Delamination Events Research Articles

Fatigue and delamination of 6061 aluminum cold spray on a similar wrought substrate

Fatigue crack growth and fracture of a thick 6061 aluminum cold spray coating on 6061-T6 aluminum substrate were studied through in-situ observation of fatigue crack growth through the coating to the interface in notched four-point bend samples. Mode I cracking was observed through the coating before delamination at the substrate. Crack tip strain fields during the delamination event were plotted with DIC. Interfacial steady-state strain energy release rates were measured using the bimaterial four-point bend solutions by Charalambides. The interfacial crack primarily spread cleanly along the coating/substrate interface, with a post-fracture surface morphology containing a wavy structure with an amplitude on the same order of magnitude as the cold spray particle diameters. The in-situ video of crack propagation and coating-substrate delamination provides lessons for improving the coating-substrate interfacial toughness and thus expands use cases for structural cold spray applications

Data-driven and physics-based methods to optimize structures against delamination

Composite materials and multi-material components often fail at their internal interfaces/adhesive joints, and hence special attention should be given to such catastrophic delamination events to guarantee the system’s functional requirements. So far, however, the majority of structural topology optimization problems have focused on optimal distribution of the bulk materials by considering interfaces as perfectly bonded. This motivates the introduction of optimization methods that explicitly take into account the role of the material interfaces to optimize structures against delamination. In this work, we propose a data-driven heuristic optimization approach for the identification of optimal cohesive interfaces with linearly graded fracture properties to increase the ability of the composite structure to withstand peeling. Moreover, for given cohesive interface properties, we investigate the applicability of the physics-based Solid Isotropic Material with Penalty (SIMP) topology optimization approach to optimize the internal structure of a substrate in problems where the stress field is affected by interface delamination.

Operando Investigation on the Role of Densification and Chemo‐Mechanics on Solid‐State Cathodes

AbstractAll solid‐state batteries are desirable for a range of energy storage applications which require high energy density. Achieving a high energy density in a solid‐state battery requires the operation of an energy dense anode with a composite solid‐state cathode. Pores and/or voids within a solid state cathode are ion‐blocking and thus control over the concentration and distribution of pores in the initial electrode and cycled electrode is desirable. This study provides an understanding of the interplay between electrode microstructure and mechanics on active material utilization in solid state cathodes composed of NCM 811 and Li6PS5Cl. Decreasing the solid electrolyte particle size leads to greater active material‐electrolyte contact and less total deformation when exposed to an external load. Composite cathodes with greater compliance can potentially decrease strain between the active material and solid electrolyte, decrease delamination events and result in higher overall active material utilization and high capacity retention.

Evidence for long-lived (>100 Myr) continental intraplate volcanism: Mongolia since the last ocean closure

Since the closure of the Mongol-Okhotsk Ocean in the Mesozoic, Mongolia has been in an intraplate tectonic setting; the nearest plate boundary being ∼3,000 km to the east, at the active Pacific subduction front. Throughout this time, Mongolia has experienced magmatism in the form of distinctive, small-volume volcanic fields dispersed along the central and eastern parts of the country. On the basis of geochemical, isotopic, palaeomagnetic and zircon data, the magmatism can be discriminated from preceding post-collisional magmatism. Gradual change from a lithospheric to an asthenospheric mantle source suggests lithospheric delamination occurred beneath Mongolia, starting at ∼140 Ma and terminating at ∼107 Ma. Accordingly, the onset of intraplate magmatism is set at 107 Ma. Regardless of the spatial and temporal occurrence and evolution of the intraplate magmatism in Mongolia, the geochemistry of the resultant volcanic rocks throughout time remains remarkably similar, although the cause of magmatism has been much debated.Through evaluation of available K-Ar and Ar-Ar data from the literature, along with newly-obtained data from three different volcanic fields, we have identified that the intraplate volcanism in Mongolia has been near-continuous since its onset, with hiatuses of only <6 Myr. Since 35 Ma, hiatuses have reduced to <1 My. In light of these findings, we re-evaluate the various models that have been proposed for the origins of this long-lived volcanism and suggest the cause of magmatism results from asthenospheric upwellings initiated by a delamination event in the Mesozoic, but have been prolonged by enhanced mantle flow relating to northward progression of India, the closure of Neo-Tethys, and ultimately the Indo-Asian collision. This example of intraplate magmatism is one of the longest-lived volcanic intraplate regimes on Earth that does not appear to relate to a geophysically-recognisable high heat-flux mantle plume.

Gondwanan flood basalts linked seismically to plume-induced lithosphere instability

Delamination of the continental lithospheric mantle is well recorded beneath several continents. However, the fate of the removed continental lithosphere has been rarely noted, unlike subducted slabs reasonably well imaged in the upper and mid mantle. Beneath former Gondwana, recent seismic tomographic models indicate the presence of at least 5 horizontal fast-wavespeed anomalies at ~600 km depths that do not appear to be related to slab subduction, including fast structures in locations consistent with delamination associated with the Paraná Flood Basalt event at ~134 Ma and the Deccan Traps event at ~66 Ma. These fast-wavespeed anomalies often lie above broad slow seismic wavespeed trunks at 500 to 700 km depths beneath former Gondwana, with slow wavespeed anomalies branching around them. Numerical experiments indicate that delaminated lithosphere tends to stagnate in the transition zone and mid-mantle above a mantle plume where it shapes subsequent plume upwelling. For hot plumes, the melt volume generated during plume-influenced delamination can easily reach ~2 to 4 × 106 km3, consistent with the basalt eruption volume at the Deccan Traps. This seismic and numerical evidence suggests that observed high-wavespeed mid-mantle anomalies beneath the locations of former flood basalts are delaminated fragments of former continental lithosphere, and that lithospheric delamination events in the presence of subcontinental plumes induced several of the continental flood basalts associated with the multiple breakup stages of Gondwanaland. Continued upwelling in these plumes can also have entrained subcontinental lithosphere in the mid-mantle to bring its distinctive geochemical signal to the modern mid-ocean spreading centers that surround southern and western Africa.

Petrological, geochemical and geodynamic evolution of the Wadi Al-Baroud granitoids, north Arabian-Nubian shield, Egypt

The Wadi Al-Baroud area, in Egypt's Eastern Desert, exposes Neoproterozoic rocks of the Arabian-Nubian Shield (ANS), including both syntectonic granitoids (granodiorite and tonalite) and post-collisional granites. We present field work, petrographic study, mineral compositions, and whole-rock geochemistry results from these granitoids and discuss their petrogenesis, magmatic sources, evolution, and tectonic significance. The syntectonic granitoids show subduction affinity and an anomalous steep trend of K-enrichment that suggests assimilation of a granitic component during their evolution. The post-collisional granites form two plutons, on opposite sides of Wadi Al-Baroud, named here the Ras Baroud pluton (RBP) and the Abu Hawis pluton (AHP). They intruded the syntectonic granitoids with sharp intrusive contacts. The post-collisional plutons are devoid of mafic enclaves and are cut by very few dikes. They dominantly consist of biotite monzogranite that grades into muscovite monzogranite. The latter lithology hosts Nb-Ta oxide minerals (columbite, tantalite, and wodginite) displaying a variety of textural and compositional features. The cores are primary columbite-(Mn), whereas rims are overgrown or partly replaced by tantalite-(Fe) and wodginite due to late interactions with highly fractionated residual melt. The highly-evolved AHP and RBP granites are typical of the post-collisional granitoids of the ANS, including high concentrations of rare earth elements (REE), Ta, Hf, Nb, Zr, Y, and Rb; elevated ratios of Ga/Al; and low contents of Sr, CaO, and MgO. Their geochemistry suggests that the parental magma of both plutons formed from an I-type tonalitic source rock that underwent partial melting during the thermal disturbance that followed a lithospheric delamination event during the post-collisional stage of the East African Orogeny. The variations in major oxide and trace element contents among individual samples of the AHP and the RBP cannot be explained as a liquid line of descent due to fractional crystallization; rather we interpret them as sampling variable proportions of an evolved liquid and the solid crystals in equilibrium with that liquid.

Extraordinary strength and ductility of cold-rolled 304L stainless steel at cryogenic temperature

In present work, tensile behaviors of cold-rolled 304L stainless steel were investigated at both room temperature (RT) and liquid nitrogen temperature (LNT). After cold-rolling with a thickness reduction of ∼92%, the 304L stainless steel exhibits an ultrahigh yield strength of 1787 MPa at the expense of ductility (1.06% of uniform elongation) at RT. At LNT, the yield strength (upper yield point of σyu = 2308.4 MPa and lower yield point of σyl = 1894.2 MPa) and uniform elongation (23%) increase greatly. Detailed microstructural investigation reveals that the cold-rolled 304L stainless steel comprises mainly of deformation induced martensite and high density of dislocations (9.06 ×1014m−2), leading to a lack of dislocation storage capacity and thus brittle fracture at RT. While interrupt tests at LNT reveal a first increase and then decline in dislocation density with tensile strain, accompanied with phase transformation from austenite to martensite. The delamination events also occur, characterized by the multiple separated laminated ligaments observed at fracture surface. Therefore, the high dense dislocations and transformation-induced plasticity (TRIP) effect as well as delamination toughening mechanism contributes to the excellent combination of strength and ductility at LNT. Our work provides experimental and microstructural insights into the deformation mechanisms of the ∼92%-cold-rolled 304L stainless steel during tensile deformation at RT and LNT.

Laser-induced heating, property changes, and damage modes in carbon fiber reinforced polymer matrix woven composites

Despite numerous efforts to understand mechanical damage in carbon fiber reinforced polymer matrix composites, there are minimal experimental and computational efforts that incorporate temperature effects on mechanical performance of composites. Recent studies have shown temperature changes can be readily monitored and predicted under relatively low heat fluxes. The present study augments such prior work by exploring effects of higher heat fluxes and increased heating rates. Plain-woven composites with T650 carbon fibers in a bismaleimide 5250-4 matrix were heated with a continuous wave laser (3.0 cm diameter flat-top beam profile at 1.0692 μm). Laser powers and durations were designed to reach temperatures near, and exceeding, matrix decomposition temperatures. Three duplicates of specimens were irradiated with four powers and two durations, yielding an irradiance range of 4.2 – 12.7 W/cm2. Resulting spatial and temporal temperature changes were measured with calibrated infrared cameras for both composite surfaces. Post-test surface photography and X‐ray CT scans were used to assess morphology changes and damage characteristics. Two key findings are reported herein: (i) delamination events dramatically impacted thermal transport, and (ii) TGA data and appropriate kinetic models can be used to account for temperature- / rate- dependent thermal responses and damage behaviors in the composites.

Insights in α-Al2O3 degradation in multilayer CVD coated carbide tools when turning IN718

The degradation behaviour of textured CVD α-alumina has received significant attention within academic literature with regard to steel turning. In contrast, the research performed on Ni-based superalloys is yet to be brought up to the same level of understanding. Hence, the objective of this report will be to offer insights with regard to the degradation mechanisms of the textured alumina layer of CVD Ti(C,N)/α- Al2O3 coated carbides when turning a Ni-based superalloy, and to explore the role of different wear mechanisms that contribute to cutting tool failure. Adhesive wear was observed to be the primary wear mechanism responsible for coating failure, which can result in sudden mechanically driven grain pull-out and delamination events. Grain-pull out was observed across the entire contact zone; delamination was observed to occur most frequently around the trailing edge and depth-of-cut notches, and towards the end of the contact zone as the chip separates from the tool. Evidence of characteristic plastic deformation induced ridges in the alumina coating surface were also revealed within the sliding zone, leading to gradual wear of the alumina layer. These findings demonstrate that there are both similarities and differences in alumina degradation behaviour when compared to previous studies conducted on steel turning.

Granite petrogenesis and the δ44Ca of continental crust

Stable Ca isotopes are an increasingly useful tool for understanding the sources and processes leading to the formation of magmatic rocks, yet Ca isotope fractionation during genesis of silicic continental crust is still poorly understood. Here, we present Ca, Sr, and Nd isotope, as well as major- and trace-element whole-rock geochemical data for A-, I-, and S-type granites (n = 30) from Australia/Tasmania, Canada, and France (δ44CaBSE of -0.6‰ to +0.2‰) and compare them to phase-equilibrium models for partial-melting (pelite, greywacke, MORB, enriched Archean tholeiite) and crystallization (hydrous arc basalt, A-type granite) that incorporate novel ab-initio predictions for Ca isotope fractionation in epidote and K-feldspar. The ab-initio calculations predict that epidote has similar δ44Ca to anorthite and that K-feldspar is the isotopically lightest known silicate mineral at equilibrium (Δ44Cakspar-melt of -0.4‰ at 1000 K). Our phase-equilibrium model results suggest that δ44Ca variations in all three granite types can be fully explained through magmatic processes, without necessarily requiring addition of isotopically exotic components (e.g., carbonate sediments). Heavy Ca isotope enrichments in A-type granites from the Lachlan Fold Belt, however, require isotopic disequilibrium between plagioclase and melt, which we use to constrain average plagioclase growth rates in these systems. This also serves to illustrate that whole-rock Ca isotope measurements can be used to estimate crystal growth rates, even in the absence of analyzable phenocrysts. In general, low Ca diffusivities and strong isotopic diffusivity ratios (D44/D40) in low-H2O granitic magmas should lead to resolvable isotopic disequilibrium effects in plagioclase, even at relatively slow growth rates (e.g., > 0.03 cm/yr). Combining our data with those from previous studies, we demonstrate that average granitoids and upper continental crust (with newly estimated δ44CaBSE of -0.25 ± 0.02‰, 2SE) have resolvable low δ44Ca compared to basalts and oceanic crust. Given that pressure has a major influence on Ca isotope fractionation across all of our models, this implies that melts feeding upper crustal granitoids dominantly evolve in the lower crust (10-14 kbar, through either partial-melting or fractional crystallization). This observation also suggests that heavier Ca isotopes are preferentially recycled back into the mantle through subduction and/or lower-crustal delamination events, but this is unlikely to have had a significant influence on the δ44Ca evolution of the upper mantle through geologic time.

Regional‐Scale Lithospheric Recycling on Venus Via Peel‐Back Delamination

AbstractWe currently have a limited understanding of the tectonic framework that governs Venus. Schubert and Sandwell (1995, https://doi.org/10.1006/icar.1995.1150) identified over 10,000 km of possible subduction sites at both coronae and chasmata rift zones. Previous numerical and experimental studies have shown the viability of regional‐scale lithospheric recycling via plume‐lithosphere interactions at coronae, yet little work has been done to study the possibility of resurfacing initiated at Venusian rift zones. We created 2D numerical models to test if and how regional‐scale resurfacing could be initiated at a lateral lithospheric discontinuity. We observed several instances of peel‐back delamination—a form of lithospheric recycling in which the dense lithospheric mantle decouples and peels away from the weak, initially 30 km‐thick crust, leaving behind a hot, thinned layer of crust at the surface. Delamination initiation is driven by the negative buoyancy of the lithospheric mantle and is resisted by the coupling of the plate across the Moho, the significant positive buoyancy of the crust arising from a range of crustal densities, and the viscous strength of the plate. Initial plate bending promotes yielding and weakening in the crust, which is crucial to allow decoupling of the crust and lithospheric mantle. When there is sufficient excess negative buoyancy in the lithospheric mantle, both positively and negatively buoyant plates may undergo delamination. Following a delamination event, the emplacement of hot, buoyant asthenosphere beneath the crust may have consequences for regional‐scale volcanism and local tectonic deformation on Venus within the context of the regional equilibrium resurfacing hypothesis.

Xenoliths reveal a hot Moho and thin lithosphere at the Cordillera-craton boundary of western Canada

AbstractProperties of the lithosphere control the transitions in elevation and plate deformation from hot, mobile orogenic belts to cooler, stronger cratons. The sharp, abrupt boundary of the North American Cordillera with the craton in western Canada has been suggested to be a result of recent (&amp;lt;50 Ma) heating and delamination of the lithosphere. To test this, we queried the fine structure in the thermal history of the mantle lithosphere approaching this transition using mantle xenolith thermobarometry. The xenoliths sampled by their host lava within ~20 km of the Cordillera-craton boundary require thinner lithosphere (by 20 km) and a hotter Moho (by 200 °C) compared to those sampled 180 km away. A hot, weak lithosphere at the boundary explains a topographic low that parallels this transition for a large length of the North American Cordillera, possibly from focused heat during edge convection. The cooling pattern of geothermometers applied to the xenoliths also suggests that any delamination event producing thinner lithosphere in the orogen is unlikely to have occurred in the past 50 m.y.

Chemomechanical weakening of muscovite quantified with in situ liquid nanoindentation

Chemomechanical weakening of layered phyllosilicate muscovite mica was studied as a function of chemical environment via in situ liquid-nanoindentation under four conditions (dry, deionized water, and two NaCl solutions of different pH). While traditional indentation analyses of layered materials with extreme mechanical anisotropy have been limited due to displacement bursts (pop-ins), here the bursts were used as proxies for delamination, fracture, and spalling events. Since displacement bursts during an indent represent a stochastic process, 120 indents were conducted for each condition to generate statistically significant amounts of data. In total, over 9000 bursts were assessed using a load–displacement threshold criterion, classifying this as a high-throughput nanoscale fracture technique. For each burst, initiation load, initiation displacement, plastic zone volume at initiation, and energy dissipation were analyzed. A power-law relationship between the burst load and burst energy was noted which separated the bursts into two continuous distributions: (1) bursts due only to the mechanics of the indent and (2) bursts due to both the mechanics of the indent and the environment. By using a cumulative probability distribution, it was found that the NaCl solutions decreased the minimum plastic zone volume necessary to initiate a displacement burst by an order of magnitude relative to the dry condition. Finally, the underlying mechanisms explaining the trends in initiation volume as a function of environment were discussed, with a focus on the chemomechanical degradation processes via chemical attack and cation exchange.

Damage monitoring of carbon fibre reinforced polymer composites using acoustic emission technique and deep learning

In this research work, a deep Convolutional Neural Network (CNN) was trained for image-based Acoustic Emission (AE) waveform classification. AE waveforms from different damage modes of Carbon Fibre Reinforced Polymer (CFRP) composites were used to train the CNN for online damage monitoring. Spectrograms of AE Waveforms from four different damage modes, matrix cracking, delamination, debonding, and fibre breakage, were obtained in their Mel scale and used as the training data and test data for the CNN. The overall prediction accuracy of the CNN is 97.9%, while the fibre breakage and delamination events were able to be predicted with 100% accuracy. Then this pre-trained CNN is used for online damage monitoring of mode I delamination test of CFRP specimens. AE waveforms generated during the mode I test are classified using the trained CNN and the results are analysed in terms of the classified AE descriptors. The classified AE descriptors proved to identify the occurrences of different damage modes, thereby validating the damage classification accuracy of the CNN.

Tether-guided lamellipodia enable rapid wound healing

Adhesion between animal cells and the underlying extracellular matrix is challenged during wounding, cell division, and a variety of pathological processes. How cells recover adhesion in the immediate aftermath of detachment from the extracellular matrix remains incompletely understood, due in part to technical limitations. Here, we used acute chemical and mechanical perturbations to examine how epithelial cells respond to partial delamination events. In both cases, we found that cells extended lamellipodia to establish readhesion within seconds of detachment. These lamellipodia were guided by sparse membrane tethers whose tips remained attached to their original points of adhesion, yielding lamellipodia that appear to be qualitatively distinct from those observed during cell migration. In vivo measurements in the context of a zebrafish wound assay showed a similar behavior, in which membrane tethers guided rapidly extending lamellipodia. In the case of mechanical wounding events, cells selectively extended tether-guided lamellipodia in the direction opposite of the pulling force, resulting in the rapid reestablishment of contact with the substrate. We suggest that membrane tether-guided lamellipodial respreading may represent a general mechanism to reestablish tissue integrity in the face of acute disruption.

Testing models of Laramide orogenic initiation by investigation of Late Cretaceous magmatic-tectonic evolution of the central Mojave sector of the California arc

Abstract The Mojave Desert region is in a critical position for assessing models of Laramide orogenesis, which is hypothesized to have initiated as one or more seamounts subducted beneath the Cretaceous continental margin. Geochronological and geochemical characteristics of Late Cretaceous magmatic products provide the opportunity to test the validity of Laramide orogenic models. Laramide-aged plutons are exposed along a transect across the Cordilleran Mesozoic magmatic system from Joshua Tree National Park in the Eastern Transverse Ranges eastward into the central Mojave Desert. A transect at latitude ∼33.5°N to 34.5°N includes: (1) the large upper-crustal Late Cretaceous Cadiz Valley batholith, (2) a thick section of Proterozoic to Jurassic host rocks, (3) Late Cretaceous stock to pluton-sized bodies at mesozonal depths, and (4) a Jurassic to Late Cretaceous midcrustal sheeted complex emplaced at ∼20 km depth that transitions into a migmatite complex truncated along the San Andreas fault. This magmatic section is structurally correlative with the Big Bear Lake intrusive suite in the San Bernardino Mountains and similar sheeted rocks recovered in the Cajon Pass Deep Scientific Drillhole. Zircon U-Pb geochronology of 12 samples via secondary ionization mass spectrometry (SIMS) (six from the Cadiz Valley batholith and six from the Cajon Pass Deep Scientific Drillhole) indicates that all Cretaceous igneous units investigated were intruded between 83 and 74 Ma, and Cajon Pass samples include a Jurassic age component. A compilation of new and published SIMS geochronological data demonstrates that voluminous magmatism in the Eastern Transverse Ranges and central Mojave Desert was continuous throughout the period suggested for the intersection and flat-slab subduction of the Shatsky Rise conjugate deep into the interior of western North America. Whole-rock major-element, trace-element, and isotope geochemistry data from samples from a suite of 106 igneous rocks represent the breadth of Late Cretaceous units in the transect. Geochemistry indicates an origin in a subduction environment and intrusion into a crust thick enough to generate residual garnet. The lack of significant deflections of compositional characteristics and isotopic ratios in igneous products through space and time argues against a delamination event prior to 74 Ma. We argue that Late Cretaceous plutonism from the Eastern Transverse Ranges to the central Mojave Desert represents subduction zone arc magmatism that persisted until ca. 74 Ma. This interpretation is inconsistent with the proposed timing of the docking of the Shatsky Rise conjugate with the margin of western North America, particularly models in which the leading edge of the Shatsky Rise was beneath Wyoming at 74 Ma. Alternatively, the timing of cessation of plutonism precedes the timing of the passage of the Hess Rise conjugate beneath western North America at ca. 70–65 Ma. The presence, geochemical composition, and age of arc products in the Eastern Transverse Ranges and central Mojave Desert region must be accounted for in any tectonic model of the transition from Sevier to Laramide orogenesis.

Sensing delamination in composites reinforced by ferromagnetic Z-pins via electromagnetic induction

This paper investigates a novel technique for sensing delamination in through-thickness reinforced composites based on electromagnetic induction. This sensing technique features ferromagnetic Z-pins and a pair of coils attached to a laminate; the first coil creates a magnetic field that is intensified by the ferromagnetic pins, whilst the second coil detects the magnetic flux change that is caused by the pin motion relative to the coil pair when delamination happens. This approach avoids potential interferences due to contact electrical resistances that exist in electrical-based sensing approaches. The viability of this sensing technique is demonstrated by monotonic and cyclic bridging tests, involving Nickel/Iron alloy Z-pins embedded in E-glass/913 laminates under controlled delamination. A simplified electromagnetic finite element analysis is presented to help interpret the experimental results. The sensitivity of the magnetic-based sensing technique increases with loading rate. Both mode I and mode II delamination events can be detected by a voltage signal from the sensing coil, albeit there exists an initial “blind spot” at low loading rates. This sensing technique also allows monitoring the pin bridging status, e.g. the switch of pin pull-out side, without modifications to the architecture of a Z-pinned composite regarding expected mechanical response.

Dynamic instability zone analysis of laminated piezoelectric cylindrical shell with delamination under hygrothermal effects

To use effectively the shell in high-performance applications, analyzing the effect of hygrothermal effects on a piezoelectric delamination event is necessary. A laminated piezoelectric cylindrical shell with delamination is first established under hygrothermal effects, followed by an internal force analysis and an energy analysis of the shell. Then, a parametric vibration equation of the Mathieu for the shell is obtained by using the energy variation of the Rayleigh-Ritz method; later on, the harmonic balance method is employed to solve this equation. Finally, the effects of delamination parameters, geometric parameters, hygrothermal effects, and piezoelectric materials on the shell under uniformly distributed axial load are discussed.

Interplay between cracking and delamination in incrementally deposited plasma sprayed coatings

Cracking and delamination in constrained films and coatings during fabrication and service has been an important subject of scientific inquiry for several decades. Considerable past efforts have focused on developing analytical models based predicting steady state energy release rates to determine the occurrence of either cracking and/or delamination in thin films. Such models have been reconciled into a ‘Design Map’. However, the extent of available experimental validation of such Design Maps is limited. In addition, these analytical Design Maps lack the description of nuances in the processing of layered films such as progressive incremental deposition.In this study, the interplay between cracking and delamination in progressively deposited plasma sprayed coatings is defined based on the aforementioned models. Following the adaptation of the models and presiding assumptions, a carefully designed set of experiments to probe responses from different ceramics and process conditions have been conducted, which allowed the controlled observation of cracking and/or delamination events. These experiments elucidated the underlying conditions that determine the onset of such stress relaxation events. The experimental data is reconciled with an adapted analytical Design Map for single, isolated, rapidly solidified droplets (splats) and for incrementally deposited thick plasma sprayed coatings, thus providing a framework for the robust design and processing of advanced coatings.

Quantifying adherence of oxide scales on steels exposed to high temperature and pressure steam

AbstractOxide scale exfoliation is a major concern in fossil fuel power generation because it can cause tube blockages and erode valves and steam turbine components downstream. There is still considerable scientific and commercial interest to improve the mechanistic understanding of oxide failures by developing models to predict exfoliation and the extent of tube blockage as a function of operating conditions and component geometries. Tensile testing inside a scanning electron microscope was conducted on ferritic–martensitic and austenitic steel specimens with the steam side (Fe,Cr)‐rich oxides grown after exposures for up to 1000 h in steam with ~100 ppb O2 at 276 bar and 550°C. Multiple oxide layer cracks and delamination events were observed and analyzed in detail during the tests. Results from the testing agreed well with earlier observations that had identified the failure location at the outer–inner oxide layer for all tested materials. Calculated adhesion energies identified the outer–inner oxide interface of alloy 347HFG as the weakest interface.