Cycle Thermal Fatigue Research Articles

The behavior of plasma sprayed thermal barrier coating with laser microtextured bond coat under high temperature testing

In this work, the laser microtexturing is exploratory studied for controlling the interface between the oxidation resistant metallic bond coat and thermally insulating ceramic top coat in Thermal Barrier Coatings.The 80 to 100 μm thick NiCrAlY layer was deposited by Atmospheric Plasma Spraying over the nickel-based super alloy substrate. Then, the infrared fiber nanosecond laser was used for shaping the topography of bond coat prior to the top coat deposition. The surface geometry was adapted by selecting the laser set-up operational conditions, mainly: (i) laser power, (ii) frequency, (iii) scanning velocity and (iv) inter-pass spacing. The two groove-based patterns were finally selected for further work together with one as-sprayed bond coat, as a reference. The 8 wt% yttria stabilized zirconia (8YSZ) was deposited by means of Suspension Plasma Spraying over all three types of bond coats. The samples were then subjected to isothermal oxidation and thermal cyclic fatigue testing in order to study the influence of bond coat topography on the overall behavior of coatings under high temperature conditions. The microstructural studies revealed that the as-sprayed bond coat topography may be progressively modified by multistep laser microtexturing. The uniform bond coat topography is found to be beneficial in promoting formation of homogeneous, columnar-like top coat. However, the modification of bond coat topography affects the behavior of the bond coat/top coat interface during high temperature testing. The study shows that the microtexture depth should be precisely controlled, otherwise the through bond coat thickness oxidation is observed, which has a detrimental effect on the overall durability of the TBC system. The bond coat asperity width plays also an important role. If it is too narrow, then the failure may propagate locally through the bond coat or the thermally grown oxide layer.

Microstructures, thermophysical properties and thermal cyclic behaviors of Nd2O3 and Sc2O3 co-doped LaMgAl11O19 thermal barrier coating deposited by plasma spraying

In this study, La1-xNdxMgAl11-xScxO19 (x = 0.1, 0.2, 0.3; abbreviated as LNMAS-1, 2, 3) coatings which are supposed to possess better properties than LaMgAl11O19 (LMA) were plasma-sprayed and their high-temperature performance were comparatively investigated. Results show that addition of Nd3+ and Sc3+ as dopants to LMA endows corresponding coatings with reduced thermal conductivity and enhanced thermal expansion coefficient, while maintaining advantageous phase stability, although still being subjected to amorphization in plasma flame and following crystallization upon high-temperature service. Furthermore, the doping could cause adherence increasing between topcoat/bondcoat, benefiting from improved melting condition, especially in LNMAS-2 and LNMAS-3 coatings, which is related to the specific powder morphology and lowered melting point. During exposure to 1350°C, mechanical performance and structure integrity of doped free-standing LNMAS coatings can be well preserved even after 400 h aging. In thermal cyclic fatigue test, LNMAS-2 and LNMAS-3 coatings undertake thermal cycling lifetime of ∼181 and 191 cycles at 1100°C, respectively, 40% durable than that of LMA coating. These preliminary results suggest that LNMAS-2, 3 might be promising candidates for advanced thermal barrier coating applications.

Effect of Cr–N precipitations on thermal fatigue behaviour of GX-8 steel nitrided layer

Two types of nitrided layers with different nitride precipitates were prepared by salt bath nitriding on the surface of GX-8 steel. The microstructure of the nitrided layers was investigated by SEM, XRD, grazing-incidence XRD and TEM. A cyclic thermal fatigue test system was used to evaluate the influence of nitrides on the thermal fatigue properties of the two nitrided layers. Under the operation of alternating thermal cycles from ambient temperature to 600 °C on the surface, the nitrided surface with a compound layer composed of ε-Fe2-3N phase and strip-shaped CrN had more cracks and spalling than that of the nitrided layer with nanoscale nitrides. Further analysis revealed that the tessellated stress caused by different thermal expansion coefficients of CrN and α-Fe in the interlayer was responsible for the interlaminar deformation, cracking and spalling of the surface.

Accelerated Solder Interconnect Testing Under Electromigratory and Mechanical Strain Conditions

Abstract Continuous power density increases and interconnect scaling in electronic packages raises risk of electromigration (EM) induced failures in high current interconnects. Concurrently, thermal cycling fatigue also places interconnects at risk of reliability failure during electronics' operating lifetime. These two differing failure mechanisms are historically treated separately, but in operation, the combination of EM effects and thermal cycling can act synchronously in accelerating failure. Presently, there is no model to predict the complexity of reliability estimation arising from these interacting failure modes but is certainly important for high current density applications. In this work, a novel testing system has been employed to facilitate the estimation of the reliability of solder interconnects under the combined influence of EM and mechanical strain. The system subjects solder interconnects to high current density, elevated ambient temperature, and a constant tensile stress while recording the change in electrical resistance and change in length of the solder over time. The solder samples were created using two copper wires connected by a eutectic Pb/Sn solder ball to imitate flip-chip or BGA packaging interconnects, allowing for controlled testing conditions in order to demonstrate the combined effects of a mechanical load and EM on the lifetime of a solder joint. A significant reduction in lifetime was observed for samples that endured the coupled accelerating factors. Comparing the experimental results of different current densities at different stress levels provided a new outlook on the nature of coupled failure acceleration in solders. This novel test methodology can inform model generation for better anticipating the failure rate of solder interconnects which naturally experience multiple stress inputs during their lifetime.

Deterioration of performances and structures of cement pastes under the action of thermal cycling fatigue

Concrete structures in the atmosphere are continuously subjected to thermal cycle (TC) inducedby varying environmental temperature. However, the influencing mechanism of thermal cycling fatigue on the mechanical properties and microstructure of cement-based materials has not been thoroughly documented. To address this issue, the relationship between the macro-properties and microstructure of cement paste under TC was analyzed using micro-properties measurement and quantitative microcrack evaluation. In this work, ordinary Poland cement pastes with three different water-to-cement (w/c) ratios (0.4, 0.5, and 0.6) were exposed to TC in the range of 5–45 °C. The mechanical properties, pore structures, and micromorphology of cement pastes after different cycle times were measured. The result indicated that as the number of cycles increased, TC negatively affected the macro-mechanical characteristics, pore structure, and micromorphology of cement pastes. Cement pastes with greater w/c ratios were more susceptible to TC-induced deterioration. In addition, thermal cycling fatigue caused the propagation of microcracks including crack width, length, and density. Thermal cycling fatigue also coarsened the pore structure of cement pastes, especially the large pores (i.e., diameter > 100 nm). The underlying damage mechanism caused by TCis the coupled actions of fluid flow, thermal deformation, and thermal fatigue. Moreover, a negative linear relationship was established between microcrack density and Vickers hardness of cement pastes.

Thermal aging coupled with cyclic fatigue in cross-linked polymers: Constitutive modeling & FE implementation

A micro-mechanical constitutive model is presented to predict the concurrent effects of thermal aging and cyclic fatigue on the constitutive behavior of cross-linked polymers. The damage associated to each of those aging conditions is induced by mechanisms that have been extensively studied individually. Here, the main goal was to model the damage accumulated when those mechanisms work in parallel. In this respect, we modeled the effect of each aging condition separately through their corresponding aging mechanisms and then coupled them using the concept of network alteration platform. Accordingly, kinetic equations describing damage of each aging-mechanisms are coupled into the network alteration modular concept to allow consideration of mechanical and environmental damages synergies on the constitutive response of the polymer matrix. Following our recent models of thermal-oxidative aging, cyclic fatigue, and damage accumulation a model is developed based on the assumption of the full independence of mechanical and environmental damages. The model is implemented into finite element simulations. For validation, the devised model is bench-marked against a comprehensive set of experimental data. The proposed model shows promising results with reasonable precision.

CMAS corrosion and thermal cycling fatigue resistance of alternative thermal barrier coating materials and architectures: A comparative evaluation

The corrosion of ceramic thermal barrier coatings (TBCs) by molten silicate deposits, usually known as “CMAS” from their main constituents (CaO-MgO-Al2O3-SiO2), is an issue of increasing concern in modern gas turbines as the turbine inlet temperatures are increased to enhance thermodynamic efficiency. Because conventional ZrO2-7wt%Y2O3 (7YSZ) dissolves quite readily in a CMAS melt, many alternative materials have been proposed, but there are not many comparative studies among them. Multi-layer architectures featuring a tougher 7YSZ bottom layer and a more brittle, but more CMAS corrosion-resistant top layer have also been proposed; therefore, a comparison among these architectures is also in order. In this paper we studied comparatively the resistance to CMAS corrosion and to thermal cycling fatigue (an essential pre-requisite for any TBC system) of Gd2Zr2O7, ZrO2–55wt%Y2O3 and Gd/Yb/Y co-doped ZrO2, both in the form of single, dense-vertically cracked (DVC) layers deposited by plasma spraying onto an MCrAlY bond coat, and as top layers with a bottom layer of either porous or DVC 7YSZ. It was found that Gd2Zr2O7 resists CMAS corrosion, without any grain-boundary dissolution, slightly better than does ZrO2–55wt%Y2O3. They both develop a solid Gd- or Y-apatite layer (respectively) at the interface with the CMAS melt, driven by the rather large difference in optical basicity between these compounds and CMAS itself, but the Y-apatite layer is less continuous and, therefore, a bit less protective. Gd/Yb/Y co-doped ZrO2, instead, suffers as much grain-boundary dissolution in contact with molten CMAS as does 7YSZ. A Gd2Zr2O7/porous 7YSZ system would therefore exhibit simultaneously high resistance to CMAS dissolution and to thermal cycling fatigue, although there is a risk that the CMAS melt might infiltrate the segmentation macro-cracks and the microcracks of the Gd2Zr2O7 layer and undermine the porous 7YSZ bottom layer.

Fractal analysis of thermal fatigue crack growth behavior in bionic units of vermicular cast iron

PurposeThe purpose of this paper is to clarify the growth behavior of fatigue cracks on bionic coupling surface of vermicular cast iron.Design/methodology/approachThe thermal fatigue cyclic experiments were carried out on the bionic specimens processed by laser bionic treatment, in which the thermal fatigue was generated by heating at 600°C ± 5°C and cooling at 25°C ± 5°C. The thermal fatigue cracks of bionic units were analyzed using fractal theory. The relation between fractal dimensions of thermal fatigue cracks and thermal fatigue cycles was discussed.FindingsThe results show that the fractal dimensions can better characterize the fatigue crack growth behavior on bionic coupling surface of vermicular cast iron.Originality/valueThe fractal theory is first used to discuss the growth behavior of fatigue cracks on bionic coupling surface of vermicular cast iron, which is processed by laser bionic treatment.

Experimental and Numerical Investigation of High-Temperature Multi-Axial Fatigue

Abstract Gas turbines and aircraft engines are dominated by cyclic operating modes with fatigue-related loads. This may result in the acceleration of damage development on the components. Critical components of turbine blades and disks are exposed to cyclic thermal and mechanical multi-axial fatigue. In this work, planar-biaxial low-cycle-fatigue (LCF) tests are conducted using cruciform specimens at different test temperatures. The influence on the deformation and lifetime behavior of the nickel-base disk alloy Inconel 718 is investigated at selected cyclic proportional loading cases, namely, shear and equi-biaxial. The calculation of the stress and strain distribution of the cruciform specimens from the experimental data is difficult to obtain due to complex geometry and temperature gradients. Therefore, there is a need for finite element (FE) Simulations. A viscoplastic material model is considered to simulate the material behavior subjected to uniaxial and the selected planar-biaxial loading conditions. At first, uniaxial simulation results are compared with the uniaxial experiment results for both batches of IN718. Then, the same material parameters are used for simulating the biaxial loading cases. The prediction of FE simulation results is in good agreement with the experimental LCF test for both shear and equi-biaxial loadings. The equivalent stress amplitude results of the biaxial simulation are compared with the uniaxial results. Furthermore, the lifetime is calculated based on the stabilized cycle from the simulation and by using Crossland and Sines multi-axial stress-based approaches. The Crossland model predicts fatigue life significantly better than the Sines model. Finally, the simulated lifetime results are compared with the experimental lifetime.

Failure mode and effects analysis of forging die design: An integrated approach

The factors such as cyclic mechanical loads, thermal fatigue and friction condition has serious consequences on the service life of the dies as well as effects the production cost. Reduction in service life or early die failure may also occur due to improper die-design, forming defects and process parameters. Out of these, die design plays major role in failure of dies. So, there is a need to analyse reasonable design criteria and their effects. While designing of forging dies, there are several important design criteria which must be considered like material selection, selection of parting line, allowances and tolerances, draft, fillet and corner radii, design of flash and gutter, preform design, and finisher design. To improve the die life, it is required to investigate and prioritize the effect of design criteria on failure of dies, which can be done by assessing the total impact of each criterion. In this paper, a new method is proposed to prioritize the design criteria based on severity, occurrence, detection, and impact of failure. The proposed method involves using a new parameter Impact factor(I) in conjugation with traditional FMEA analysis. By considering the impact factor in the traditional FMEA it is observed that there is an improvement in ranking result. It is also observed that the ranking obtained using proposed method is well in line with the previous research.

Proposal of a Thermal Fatigue Damage Evaluation Method for Ceramic Thermal Barrier Coating Systems.

In recent years, the application of thermal barrier coatings to the components used in gas turbines for thermal power generation has become indispensable as higher inlet temperatures for requirement to further improve the efficiency of thermal power generation. Thermal barrier coatings, generally referred to as TBCs, consist of a top coat, which is a thermal barrier layer, and a bond coat, which improves the adhesion strength between the TC and the base material. As the development of new thermal barrier materials is progressed, it is also demanded to clarify the stress and damage behavior of TBCs under the complex thermal fatigue loading conditions in actual gas turbine operation. In this study, comprehensive finite element analysis is performed on a TBC system under cyclic thermal fatigue loading conditions with temperature and stress variations to clarify the deformation behavior and crack initiation life of the TBC, and to develop a fatigue life evaluation method for TBCs.

Effect of microstructure on thermal cycle fatigue resistance in a SPS-TBC

The turbine blades of gas turbine engines used in thermal power plants are coated with a thermal barrier coating (TBC) made of ceramics to provide heat resistance. In recent years, gas turbines for power generation have been utilized as a regulating power source for engines, which are subject to frequent start-up and shutdown and output fluctuations. In this context, the suspension plasma spraying (SPS) method, which has been developed recently, has been studied intensively because it has a porous columnar structure and superior thermal cycle properties compared with the conventional atmospheric plasma spraying method. In this study, we evaluated the thermal cycle properties of TBCs with different microstructures prepared by varying the deposition conditions of the SPS method, and investigated the effect of microstructures on the thermal cycle properties. The experimental results indicated that the thermal cycle fatigue life of SPS-TBC increased with decreasing column diameter. The effect of microstructure on the thermal cycle fatigue life was discussed based on the thermal stress in top-coating evaluated by the FE analysis.

Finite element analysis on the thermal fatigue life of full vs peripheral array packages

PurposeThis paper aims to examine the thermal cycling fatigue life performance of two-common solder array configurations, full and peripheral, using three-dimensional nonlinear finite element analysis.Design/methodology/approachThe finite element simulations were used to identify the location of the critical solder interconnect, and using Darveaux's model, solder thermal fatigue life was computed.FindingsThe results showed that the solder array type does not significantly influence thermal fatigue life of the interconnect. However, smaller size packages result in improved life by almost 45% compared to larger package designs. Additionally, this paper provided an engineered study on the effect of the number of rows available in a perimeter array component on solder thermal fatigue performance.Originality/valueGeneral design recommendations for reliable electronic assemblies under thermal cycling loaded were offered in this research.

Optimization of Dwell and Ramp Times for SAC305 Solder Thermal Cycling Fatigue Life for Testing and Real-Life Applications

Optimization of Dwell and Ramp Times for SAC305 Solder Thermal Cycling Fatigue Life for Testing and Real-Life Applications

Tailoring microstructure of double-layered thermal barrier coatings deposited by suspension plasma spray for enhanced durability

Gadolinium zirconate (GZ)-based TBCs comprising GZ as the top layer and yttria stabilized zirconia (YSZ) as the base layer, are attractive double-layered thermal barrier coatings (TBCs) for high temperature gas turbine engine application. This work attempts to understand the influence of individual layer microstructure on the durability of GZ/YSZ double-layered TBCs processed by suspension plasma spray (SPS). Two different spray parameters were chosen to obtain a combination of three microstructurally distinct GZ/YSZ double-layered TBCs i.e. GZ porous (P)/YSZ porous (P), GZ dense (D)/YSZ porous (P) and GZ dense (D)/YSZ dense (D). Thermal diffusivity of the as-deposited coatings was measured using Laser Flash Analysis (LFA) technique and the thermal conductivity of the TBCs was calculated. The GZ/YSZ double-layered TBC specimens were subjected to two different durability tests, i.e. thermal cyclic fatigue (TCF) and burner rig test (BRT). Sintering behavior of the individual layer TBC microstructures was evaluated by comparing the porosity evolution in as-deposited and TCF tested TBCs. Fracture toughness measurements performed on each layer of the double-layered TBCs were correlated with the durability results. Thermal cycling results amply demonstrate that the individual layer microstructure of GZ/YSZ double-layered TBC influenced its durability. Detailed failure analysis of the TCF and BRT failed specimens revealed similar failure modes for GZ (P)/YSZ (P), GZ (D)/YSZ (P) and GZ (D/YSZ (D) TBCs under identical thermal cyclic test conditions. However, failure modes differed when subjected to different thermal cyclic test conditions (TCF and BRT) and the probable causes are discussed. Findings from this work provide key insights on designing durable GZ/YSZ double-layered TBCs.

Thermo-oxidative aging and thermal cycling of PETI-340M composites

Polyimide composites (PETI-340M) were fabricated and subjected to high-temperature aging and thermal cycling to evaluate resistance to degradation. Mechanical-degradation mechanisms and kinetics depended on aging temperature. Aging at 232°C resulted in strength loss due to polymer degradation, while intra-tow cracking was the dominant mechanism during aging at 288°C. Composite panels subjected to thermal-cycling fatigue (−54°C to 232°C) retained mechanical properties without microcracking. However, in regions containing pre-existing fabrication-induced defects (primarily voids), intra-tow microcracks were observed after thermal cycling. Unlike some polyimide composites (PMR-15), oxidative aging effects during thermal cycling were negligible. The thermo-oxidative stability and the retention of mechanical performance after thermal cycling indicates potential for long-term, high-temperature structural applications.

Cyclic fatigue life characteristics of ceramic balls under variable thermal shock loadings

Ceramic balls made of silicon nitride (Si3N4) exhibited excellent mechanical properties are used in high-end components operating at ultra-high speeds, and high and low temperatures. Previously, studies have involved the cyclic mechanical and thermal fatigue tests of ceramic balls under a constant temperature. However, the thermal fatigue characteristics of brittle materials have not been theoretically or experimentally investigated under variable thermal shock loadings to date. Herein, cyclic thermal shock fatigue (CTSF) life characteristics of Si3N4 ceramic balls subjected to single- and two-stage cyclic thermal shock loadings were theoretically and experimentally investigated using a probabilistic model based on slow crack growth concept in conjunction with Weibull distribution. Consequently, the fracture criterion derived from the probabilistic model was related to the linear cumulative damage law (Miner’s rule). Thereafter, the predicted CTSF life of the ceramic balls was compared with the experimental results to validate the proposed probabilistic model. Therefore, the proposed model accurately reproduced the experimental results to a certain extent.

Thermal cyclic fatigue damage evolution of fiber-reinforced ceramic-matrix composites under constant loading

ABSTRACT Under thermal cyclic fatigue loading, temperature and cyclic-dependent damage mechanisms affect thermal fatigue damage evolution in fiber-reinforced ceramic-matrix composites (CMCs). Stress-strain hysteresis loops occur with the changing of temperature and correspond to internal damage evolution in CMCs. In this work, fatigue hysteresis-based damage features, including hysteresis-based dissipated energy, hysteresis modulus, hysteresis width, and peak strain, were developed to monitor thermal cyclic fatigue damage evolution in CMCs considering synergistic impacts of thermal and mechanical loading. Experimental thermal fatigue damage evolution of the 2.5D woven C/SiC composite subjected to various thermal fatigue loads were predicted with the newly developed fatigue hysteresis-related damage parameters. The effects of the composite’s material features, peak stress, damage state, and cycle number on thermal fatigue damage evolution in the C/SiC composite were analyzed.

Manufacturing and high heat flux testing of flat-type W/Cu/CuCrZr mock-up by HIP assisted brazing process

Divertor is one of the most challenging plasma facing components (PFCs) for fusion reactors both from the design and fabrication technology point of view. In this work, the new flat-type W/Cu/CuCrZr mock-ups were fabricated using hot isostatic pressing (HIP) and optimized brazing techniques. High heat flux (HHF) tests of the mock-up were performed on a comprehensive experimental platform to assess the heat removal capability and thermal fatigue resistance. The results indicate that the mock-up successfully endured the cyclic absorbed heat flux at 20 MW m−2 for 1000 cycles with an inlet pressure of 1 MPa, an inlet water temperature of 20 °C and a velocity of 6.88 m s−1. The peak temperature of the tungsten (W) surface reached 926 °C at the 1000th cycle, which is less than the recrystallization temperature. In addition, no substantial melting at the loaded W surfaces, no detachment of any W/Cu units and no occurrence of any ‘hot spot’ during thermal fatigue cycling were observed. These results indicate that HIP assisted brazing technique is a powerful method for fabricating PFCs employed in HHF tests, and the flat-type W/Cu/CuCrZr structure is very promising to be used to upgrade the lower divertor of Experimental Advanced Superconducting Tokamak(EAST) and manufacture the divertor for China Fusion Engineering Test Reactor(CFETR).

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.