussed. The results indicated that the ASC sample had the good stability during the thermal cycle testing. The excellent anti-cracking performance of the ASC was attributable to two aspects. Firstly, the TEC of the anode support is more close to that of the SUS430 material; secondly, the phase transformation of zirconia from monoclinic phase to tetragonal phase induced by stress is favorable for contraction of the anode support layer during the cooling process.

Effects of thermal cycling on physical and tensile properties of injection moulded kenaf/carbon nanotubes/polypropylene hybrid composites

Polymer as well as polymer composites are inclined to premature due to effect on mechanical and physical properties during service time. In this paper, the effect of thermal cycling (−30 to 80 °C) on the physical and tensile properties of Polypropylene (PP), Kenaf/PP, Kenaf/PP/CNTs and Kenaf/CNTs/MAPP/PP hybrid composites for the injection moulded car battery tray was investigated. Although this study had found no physical changes on the samples in terms of colour or cracking, the samples, however, had experienced warpage and dimensional changes. The dimension of samples containing CNT had increased by 20%, while the PP and PP/Kenaf samples had decreased by 3.5% and 87%, respectively. Although the process of thermal cycling was found to have rapidly decreased the hardness of Pure PP and Kenaf/PP composites, it had, however, gradually increased the hardness of composites with CNT fillers. The tensile strength, Young's modulus and elongation of the composites had also been examined in this research. Furthermore, according to the fractographic investigations using scanning electron microscope, it is perceived that the fracture morphology of the samples is strongly influensed by thermal cycling.

Phase-Field Study of Microstructure and Plasticity in Polycrystalline MnNi Shape Memory Alloys

The evolution of microstructure and plasticity in polycrystalline MnNi shape memory alloys was simulated by a phase-field method considering plastic deformation. Plastic strain was found to occur around grain boundaries and intersections between martensitic bands. In addition, the accumulation of plastic strain would keep on continuously occurring during the thermal or stress cycling process. The occurring of plastic strain could be caused by the lattice incompatibility between austenite and martensite near the tip of martensite plate.

Self-marked HCN gas based FBG demodulation in thermal cycling process for aerospace environment.

The thermal cycling process experienced by spacecraft during orbital operation would lead to deterioration of the demodulation performance of fiber Bragg grating (FBG). A new demodulation method based on Fabry-Perot (F-P) filter and hydrogen cyanide (HCN) gas is proposed to improve the performance. The method skillfully utilizes the self-marked HCN absorption lines as absolute wavelength references. In the thermal cycling environment whose temperature ranging from 5°Cto 65°C,the fluctuation of demodulation wavelength reduces to ± 2.6 pm, which is improved by 3.1 times compared with traditional method. The proposed method also shows a good robustness in the cases of weak light source intensity and poor signal-to-noise ratio (SNR) of HCN spectrum.

Thermodynamic mechanism of self-heat recuperative heat circulation of vapour system

Self-Heat Recuperation Technology has recently been proved to be an effective method to cut the huge energy consumption in the chemical industry. In the present paper, the thermodynamic mechanism of the self-heat recuperative heat circulation of the vapour system without chemical reaction is studied in terms of exergy analysis using process module, temperature-entropy and energy conversion diagrams. The self-heat recuperative thermal vapour cycle process was modularized by combining four types of thermodynamic elementary process modules, namely isobaric heating and cooling process modules (heat receiver (HR) and heat transmitter (HT)) and isentropic compression and expansion process modules (work receiver (WR) and work transmitter (WT)), and a heat exchange process module (heat exchanger (HX)). In the four types of thermodynamic elementary process modules (HR, HT, WR, WT), both exergy and anergy are conserved. It is only in the heat exchange process module (HX) that exergy destruction takes place and the destructed exergy transforms into the same amount of anergy due to irreversibility of heat transfer. In the self-heat exchange process, the process fluid undergoes temperature change and phase transition. Therefore, the self-heat exchange process should be divided into three stages, namely the self-heat exchange of the liquid sensible heat, the self-heat exchange of the latent heat, the self-heat exchange of the vapour sensible heat. Correspondingly three HXs are necessary, and only in these three HXs do all the exergy destructions of the self-heat recuperative thermal vapour cycle process take place. The work provided as the minimum work required for the self-heat recuperative heat circulation of the vapour system by compressing the process fluid in the vapour phase through one WR, i.e. work input, equals the sum of the exergy required to compensate for the three exergy destructions of the three HXs and the exergy required to discard waste heat to the environment. The work input eventually converts to the waste heat, i.e. heat output, the exergy of which is the exergy required to discard the waste heat to the environment and the anergy of which results from the three exergy destructions of the three HXs.

Second Cooling Test of 1000-m Superconducting DC Cable System in Ishikari

A 1000-m-long superconducting dc power transmission system was built in Ishikari City, Hokkaido, Japan, as a national project (“Ishikari project”). The objectives of the project are to design and verify the validity of a system for a practical use, and also to obtain the properties required to get a future prospect for longer length cable system, such as over 10 km. Until the end of 2016, the cooling test was carried out two times. Important issues for the cooling test are: release of thermal contraction/expansion force below the rapture strength of the cable and the reliability and life time of the system after several cooling/warming procedures, as well as long-time operation. For the former issue, two techniques (a movable terminal cryostat and the helical core deformation) were adopted and these techniques were found to release the axial tension of the cable core effectively. For the latter issue, several types of current loading test, such as Ic measurements, continuous rated current test (2.5 kA-3 hrs), load cycling test (1 kA-8 hrs + 0 A-16 hrs for 20 days), etc., were performed. All the tests showed no deterioration of the electrical properties of the cable core, after cable laying and thermal cycling process, and also the stability of the system.

A comparative study on effects of thermal fatigue caused by thermal-oil cycling on tensile properties of single lap composite joints bonded with different kinds of adhesives

ABSTRACTIn this study, thermal-oil cycling process was applied to adhesively bonded glass fibre reinforced single lap composite joints (SLJs) in order to investigate the effects of thermal fatigue on their tensile properties. Joints were subjected to thermal cycling to achieve the thermal fatigue effect. Initially, separated specimens were heated on a magnetic stirrer from 25°C to 80°C, 25°C to 100°C and 25°C to 120°C and kept at these temperatures for 10 min. Right after that specimens were immersed into heat transfer oil cooled with dry ice at −10°C for 10 min. and placed back into the magnetic stirrer to reach intended temperatures again. Thus, one cycle is completed. This thermal cycling process was repeated for 1, 10, 20, 30, 40 and 50 times for different groups of specimens. Single lap shear (SLS) tests have been performed for the determination of mechanical properties. As a result of this study, it is found that the load carrying capacities of specimens generally decrease as the thermal cycling count is increased. However, it is observed that specimens subjected to 30 times thermal cycling have the maximum load carrying capacity.

Mechanical Properties of Layered La2Zr2O7 Thermal Barrier Coatings

Lanthanum zirconate (La2Zr2O7) has been proposed as a promising thermal barrier coating (TBC) material due to its low thermal conductivity and high stability at high temperatures. In this work, both single and double-ceramic-layer (DCL) TBC systems of La2Zr2O7 and 8 wt.% yttria-stabilized zirconia (8YSZ) were prepared using air plasma spray (APS) technique. The thermomechanical properties and microstructure were investigated. Thermal gradient mechanical fatigue (TGMF) tests were applied to investigate the thermal cycling performance. The results showed that DCL La2Zr2O7 + 8YSZ TBC samples lasted fewer cycles compared with single-layered 8YSZ TBC samples in TGMF tests. This is because DCL La2Zr2O7 TBC samples had higher residual stress during the thermal cycling process, and their fracture toughness was lower than that of 8YSZ. Bond strength test results showed that 8YSZ TBC samples had higher bond strength compared with La2Zr2O7. The erosion rate of La2Zr2O7 TBC samples was higher than that of 8YSZ samples, due to the lower critical erodent velocity and fracture toughness of La2Zr2O7. DCL porous 8YSZ + La2Zr2O7 had a lower erosion rate than other SCL and DCL La2Zr2O7 coatings, suggesting that porous 8YSZ serves as a stress-relief buffer layer.

Cyclic cryogenic pretreatments influencing the mechanical properties of a bulk glassy Zr‐based alloy

AbstractIn this study, cryogenic thermal cycling was applied to bulk glassy Zr52.5Cu17.9Al10Ni14.6Ti5 (Vitreloy 105) bending samples. After that, significantly improved plasticity and better fatigue properties at three‐point bending as well as higher impact toughness were measured in dependence of the duration and the cooling rate of the thermal cycling process. This improved material behaviour is caused by reinforced shear banding, visible in scanning electron microscopy at the side faces of the specimens after fracture. A comprehensive analysis of the fracture surfaces of both quasi‐static and cyclic bent specimens revealed intense crack propagation along major shear bands and increased fatigue fracture regions, respectively. It is supposed that there is a structural rejuvenation due to the local variations of the thermal expansion coefficients within the multicomponent alloy affecting the mechanical properties.

Triple Signal Amplification Strategy for Ultrasensitive Determination of miRNA Based on Duplex Specific Nuclease and Bridge DNA-Gold Nanoparticles.

Abnormal expression of miRNAs always occurs in solid tumors. Thus, it is critical to sensitively and selectively detect such biomarkers for the diagnosis and prognosis of diseases. Here, we report a biosensing scheme for the determination of miRNA with triple signal amplification based on target-triggered cyclic duplex specific nuclease digestion and bridge DNA-gold nanoparticles. Electrochemical signals are recorded to present initial levels of miRNA. This method is ultrasensitive with a wide linear range of 10-17 to 10-11 M. The limit of detection is down to 6.8 aM. Moreover, the overexpression of miR-21 is confirmed in lung cancer patients by the proposed method, which is in good accordance with qRT-PCR results. In addition, the developed biosensor does not need a reverse transcription process or any thermal cycling processes. Its performance satisfies the requirement for convenient, rapid, sensitive, and specific early diagnosis of cancers. Therefore, it may have great potential utility in the near future.

Effect of freeze-thaw cycles in mechanical behaviors of frozen loess

A series of triaxial compression, creep and stress relaxation tests at temperature of −6°C were conducted on frozen loess, experienced different freeze-thaw numbers (0–12times), in order to study the thermal cycling effect in mechanical behaviors. The freeze-thaw process has a strong influence in the mechanical behaviors of frozen loess. The strength, stiffness and viscosity properties of frozen loess weaken gradually with the increase of the freeze-thaw procedure until the cycle number gets to the critical value for steady state of soil sample. The freezing low temperature ranged from −6°C to −12°C has no evident effect in the testing results of same freeze-thaw numbers. The strength distribution loci of frozen loess in the equivalent stress-mean stress space exhibits a unidirectional shrinkage over the range of the freeze-thaw process studied. Triaxial strength characteristics of frozen loess, experienced different freeze-thaw numbers, are more in agreement with the Ma's failure criterion for frozen soils (Ma et al., 1993). The stiffness properties (elastic modulus, elastoplastic coupled degree and damage degree) and the viscosity properties (relaxing stress, stable relaxation time, stable creep rate and viscoelastic modulus) of frozen loess both depend on the freeze-thaw process. The microstructure change of frozen loess induced by the thermal cycling effect is analyzed detailly so as to explore the micro-mechanism of property degeneration. Finally, a developed constitutive model, considering the freeze-thaw and confining pressure effect, is proposed to research and predict the triaxial strength and deformation characteristics of frozen loess experienced different thermal cycling process.

Thermodynamic Mechanism of Self-Heat Recuperative and Self-heat Recovery Heat Circulation System for a Continuous Heating and Cooling Gas Cycle Process

The thermodynamic mechanism of self-heat recuperative and self-heat recovery heat circulation system for a continuous isobaric heating and cooling gas cycle process without chemical reaction has been studied in terms of the exergy analysis by using energy conversion and temperature-entropy diagrams. The modularization of the thermal gas cycle process which is decomposed into four thermodynamic elementary process modules, isobaric heating and cooling process modules (HR and HT) and adiabatic compression and expansion process modules (WR and WT), and a heat exchange process module (HX) indicates that in four thermodynamic elementary process modules (HR, HT, WR, and WT) both exergy and anergy are conserved except for HX in which the exergy is transformed into the anergy because of the exergy destruction due to the heat transfer. In the self-heat recuperative heat circulation system for the heating and cooling gas cycle process, providing the minimum work required for the heat circulation to compensate for the exergy destruction in HX the process heat is recuperated with increasing temperature of process fluid from T to T+ΔT and then recirculated through HX. The minimum work required for heat circulation, or work input, is converted to heat output, or the thermal energy of which anergy and exergy are the exergy destruction due to heat transfer in HX and the exergy to discard the anergy transformed by the exergy destruction, respectively. For the conventional self-heat recovery heat circulation system by providing heat instead of work the additional exergy to discard the anergy of heat input into the environment is needed with the minimum work required for heat circulation to compensate for the exergy destruction due to the heat transfer in HX, increasing the energy requirement for heat circulation by self-heat recovery.

Transport properties of MnTe films with cracks produced in thermal cycling process

As a promising material in antiferromagnetic spintronics, MnTe films manifested complex characteristics according to previous reports. In this work, we investigate in details the temperature dependence of resistivity of MnTe films grown on SiO2/Si substrate and focus on the divaricating of cooling and warming resistivity-temperature (R-T) curves. It is found that such a divaricating in resistivity is associated with cracks produced in thermal cycles. By comparing the crystalline character and the morphology before and after the cycles, we verify the appearance of cracks and the release of stress in the films. Based on the temperature dependence of thermal-expansion coefficient of Si and MnTe, the origin of the cracks is the mismatched thermal-expansion coefficient (α). The humps, which only appear in the R-T curve of the first cooling process, are attributed to the produced cracks and/or the unreleased stress.

Mullite whisker toughened mullite coating to enhance the thermal shock resistance of SiC pre-coated carbon/carbon composites

In order to improve the thermal shock resistance of the coated carbon/carbon (C/C) composites, a mullite whisker toughened mullite coating was fabricated on the surface of SiC pre-coated C/C composites (SiC-C/C) by molten-salt method with a later hot dipping process. The phase compositions, surface and cross-section microstructures, high temperature thermal shock resistance of the as-prepared multi-layer coatings were investigated. Results show that the introduction of mullite whiskers can effectively improve the density of the mullite outer coating and decrease the cracking of the coating during the thermal shock cycle process. After 100 times thermal shock cycles between 1773K and room temperature, only 1.87 × 10−3gcm−2 weight loss has been detected, indicating the achievement of the excellent thermal shock resistance.

Effects of Chromium Content on Thermal Shock Cycle Resistance of (TiCr)N Hard Reactive Films

The (TiCr)N hard reactive films with 4 different Ti/Cr atomic ratios are prepared by using multi-arc ion plating. The Ti and Cr targets are used as cathodes in the co-deposition process. The high speed steel (HSS) specimens are adopted as substrate. The thermal shock cycle tests in air cooling (AC) way for the (TiCr)N films are carried out. The test temperatures are chosen as 600 °C and 700 °C, respectively. The changes of the surface compositions and morphology in the thermal shock cycle tests are investigated. The effects of Cr content in the (TiCr)N films, the temperature at which the thermal shock cycle tests are performed and the cycling times on the thermal shock resistance of the (TiCr)N films are discussed and analyzed in detail. The thermal shock behaviors of the (TiCr)N films show that the thermal shock cycling process of the (TiCr)N films consists of two stages, the steady-state oxidation stage with the increase of oxygen content at the early stage of thermal cycles, and, the instable oxidation stage with the oxidation aggravation and the occurrence of the surface cracks. The simple increase of Cr content in the (TiCr)N film does not improve the thermal shock resistance of the (TiCr)N films but easy to aggravate the surface oxidation process during the thermal shock cycles.

Thermocouple measurements to investigate the thermal fatigue of a cyclic thermal mixing process near a dissimilar weld seam

To investigate the thermal fatigue of piping systems in nuclear power plants, the Fluid-Structure-Interaction (FSI) test facility is operated at the University of Stuttgart. In the modular FSI-facility, a hot-water flow (265°C) in the main pipe (DN80) and a cold-water flow (20°C) in the branch pipe (DN40) are mixed within a horizontal mixing tee at 75bars. For the investigation of the impact of possible incomplete mixing on a dissimilar weld seam, a pipe section (module) with a dissimilar weld connection of an austenitic and a ferritic steel section is arranged near the mixing position. In order to achieve large temperature fluctuations the cold flow, which aims directly at the weld seam, is actively switched on and off by a valve-and-bypass system, while the hot flow is continuously maintained. The durations of the injection and bypass are varied with values of 30s (injection)/30s (bypass), 10s/10s, 5s/5s and 1s/1s.In this paper, the temperature fluctuations of these experiments are presented and analyzed in order to characterize the unsteady thermal loads on the weld materials. For this purpose, forty micro-thermocouples are installed in the weld seam module to measure the temperature in the near-wall fluid with a sampling rate of 100Hz. The distributions of the mean temperature and the temperature fluctuations in the flow within the weld seam module during the measurements are reconstructed. Fourier analyses are conducted and the results are summarized in the form of frequency spectra. Areas of the pipe wall with the highest potential for material damage due to thermal fatigue are identified with the help of these spectra. Furthermore, the possibility of thermal fatigue is confirmed by a metallographic investigation, in which a material crack is found.