Thermal Fatigue Behavior Research Articles

Characterizing thermal fatigue behaviors of asphalt concrete waterproofing layer in high-speed railway using customized overlay test

The novel asphalt concrete waterproofing layer (ACWL) in high-speed railway faced a severe challenge from thermal fatigue cracking, while there was absence of a feasible evaluation method for this unique thermal fatigue mode. In this study, the overlay test (OT) was customized in terms of test temperature and open displacement to simulate the cyclic thermal load on in-service ACWL and characterize the thermal fatigue behaviors of railway asphalt mixtures. Four classical and two dissipated energy-derived indicators, namely maximum tensile load (L0), cracking rate index (CRI), the ratio of transitional tensile load L1 to L0 (L1/L0), pseudo fracture energy (PFE), initial dissipated energy (IDE), and cumulative dissipated energy (CDE), were utilized to evaluate the fatigue characteristics. It was found that the OT at a test temperature of 20 °C and open displacement of 0.6 mm was the most efficient in distinguishing fatigue characteristics, and the CRI, L1/L0, IDE, and PFE were statistically recognized to be feasible and effective. In addition, railway asphalt mixtures could achieve a 10-year fatigue life under moderate conditions while might crack rapidly at a low temperature and a large open displacement. Meanwhile, several indicators, including L0, CRI, L1/L0, PFE, and CDE, demonstrated linear relationships with the fatigue life on a normal or log scale at low temperatures, implying their potential to predict fatigue life. Finally, a Weibull damage model was applied based on load ratio-based damage degree, which had fair linear correlation with actual damage degree, to correlate with the thermal fatigue damage process. As expected, the proposed evaluation method, indicator, and fatigue damage model could fairly characterize the thermal fatigue behaviors of railway asphalt mixtures and further guide the construction and maintenance of ACWL.

Microstructural analysis of the thermal fatigue tested Be/CuCrZr joint with artificial defects between Ti/Cu interlayers

The ITER enhanced-heat-flux (EHF) FW fingers undertook by China are made by hot isostatic pressing (HIP) method to bond beryllium armor tiles to CuCrZr/316L(N) heat sinks with 10 μm-thick Ti coating on beryllium tiles and 0.5 mm-thick oxygen free copper sheet as interlayer. To study its thermal fatigue behavior, small scale mock-up was manufactured with artificial defects (AD) on the beryllium tile surface with Ti coating. Thermal cycling of the mockup was carried out at 4.7 MW/m2 high heat flux (HHF) for 5000 cycles. The interface between Be/Ti/Cu and the fracture surface on beryllium tiles were observed by stereomicroscopy and scanning electron microscopy with energy spectrometer. The Be/Ti/Cu interfacial phase composition and the behaviors of defects after high heat flux test were analyzed. In addition, the generation and propagation mechanism of thermal fatigue defects were preliminarily studied in this paper. The results show that uniform bonding between Be and Cu was achieved and the interfacial phases are Be base/ Be-Ti intermediate/ α-Ti/ Ti2Cu/ TiCu /Cu base in the sequence. The formation of complex brittle phases reported in previous study, such as Ti3Cu4 or α-TiCu4, can be avoided by using Ti single interlayer. When the original defect dimension is only 3 × 3 mm2, the defect will not propagate after 5000 cycles 4.7 MW/m2 HHF testing (HHFT). Besides, decreasing beryllium tile size can reduce the possibility of thermal fatigue failure. In addition, from the research on fracture surface on beryllium tiles, the final fracture made for beryllium detachment mainly happened in Ti layer near the beryllium side. While thermal fatigue cracks preferentially originated at Be/Ti interface and the oxidation of beryllium surface under thermal cycling test would accelerate the generation and propagation of thermal fatigue defects.

Thermal fatigue analysis of structures subjected to liquid metal jets at different temperatures in the Gen-IV nuclear energy system

In the Generation-IV (Gen-IV) nuclear reactor system, the liquid metal cooled fast reactor is regarded as a promising reactor type, especially the sodium-cooled fast reactor (SFR). It is necessary to investigate the thermal striping of liquid metal jets and the thermal fatigue behavior of adjacent structures at the core outlet of a liquid metal cooled fast reactor where coolant at different temperatures is mixed and causes thermal fatigue of adjacent structures. In this work, a fluid-structure coupling model and thermal fatigue assessment methodology are proposed and employed to study the thermal fatigue of structures subjected to liquid mental jets at the core outlet of the SFR. The temperature field and velocity distribution of the fluid, as well as the deformation and thermal stress of structures are obtained. The transient load and thermal fatigue damage of the structure at different locations are also calculated and analyzed. The fatigue damage factor of the structure is less than 1.0. The max deformation is predicted and a relatively large von Mises stress is located in the junction of central column and control rod guide tube, as well as the area of geometric structure mutation.

Influence of porosity and blistering on the thermal fatigue behavior of tungsten

Tungsten is the leading plasma-facing material (PFM) for nuclear fusion applications. It faces severe operating conditions, including intense hydrogen plasma exposure and high-cycle transient heat loading, which create various defects in tungsten. Additionally, defects have often already been introduced during manufacturing. Little is understood regarding the synergistic effect of such defects on the lifetime of tungsten so far. Here, we investigate the influence of porosity and blistering on the thermal fatigue behavior of tungsten. The pores resulted from powder metallurgy whereas the blistering was induced by hydrogen plasma exposure. Both conditions were subjected to transient heat loading by a high-power pulsed laser. The exposure was performed in the linear plasma generator Magnum-PSI, which closely mimics the expected particle and heat flux in the world’s largest fusion experiment, ITER. Both porosity and blistering degraded the fatigue resistance of tungsten. Pores tended to aggregate at high-angle grain boundaries (HAGBs) and assisted crack initiation therein, as revealed by focused ion beam cross-sectioning and electron backscatter diffraction (EBSD) analysis. The blisters were characteristic of subsurface cavities, which were located at a depth close to the surface roughness induced by transient heat loading. The stress concentration at the tip of the cavities is considered to promote crack initiation. The results highlight the necessity of a ‘life cycle assessment’ of the tungsten PFM for nuclear fusion reactors.

Different thermal fatigue behaviors between gray cast iron and vermicular graphite cast iron

Different thermal fatigue behaviors between gray cast iron and vermicular graphite cast iron

Study on tensile and thermal fatigue behaviors of additively manufactured cobalt-based alloys alloying with Al and Ni

The paper explores the effects of Al and Ni on the performances of tensile and thermal fatigue of the additive manufactured cobalt-based alloys. Additions of Al and Ni influence the stacking fault energy, amounts of carbides and oxidation capacity. The 1Al15Ni alloy exhibits the best thermal fatigue resistance and elongation.

Thermal fatigue behavior of 441 ferritic stainless steel in air and synthetic automotive exhaust gas

Thermal fatigue behavior of 441 ferritic stainless steel in air and synthetic automotive exhaust gas

Thermal Fatigue Model of Aluminium Alloy Die Casting H-13 Dies under Thermo-Mechanical Cycle

In industrial fields, thermal fatigue behavior has recently acquired an important role which is mainly related to the interaction between mechanical and thermal conditions. This paper proposes a thermal fatigue model of H13 tool steel under thermos-mechanical cycles. A test apparatus was used to assess the thermal fatigue resistance of materials to estimate surface crack area when specimens are subjected to thermal cycling. Thermal cycling up to 700°C was used, and crack patterns were examined after 1850, 3000, and 5000 cycles. Temperature distributions were measured at different locations in the test specimens. A model was developed to establish a relationship between mechanical cycling and thermal analysis. From the results, the thermal fatigue resistance was significantly improved over the control parameter after heating and cooling during thermomechanical cycles. The model was applied to determine the best performance and in-service life of die casting tools.

Comparative thermal fatigue behavior of AlSi7Mg alloy produced by L-PBF and sand casting

By increasing the demand for additively manufactured Al parts for industrial applications, the knowledge about their thermal and mechanical behavior in service environments becomes highly required. Since Al alloys are widely used for the production of lightweight structures in transportation industry including several engine components, their thermo-mechanical behavior deserves special attention, considering the thermal and mechanical load fluctuations experienced in parts like cylinder heads, pistons, brake disks and calipers. In the present study, a comparative research has been carried out on the thermal fatigue (ThF) behavior of an AlSi7Mg (A357) alloy processed either by sand casting or laser powder bed fusion (L-PBF). Both alloy conditions were cycled within three temperature intervals with a lower temperature of 100 °C and upper limits of 200, 240 and 280 °C, in presence of a constant uniaxial tensile load. Three tensile loads of 110, 120 and 150 MPa were applied for each temperature range in order to explore the effect of both thermal cycling and concurrent tensile load on thermal fatigue resistance. Both alloys showed a similar ThF lifetime when exposed to temperature cycles from 100 to 200 °C under all the three tensile loads investigated, while the L-PBF A357 alloy tested to the highest temperature limits of 240 °C and 280 °C comparatively revealed an improved ThF resistance than the cast counterpart. Microstructural analyses on the cross-sections of both samples revealed that a large amount of strain was accumulated close to the fracture regions and several micropores and microcracks were developed in these areas. Microcracks preferentially nucleated at eutectic Si and Fe-bearing coarse intermetallics in the ThF tested cast alloy, while micropores nucleated from the fragmented silicon network in L-PBF samples on exposure to thermal cycling.

Effect of thermal degradation on the properties and wear behavior of Cr−V−C composite coatings grown on ductile iron

The thermal fatigue behavior of chromium vanadium carbide (Cr − V − C) coatings and the wear of the coatings after thermal fatigue cycling was studied. The Cr − V − C coatings were grown on the surface of a ductile iron using thermo-reactive diffusion (TRD) and subjected to thermal fatigue in the temperature range of 25 to 750 °C for up to 500 cycles. Characterizations were made using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, microhardness measurements and wear tests . The Cr − V − C coated samples displayed superior thermal fatigue and wear resistance compared to the untreated ductile iron, mainly due to the dissolution of graphite nodules in the vicinity of the surface during TRD. The dissolution of graphite reduced the possibility of failure initiating from graphite nodules and graphite-matrix interfaces. Increasing the number of cycles resulted in increased flaking and decreased wear resistance in both the Cr − V − C coatings as well as the untreated ductile iron. Although much of the Cr − V − C coating was lost (due to flaking) after thermal cycling, the absence of graphite near the surface still provided improved resistance to wear in the TRD-treated samples. The results of this study indicate that TRD coatings hold great promise for use in the industrial applications. • Failure and wear behavior of the thermally cycled Cr-V-C coatings were investigated. • The Cr-V-C coating improved thermal fatigue and wear resistance • Graphite nodules serve as initiation sites for microcracking in ductile iron. • The dissolution of the graphite nodules helped improve thermal fatigue and wear resistance • Cr-V-C coatings hold great promise for use in industrial applications.

Corrosion and thermal fatigue behaviors of induction-clad Ni-coated TiC particle-reinforced Ni60 coating in molten aluminum alloy

The Ni60 coatings were fabricated via induction cladding with Ni-coated TiC reinforcement particles using electroless plating to improve the coating quality. The corrosion and thermal fatigue behaviors of the H13, Ni60 coating and Ni-coated TiC particle-reinforced Ni60 coating in molten aluminum alloy were investigated. The results showed that Ni-coated TiC by electroless plating significantly improved preparation quality of ceramic particle-reinforced Ni60 coating. The weight loss of the received coating in molten aluminum alloy was about 25% of that of the H13 and 66% of that of the Ni60 coating. The corrosive mechanisms of the H13 steel and Ni60 coating in molten aluminum alloy involve the matrix phase Fe and Ni60 alloy being corroded by aluminum to form M-Al(M = Fe,Cr) intermetallic compounds (IMCs) and M-Al (M = Ni, Fe, Cr) IMCs, respectively. The corroded surface of the H13 steel showed flaky exfoliation happened at the Fe-(Fe,Cr) 2 Al 5 interface, while that of the Ni60 coating presented some large-scale cotton-like morphology due to fracture occurring at the Al-(Ni,Fe,Cr)Al 3 interface. The addition of the Ni-coated TiC particles effectively reduced further dissolution of Fe, Cr and Ni of the received coating into molten aluminum alloy, and changed interface morphology of Al-(Ni,Fe,Cr)Al 3 interface from cotton like to little serrate like, and significantly enhance the corrosive resistance to molten aluminum alloy. The thermal fatigue failure mode of the H13 steel is mainly surface oxidation and lamellar spalling of the oxide layer, and the thermal fatigue cracks of the Ni60 coating initiated in the oxide layer of M-Al (M = Ni, Fe, Cr) IMCs and propagated longitudinally under the action of thermal stress, while cracks of the Ni-coated TiC-reinforced Ni60 coating originated at the junction of non-eroded titanium carbide and eroded Ni60 alloy at the erosion front and propagated in the TiC particles and coating matrix phases. • Process combination of induction cladding and electroless plating • Induction-clad Ni60 coatings with Ni-coated TiC reinforcement particles using electroless plating • Significant improvement of preparation quality of TiC-reinforced Ni60 coating using electroless plating • Corrosion and thermal fatigue behaviors of H13, Ni60 coating and Ni-coated TiC-Ni60 coating in molten aluminium alloy

Recrystallization-mediated crack initiation in tungsten under simultaneous high-flux hydrogen plasma loads and high-cycle transient heating

Tungsten and tungsten-based alloys are the leading material choices for the divertor plasma facing components (PFCs) in future fusion reactors. Recrystallization may occur when they undergo high heat loads, drastically modifying the predesigned grain structures and the associated desired mechanical properties. However, the influence of recrystallization on the thermal fatigue behavior of tungsten PFCs still remains unclear. In this study, ITER-grade tungsten was simultaneously exposed to a high-flux hydrogen plasma (∼5 × 1024 m−2 s−1) and high-cycle (104–105) transient heat loads in the linear plasma device Magnum-PSI. By correlating the surface temperature distribution, obtained by analyzing temperature-, wavelength-, and surface-dependent emissivity, and the surface modifications of the plasma exposed specimens, the crack initiation heat flux factor threshold was found to be ∼2 MW m−2 s0.5 (equivalently, ∼0.07 MJ m−2 for a 1 ms pulse). Based on electron backscatter diffraction analyses of cross-sections near the crack initiation sites, faster recrystallization kinetics near the surface compared to literature was observed and the surface cracks preferentially initiated at high angle grains boundaries (HAGBs). Upon recrystallization, the yield strength decreases which entails increasing cyclic plastic strains. The HAGBs fraction is increased, which constrains the transfer of plastic strains at grain boundaries. The recrystallization decreases the dislocation density, which promotes heterogeneous deformation. All these mechanisms explain the reduced crack initiation threshold of recrystallized tungsten compared to its as-received counterpart. The results provide new insights into the structural failure mechanisms in tungsten PFCs exposed to extreme fusion plasmas.

Numerical analysis and thermal fatigue life prediction of solder layer in a SiC-IGBT power module

Limited by the mechanical properties of materials, silicon (Si) carbide insulated gate bipolar transistor (IGBT) can no longer meet the requirements of high power and high frequency electronic devices. Silicon carbide (SiC) IGBT, represented by SiC MOSFET, combines the excellent performance of SiC materials and IGBT devices, and becomes an ideal device for high-frequency and high-temperature electronic devices. Even so, the thermal fatigue failure of SiC IGBT, which directly determines its application and promotion, is a problem worthy of attention. In this study, the thermal fatigue behavior of SiC-IGBT under cyclic temperature cycles was investigated by finite element method. The finite element thermomechanical model was established, and stress-strain distribution and creep characteristics of the SnAgCu solder layer were obtained. The thermal fatigue life of the solder was predicted by the creep, shear strain and energy model respectively, and the failure position and factor of failure were discussed.

The mechanism of thermal corrosion fatigue (TCF) on nickel-based single crystal superalloy and the corresponding structure shape effect

The thermal fatigue behavior under hot corrosion is studied at 25 ℃ - 900 ℃. The whole process of thermal corrosion fatigue (TCF), including crack initiation and propagation, is analyzed in detail from the perspective of driving force and the intensity factor for cracking. By controlling the Cr content in nickel-based single crystal superalloy, different hot corrosion degrees and reaction products are obtained, and its influence on the thermal fatigue mechanism of the alloy is analyzed comprehensively. It can be concluded from the research that hot corrosion has a great influence on thermal fatigue. Firstly, severe hot corrosion which induces spallation can lead to crack initiation dominantly. Secondly, the thermal mismatch between the hot corrosion products and the matrix provides a high driving force for thermal fatigue. Subsequently, the driving force can influence the thermal corrosion fatigue (TCF) process by stress concentration generated by crack tip and products shape. Finally, the loose and fragile nature of the hot corrosion products can provide a channel for crack propagation. These characteristics of thermal corrosion fatigue (TCF) behaviors are obvious in low Cr content Nickel-based single crystal superalloy.

Development of Highly-Sensitive and Reliable Fiber Bragg Grating Temperature Sensors With Gradient Metallic Coatings for Cryogenic Temperature Applications

Temperature monitoring is an essential task in cryogenic engineering to ensure the safety of equipment, where highly sensitive and reliable sensors are required to provide real-time and accurate information about temperature. Titanium (Ti)-copper (Cu)-coated fiber Bragg grating (FBG) temperature sensors with a gradient of material properties to minimize thermal stresses are hence fabricated by a combination of Ti/Cu magnetron sputtering and Cu electroplating. The thermal characteristics and thermal fatigue behavior of the sensors are investigated. The sensors exhibit significantly higher sensitivity than that of the bare FBGs at cryogenic temperatures down to 79 K, with good repeatability and stability. Their response to the temperature changes can be precisely described by a quadratic-polynomial equation. No obvious variations in the zero-point, the reflection spectrum, and the temperature sensitivity of the sensors exposed to thermal fatigue from 77 K to room temperature are observed before fatigue failure which could be attributed to the formation and growth of subcritical cracks within the fiber rather than that of fatigue cracks within the metallic coatings, as a result of the cyclic thermal stresses induced by the large differences in coefficient of thermal expansion between the silica optical fiber and the metallic coating materials. The results demonstrate that the multilayer metal-coated FBG sensors provide great potential for temperature measurements or temperature compensation in cryogenic engineering by proper selection of metallic coatings with a gradient of material properties.

WITHDRAWN: Comparison of magnesia ramming mass and zirconia for refractory wall of induction furnace

Abstract Furnaces are most commonly used for melting of ferrous metals and its alloy materials. Induction furnaces use electrical power so that they are more advantageous as no fuel is required. It is a very critical problem to find life span of induction melting furnace wall under thermal fatigue conditions. The life cycle of induction furnace refractory wall is a variable as minor variation is always present due to effect of skill of workers and many other factors. The heating cooling cycle of induction furnace wall will result in increasing and decreasing thermal stresses. The thermal fatigue behaviour of induction furnace wall is compared in this paper for magnesia ramming mass and zirconia. We have used two different methods including experimental investigation and numerical analysis.

Numerical analysis of fatigue behaviors for tungsten armor of ITER divertor

Abstract Thermal responses and fatigue behaviors of the tungsten armor of monoblock divertor under steady-state and transient high heat flux (HHF) loads as well as the coupling of the two were simulated and analyzed by the finite element method. It was found that, under the action of thermal cycle loads, the earliest fatigue failure area of tungsten armor is on the surface, and with the increasing of HHF load, the damage area of the armor extends also, while the transient load only causes damage on surface of the armor. The fatigue lifetime of tungsten armor decreases rapidly with the increase of load, whether under steady-state load or transient load. Different transient load under the same steady-state load is researched. When two loads are coupled, the fatigue life is shorter as the load value is high, while the fatigue lifetime is basically unchanged when the transient load is the same under different steady-state loads, that is to say, the steady-state load has little influence on the results, and the transient load during ELMs is the leading factor for the fatigue lifetime.

Improved thermal fatigue resistance in thermal barrier coatings via suspension plasma spray technique

The thermal cycle fatigue behavior of a suspension plasma-sprayed thermal barrier coating (SPS-TBC) with cauliflower-like columnar microstructure was investigated. The damage behavior of SPS-TBC was investigated compared with a conventional atmospheric plasma-sprayed (APS-) TBC. The thermally grown oxide (TGO) grew at the interface between the top- and bond-coats during not only the isothermal oxidation but also the thermal cycle fatigue. In the SPS-TBC, the growth of mixed oxide-type TGO can be suppressed. Additionally, the columnar structure of the SPS-TBC can prevent the propagation of delamination crack from the specimen edge promoted by thermal cycles. These results suggested that the SPS-TBC had superior thermal fatigue resistance because of its columnar structure.

Thermal fatigue behavior of functionally graded W/EUROFER-layer systems using a new test apparatus

Abstract In future fusion reactors tungsten coatings shall protect First Wall components, made of reduced activation ferritic martensitic steel, against the plasma, because of tungsten’s favourable thermo-mechanical properties and low sputtering yield. Functionally graded material layers implemented between the coating and the steel substrate, compensate the difference in the coefficient of thermal expansion. By using the vacuum plasma spraying technique several layer systems were successfully produced and tested, among other aspects, in regard to their thermal fatigue behaviour up to 500 thermal cycles in a vacuum furnace. However, higher numbers of thermal cycles are anticipated for future fusion reactors and, therefore, a less time consuming approach for thermal fatigue testing is required. Hence, a new testing apparatus with induction heating and inert gas cooling was built and first thermal fatigue experiments with up to 5000 cycles were carried out on different functionally graded tungsten/steel layers systems. The subsequent investigations of these samples show that the layer systems are stable for the applied number of thermal cycles and their properties are solely determined during their respective coating processes.

Effect of additional holes on crack propagation and arrest in gas turbine casing

Gas turbines casings are susceptible to cracking at the edge of eccentric pin hole, which is the most likely position for crack initiation and propagation. This paper describes the improvement of transient thermal fatigue crack propagation life of gas turbines casings through the application of additional holes. A series of finite element patterns were developed and tested in ASTM-A395 elastic perfectly-plastic ductile cast iron. The effect of arrangement of additional holes on transient thermal fatigue behavior of gas turbines casings containing hole edge cracks was investigated. ABAQUS finite element package and Zencrack fracture mechanics code were used for modeling. Thermal fatigue test was performed. The result shows that the fractured surfaces of the failed specimen are in good agreement with the stress concentration areas and cracked areas of the casing. The effect of the reduction of transient thermal stress distribution around the eccentric pin hole on the transient thermal fatigue crack propagation life of the gas turbines casings was discussed. The result shows that transient thermal fatigue crack propagation life could be extended by applying additional holes of larger diameter and decreased by increasing the vertical distance, angle, and distance between the eccentric pin hole and the additional holes. The results from the numerical predictions were compared with experimental data.