Thermo-mechanical Stress Research Articles

Analytical modeling of thermomechanical stresses in short hyperelastic tubes under axial and torsional loading

Abstract This study introduces an analytical model for analyzing thermomechanical stresses in finite-length hyperelastic hollow cylinders under axial-torsional loading and non-isothermal conditions. The model incorporates an axial temperature distribution and decomposes strain responses into thermal expansion and mechanical stretches. Governing equations are derived using large deformation kinematics and the Neo-Hookean strain energy function. Solutions for displacements, stresses, and pressure variables are obtained with appropriate boundary conditions. Validation against 3D finite element analysis demonstrates strong agreement with significant computational cost savings. These findings challenge the conventional linear assumption for twist angles under large deformations. Increasing temperature differences introduce noticeable nonlinearities in radial and axial stress distributions, resulting in significant nonlinear axial stress distributions along the vertical walls. Additionally, higher temperature differences reduce axial stress at the inner radius, while shear stresses predominantly remain radial with minimal variation. In summary, this efficient analytical tool provides invaluable insights into thermomechanical stresses in soft active cylindrical components, with broad potential applications across various fields.

The lightweight design of steel pistons for diesel engines based on thermo-mechanical characteristics

Traditional aluminum–silicon alloy pistons are gradually replaced by steel pistons, which has become the trend of future diesel engine development. However, the efficient design and broad application of steel pistons are limited by the higher density of steel. For this reason, a new lightweight design method for steel pistons in diesel engines was proposed in this paper. The progressive design of the cooling gallery cross-section and the topology optimization of the window region were carried out to meet the strength and deformation requirements. Ultimately, a lightweight steel piston (LSP) was obtained. The results of the study showed that the total mass of LSP could be reduced by 8.86% compared to the original steel piston (OSP). The thermal states of LSP are all superior to those of OSP. The highest temperature, maximum thermal stress, maximum longitudinal thermal deformation, and maximum transverse thermal deformation can be reduced by 0.96 °C, 3.03%, 11.65%, and 8.99%, respectively. LSP has a larger thermo-mechanical coupling stress manifestation compared to OSP. However, the maximum longitudinal and transverse thermo-mechanical coupling deformations can be obtained with a significant reduction of 8.33% and 42.19%, respectively.

Thermo-mechanical stress modelling and fracture analysis on ultra-thin silicon solar cell based on super multi-busbar PV modules

Thinning of crystalline silicon (c-Si) wafers will reduce material cost and improve productivity, which significantly impacts the development of solar photovoltaic (PV) industry. However, this process leads to reduction in mechanical strength of the cell and increased solar cell fracture during the manufacturing process. This study investigates the mechanical property of full wafers and half wafers with varying thicknesses, both before and after the slicing process. Thermo-mechanical stress in half cells was analyzed using finite element modeling (FEM) to clarify the origin of cracks, the influence of Si thickness on cracking and the process impacts on eventual cell breakage. Fracture analysis was implemented not only in soldering process but also during lamination and dynamic mechanical loading (DML) tests. Our findings reveal that the thinner solar cells become even more fragile and susceptible to fracture or power attenuation during the module manufacturing process and operation as well. FEM simulations also verify that the highest stress occur in the thinnest Si wafers after soldering, lamination and DML processes, respectively. However, the choice of 16 Cu ribbons with a diameter of 0.26 mm, which is verified and confirmed as the optimal super multi-busbar (SMBB) technology for the ultra-thin solar cells based PV module, can help to reduce the cell stress and improve the module reliability in mass production.

Highly-Buckled Nanofibrous Ceramic Aerogels with Ultra-Large Stretchability and Tensile-Insensitive Thermal Insulation.

Ceramic aerogels have exhibited many superior characteristics with promising applications. As an attractive material system for thermal insulation under extreme conditions, ceramic aerogels are required to withstand complex thermomechanical stress to retain their super-insulating properties but, they often suffer from severe fracture damage that can lead to catastrophic failure. Herein, inspired by the tendrils of Parthenocissus, we report a design and synthesis of ultra-stretchable ceramic aerogels constructed by highly buckled nanofibers. The buckling of nanofibers is formed by asymmetric deformation through two-component off-axial electrospinning method. The resulting aerogels feature an ultra-large stretchability with a tensile strain of up to 150% and high restorability with a tensile strain of up to 80%. They also display a near-zero Poisson's ratio (4.3 × 10-2) and a near-zero thermal expansion coefficient (2.6 × 10-7 per°C), resulting in excellent thermomechanical stability. Benefiting from this ultra-stretchability, the aerogels exhibit a unique tensile-insensitive thermal insulation performance with thermal conductivities remaining only ≈106.7 mW m-1 K-1 at 1000°C. This work promotes the development of ceramic aerogels for robust thermal insulation under extreme conditions and establishes a set of fundamental considerations in structural design of stretchable aerogels for a wide spectrum of applications.

Occlusion failure analysis and optimization design for steel piston pin hole-pin friction pair

The focus of the present study was on the D25TCIF steel piston, and the underlying causes of pin hole occlusion failure were systematically analyzed. The investigation considered factors such as heat transfer, mechanics, lubrication, material properties, and forging processes. Additionally, an optimization strategy was introduced based on the cause of the failure to reduce the risk of occlusion failure of the pin hole. At the same time, the influence of the structural parameters of the connecting rod small head on the lubrication performance of the pin hole bearing was investigated, providing a theoretical basis for the matching design of the structural parameters of the double friction pair of the piston pin bearing. The findings indicate that the primary cause of pin hole occlusion failure in steel pistons is the concentration of thermo-mechanical coupling stresses and elevated temperatures within the pin hole. This condition results in the rupture of the lubricating oil film in the pin hole bearing, leading to dry friction between the piston pin and the bearing surface. The optimization method designed in the present study enhanced the minimum oil film thickness of the pin hole bearing from 0.354 μm to 0.377 μm, reflecting an increase of 6.50 %. Additionally, the minimum oil film thickness of the small head bearing was improved from 0.599 μm to 0.691 μm, corresponding to a 15.36 % increase compared to the original configuration. Meanwhile, the optimization method predicted a minimum oil film thickness of 0.382 μm for pin hole bearings and 0.693 μm for small-head bearings, with a relative error of less than 5 % from the simulated values. Such findings demonstrate that the optimization method has a good optimization effect and accurate prediction. This approach offers novel insights for the development of future solutions to address the failure of steel pistons in engineering applications.

Thermal and structural improvements of a motorcycle piston using a fully coupled thermo-mechanical FEM simulation

This paper aims to conduct thermo-mechanical simulations using the finite element method (FEM) to enhance the design of the piston in a single-cylinder, water-cooled motorcycle engine. The finite element model of the piston was developed to represent its thermo-mechanical behavior under combustion processes and transient heat transfer phenomena. Realistic engine boundary conditions were applied using the non-linear dynamic tool in Solidworks design software. Two different design configurations were investigated concerning the oil jets and the upper face of the piston pins. The results revealed lower piston temperatures by 12.2% as three oil jets targeted the upper region of the piston bosses. Additionally, an optimum radius fillet in the upper face of the piston holes showed potential for minimizing thermo-mechanical stresses. This finding suggests that optimizing the piston design can reduce developed thermo-mechanical stresses while addressing elevated temperatures.

Integrated Autothermal Reformer, Heat Exchanger and Solid Oxide Fuel Cell in Single-Stack for Aircraft Gas-Turbine Applications

To take advantage of carbon-neutral aviation fuels such as synthetic liquified natural gas, aircraft engines must increase their efficiency through novel approaches, such as hybrid electric gas-turbine/solid oxide fuel cells (GT/SOFCs). To date, most hydrocarbon-fueled SOFC stack designs utilize rigid architectures and independent pre-reformers that require complex manifolding and rigid sealing. To enable SOFCs to operate effectively and robustly within an aircraft GT engine flow path upstream of a combustor, our team is developing an innovative integrated SOFC stack with an inline autothermal reformer/heat exchanger (ATR/HX) to provide adequate operating conditions for high-power (W/cm2) performance. The ATR/HX, integrated upstream of the stack, provides preheating of the cathode air through mildly exothermic reforming of the fuel with a bleed of combustor air and recycling of some anode exhaust. The exothermic ATR provides adequate heat to the cathode air to allow intermediate-temperature SOFCs, with either gadolinium-doped ceria (GDC) electrolytes or thin-film yttria-stabilized zirconia (YSZ) electrolytes, to operate on GT compressor outlet temperatures just above 400 °C. To enable rapid thermal response of the integrated ATR/HX/SOFC, the stack design eliminates rigid seals to mitigate the risks of SOFC failure due to thermomechanical stresses. This paper presents the design and preliminary testing of the integrated ATR/HX/SOFC under rapid heating conditions to suggest the potential for SOFCs for next generation hybrid-electric aircraft application.The ATR/HX/SOFC stack design is supported by 441 stainless steel plates with electrochemically etched, air-flow channels through the upstream HX and the SOFC cathode. The plates also include a pocket for the ATR, which consists of a woven metal-mesh with an Al2O3-washcoat supported Pt catalyst that can light off with CH4/bleed air/H2O inlet temperatures of 400 °C. The SOFC membrane electrode assembly (MEA), 10 cm*10 cm with 81 cm2 active cathode area, rest within a frame that supports the MEA as well as a silver mesh cathode collector and a nickel mesh anode current collector. The cell is sealed by compressing a thermiculite seal that extends over the full area of the stack and compresses on the exposed electrolyte area bordering the cathode. Testing at operating temperatures indicated minimal leakage (<1%) from the anode and from the cathode to the external environment. This design, which lacks rigid seals or confinement of the MEA, enables ease of assembly and disassembly and minimizes external stresses on the MEA to enable rapid heating during ATR light-off.Integrated ATR/HX/SOFC stack has been initially incorporated into a low-pressure test facility shown in Figure 1a), which provides steam generation for the ATR inlet and premixing and preheating for the ATR inlet and air-side HX inlet flows. The ATR/HX/SOFC stack is preheated to 400 °C or more to achieve rapid light-off that rapidly preheats the SOFC inlet to desirable temperatures. For a 3-cell ATR/HX/SOFC short stack, light-off test to SOFC operating temperatures of 550 °C for thin-film YSZ-electrolyte MEAs from Elcogen are achieved in < 1 h. Such start-up times are expected to be reduced for larger ATR/HX/SOFC stacks with reduced heat loss per stack volume. Tests to date have only achieved maximum MEA power densities of 0.26 W/cm2 at 0.65 V/cell operating on the ATR outlet. Simulated performance shows pathway to higher power densities > 1.0 W/cm2 with higher temperature operation that will be achieved with coated interconnect materials. Tests to date show that the thin-film YSZ cells avoid cracking after undergoing multiple assembly and disassembly cycles, as well as high-temperature ATR light-off and fuel cell testing. These results indicate that both mechanical and thermal stresses remain sufficiently low to prevent cell cracking throughout start-up, normal operation, and shut-down processes, thus affirming the robustness and reliability of our integrated stack design. Figure 1

Assessment of the Risk of Crack Formation at a Hybrid Bonding Interface Using Numerical Analysis.

Hybrid bonding technology has recently emerged as a promising solution for advanced semiconductor packaging technologies. However, several reliability issues still pose challenges for commercialization. In this study, we investigated the possibility of crack formation caused by chemical mechanical polishing (CMP) defects and the misalignment of the hybrid bonding structure. Crack formation and thermomechanical stress were analyzed for two common hybrid bonding structures with misalignment using a numerical simulation. The effects of annealing temperature and dishing value on changes in the non-bonding area and peeling stress were systematically analyzed. The calculated peeling stresses were compared to the bonding strength of each bonding interface to find vulnerable regions prone to cracking. The non-bonding area in the bonding structure increased with a decreasing annealing temperature and an increasing dishing value. To achieve a sufficient bonding area of more than 90%, the annealing temperature should be greater than 200 °C. During the heating period of the annealing process, the SiCN-to-SiCN bonding interface was the most vulnerable cracking site with the highest peeling stress. An annealing temperature of 350 °C carries a significant risk of cracking. On the other hand, an annealing temperature lower than 250 °C will minimize the chance of cracking. The SiCN-to-SiO2 bonding interface, which has the lowest adhesion energy and a large coefficient of thermal expansion (CTE) mismatch, was expected to be another possible cracking site. During cooling, the SiCN-to-Cu bonding interface was the most vulnerable site with the highest stress. However, the simulated peeling stresses were lower than the adhesion strength of the bonded interface, indicating that the chance of cracking during the cooling process was very low. This study provides insights into minimizing the non-bonding area and preventing crack formation, thereby enhancing the reliability of hybrid bonding structures.

Flexibilizing Mechanisms of Spinel-, Hercynite-, Galaxite-, and Chromite-Containing Basic Refractories for Cement Rotary Kilns

Background: Refractory linings of cement rotary kilns are subjected to severe thermomechanical stresses of cranking, ovality, tyre hooping/migration, and uneven thermal distribution. An insistent demand is to discover the significance of spinel, hercynite, galaxite, and chromite in magnesia refractories, as well as their flexibilizing mechanisms. Objectives: The objectives are to compare the fracture behavior of magnesia–spinel, – hercynite, -galaxite, and -chromite refractories and to unveil the flexibilizing mechanisms of different spinels. Methods: The wedge-splitting test is carried out to produce various fracture parameters. Their flexibilizing mechanisms are unveiled by performing microstructural observations and analyses. Results: Various fracture parameters are obtained, including specific fracture energy, brittleness number, characteristic crack length, and thermal-shock resistance parameter. Generally, magnesia–hercynite bricks and magnesia–galaxite bricks have demonstrated the obvious advantages of fracture resistance, which are more flexible than magnesia–spinel bricks and magnesia–chromite bricks. Conclusion: The flexibility of magnesia–spinel bricks is attributed to microcracks generated from the thermal mismatch between spinel grains and surrounding periclase, which is recognized as the thermal-expansion mismatch mechanism. In magnesia–hercynite and magnesia-galaxite refractories, the active-ion-diffusion mechanism is predominant beyond similar microcracks, to drive the flexibility by the continuous diffusion of Fe2+, Mn2+, and Mg2+ during high-temperature processes. In magnesia–chromite bricks, the pore rims contribute to the flexibility as a silicate-migration mechanism, after silicate envelopes first arise around chromite grains and then vanish into the surrounding magnesia by the suction of capillary force during the burning process.

Compliant Interconnects Based on Single Micrometer-sized Metal-Coated Polymer Spheres.

The rapid evolution of multifunctional electronics necessitates interconnection technologies appropriate for large dies with high-density and/or ultrafine pitch input/output pins. Existing technologies face numerous challenges, including demands for bonding equipment that can deliver extremely high force as well as thermo-mechanical stresses induced in the assembled packages due to mismatched thermal expansion of materials involved. This study proposes an approach to compliant interconnects comprising single micrometer-sized metal-coated polymer spheres, being joined to mating electrodes by sintering of Ag nano ink at low temperature (140 °C) and low pressure (∼15 mN/particle). Such an interconnection technology is expected to enhance the thermo-mechanical robustness of the assembled packages as well as be capable of high-density, ultrafine pitch interconnects. Our approach demonstrates control over conductive particles during assembly, achieving a 98% success rate in individual interconnects with a single captured particle. The use of sintered Ag not only secures free-standing particles on electrical pads (with an adhesion force above 2 μN) but also results in a 15% reduction in interconnect resistance, with measured resistance as low as 0.5 Ω, compared to interconnects without Ag ink. This method presents an alternative to metallurgical joints, particularly suited for high-density, ultrafine pitch applications, offering low bonding pressure and temperature, along with improved interconnect compliance to enhance the thermo-mechanical robustness of the packages.

Post‐Mortem Analysis of Building‐Integrated Flexible Thin Film Modules

ABSTRACTFlexible, lightweight thin film (TF) photovoltaic (PV) modules offer a unique opportunity for integration into non‐planar surfaces unable to support heavy weights. While such applications increase the potential for PV in urban areas, the reliability implications are yet to be investigated. Here, prototypes of corrugated rooftiles with integrated Cu (In,Ga)Se2 (CIGS) modules were investigated after 3 years of outdoor operation. Their performance before and after the outdoor exposure was compared and defects were localized. An unpackaging method was developed, allowing access to the solar cells for more detailed characterization of present defects without causing additional damage or changes to existing defects. To our knowledge, this was the first time such an unpackaging method was successfully applied to flexible TF PV modules. The relative efficiency loss ranged from 17% to 43%, mostly due to short‐circuit current (ISC) loss and series resistance (RS) increase. The predominant cause of the RS increase was the delamination at the interconnects, ascribed to thermomechanical stresses caused by outdoor temperature fluctuations. The ISC loss was mainly caused by localized delamination of CIGS from the molybdenum (Mo) back‐contact. The occurrence of such delaminated areas pointed to presence of high local stresses during outdoor operation, possibly due to thermal fluctuations, applied deformation and/or mechanical impact. Two other types of delamination defects were found with no observable impact on performance. These results show the necessity for further optimization in the material choice and processing of TF flexible modules, to avoid mechanical stress related failures upon integration into curved surfaces.

Bluestein–Gulyaev(B-G) waves in a piezo-thermoelastic half-space in the context of modified multi-phase-lag theory

In the years 1968–69, Bluestein and Gulyaev discovered a new kind of surface wave in a piezoelectric material known as B-G wave after their name. Although it was discovered in few decades ago, but till now, no work has been done related to B-G wave propagation based on modified multi-phase-lag theory. In the present work, the authors have investigated the propagation behavior of Bluestein-Gulyaev-type waves in a piezo-thermoelastic half-space in the context of modified multi-phase-lag theory. The normal mode technique is employed to obtain the principal variables, for example, displacements, temperature, electric potential, electric displacements, and thermo-mechanical stresses. The boundary conditions are adopted in such a way that the upper surface of the piezo-thermoelastic half-space is stress free and the half-space is implicated by a perfectly conducting electrode that is grounded (i.e., electrically short conditions at the free surface). Based on these boundary conditions, secular equations are derived for the proposed model. Some special cases have also been discussed, and it is found that the secular equation is in well-agreement with the pre-established thermoelasticity theory. Moreover, some analyses are made to highlight the important peculiarities of the problem. The mathematical framework of the present study is momentous for both theoretical and practical expositions for temperature sensors and piezoelectric surface acoustic wave (SAW) devices. Also present study helps the researchers who are engaged on this domain.

Sequential thermomechanical stress and cracking analysis of photovoltaic modules with full and half-cut cells

The transition from conventional full-cell patterns to half-cell modules in the photovoltaic (PV) industry promises enhanced stability and efficiency. This study investigates the thermomechanical behaviour and stress distribution within half-cell and full-cell PV modules during the manufacturing and operational phases. Using finite element modeling, the research simulates sequentially the manufacturing and operating processes such as laser cutting, soldering, lamination, mechanical loading and thermal cycling. The Extended Finite Element Method (XFEM) predicts crack initiation and propagation in the crack-sensitive regions in PV modules during their entire life. Key findings highlight stress concentrations during manufacturing, influenced by parameters like laser power, scribing length and Silicon wafer size. Mechanical loading (ML) and thermal cycling (TC) induce additional stresses, impacting module reliability. The results are useful for the optimization of material properties and the development of advanced design strategies contributing to the durability and efficiency of PV systems.

Power Cycling Performance of 3.3 kV SiC-MOSFETs and the Impact of the Thermo-Mechanical Stress on Humidity Induced Degradation

Recently, silicon carbide (SiC) power modules of the 3.3 kV voltage class became available and are a promising candidate to replace silicon power modules in traction applications. However, the more than three times higher Young’s Modulus compared to silicon leads to a reduced lifetime under thermo-mechanical stress. This could pose a significant obstacle in their implementation, since traction applications are particularly demanding in their mission profiles with respect to load cycling, but also to environmental conditions. Thus, the thermo-mechanical stress is not just limiting the lifetime itself, but might also promote the humidity induced degradation due to delamination or micro-cracks. In this work, multiple power cycling tests at different temperature swings on 3.3 kV SiC MOSFET chips in a power module were performed, to assess their ruggedness under thermo-mechanical stress. Before or afterwards, these modules were tested under standard HV-H3TRB conditions to verify the interaction between thermo-mechanical and humidity stress on the robustness of the modules.

Influence of Material Properties on Ruggedness Evaluation of Package Architectures for SiC Power Devices

Button shear tests at different temperatures between different mold compounds and Cu-leadframes have been performed to evaluate the adhesion of mold compounds to the inner surfaces of SiC-power devices. The results at different temperatures show the behavior of different material and layer stack combinations under storage at room temperatures as well as under operating conditions with elevated temperatures, where adhesion and thus the hermeticity of the device against moisture is significantly lowered. It has been shown that different thermomechanical properties of the mold compounds as well as the usage of different adhesion promoter materials have a significant effect on the adhesion properties of the mold compound to the leadframe surface of the SiC power devices, which have direct impact on the ruggedness and lifetime stability. Furthermore, these results have been correlated to thermomechanical simulations of the package architecture of SiC power devices under stress. Different wire bond architectures have been evaluated in simulations with and without die top delamination taken into account, showing that EMC delamination may play a major role in the lifetime stability of SiC power devices under thermomechanical stress like simulated in TCT- , IOL- and PTC-testing.

Analysis of micro-defect-induced cracking in the IPyC layer of TRISO particle with the XFEM

PurposeWe use the extended finite element method (XFEM) to model the whole process of initiation and propagation of cracks in the inner dense pyrolytic carbon (IPyC) layer of tri-structural isotropic (TRISO) particle induced by the microdefect in an irradiation-induced thermomechanical coupling environment and study the effect of microdefect sizes on the propagation path.Design/methodology/approachThe irradiation-induced thermal–mechanical coupling analysis is first conducted for the representative volume element (RVE) of the TRISO particle by using the conventional finite element method (CFEM) so that the stress distribution is obtained. The stress results are then restored for the enriched elements, and the simulation of crack initiation and propagation is eventually carried out by using the XFEM.Findings1. As a crack initiates in the IPyC layer, it will terminate at the free edge of the RVE TRISO particle in the end. 2. The size of the microdefect has a significant impact on the propagation path.Originality/valueThe ceramic dispersion microencapsulated (CDM) fuel is a good accident-resistant fuel whose safe operation is crucial to the safety and reliability of the whole nuclear reactor. It is of great scientific significance and practical value to study the irradiation-induced thermomechanical coupling stress distribution and cracking behavior in the IPyC layer of TRISO particles for the CDM fuel. Crack initiation and propagation analysis is challengeable for this complex multi-layer structure. This can help understand the failure mechanism of TRISO particles and evaluate the operation safety of the reactor.

Thermal cycling characterization of an integrated low-inductance GaN eHEMT power module

To exploit the potential of wide-bandgap semiconductors in high-frequency applications, innovative packaging designs are developed to minimize the parasitic inductance of power modules. This study presents an integrated power module with a hybrid PCB/DBC structure, which uses top-side cooling prepackaged GaN enhancement-mode high-electron-mobility transistors. The module achieves a remarkably low parasitic inductance of 2.65 nH. However, there is relatively scarce research on the reliability of this heterostructure, particularly its sensitivity to thermomechanical stress due to the coefficients of thermal expansion mismatch among material interfaces. In this work, the thermal cycling characteristics of the integrated power module are comprehensively investigated. Electrical and thermal parameters were periodically and separately measured offline on a simplified package to monitor the health conditions and decouple possible synergy and competition effects among the failure modes from all packaging components. A thorough failure analysis was conducted using nondestructive visual inspections and scanning acoustic microscopy, complemented by destructive cross-sectional examination and scanning electron microscopy. The findings identified the delamination of the DBC upper copper layer, which exhibited a conchoidal fracture interface, as the primary factor that contributed to the failure of the power module with increased thermal resistance. Furthermore, the study dissected its initiation and propagation mechanisms. This investigation provides valuable insights for the development of more reliable low-inductance power module designs.

Simulation of Thermo-Mechanical Stresses After a Quench in the 15 T Test Facility Dipole Magnet

Simulation of Thermo-Mechanical Stresses After a Quench in the 15 T Test Facility Dipole Magnet

Wear mechanisms and material deposition of high-performance polymer composites for hydrogen compression

The transistion to renewable energy production is a main component in achieving the climate targets defined in the 2015 Paris Agreement. Power-to-gas concepts, where electrical energy is stored as hydrogen gas, require the design and operation of state-of-the-art reciprocating compressor technology to realize high pressure ratios and high volumetric flow rates for gas supply demands. The main challenges in designing machines suited for these operating conditions are high thermo-mechanical stresses acting on the piston sealing rings. High shear loads and minimal ring gap sizes demand material pairings with excellent wear resistance and sliding properties. This work investigates the life cycle limiting wear mechanisms present in the piston compressor and develops advanced concepts for piston rings in cylinder tribo-contacts. PI and PPS polymers reinforced with carbon fiber were modified with dry lubricating PTFE to fulfil the requirements of this highly stressed tribo-system. Tribo-tests were performed against steel countersurfaces with a linear oscillating tribometer in pin-on-plate configuration. The failure mechanisms were analysed utilizing scanning electron microscopy on cross-sections cut into the depth of the countersurface material with focused ion beam milling. 2D scanning transmission electron microscopy mapping supported by energy dispersive X-ray spectroscopy were performed to analyze the depth profile of the deposited tribo-layer elements on the wear track.

Microstructural Modifications and Failure Mechanisms of an Aluminum‐Based Abradable Coating System during Isothermal and Cyclic Aging

Abradable systems are used in the aeronautical industry to improve the efficiency of gas turbine. Those materials are exposed in service to temperature up to 450 °C. The increase in gas turbine efficiency requires to increase the operating temperature and therefore the service temperature of abradable coating. The present study focuses on the isothermal and cyclic thermal aging of the Al–Si abradable coating system in a laboratory air at high temperature up to 500 °C. The investigation encompasses the microstructural evolution, phase transformation, and the formation of cracks, along with their interrelated effects. During aging, silicon particles precipitate in the abradable top coat. In addition, coarsening of those particles is observed and the coarsening kinetics appears to be faster in cyclic thermal aging conditions compared to isothermal aging. During cyclic and isothermal aging, brittle aluminides develope at the abradable top–coat/bond–coat interface, due to the interdiffusion of Al and Ni species. During cyclic aging, thermal cycles create thermomechanical stress at the top‐coat/bont‐coat interface due to coefficient of thermal expansion mismatch between the Al‐Si deposit and intermetallic phases. The stress generated results in the formation of cracks and porosities at the top–coat/bond–coat interface resulting in a dramatic failure of the system.