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Three-point bend testing
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Proceedings Papers
Exploring the Crack Propagation Behavior in Suspension Plasma Sprayed Thermal Barrier Coatings: An In-Situ Three-point Bending Study in Scanning Electron Microscope
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ITSC2024, Thermal Spray 2024: Proceedings from the International Thermal Spray Conference, 139-151, April 29–May 1, 2024,
Abstract
View Papertitled, Exploring the Crack Propagation Behavior in Suspension Plasma Sprayed Thermal Barrier Coatings: An In-Situ Three-point Bending Study in Scanning Electron Microscope
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for content titled, Exploring the Crack Propagation Behavior in Suspension Plasma Sprayed Thermal Barrier Coatings: An In-Situ Three-point Bending Study in Scanning Electron Microscope
In this study, the in-situ technique was used to observe crack formation and growth in multilayer suspension plasma spray (SPS) thermal barrier coatings (TBCs). Utilizing synchronized three-point bending (3PB) and scanning electron microscopy (SEM), coupled with digital image correlation (DIC), we provide real-time insights into strain field dynamics around cracking zones. Bending-driven failure was induced in both single and composite-layer SPS coatings to investigate the crack behavior in these columnar-structured multilayer TBCs. The real-time observations showed that columnar gaps can facilitate crack initiation and propagation from the coatings' free surface. The composite-layer SPS coating exhibits lower susceptibility to vertical cracking than the single-layer SPS coating, possibly due to the presence of a gadolinium zirconate (GZ) dense layer at the coating's free surface that enhances the bonding strength within the coating's columnar structure. The splat structure of the bond coat (BC) layer contributes to the crack path deflection, thereby potentially improving the SPS coating' fracture toughness by dissipating the energy required for crack propagation. Moreover, it was revealed that grit particles at the BC/substrate interface seem to promote crack branching near the interface, localized coating delamination, and serve as nucleation sites for crack development. Hence, optimizing the grit-blasting process of the substrate before BC layer deposition is crucial for minimizing the possibility of crack formation under operational conditions, contributing to enhanced durability and prolonged lifespan. This study underscores the critical role of in-situ observation in unravelling the complex failure mechanisms of multi-layered coatings, paving the way for the design of advanced coatings with enhanced structural complexity and improved performance for more extreme environments.
Proceedings Papers
Investigation of Mechanical Properties of Twin Wire Arc Repair of Cast Iron Components
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ITSC 2021, Thermal Spray 2021: Proceedings from the International Thermal Spray Conference, 530-541, May 24–28, 2021,
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View Papertitled, Investigation of Mechanical Properties of Twin Wire Arc Repair of Cast Iron Components
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for content titled, Investigation of Mechanical Properties of Twin Wire Arc Repair of Cast Iron Components
Twin wire arc is a commonly used thermal spray technology for application of steel coatings to cast iron components. Hardness and adhesion strength are critical properties of such coatings, and significant research is available reporting these properties. However, residual stresses and the anisotropic structure of the coatings leads to significantly different behavior in bending applications than in the purely tensile loading of the standard adhesion test. In addition, microstructural features that are controlled by certain process parameters during deposition of the coating can have a significant effect on these properties. This work seeks to relate the hardness and pull-off adhesion strength to the coating microstructure, and to assess the related bending strength and failure mode. Comparisons between bend tests and pull-off adhesion tests show significant differences to consider when evaluating twin wire arc coatings.
Proceedings Papers
Mechanical Properties of Yttria-Stabilised-Zirconia for Thermal Barrier Coating Systems: Effects of Testing Procedure and Thermal Aging
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ITSC 2017, Thermal Spray 2017: Proceedings from the International Thermal Spray Conference, 302-307, June 7–9, 2017,
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View Papertitled, Mechanical Properties of Yttria-Stabilised-Zirconia for Thermal Barrier Coating Systems: Effects of Testing Procedure and Thermal Aging
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for content titled, Mechanical Properties of Yttria-Stabilised-Zirconia for Thermal Barrier Coating Systems: Effects of Testing Procedure and Thermal Aging
Cyclic oxidation failure of Atmospheric Plasma Sprayed Thermal Barrier Coatings systems (APS TBCs), commonly used to insulate hot sections in gas turbines, usually results from the spallation of the ceramic top coat. Consequently, in order to predict such spalling phenomena, understanding the mechanisms for cracks initiation and propagation in thermal barrier coatings is of utmost concern for engine-makers. Failure of the TBC is strongly related to the thermal and mechanical properties of each component of the multi-materials system (substrate, bond coat and ceramic) but also to the response of the TBC as a whole. The purpose of the work is to assess the mechanical behaviour of thick TBC using experimental approach for TBC standard lamellar, porous and microcracked microstructure (classically obtained through APS coatings). The experimental characterisation of the mechanical behaviour of the ceramic top coat of the TBC is addressed on specifically designed and prepared free-standing specimens using three points bending (3PB) tests and Small Punch Testing (SPT). The tests are performed on free-standing top coats made of YSZ in the as deposited states and for specimens that undergone isothermal aging at 1100°C for various durations (1h, 10h and 100h). The results of test performed at room temperature using both mechanical testing techniques are compared. This allows to show the evolution of mechanical properties after thermal aging. Tests performed at 850°C in the SPT ring show that the evolution of properties resulting from this aging may be different at room temperature as compare to 850°C.
Proceedings Papers
Failure Behavior of the Plasma-Sprayed Yttria Stabilized Zirconia Thermal Barrier Coatings Under the Three Point Bending Test Via Acoustic Emission Technique
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ITSC2016, Thermal Spray 2016: Proceedings from the International Thermal Spray Conference, 866-873, May 10–12, 2016,
Abstract
View Papertitled, Failure Behavior of the Plasma-Sprayed Yttria Stabilized Zirconia Thermal Barrier Coatings Under the Three Point Bending Test Via Acoustic Emission Technique
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for content titled, Failure Behavior of the Plasma-Sprayed Yttria Stabilized Zirconia Thermal Barrier Coatings Under the Three Point Bending Test Via Acoustic Emission Technique
Failure is an inevitable consequence with thermal barrier coatings and failure modes are complicated due to irregular microstructure in the coating layers and wide range of external conditions. In this study, three-point bend tests are used to monitor damage evolution in YSZ-CoNiCrAlY TBCs on superalloy and stainless steel substrates. Coating samples, consisting of the bond coat and topcoat, were deposited by atmospheric plasma spraying on test specimens measuring 80 x 6 x 4 mm. The long, narrow specimens were subjected to three-point bend testing, using acoustic emission sensors to detect the formation and propagation of cracks in the coatings and plastic deformation in the substrates. The investigation results indicate that variations in acoustic emission signals correspond well with changes observed in the stress-strain curves of the coatings and substrates and that failure mechanisms can be systematically analyzed based on the amplitude, frequency, and energy of the acoustic emission signals. A detailed description of the actual failure process is provided.
Proceedings Papers
WC-Co/Metal Multi-Layer Coatings by Warm Spray Deposition
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ITSC 2011, Thermal Spray 2011: Proceedings from the International Thermal Spray Conference, 727-733, September 27–29, 2011,
Abstract
View Papertitled, WC-Co/Metal Multi-Layer Coatings by Warm Spray Deposition
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for content titled, WC-Co/Metal Multi-Layer Coatings by Warm Spray Deposition
WC-Co/copper coatings with 8 layers were fabricated by warm spray deposition in order to investigate the effect of ductile layer inclusion on their fracture behavior. Bending strength, work of fracture, and surface hardness of freestanding coatings were examined by three point bending tests after removal of the substrates. The multilayered samples showed nonlinear stress-strain curves due to cracks in the WC-Co layers and plastic elongation of the copper layers. The multilayered samples with lower volume fraction of copper showed even lower bending strength than the monolithic samples of WC-Co and copper and no beneficial feature in mechanical performance was found. On the other hand, the samples containing higher volume fraction of copper exhibited more than twice higher work of fracture and moderately better bending strength than the monolithic WC-Co coatings, while the surface hardness was almost identical among all samples instead of the monolithic copper. The ductility of copper layers and the plastic constraint by the intact WC-Co layers attributed to enhance their mechanical properties. It has been concluded that cermet/metal laminate coatings can be one alternative approach to further improvement of the mechanical properties of thermal sprayed cermet coatings.
Proceedings Papers
Arc Spraying of WC-FeCSiMn Cored Wires – Part 1: Bending, Compression and Tension Behavior
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ITSC 2010, Thermal Spray 2010: Proceedings from the International Thermal Spray Conference, 592-600, May 3–5, 2010,
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View Papertitled, Arc Spraying of WC-FeCSiMn Cored Wires – Part 1: Bending, Compression and Tension Behavior
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for content titled, Arc Spraying of WC-FeCSiMn Cored Wires – Part 1: Bending, Compression and Tension Behavior
This is the first of two papers concerning the intrinsic mechanical properties of arc-sprayed WC-FeCSiMn coatings. In part 1 the elastic and plastic forming behavior of the layers are investigated by indentation, bending and tensile tests. They were performed on coated mild steel substrates as well as freestanding as-sprayed samples with different geometries. Considering the coatings microstructure, element and pore distribution, as well as the local microhardness the results of the indentation, bending, and tensile tests were evaluated. The critical role of pores and inhomogeneities within the sprayed coating was examined in detail. Micro- and macrocracking were investigated by SEM after the indentation and tensile tests. In-situ surface observation by optical 3D-microscopy was used to study the onset of cracking during the 3-point bending test.
Proceedings Papers
Mechanical Properties of W-Re and W-Re-HfC Alloys Made by Vacuum Plasma Spray
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ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 288-292, June 2–4, 2008,
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View Papertitled, Mechanical Properties of W-Re and W-Re-HfC Alloys Made by Vacuum Plasma Spray
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for content titled, Mechanical Properties of W-Re and W-Re-HfC Alloys Made by Vacuum Plasma Spray
The mechanical properties of tungsten-rhenium and tungsten-rhenium-hafnium carbide alloys produced by vacuum plasma spray forming have been evaluated. The results of both tensile and three-point bend tests at room temperature and elevated temperatures will be discussed. In addition, the results of a microstructural analysis will be presented.
Proceedings Papers
Characterisation of Thermally Sprayed Near Net Shape Oxide Ceramic and Cermet Coatings by Acoustic Emission Analysis
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ITSC 2008, Thermal Spray 2008: Proceedings from the International Thermal Spray Conference, 585-590, June 2–4, 2008,
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View Papertitled, Characterisation of Thermally Sprayed Near Net Shape Oxide Ceramic and Cermet Coatings by Acoustic Emission Analysis
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for content titled, Characterisation of Thermally Sprayed Near Net Shape Oxide Ceramic and Cermet Coatings by Acoustic Emission Analysis
Near net shape coating is a trend in thermal spraying being aimed at for several years to lower costs through shortened spray time and reduced after treatment work. Because of better microstructure compared to conventional coatings, the thickness is often also reduced. To characterise the quality of those thin layer systems the standardized tensile adhesive test is not suitable, as the adhesion outweighs the cohesion by far due to reduced quantities of coating defects. To characterize the coatings behaviour under tensile stress, three-point bending tests were performed. As especially thin cermet coatings do not show abrupt catastrophic failure in bending tests, ultrasonic signals being emitted from cracks propagating through the coatings were taken during the tests. Three coating systems (Cr 2 O 3 , Cr 3 C 2 -NiCr and WCCoCr) were investigated in this work using fine grained feedstock powders with three different size distributions per system. The tests showed the negative influence of stress moments in case of the oxide ceramic and the embrittlement of the cermets, especially the Cr 3 C 2 -NiCr, with increasing spraying temperature regime due to increased formation of solid solutions and decarburization. It can be said, that the analysis of acoustic emission during bending tests gives valuable information about how to achieve thin wear and corrosive protecting coatings being qualified for high operational demands.
Proceedings Papers
HVOF Coating of Metallic Surfaces: Corrosion and Bending Characteristics of Coating
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ITSC 2005, Thermal Spray 2005: Proceedings from the International Thermal Spray Conference, 695-699, May 2–4, 2005,
Abstract
View Papertitled, HVOF Coating of Metallic Surfaces: Corrosion and Bending Characteristics of Coating
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for content titled, HVOF Coating of Metallic Surfaces: Corrosion and Bending Characteristics of Coating
HVOF coating finds wide applications in power generation industry to protect the hot path components from high temperatures gases. The mechanical properties influence the life span of such components. In the present study, mechanical properties of HVOF spray of Inconel-625 alloy onto stainless steel surface was examined. The three point bending tests are carried out to determine the load and the flexural displacements characteristics of the coated workpieces. The workpieces were subjected to aqueous static corrosion environment before and after the three point bending tests. The surface morphology and elemental composition of the coating after the bending tests are examined using SEM and EDS. It is found that the local corrosion site in the coating result in high stiffness of the coating and the cracks extending along the surface of the coating are resulted due to the shear on the surface of the coating.
Proceedings Papers
Dynamical Mechanical Analysis of the Mechanical Properties of Al- and Fe-Based Thermal Spray Coatings
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ITSC 2001, Thermal Spray 2001: Proceedings from the International Thermal Spray Conference, 999-1002, May 28–30, 2001,
Abstract
View Papertitled, Dynamical Mechanical Analysis of the Mechanical Properties of Al- and Fe-Based Thermal Spray Coatings
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for content titled, Dynamical Mechanical Analysis of the Mechanical Properties of Al- and Fe-Based Thermal Spray Coatings
Static mechanical properties such as Young's Modulus, Yield Stress and Ultimate Tensile Strength and especially fatigue behavior are important material properties for thermal spray coatings and their industrial application in automotive and aerospace industry. The static and dynamic mechanical properties of Al-Si, Al-Sn, Fe-Cr and Fe-Cr-B based coating materials deposited by APS, TWAS and HVOF were investigated by nanoindentation and in a three point bending test using DMA (Dynamic Mechanical Analysis). This method permits the determination of pure coating material static and dynamic mechanical properties without substrate influence over a wide temperature range. In this investigation all measurements were carried out at room temperature. The DMA method was verified by comparison of Young's modulus to those obtained by nanoindentation.