Thermal Fatigue Crack Propagation Research Articles

Thermal Stability and Thermal Fatigue Resistance Improvement of New High Toughness 5% Cr Hot Working Die Steel

This work developed a new high toughness 5% Cr martensitic hot working die steel (GYDCK-20), which exhibits better thermal stability and thermal fatigue resistance than AISI H13 steel. The concrete study involves: conducting on the evolution of microstructures and mechanical properties of two steels during the 60-hour holding process at 600°C, as well as the thermal fatigue behavior under the cyclic heating-water quenching conditions. The experimental results showed that in the case of ensuring the same initial hardness of two steels (43-43.5 HRC), GYDCK-20 emerged better thermal stability and superior toughness after 60-hour holding process at 600°C. After thermal cycling was increased from 1000 to 2000 times, the average crack length growth rate of GYDCK-20 was 31.8% lower than that of H13 and the maximum crack width growth rate was 35.1% lower than that of H13. It was found that thermal fatigue cracking was dominated by transgranular propagation at lower cycle numbers, while more inclined to propagate along the grain boundaries at higher cycle numbers. The higher toughness of GYDCK-20 steel promotes the dispersion of thermal stress, thereby enhancing the thermal fatigue resistance. It is mainly attributed to the lower V content of GYDCK-20 steel, which reduces the density of large-sized MC primary carbides. On the other hand, the lower Si content promotes the dissolution of cementite particles, and the secondary carbides precipitate in a smaller and uniformly distributed form, which hinders the propagation of thermal fatigue cracks, while also delays the coarsening of the fatigue-adverse phase M23C6 carbides.

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.

The effects of Ni and Al elements on microstructure and mechanical properties of low carbon CoCrMo alloy coatings

Low-carbon cobalt-based alloy coatings with high ductility and low thermal fatigue crack propagation rates were prepared using laser cladding (LC) technology. The microstructure of the coatings was characterized using SEM, EBSD, and TEM, while the mechanical properties were tested and analyzed. The CoCrMo alloy primarily consists of γ-Co and a minor amount of ε-Co. The addition of Ni increased the stacking fault energy (SFE), resulting in the retention of γ-Co in the alloy. However, the increase of Al content reduced the SFE, leading to the precipitation of Al3Ni intermetallic compound along with a eutectic region with Al3Ni, Cr23C6, and ε-Co. More ε-Co phase appeared after tensile deformation due to the stress-induced transformation induced plasticity (TRIP) effect. Ni addition increased the content of face-centered cubic (fcc) γ-Co, enhancing the coating's ductility by approximately 85 % compared to CoCrMo. With higher Al content, the ε-Co phase increased, and the dispersion of Al3Ni improved the coatings' strength. The jagged structure of the eutectic region increased the resistance to thermal fatigue crack propagation, causing the crack propagated along the grain boundary. Optimal mechanical properties were achieved with the addition of 13 wt% Ni and 7 wt% Al, which achieved a 53 % increase in ductility and a 40 % reduction in the thermal fatigue crack propagation rate compared to CoCrMo.

Unraveling the plastic deformation, recrystallization, and oxidation behavior of Waspaloy during thermal fatigue crack propagation

Thermal fatigue is one typical failure mode for engine components involving cyclic thermal stresses/strains. However, the microstructure evolution and its microscopic interaction with thermal fatigue cracking in Ni-based superalloys featuring intragranular γ′ and intergranular carbides have yet to be clarified. In this study, cyclic temperature variations ranging from 25 °C to 700 °C were conducted on Waspaloy to unravel the synergistic damage mechanisms including stress distribution, plastic deformation, recrystallization, oxidation, and crack propagation. The thermal fatigue cracks are found to predominantly propagate along grain boundaries with a gradually descending rate from 3.5 μm/cycle to 1.5 μm/cycle. Compared with the macroscopic thermal stress up to ∼800 MPa, the local thermal stress induced by different sizes of M23C6 carbides marginally affects the crack propagation. Intensive slip bands and sparse deformation twins in the deformed matrix are observed, indicating the plastic deformation is mainly achieved by dislocation slipping and supplemented by twinning. Trans-granular cracks parallel to {111} planes form occasionally when the propagation directions of intergranular cracks are almost parallel to the {111} slip bands. Besides, dislocations promote the oxidation damage of the crack surface through pipe diffusion of solutes, and the γ′-precipitate free zones (PFZs) and recrystallized areas are produced accordingly. The quantitation analysis of the PFZ thickness provides a reference for predicting crack initiation time during thermal fatigue.

High-temperature thermal fatigue of Ni3Al-based single crystal alloy affected by wall thickness and peak temperature

Complex thin-walled structures are commonly employed in turbine components to improve cooling efficiency. However, thin-walled blades are prone to thermal fatigue failure due to the high thermal stress induced by frequent and abrupt temperature fluctuations during duty cycles. The thermal fatigue behavior of Ni3Al-based single crystal alloy with thin-walled structure during 25 °C ↔ 1000 °C/1100 °C was investigated by combining thermal fatigue tests and finite element simulation. The thermal fatigue demonstrated a significant thickness debit effect, with thermal fatigue property dropping as peak temperature and wall thickness increased. Wall thickness had a more pronounced effect than peak temperature. Visible slip traces were found on the wall thickness surface, and their density was positively correlated with wall thickness. Further investigation revealed that thermal fatigue is primarily driven by the octahedral slip system ({111}<110>), with significant contributions from (111)[101‾] and (1‾1‾1)[101]. Simulations of thermal stress distribution and J-integral at the crack tip during crack initiation and propagation stages indicated that wall thickness influences thermal fatigue properties by affecting thermal stress concentration at the notch and crack tip. Higher peak temperatures increased thermal stress and reduced yield strength, thus diminishing thermal fatigue performance. A thermal fatigue crack propagation prediction model was constructed incorporating Paris' law and the J-integral. The model revealed an unfavorable correlation between material Cj/ nj and both peak temperature/wall thickness, indicating that both factors adversely affect thermal fatigue resistance.

Thermal fatigue performance enhancement of new high-Cr martensitic die steels based on overall microstructure manipulation by trace TiC–TiB2 nanoparticles

Thermal fatigue failure is one of the main factors affecting the service life of hot work die steel. Achieving excellent thermal fatigue resistance for hot working die steels can benefit the industry economically. In this work, (TiC + TiB2)/Al master alloys were used to add TiC–TiB2 nanoparticles into high-Cr die steels, which achieves microstructure manipulation and obtains excellent thermal fatigue resistance and strength-plastic combination. The results showed that after being manipulated by 0.02 wt% TiC–TiB2 nanoparticles, the surface oxidation zone of the high-Cr die steel after different thermal fatigue cycles is reduced than high-Cr die steel without manipulation. TiC–TiB2 nanoparticles effectively refined the heat-treated microstructure of high-Cr die steel, promoting the Cr element and alloy carbides being more uniformly distributed in the matrix, which prevents the occurrence of oxidative pitting and conducive to the formation of a dense and uniform Cr2O3 oxide layer, and further preventing the initiation of thermal fatigue cracks. Moreover, these finer and more uniformly distributed precipitates in TiC–TiB2 nanoparticles manipulated high-Cr die steels will promote stress dispersion and hinder thermal fatigue crack propagation. This work provides a promising avenue for the design of low-cost, high-performance, and long-life die steels for industrial applications.

Low cycle fatigue behavior and life prediction of a directionally solidified alloy

Low cycle fatigue behavior and life prediction of a directionally solidified alloy

A strategy to improve the thermal fatigue resistance of solder joints based on amorphous Co-P coating to spontaneously build skeleton of CoSn3 laths

Integrated circuit systems are always suffering the temperature cycling environment caused by frequent power on and off. Mismatch in thermal expansion coefficients among chip package components will cause severe cyclic stress to the solder joints. During thermal fatigue, β-Sn grains tended to generate thermal fatigue cracks at the grain boundaries. This work proposed a strategy of using amorphous Co-15 at.% P coating as the interface layer to inhibit the initiation and propagation of thermal fatigue cracks and improve the shear strength of solder joints by numerous endogenous CoSn3 laths. Mechanistically, based on the amorphous structure of the Co-P coating, Co atoms would massively and rapidly diffuse into the molten solder during the liquid-solid diffusion stage of reflow soldering, and the eutectic solidification together with β-Sn spontaneously precipitated numerous laths of CoSn3 intermetallic compounds (IMC), which were evenly distributed and became the skeleton of the solders. The skeleton-like CoSn3 laths with high elastic modulus were the reinforcing phase of Sn-based solder, but also refined the grains of β-Sn. The refinement of β-Sn grains and the strengthening of CoSn3 laths played an important role in inhibiting the initiation and propagation of thermal fatigue cracks. In addition, a discontinuous Co-Sn IMC layer was formed between the amorphous Co-P and the solder. The alternating appearance of CoSn3 and relatively soft β-Sn at the interface avoided the generation of cracks at the interface during temperature cycling.

Influence of hot corrosion on thermal fatigue behavior of Ni-based single crystal superalloy: Invisible and accelerated crack

As an important failure model for single crystal materials in service, with the increasing complexity of working environments, the thermal corrosion fatigue failure needs to be studied urgently. In this study, the thermal corrosion fatigue crack initiation and propagation behaviors of an Ni-based single crystal superalloy in both air and hot corrosion environments at 25–900 °C were studied by using a designed precise thermal fatigue test device. The microstructure characteristics and crack composition were analyzed by SEM, TEM and EDS, and the internal stress and recrystallization during thermal fatigue were characterized by EBSD. Moreover, the detailed and comprehensive crack morphology was characterized with different surface treatments. The results showed that the crack morphology was invisible in the hot corrosion environment, which is worthy of being highlighted. The initiation and propagation of thermal fatigue cracks were also accelerated in the hot corrosion environment, which contributed to the sufficient thermal stress, the accelerated material degradation of the inner/outer layers in the crack region, and the rapid forward diffusion of O2 in the inner crack layer. Finally, the influence mechanism of hot corrosion on the thermal fatigue behavior of the Ni-based single crystal superalloy is proposed.

Application of a ΔJ Approach for Thermal Fatigue Crack Growth Assessment on the Large Scale Yielding PACIFIC Experiment

Austenitic stainless steel large nuclear components, with high thicknesses, may experience cyclic Large Scale Yielding due to mechanical and thermal loadings during their service life. International codes and standards only provide inadequate and very conservative methods for dealing with the thermal fatigue crack growth associated with this situation. Non-codified alternatives, such as ΔJ approaches, then appear to be good candidates for predicting fatigue crack growth beyond Small Scale Yielding.This paper aims to apply a ΔJ approach on the so-called PACIFIC experiment permitting thermal fatigue crack propagation in Large Scale Yielding conditions. Numerical protocol and modelling assumptions are detailed. Then, a particular focus is given, through sensitivity analyses, on the choice of the cyclic elastic-plastic stress-strain curve used in the Finite Element Analyses. Finally, comparisons between numerical results and experimental fatigue crack growth data are provided and discussed.

Effects of deep cryogenic treatment on the microstructure evolution, mechanical and thermal fatigue properties of H13 hot work die steel

The service life of hot work die steel is significantly influenced by its microstructure and thermal fatigue properties. This paper explores the impact of deep cryogenic treatment (DCT) on H13 hot work die steel's microstructural evolution and mechanical as well as thermal fatigue properties. The results demonstrate that a portion of unstable retained austenite transforms into martensite during deep cryogenic treatment and numerous finely dispersed carbides precipitate from the matrix, thereby enhancing hardness. Analysis of the average crack length and distribution of thermal fatigue test samples reveals that the average crack length and crack density of DCT-treated samples are lower than those of non-DCT-treated samples. Thermal fatigue cracks in the specimens primarily originated from trigeminal grain boundaries and the carbides are found at the crack tips. DCT facilitates the precipitation of fine and dispersed carbides, imparting a robust pinning effect on boundary migration and thereby impeding the initiation and propagation of thermal fatigue cracks. Furthermore, deep cryogenic treatment results in a reduction in the number of M23C6 type carbides with large particles and an increase in smaller M6C type carbides during the thermal fatigue test. This indicates a positive influence on the carbide distribution and further contributes to the improved thermal fatigue resistance of the hot work die steel.

Conventional shot peening treatment effects on thermal fatigue crack growth and failure mechanisms of a solid solution alloy

This study presents the effects of conventional shot peening as a surface post-treatment method on the fatigue crack growth behavior and failure mechanism of a solid solution alloy used in the flat seal component under thermal fatigue conditions. The study employs a combination of experimental tests and finite element simulations to evaluate the effect of shot peening on thermal fatigue crack growth behavior. The corrected J-integral and Paris model are used to calculate the stress intensity factor and predict the thermal fatigue crack growth behavior, respectively. Additionally, the ZENCRACK method is employed to predict thermal fatigue life. The results indicate that shot peening induces compressive residual stress, leading to a decreased distribution of thermal stress, particularly along the crack propagation path. The simulated fatigue life curve obtained by ZENCRACK demonstrated a good agreement between the simulated and experimental crack growth results. The incorporation of shot peening caused a significant reduction in the rate of thermal fatigue crack growth, and the simulated stress intensity factor analysis revealed an increase during the heating stage. Consequently, the thermal fatigue crack propagated during the heating-up process. SEM evaluation reveals that the shot peening post-treatment impacts both thermal fatigue crack initiation and propagation. Furthermore, the failure mode of shot-peened specimens involves inter- and trans-granular cracking, while non-shot-peened specimens exhibit trans-granular cracking.

Thermal fatigue crack initiation and propagation behaviors of GH3230 nickel‐based superalloy

AbstractThe drastic severe temperature cycle in an aero‐engine combustion chamber leads to large thermal fatigue stress, which may induce thermal fatigue failure of the combustion chamber. In this paper, thermal fatigue crack initiation and propagation behaviors of GH3230 nickel‐based superalloy sheet specimens with V‐notch were studied under different peak temperatures 800°C, 900°C, and 1,000°C using self‐built thermal fatigue equipment. The temperature, stress, and crack propagation driving force of the V‐notch specimen were discussed in detail. Results show that the thermal fatigue crack initiation life gradually decreases with the increase of the peak temperature. Oxidation caused by high temperature will weaken alloy's strength and accelerate its crack propagation. Higher peak temperature will make the crack propagate faster and the thermal deformation at V‐notch end easier to accumulate. At last, there is a good consistency between fitting curves from the modified Paris formula and the experiment results.

Numerical simulation and mechanism analysis of thermal fatigue crack for low-alloy steel brake disc of high-speed train

ABSTRACT High-speed train brake discs face severe service conditions and subsequently risk of material failure during emergency braking. Thermal fatigue cracking is a major concern leading to catastrophic disc failure and is regarded as a primary service bottleneck in rapid rail transportation. Our proposed work establishes a numerical prediction model to estimate thermal fatigue crack initiation and propagation in low-alloy steel. We used a modified Cockcroft-Latham criterion and material property tests to determine the critical crack initiation value. Through numerical simulations and in-situ experiments, we observed plastic deformation at the median temperature of the thermal fatigue cycle and found that tailored material composition improves brake disc fatigue performance. This research aims to enhance understanding of the cracking mechanism and improve the reliability of brake systems for high-speed trains.

A predictive approach for thermal fatigue crack growth behaviour of shot peened Ni75 alloy

This study presents an approach to predict the effects of shot peening on the thermal fatigue crack propagation behaviour of nickel-based Ni75 alloy. For this purpose, from an engineering perspective, comprising experimental tests data and finite element simulations, were used to estimate the thermal fatigue crack propagation behaviour of the material. Despite many other studies that have been performed to evaluate the fatigue crack growth behavior, only a few were previously conducted on thermal fatigue damage in different types of materials. Furthermore, the interaction of shot peening treatment and thermal fatigue crack propagation behavior is rare. Comparison of the results from the experimental test and FE model showed that the model appropriately predicted the thermal fatigue crack growth behaviour. The fracture mechanism evaluation showed that the compressive residual stress, induced by shot peening treatment, reduced both the crack opening and secondary crack branching. Also, the results show the crack initiation life of the shot peened specimen (SP) is about 2.5 times more than the non shotpeened specimen (NSP). Moreover, the microscopy analysis showed that the failure mechanism of the NSP and SP specimens were transgranular and a combination of intergranular and transgranular cracking, respectively

Thermal Fatigue Crack Propagation Process and Mechanism of Multicomponent Al-7Si-0.3Mg Alloy

The thermal fatigue behavior of multicomponent Al-7Si-0.3Mg alloys in four different treatment states at typical temperature amplitudes 20 °C→350 °C was studied. The morphology of the second phase particles and crack propagation, and distribution characteristics of dislocations in the thermal fatigue specimens of multicomponent Al-7Si-0.3Mg alloys, were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX spectrum), and transmission electron microscopy (TEM). The influencing factors, the process, and the mechanism of thermal fatigue crack propagation were mainly studied. The results show that under the same temperature amplitude, the thermal fatigue properties and dislocation densities of the new aluminum alloy and the new aluminum alloy under T6 heat treatment are significantly higher than that of the multicomponent Al-7Si-0.3Mg alloy in cast and refined and modified treatment. The crack growth of thermal fatigue specimen depends on three factors: the temperature amplitude, oxidation, and residual stress. The process of thermal fatigue crack propagation mainly experiences crack initiation and the formation of microcracks, but only a few microcracks continue to expand rapidly or preferentially expand into main cracks. The mechanism of thermal fatigue crack propagation is mainly under the action of thermal stress, the crack tip undergoes a cycle of repeated alternation of sharpening → passivation → sharpening, and the crack continues to move forward from its tip intermittently in the way of propagation → stopping → propagation until fracture failure.

Study on thermal fatigue behaviors of two kinds of vermicular graphite cast irons

Abstract Due to the good thermal stability and mechanical properties, vermicular graphite cast iron is widely used to make industry components. Many of them are inevitably impacted by alternating temperature load. Therefore, two kinds of vermicular graphite cast irons, RuT400 and RuT450, were employed to study the features of thermal fatigue crack initiation and propagation in different temperature ranges. And the relationship between the length of thermal fatigue crack and number of cycles were also analyzed. It can be found that the thermal fatigue properties between the two materials are obviously different because of different microstructures. At present testing temperatures, RuT450 has higher pearlite content, lower thermal crack growth rate, higher transition temperature. The grain boundary slide temperature of ferrite and transition temperature of pearlite have important influences on the thermal fatigue cracks of two kinds of vermicular graphite cast irons.

Temperature Distribution on Rectangular Composite Plate under Thermal Gradient Loading Environment: Experiment and Simulation

In this paper, the problem is how to calculate the dynamic mechanical and thermal properties. These properties are a function of the temperature at each conditioning load stage. This paper aims to investigate the influence of temperature distribution on a normal deflection through the plate thickness. In the numerical simulation, ANSYS software Ver. 18.2 is used. Both mechanical and thermal properties have been used as inputs in ANSYS software to simulate each point’s temperature distribution on the composite plate. The purpose of this paper is to show that the temperature distribution is crucial in the phases of thermal fatigue (self-heating, thermomechanical degradation, and crack propagation). The composite laminate plate is exposed to out-off plane temperatures in which the temperature gradient is varied between (60 C° and -15 C°). The experiment setup’s potential is the heating and cooling rig environment and the thermocouple connected to an analog interface card. The implication of temperature distribution is in diesel engine design based on durability and reliability. Points (1, 2, 3) have a regular heating and cooling rate (1.574 C/min or -1.574 C/min), while points (4, 5, 6) have an irregular rate of heating and cooling.

Comparative study of protective coatings for heat resistance

Modern gas turbine engines operate under changing temperature loads. Therefore, one of the important characteristics of the protective coatings used on the turbine blades is their high resistance to the occurrence and development of cracks under mechanical and thermal loads. The applied effective systems of internal heat removal of the cooled turbine blades lead to an increase in their heat stress. At present, cracks arising from thermal fatigue are one of the common defects of the protective coatings used on turbine blades. The heat resistance of coatings at high temperatures is determined by three factors: the shape of the part on which the coating is applied, the thickness of the coating and the phase composition of the surface layers or the maximum aluminum content in the coating. Therefore, when choosing a protective coating for these operating conditions, it is important to know the impact of these factors on the thermal stability of the coating. The paper presents a comparative study of various coatings on their resistance to crack formation under cyclic temperature change. The dependence of the heat resistance of the considered coatings on the method of their application and phase-structural state is established. Especially valuable is the established mechanism of formation and propagation of thermal fatigue cracks depending on the phase composition of the initial coating. It is shown that the durability of protective coatings with cyclic temperature change depends on the chemical composition of the coating and the method of its formation. The dependence of the formation of thermal fatigue cracks on the samples with the coatings under study on the number of cycles of temperature change is established.

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.