Thermal Fatigue Crack Initiation Research Articles

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.

Thermal fatigue failure analysis and life assessment of Ni-based single crystal superalloys with film cooling holes

The transient thermal fatigue behavior of Ni-based single crystal superalloys with film cooling holes under different peak temperatures (25 °C → 980 °C and 25 °C → 1050 °C) were investigated by a combination of test and finite element simulation. The initiation position and propagation direction of thermal fatigue cracks in both single hole and multi-hole specimens exhibit the angles of ± 45° with respect to the horizontal direction at the four corners of the holes. Octahedral slip failure mainly occurred at the crack initiation location and crack tip. The cyclic oxidation around the film cooling hole promotes the initiation and propagation of cracks. Based on the crystallographic theory, the strain–stress constitutive equation of the Ni-based single crystal superalloy under transient thermal shock was established. The location and evolution of thermal stress around the hole at different temperatures were obtained by finite element calculation. The kinetic behavior of cyclic oxidation has been quantitatively characterized. A thermal fatigue crack initiation life model considering heating temperature, transient thermal stress, and cyclic oxidation has been established. The simulation results are in good agreement with the tests.

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.

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.

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.

Effect of High Temperature on Thermal Fatigue Crack Initiation Life of Automotive Gray Cast Iron Brake Disc

Effect of High Temperature on Thermal Fatigue Crack Initiation Life of Automotive Gray Cast Iron Brake Disc

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.

Effect of initial hardness on the thermal fatigue behavior of AISI H13 steel by experimental sand numerical investigations

AbstractBased on the Uddeholm thermal fatigue test, the mechanism of thermal fatigue crack initiation and propagation and the influence of initial hardness on the thermal fatigue behavior of AISI H13 steel were investigated. Furthermore, an electromagnetic‐thermo‐mechanical coupled finite element model was established to analyze the temperature evolution and stress accumulation in specimen during thermal cycles. The experimental results demonstrate that, after 3000 thermal cycles, the surface hardness of specimen markedly decreases, and the lath martensite structure seems to completely evolve into a mixture of ferrite and irregularly sphere‐like and bar‐like M23C6 and M6C carbides. According to the numerical results, the effective stress of specimen will increase slightly after every thermal cycle. It presents a distinct stress accumulation phenomenon with increasing number of thermal cycles. Especially at the corner of specimen, it is more significant. The thermal fatigue test results also prove that it is a major site where the initiation and propagation of thermal fatigue primary cracks occur. Both the numerical and experimental results suggest that specimen with initial hardness of 46HRC has the slowest stress accumulation rate, the lowest thermal fatigue damage factor, and the longest thermal fatigue life.

Thermal fatigue crack behavior of SiCp/A356 composites prepared by stirring casting

The thermal fatigue crack initiation and propagation behavior of SiCp/A356 composites which is produced by stirring casting were studied. Specimens with a V-shaped notch were used in the thermal fatigue experiment. Optical microscope (OM) and scanning electron microscope (SEM) were used to observe the crack growth. Crack initiated at the notch tip after about 150 cycles of heating and cooling from room temperature to 250°C. The crack propagation stage was dominated during the whole crack growth. Cracks mainly propagated along the interface of particle and through the matrix. The propagation stage experienced the cycle of slow propagation and fast propagation, and a Step-Like shape was observed during the crack growth process. The micro cracks appeared in the interface of particle and the matrix after repeated thermal cycles, and induced fast propagation by coalescing with the main cracks. Distributions of the particle play an important role in hindering thermal fatigue crack propagation. Hardness of the composites decreased with the increase of the number of cycles, and decreased by 46.1% after thermal 290 cycles.

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.

Kinetics and Mechanisms of Degradation of the Surface Layers of Gas-Turbine Engine Structural Components Under Cyclic Thermal Loading During Initiation and Propagation of Thermal Fatigue Cracks

Studies of surface layer material degradation of the most loaded elements of gas turbine engine structural components revealed the essential changes in the structure and elemental composition of this layer in the thermal fatigue crack initiation zones, as well as along the propagating crack lips. The intensity of the observed changes implies the necessity of their account in the stress-strain state calculations and residual life estimations of high-temperature structural components of gas turbine engines.

Effect of Maximum Temperature on the Thermal Fatigue Behavior of Superalloy GH536

Thermal fatigue tests of superalloy GH536 were carried out at different maximum temperature. Three-dimensional numerical finite element computations were performed to simulate thermal fatigue test process. The crack initiation, propagation and thermal fatigue failure mechanism of GH536 plate at different maximum temperatures were obtained by experiments and numerical methods. Result shows that the crack initiation life is shortened and the crack growth rate is accelerated with the increase of the maximum temperature of thermal fatigue test. The numbers of appearing 1 mm length cracks are 180, 74 and 37, respectively, when the maximum temperature is 800°C, 850°C and 900°C respectively. So the thermal fatigue performance decreases with the increase of the maximum temperature. But in the thermal fatigue tests of different maximum temperature, the thermal fatigue crack initiation is all caused by a single crack initiation source, and the thermal fatigue cracks initiate transgranularly, develop and propagate intergranularly.

Analysis of the Material Damage Influence on the Stress-Strain State of Gas-Turbine Engine Blades

Thermal and stress-strain states of the wedge-shaped specimen, which simulate GTE blade edge material state, have been analyzed under thermal cyclic loading in a gas flow. A significant influence of the mechanisms and kinetics of degradation in the surface layer material properties on the stress state of various zones of the wedge-shaped specimens and the character of thermal fatigue crack initiation and growth depending on the damage level is shown. The results of investigation of the influence of dimensions, localization and kinetics of thermal fatigue cracks on the change of the structure (specimen) stress-strain state as a whole are presented.

Theoretical and numerical research on thermal fatigue crack initiation direction in pipe of residual heat removal system

Theoretical and numerical research on thermal fatigue crack initiation direction in pipe of residual heat removal system

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.

Crack Propagation and Simulation of Thermal Fatigue

In this paper, the thermal fatigue damage phenomenon in the comprehensive temperature environment is studied by means of thermal fatigue damage mechanics and FEM technology, the thermal-stress analysis modal under the comprehensive thermodynamic boundary conditions is established, the regularities of distribution of temperature fields, thermal stress fields effected by the comprehensive coupled variables are investigated. According to the modify of material characteristics under the high-temperature alternating thermal impact conditions and the integrated influences of environment, mechanical parameter and material microstructure to the fatigue fracture, numerical modal of thermal fatigue crack initiation and propagation are developed, so the characteristics of thermal fatigue crack propagation are studied, which are verified by the experiments, it is very significant to study thermal damage question of working equipments in the similar conditions.