Thermal Fatigue Process Research Articles

Enhancing strength, ductility, and thermal fatigue resistance in Stellite 21 coatings via Mn alloying and Transformation-Induced Plasticity

This study investigates the effect of Mn on the microstructure and mechanical properties of Stellite 21 cobalt-based coatings prepared by laser cladding on 24CrNiMo steel substrates, focusing on utilizing the Transformation-Induced Plasticity (TRIP) mechanism to enhance toughness and thermal fatigue performance. The results indicate that the microstructure of the Stellite 21 alloy coating is primarily composed of γ-Co (FCC) with a minor presence of ε-Co (HCP), M23C6, and M7C3 carbides, which predominantly precipitate at or near the grain boundaries. Upon the addition of Mn, it dissolves into the γ-Co matrix, causing lattice distortion and increasing dislocation density, thereby contributing to solid solution strengthening. Compared to the Mn-free Stellite 21 alloy coating, the coating with 5% Mn exhibits an approximately 21% increase in tensile strength (∼1135 MPa) and a 74% increase in elongation (∼14.5%). This improvement is mainly attributed to the solid solution strengthening caused by lattice distortion due to Mn addition and the synergistic enhancement from the TRIP mechanism facilitated by the lower stacking fault energy. Moreover, the thermal fatigue crack propagation rate in the coating with 5% Mn is reduced by approximately 42.5% compared to the Mn-free Stellite 21 alloy coating. The enhancement in thermal fatigue performance is primarily due to the Mn addition, which stabilizes the ε-Co phase during thermal fatigue processes, enhancing plastic deformation capacity. The phase transformation process alleviates stress concentration, effectively reducing crack propagation rates and ultimately improving the material's thermal fatigue performance.

Thermal Fatigue Failure of Micro-Solder Joints in Electronic Packaging Devices: A Review

In electronic packaging products in the service process, the solder joints experience thermal fatigue due to temperature cycles, which have a significant influence on the performance of electronic products and the reliability of solder joints. In this paper, the thermal fatigue failure mechanism of solder joints in microelectronic packages, the microstructure changes of the thermal fatigue process, the influence factors on the joint fatigue life, and the simulation analysis and forecasting of thermal fatigue life are reviewed. The results show that the solder joints are heterogeneously coarsened, and this leads to fatigue cracks occurring under the elevated high-temperature phase of alternating temperature cycles. However, the thickness of the solder and the hold time in the high-temperature phase do not significantly influence the thermal fatigue. The coarsened region and the IMC layer thicken with the number of cycles, and the cracks initiate and propagate along the interface between the intermetallic compound (IMC) layer and coarsened region, eventually leading to solder joint failure. For lead-containing and lead-free solders, the lead-containing solder shows a faster fatigue crack growth rate and propagates by transgranular mode. Temperature and frequency affect the thermal fatigue life of solder joints to different degrees, and the fatigue lifetime of solder joints can be predicted through a variety of methods and simulated crack trajectories, but also through the use of a unified constitutive model and finite element analysis for prediction.

Investigation into the failure of a superheater tube in a power generation plant utilizing waste material combustion in a furnace

This study presents an investigation into the failure of a superheater tube. To pinpoint the primary cause of failure, a range of destructive and non-destructive analyses were conducted at various points on both the failed and non-failed sides of the tube. Visual inspection unveiled longitudinal fissures indicative of the initiation of a fish-mouth opening, along with minor bulging, a slight diameter increase, and a marginal thickness reduction at the failure zone. Through chemical composition analysis, mechanical testing, and hardness measurements, it was determined that the material satisfies the specification for low-alloyed steel as per P265GH standard. The microscopic examination revealed the non-fireside (not failed) of the tube consisted of ferrite and pearlite structure, whilst the fireside (failed) showed spheroidization of the pearlite colonies without any evidence of recrystallized grain structure. A more in-depth examination using scanning electron microscopy on the failed section indicated that the tube rupture on the fireside was triggered by an interactive mechanism involving sulfidation corrosion and thermal fatigue. The propagation of cracks occurred through an environmentally assisted thermal-fatigue process. Suggestions for corrective actions have also been proposed to prevent this type of failure.

Failure mechanism of parallel gap resistance welding joint between Ag foil and GaAs solar cell by temperature cycling

Reliability of joints in solar arrays significantly influences the service life of satellites. Interface between solar cell and interconnector experiences serious temperature cycling during space service which would further lead to failure. To further improve the interface joining thermal reliability, elucidation of the interface formation and corresponding microstructure evolution during thermal fatigue is necessary. In this study, parallel gap resistance welded (PGRW) multi-layered joint between GaAs solar cell and Ag foil are subjected to different temperature cycling tests (−160–120 °C, −165–160 °C) with various cycles. Obtained results confirm the joining mechanism of the joint as solid-solution interdiffusion between Ag foil and Au surface of solar cell electrode. Also, conducted temperature cycling essentially lead to thermal fatigue process at Ag/Au interface, therefore more serious interface strength degradation is generated by larger temperature cycling range. Joint failure is initiated by thermal fatigue induced dislocation and residual strain concentrations around dissimilar interface. And the large mismatch in coefficients of thermal expansion (CTE) of the multilayer structure amplifies the thermal fatigue effect.

Thermal fatigue crack growth behavior of Ni60 coating and bonding area on 20CrNiMo alloy strengthened by laser shock processing

After the laser cladding repair of the brake disc surface in high-speed trains, thermal fatigue cracks in the cladding layer and bonding area are easily observed during the service process. With the aim of solving this problem and decreasing hidden risks, effects of laser shock processing (LSP) on the thermal fatigue life and crack growth behavior of the coating and bonding area of the brake disc were investigated. The results indicate that LSP can refine the columnar grain structures of the cladding layer and bonding area while simultaneously converting residual tensile stress into compressive stress; as a result, the thermal fatigue performance of the brake disc repaired by laser cladding is enhanced. After strengthening by LSP, on the one hand, grain refinement made the structure more uniform and generated more grain boundaries; on the other hand, a pre-set compressive stress field in the cladding layer and bonding area existed. Both aspects were beneficial to dissipate the alternating stress generated by the thermal fatigue process, dissipating the driving force of crack extension and promoting the transformation of thermal fatigue cracks from lateral growth along the interface between the cladding layer and bonding area to the growth into the substrate.

High-performance mullite fibrous ceramic filter enhanced by composite sintering aids for dust-laden gas filtration

Fibrous ceramic filter is one of the promising candidates for high-temperature gas cleaning but is constrained seriously by its mechanical strength. In this work, we successfully prepared a mullite fibrous ceramic filter (MFCF) with high bending strength reinforced by a composite sintering aid of kaolin and feldspar. The bending strength of the MFCF can reach up to 13.1 MPa that was much higher than those reported in the literature. The mullite phase was formed on the neck during the sintering process and greatly enhanced the bending strength as can be characterized by X-ray diffraction (XRD) patterns and three-point bending test. These ceramic filters at the optimized fabrication conditions have a porosity of 61.8%, an average pore size of 14.8 μm, and nitrogen permeance of above 673 m3·m−2·h−1·kPa−1, respectively. Moreover, the mullite-fiber-based filters exhibited satisfactory thermal shock resistance and corrosion resistance after experiencing thermal fatigue and acid corrosion process. In addition, these prepared ceramic filters still showed a removal efficiency of above 99.9% for PM2.5. Therefore, the MFCF reported in this work exhibited great potential for industrial hot gas filtration.

Effect of thermo-mechanical ageing on materials and interface properties in flexible microelectronic devices

The effect of thermal ageing, fatigue and thermo-mechanical ageing on flexible microelectronic devices is studied and reported from a materials and functional durability perspective. The degradation mechanisms of encapsulant and substrate were both studied. Property changes in encapsulant and substrate materials are analyzed and their relationships in the failure mechanisms of the flexible devices determined. Stiffening of the resin under thermal ageing conditions is associated with delamination in test vehicles, which leads to a loss of functional electrical properties. Degradation was due to the prominence of crosslinking reactions occurring during thermal oxidation at 120 °C. A moderate stiffening of the resin occurs after fatigue stress testing. Whereas this latter stiffening is similarly associated with crosslinking reactions, here, stiffening could not be induced by thermal degradation of the resin, because the stress frequency employed was low. Instead thermo-mechanical coupling occurred in two stages. Under mild conditions, the degradation mechanisms correspond to the combined effect of thermal ageing and fatigue processes. Under harsher thermo-mechanical conditions, the chain-scission mechanisms become more efficient and induce a softening of the resin.

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.

Effect of moisture and temperature on the thermal and mechanical properties of a ductile epoxy adhesive for use in steel structures reinforced with CFRP

CFRP has proven to be a material capable of being used in many engineering applications, highlighting its good properties for reinforcement of steel structures. In this study, a new CFRP-steel adhesive joint is evaluated by using a structural and ductile epoxy adhesive to join the CFRP reinforcements to the steel structure. On the one hand, the epoxy adhesive has been thermally characterized by means of its kinetics of curing (Kissinger and Model Free Kinetics methods), finding behavior similar to other epoxy adhesives. On the other hand, different surface treatments are studied in order to achieve the best mechanical properties of the joint. In addition, the suitability of this kind of joints is assessed under durability conditions (60 °C and 99% relative humidity) and under thermal fatigue. Shear tests are realized on specimens subjected to different exposure times, studying the mechanisms that affect the degradation of the adhesive joint in each environment. Breaking surfaces were analyzed by Scanning Electron Microscopy (SEM) and by Energy-dispersive X-ray Spectroscopy. A simplified Weibull model is used to evaluate the reliability of the joints during both durability and thermal fatigue processes. The thermal and mechanical properties of the adhesive are determined, showing better behavior against thermal fatigue because moisture in the durability process accelerates degradation of the adhesive joint.

Thermal Fatigue Characteristics of Type 309 Austenitic Stainless Steel for Automotive Manifolds

The thermal fatigue behavior of type 309 austenitic stainless steel was investigated by cyclic tests ranged from 100 °C to the maximum temperatures 800 and 900 °C. The microstructures of the specimens were characterized by optical microscope, scanning electron microscope and X-ray diffraction. With changing the maximum temperature from 800 to 900 °C, the stainless steel exhibits much lower strength, higher elongation and a decrease of fatigue life about 56.6%. After the thermal fatigue failure, the specimens show micro-void coalescence fractures caused by the creep during the holding period at the maximum temperatures, and the quasi-cleavage feature also appears in the case of the maximum temperature 800 °C. During the thermal fatigue processes, the cavities usually form at the grain and twin boundaries, facilitating the initiation and growth of cracks. Furthermore, the high-temperature oxidation produces oxides on the specimen surfaces and in the cracks, deteriorating thermal fatigue properties. With an increase in the maximum temperature, the enhanced synergetic effect of strength, grain size, creep and oxidation is responsible for the accelerated fatigue failure of 309 stainless steel during the thermal cycles.

Microstructure evolution and crack propagation feature in thermal fatigue of laser-deposited Stellite 6 coating for brake discs

In order to reveal the mechanism of microstructure evolution and crack propagation in laser-deposited Stellite 6 alloys, a quenching thermal fatigue test was conducted. Various detection methods were applied to observe differences between the coatings as deposited and after thermal fatigue. The results showed that the γ → ε martensitic transformation occurred in the as-deposited γ-Co matrix during the thermal fatigue process, driven by a fast cooling and thermal stress. The generated ε-Co phase presented variant selection, obeying Schmidt's law. In the ε-Co phase, the slip activity derived from different 111γ112¯γ slipping systems that produced stacking faults and planar defects during the phase transformation. In addition, the stacking faults on {1 1 1}γ planes promoted the precipitation of directional M7C3 fine particle carbides. The net-like eutectic structures and γ/ε interfaces acted as paths for thermal crack propagation.

Crack initiation and propagation mechanisms during thermal fatigue in directionally solidified superalloy DZ125

Dramatic temperature changes will lead to uneven expansion and contraction, and then create transient stress cycles that inevitably result in thermal fatigue damage. In this study, the thermal fatigue crack initiation and propagation behaviors of a typical directionally solidified superalloy DZ125 under 900 °C and 1000 °C were investigated systematically using a homemade and calibrated thermal fatigue facility. The maximum thermal stress was evaluated by the finite element method, and the evolutions of the microstructures and the changes of mechanical properties during thermal fatigue process were characterized by scanning electron microscopy, transmission electron microscopy, and nanoindentation. Results show that the crack was initiated at the phase interfaces and grain boundaries, and the crack propagated along the weakened channel formed by the deformed γ' phase and the oxide. The stress field at the crack tip and the degree of oxidation reaction together determine the rate of crack growth. This work may provide new insights into thermal fatigue mechanisms and advanced superalloy design.

Analysis of the Failure of the Engine Piston of the AlSi Alloy

The aim of the article is piston damage evaluation of a highly exposed combustion engine. The analysed piston was made of an AlSi-based alloy. Atypical damage, which occurred relatively early in the lifetime of the component, was evaluated by metallographic and fractographic analyses. The analysis took into account influences of mechanical and thermal fatigue processes in relation to the microstructure of the material. The metallographic observations of the microstructure revealed the occurrence of cracks extending over the secondary phases and precipitates. Cracks were initiated on the coarser Si phase particles. The crack initiation site is located at the root of the bridge between the sealing piston rings. The damage of the piston was metallographically documented in wide range.

Effect of Skew Angle of Holes on the Thermal Fatigue Behavior of a Ni-based Single Crystal Superalloy

In the present work, holes of various skew angles were electrochemically machined in the middle of the plate specimens in a Ni-based single crystal superalloy and crack initiation and propagation around holes during thermal fatigue cycles (20–1100 °C) were investigated. It was demonstrated that the skew angles had a significant effect on the initiation and propagation of thermal fatigue cracks. During thermal fatigue process, stress concentration occurred at the edge of the holes. As for skew angles, the maximum stress concentration appeared at the acute side of holes. The maximum stress concentration resulted in plastic deformation at the acute side of the 30° hole, driving the thermal fatigue cracks to initiate after 220 cycles and propagate along \([0\bar{1}1]\) direction. However, the stresses concentrated at the edge of 90° or 60° holes were not large enough to initiate cracks even after 580 thermal cycles. This work will help to understand the local deformation behavior in the vicinity of cooling holes with various skew angles and have serious design implications for turbine blades.

Thermal fatigue mechanism of recrystallized tungsten under cyclic heat loads via electron beam facility

Thermal fatigue resistance of plasma facing materials (PFMs) is an inevitable concern for component lifetime and plasma operations, since the temperature fluctuations will always exist in future nuclear fusion facilities and reactors. Accordingly, experiments were performed in the electron beam facility to investigate the thermal fatigue behavior under operational loading conditions. The tungsten is investigated in its stress relieved and fully recrystallized state for a better understanding of the thermal fatigue process when exposed to cyclic heat loads. The heat loads range from 24 to 48MW/m2 and the number of cycles increases from 100 to 1000 times. The results indicate that the thermal fatigue damage (surface roughening) due to plastic deformation strongly depends on the loading conditions and the cycle index. As the power density and the number of cycles increase, the density of the intragranular shear bands in each grain becomes higher and the swelling of grain boundaries becomes more pronounced. The shear bands are generally parallel to different directions for varying grains, showing strong grain orientation dependence. Additionally, extruded flake structures on shear bands were observed in these damaged areas. It found that the shear bands are generally parallel to the traces of {112} slip planes with the surface. The results suggest that slip plastic deformation represent the predominant mechanism for thermal fatigue and a set of schematic diagram is presented to explain the formation of thermal fatigue damage morphology (extrusion and intrusion structures).

Testing of Power Plant Steel Deterioration by Adaptive Nonlinear Harmonics Method (ANLH)

Nowadays, there is increasing importance of the remaining life time estimation of engineering structures. In this work the thermal fatigue process induced deterioration of the three different power plant steels was investigated. The tested steels are widely used as steam pipeline base material of power plants. The applied thermal fatigue test can model the material degradation due to long term service in high temperature environment. In this paper a new high sensitivity magnetic measuring technique is presented called Adaptive Nonlinear Harmonic (ANLH) method. The sensitivity of this measurement is optimized for controlling the thermal fatigue deterioration. The presented novel measurement was developed for non-destructive testing of pipelines and pressure vessels of power plants.

Magnetic Testing of Power Plant Steel Deterioration

Nowadays, there is increasing importance of the remaining life time estimation of engineering structures. In this work the thermal shock fatigue process induced deterioration of the three different power plant steels was investigated. The tested steels are widely used as steam pipeline base material of power plants. The applied thermal shock fatigue test can model the material degradation due to long term service in high temperature environment. A special AC magnetometer was designed and used for the magnetic measurements at the Department of Materials Science and Engineering of BUTE. In this paper a new high sensitivity magnetic measurement is presented for controlling the thermal shock fatigue deterioration. This measurement technique was developed for non-destructive testing of pipelines and pressure vessels of steam power plants.

Thermal fatigue crack growth behaviours of laser deposited Ti60A near α titanium alloy

Thermal fatigue damage of high temperature titanium alloys and thermal fatigue crack growth (TFCG) behaviours are of great concern for severe temperature fluctuating environments. Cyclic thermal fatigue tests of heating to 700°C for 55 s followed by water cooling for 3 s at 20°C per cycle were performed with laser deposited Ti60A (Ti–5·54Al–3·38Sn–3·34Zr–0·37Mo–0·46Si) alloy. Thermal fatigue crack growth paths including crack length and crack growth directions were examined, as were their correlations with microstructure changes during the thermal fatigue process. Results show that local coarsened lamellar α developed by the interaction between cyclic thermal stress and oxygen atom interstitial solution effect occurs in the alloy after 800 cycles. Thermal fatigue cracks initiate after 800 cycles. Subsequently, total crack length increases with the volume fraction of local coarsened lamellar α from 800 to 2000 cycles. The enhanced oxygen penetration process plays a key role in the TFCG process.

Thermal Fatigue Crack Initiation of Laser Deposited High-temperature Titanium Alloy Ti60A in 20–700 °C

AbstractThermal fatigue damage of high-temperature titanium alloys is of great concern for severe temperature-fluctuating environment, and the thermal fatigue crack initiation stage plays a crucial role in thermal fatigue life. In present study, thermal fatigue tests keeping 55 seconds at 700 °C followed by water cooling 15 seconds at 20 °C were performed for the laser deposited high-temperature titanium alloy Ti60A (Ti5.54Al3.38Sn3.34Zr0.37Mo0.46Si). Thermal fatigue cracks initiate after 800 thermal fatigue cycles with a length of 20 µm. Subsequently numerous cracks grow to 500 µm and cause severe degradation after 1000 cycles. To investigate the crack initiation behavior, microstructural changes during thermal fatigue process were examined by OM, SEM, EPMA and TEM. Thermal fatigue cracks initiate preferably at grain boundaries, α/β interfaces, microvoids, and abnormal coarsened α produced by oxygen interstitial solution. Mechanisms of thermal fatigue crack initiation are related to compatibility of local deformation and microstructural changes during thermal fatigue process.

Thermal fatigue behaviors of Sn–4Ag/Cu solder joints at low strain amplitude

Thermal fatigue behaviors of the Sn–4Ag/Cu solder joints were investigated in this study. The solder joints were clamped by special designed clamps and cycled at low temperature amplitudes, their deformation morphologies were observed by Scanning Electron Microscope (SEM) and evolution in microstructures of the solder were characterized using Electron Back-scattered Diffraction (EBSD). The results reveal that the thermal fatigue process consists of a strain hardening stage and a consequent accelerating fracture stage. During the initial cycles, strain hardening of the solder keeps developing, until it becomes balance with the dynamic recovery. Due to the strain concentration, damage of the solder around the joint interface is serious and cannot release through recovery, inducing microcracks at the corner of the solder joint. After that, the nominal strength of the solder joint decreases gradually, and the damage rate accelerates with increasing cycles. The fracture surface also consists of two regions, one is covered by trace of friction and the other is similar to the shear fracture surface. Plastic deformation, grain rotation and grain coalesce occur in the solder during the thermal fatigue process, while grain subdivision or recrystallization was not observed, because the dynamic recovery keeps the strain energy of the solder at a low level.