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Polymeric hydrogels can undergo dramatic shape and volumetric change when immersed into an appropriate solvent due to swelling or shrinking. Experimental studies have observed a variety of instability patterns in hydrogels. The telephone cord blister (TCB) with large deformability is one intriguing instability pattern but the assessment of its global morphology parameters, that is, the wavelength and transverse amplitude are still of inadequate appreciation. The present paper considers swelling-induced TCBs in a hydrogel-based film on a rigid substrate. Based on a previously developed theoretical framework for TCBs under small deformation, typically in a hard thin film, the theoretical derivations for the two global morphological parameters are furthermore developed for TCBs under large deformation in a soft thin film. Predictions for the morphology parameters of the developed theory agree very well with extensive experimental results. The critical mechanical conditions associated with the material-specific parameters such as the cross-linking density and swelling ratio are revealed. In addition, by reversing the calculation, the swelling-induced compressive stress in the un-delaminated film and the interfacial adhesion toughness are also accurately determined from measurements of the hydrogel TCBs. The present work provides an insight to design the microfluidics by controlling the morphology parameters with high precision.

Martensitic steels strengthened by Boron and Nitrogen additions (MarBN) were developed for high temperature/high stress service in power plant for periods of many years and are being considered as a promising candidate for the replacement of the more conventional Grade 91/92 steels. In the present study, extensive microstructural observation of physically simulated Heat Affected Zone (HAZ) MarBN material has been carried out after dilatometry simulations to link the variation in microstructure with weld thermal cycles. The microstructure in the MarBN HAZ has been observed to vary from a refined equiaxed morphology to a duplex microstructure consisting of refined grains distributed on the pre-existing Prior Austenite Grain Boundaries (PAGBs) as the peak temperature of the weld thermal cycle decreases. The temperature range corresponding to the formation of the duplex grain structure coincides with the temperature regime for the dissolution of the pre-existing M23C6 carbides. An even distribution of the M23C6 carbides within the martensitic substructure was also observed after Post Weld Heat Treatment (PWHT), which is beneficial for the creep performance of the weld HAZ. The MX precipitates are more resistant to thermal exposure and are not completely dissolved until the peak temperature reaches 1573 K (1300 °C). The Nb-rich MX precipitates are the predominant type observed both after weld simulations and PWHT. The hardness between the materials experienced with the thermal cycles with different peak temperature does not significantly vary after PWHT conducted in an appropriate condition, which is likely to mitigate an unfavoured stress condition in the localised area within the HAZ.

A model has been developed to predict the interdiffusion behaviour of elements between a substrate and a coating. This model, however, relies on knowing accurate diffusion coefficients. However, only limited diffusion data are available in the literature. Recently, it has been demonstrated that Density Functional Theory (DFT) can be used to calculate relevant diffusion coefficients with reasonable accuracy. According to the vacancy diffusion mechanism , diffusion coefficient has an Arrhenius form. The diffusion activation energy can be written as a sum of the diffusion energy barrier and the vacancy formation energy adjacent to a solute.

Meaningful characterization of the microstructure in metallurgically complex steels is complicated by the diversity of thermal cycles experienced by multipass fusion welds. To overcome the problems of relevant documentation, it is necessary to balance information from macro-, micro-, and nano-evaluation with appropriate analysis. This paper presents details regarding recommended approaches that optimize this characterization. Initially, specific procedures relevant to macroanalysis, including hardness mapping and calculation of the peak temperature through the width of the heat-affected zone (HAZ), are described. Then, assessment of the distribution of creep damage in feature-type, cross-weld creep tests using laser microscopy is detailed. Using these methods, the extent of damage through the HAZ was compared to the local reduction in the HAZ hardness and to the calculated peak temperatures in the HAZ. The implications of these findings are discussed with respect to damage, deformation, and sample geometry.

Bronchiectasis is reported to be more frequent in females. There have been no large studies examining the impact of biological sex on disease characteristics, aetiology, severity, quality of life or management. Patients were prospectively enrolled from 2015 -2018 in 3 linked bronchiectasis registries in Australia, Europe and India. Disease information was collected, including quality of life (QoL-B). Analyses were conducted cross-sectionally using baseline data. 13859 patients were included from 29 countries. 57.6% were female. The highest proportion of females were in Australia (70.9%) and lowest in India (43.1%). Male sex was associated with bronchiectasis caused by COPD and TB; while female sex was associated with post-infectious bronchiectasis, asthma, connective tissue disease and NTM. Men had more severe disease as measured by the bronchiectasis severity index, but females more likely to be infected with Pseudomonas aeruginosa. Women had greater disease impact across multiple QoL-B domains including social, emotional and treatment burden domains. Cough and sputum purulence were more severe in women while men most frequently complained of wheeze and breathlessness. Men were significantly less likely to receive evidence based interventions including testing for immunodeficiency and ABPA, long term antibiotic treatment for frequent exacerbators, pulmonary rehabilitation and airway clearance techniques. Conclusion: There are striking sex differences in aetiology, severity, quality of life and treatment in patients with bronchiectasis

Introduction: Pulmonary rehabilitation is recommended for people with bronchiectasis, but the content for an educational program is not directed towards people with this condition. The goal of the qualitative study was to identify the educational needs of people with bronchiectasis in a pulmonary rehabilitation setting. Methods: A qualitative study of people with bronchiectasis, registered on the Australian Bronchiectasis Registry using individual semi-structured interviews was undertaken. Transcripts were coded independently by two investigators and themes developed through consensus. Results: A total of 21 people with bronchiectasis (mean age 72±11 years, FEV1 83.1±25.4% predicted) participated in an interview. Participants indicated they have a good understanding of their condition, which factors may increase risk of an acute exacerbation, their medications and that physiotherapy is an important part of treatment. Major themes for which further education was sought were the scope of airway clearance therapy options, methods of maintaining motivation for physiotherapy, coping strategies for psychosocial symptoms, and how to self-manage their condition. Participants perceived benefit in receiving information in a group setting. Conclusions: Unmet education needs of people with bronchiectasis include options for airway clearance therapy, development of coping strategies to manage the psychosocial challenges of the condition and self-management. This may provide a foundation for the development of structured education sessions that could be delivered within pulmonary rehabilitation for this population.

Mechanical models are developed to determine the mode I and II adhesion toughness of monolayer thin films using circular blister tests under the pressure load. The interface fracture of monolayer thin film blisters is mode I dominant for linear bending with small deflection while it is mode II dominant for membrane stretching with large deflection. By taking the advantage of the large mode mixity difference between these two limiting cases, the mode I and II adhesion toughness are determined in conjunction with a linear failure criterion. Thin films under membrane stretching have larger adhesion toughness than thicker films under bending. Experimental results demonstrate the validity of the method.

The microstructure in the heat-affected zone (HAZ) of multipass welds typical of those used in power plants and made from 9 wt pct chromium martensitic Grade 92 steel is complex. Therefore, there is a need for systematic microstructural investigations to define the different regions of the microstructure across the HAZ of Grade 92 steel welds manufactured using the traditional arc welding processes in order to understand possible failure mechanisms after long-term service. In this study, the microstructure in the HAZ of an as-fabricated two-pass bead-on-plate weld on a parent metal of Grade 92 steel has been systematically investigated and compared to a complex, multipass thick section weldment using an extensive range of electron and ion-microscopy-based techniques. A dilatometer has been used to apply controlled thermal cycles to simulate the microstructures in distinctly different regions in a multipass HAZ using sequential thermal cycles. A wide range of microstructural properties in the simulated materials were characterized and compared with the experimental observations from the weld HAZ. It has been found that the microstructure in the HAZ can be categorized by a combination of sequential thermal cycles experienced by the different zones within the complex weld metal, using the terminology developed for these regions based on a simpler, single-pass bead-on-plate weld, categorized as complete transformation, partial transformation, and overtempered.

9Cr–1Mo steels have been used extensively in the power generation industry. In this study, a wide range of experimental samples exposed at different times and temperatures in a CO2 environment were...

The microstructure in the heat-affected zone (HAZ) of welds made from the 9 wt pct chromium martensitic Grade 92 steel is complex and has not yet been completely understood. There is a lack of systematic microstructural investigations to define the different regions of the microstructure across the HAZ of Grade 92 steel welds as a function of the welding process. In this study, the microstructure in the HAZ of an as-fabricated single-pass bead-on-plate weld on a parent metal of Grade 92 steel was systematically investigated by using an extensive range of electron and ion-microscopy-based techniques. A dilatometer was used to apply controlled thermal cycles to simulate the microstructures in the different regions of the HAZ. A wide range of microstructural properties in the simulated materials were then characterized and compared with the experimental observations from the weld HAZ. It was found that the microstructure in the HAZ of a single-pass Grade 92 steel weld can be categorized as a function of a decreasing peak temperature reached as (1) the completely transformed (CT) region, in which the original matrix is completely reaustenitized with complete dissolution of the pre-existing secondary precipitate particles; (2) the partially transformed (PT) region, where the original matrix is partially reaustenitized along with a partial dissolution of the secondary precipitate particles from the original matrix; and (3) the overtempered (OT) region, where the pre-existing precipitate particles coarsen. The PT region is considered to be the susceptible area for damage in the commonly reported HAZ failures in weldments constructed from these types of steels.

The short fatigue crack growth behaviour in a model cast aluminium piston alloy has been investigated. This has been achieved using a combination of fatigue crack replication methods at various intervals during fatigue testing and post-mortem analysis of crack profiles. Crack–microstructure interactions have been clearly delineated using a combination of optical microscopy, scanning electron microscopy and electron backscatter diffraction. Results show that intermetallic particles play a significant role in determining the crack path and growth rate of short fatigue cracks. It is observed that the growth of short cracks is often retarded or even arrested at intermetallic particles and grain boundaries. Crack deflection at intermetallics and grain boundaries is also frequently observed. These results have been compared with the long crack growth behaviour of the alloy.

Circular blisters and telephone cord blisters (TCBs) can spontaneously occur in thin films under constant bi-axial compressive residual stress. In this work, new mechanical models are used in conjunction with measurements of blister morphology parameters to determine the residual stress in films and the adhesion toughness at interfaces. These new models are based on the hypothesis that pockets of energy concentration (PECs) drive the nucleation and growth of blisters instead of buckling, as in the conventional models, since the thin films are under constant compressive residual stress. Predictions from the models are in excellent agreement with independent experimental data.

Telephone cord blisters (TCBs) are frequently observed in film/substrate material systems. They nucleate and propagate forward with wavy boundaries between the film and the substrate. The current study views the problem from a completely new angle: It is discovered that the spontaneous formation and morphology of TCBs in thin films under biaxial compressive residual stresses can be accurately explained and determined by assuming the existence of a pocket of energy concentration (PEC) instead of the existence of a separation of critical size. For the first time, completely-analytical formulae—the ‘Ω formulae’—are derived for the two local morphology parameters of TCBs of any shape, that is, width and height, and for the two global morphology parameters of TCBs of sinusoidal shape, that is, the wavelength and transverse amplitude. Mechanical conditions are also given for the first time for the formation of TCBs. Predictions for the four morphology parameters of the developed theory agree very well with extensive experimental results. In addition, by reversing the calculation, the residual stress and the film/substrate interface fracture toughness are also accurately determined from measurements of the TCB morphology parameters.

The microstructure in the heat affected zone of the multi-pass welds constructed using the 9% Cr tempered martensitic steels is complex and susceptible to premature creep failure. In the present research, a systematic investigation has been conducted after long-term creep exposure in the heat affected zone of a multi-pass weld on the 9% Cr Grade 92 steel to identify the sub-optimal microstructures with a high susceptibility to creep cavitation. The characterisation techniques employed include hardness mapping and a range of electron-based microscopy methods. The results provide quantitative data for microstructure and creep cavities. In this case, preferential creep cavitation has been confirmed in the regions within the heat affected zone that possesses a microstructure with an inhomogeneous distribution of the M23C6 carbides and a refined martensitic grain structure. Creep cavities have been observed on the secondary phase particles including the Al2O3, the MnS and the BN phases. The observations from the current research confirm that creep cavitation preferentially occurs in the partially-transformed zones that were subjected to thermal cycles associated with peak temperatures between the Ac1 and the Ac3 transus temperatures during weld fabrication.

An excessive concentration of boron in the 9% Cr tempered martensitic steels alloyed with nitrogen has a detrimental effect on creep performance, as relatively large boron nitride phases are formed and can act as the preferred sites for cavity nucleation. In the current research, a systematic investigation has been performed documenting details of creep damage in the heat affected zone of a weld joint constructed by using a 9% Cr Grade 92 steel. A combination of correlative characterisation techniques has been applied to monitor and quantify the evolution of creep damage within the heat affected zone through the entire creep life. The utilisation of cryo-fractography, two-dimensional electron-based microscopic characterisation and three-dimensional tomography based on focused ion beam microscopy have confirmed the close association between creep cavities and boron nitride phases from the initial stage of creep. It is revealed that the thermal transients imposed during welding result in the decohesion at the interface of boron nitrides with the surrounding matrix. This decohesion is a result of significant thermo-mechanical mismatch between boron nitrides and the tempered martensitic matrix. The voids initiated at these locations grow and eventually link-up during creep exposure, leading to cracking and fracture.

The microstructural evolution of the Ni-based superalloy CMSX-4 including the change in gamma prime morphology, size, and distribution after high-temperature degradation and subsequent rejuvenation heat treatments has been examined using field emission gun scanning electron microscopy and transmission electron microscopy. In this paper, it is shown that there are significant differences in the size of the ‘channels’ between gamma prime particles, the degree of rafting, and the size of tertiary gamma prime particles in each of the different microstructural conditions studied. Chemical analysis has been carried out to compare rejuvenated and pre-service samples after the same subsequent degradation procedure. The results indicate that although the microstructures of pre-service and rejuvenated samples are similar, chemical differences are more pronounced in the rejuvenated samples, suggesting that chemical segregation from partitioning of the elements was not completely eliminated through the applied rejuvenation heat treatment. A number of modified rejuvenation heat treatment trials were carried out to reduce the chemical segregation prior to creep testing. The creep test results suggest that chemical segregation has an immeasurable influence on the short-term mechanical properties under the test conditions used here, indicating that further work is required to fully understand the suitability of specific rejuvenation heat treatments and their role in the extension of component life in power plant applications.

Nb is a very important micro-alloying element in low-carbon steels, for grain size refinement and precipitation strengthening, and even a low content of Nb can result in a significant effect on phase transformation kinetics from austenite to ferrite. Solute Nb atoms and Nb precipitates may have different effects on transformation behaviors, and these effects have not yet been fully characterized. This paper examines in detail the effects of solute Nb atoms and Nb precipitates on isothermal transformation kinetics from austenite to ferrite. The mechanisms of the effects have been analyzed using various microscopy techniques. Many solute Nb atoms were found to be segregated at the austenite/ferrite interface and apply a solute drag effect. It has been found that solute Nb atoms have a retardation effect on ferrite nucleation rate and ferrite grain growth rate. The particle pinning effect caused by Nb precipitates is much weaker than the solute drag effect.

In order to quantify precipitates such as Laves phase, M23C6 carbides and modified Z-phase in 9–12 wt% Cr power plant steels, a range of microscopy techniques, including scanning electron microscope (SEM) and focussed ion beam (FIB) imaging, are currently used. This paper's key finding reports on the novel application of a field emission SEM (FESEM) in-column upper secondary electron detector (USD) for imaging and quantification of precipitates in a thermally aged 11–12 wt% Cr steel sample. The USD produces images from first order secondary electrons generated directly from primary electron beam interaction. These images were found to not only show significant contrast between the matrix and the precipitates to enable quantification, but between particles which otherwise have identical greyscale intensities in FIB images. Previously assumed to be the same phase, some of these precipitates appeared significantly darker than others. The greyscale differential between these precipitate types was sufficient for separate quantification. Energy dispersive x-ray spectroscopy and selected area diffraction analysis identified the darker particles as modified Z-phase and the lighter grey particles as M23C6 carbides. When analysing all particles together, comparison of data from FESEM USD and FIB images confirmed that both techniques produce statistically comparable precipitate analysis results. However, as modified Z-phase and M23C6 carbide distributions can be analysed separately from a FESEM in-column USD image at low accelerating voltages, it was found that this technique provides for more reliable precipitate quantification than FIB imaging alone in these steels. With future work, this could enable faster characterisation and may lead to automated larger area mapping.

By combining modelling and experimental work, new insights have been gained into the combined oxidation/carburisation of 9Cr-1Mo steels in CO2 rich environments. The breakaway-oxidation process is preceded by the rejection of carbon into the scale due to the poor solubility of carbon in the metal. Experimental TEM work reveals the formation of a carbide rich layer near the substrate surface which forms a further barrier against carbon ingress. The eventual oxidation of this layer could contribute to breakaway oxidation. A 2D finite-difference based diffusion model developed in combination with Thermo-Calc software underlines the role of specimen geometry on breakaway initiation.

Multilayer thermal barrier coating (TBC) systems typically consist of three layers of materials: A thermal barrier top coat (TC), a thermally-grown oxide (TGO), and a bond coat (BC) in addition to the substrate. Local strain energy concentrations, called ‘pockets of energy concentration (PECs)’ in this work, often occur around the interface between the TGO and the BC. They have various causes, including local phase changes, and non-uniform creep and plastic relaxation. It is discovered that both PECs and buckling drive the spallation of a TBC in a new spallation mechanism. A PEC-based mechanical model is developed that describes, explains and predicts how blisters nucleate in a TBC under constant biaxial compressive residual stress, steadily and then unsteadily grow, and finally spall off. Two conditions are established for the occurrence of TBC spallation, which depend on the compressive residual strain energy density in the TC and the TGO, and the interface fracture toughness. Experimental validation of the model was performed using aircraft jet engine turbine blades with electron beam physical vapor deposition (EBPVD) TBCs. The predictions from the developed PEC-based mechanical model for the radii of spallation in the TBC are in a good agreement with experiment results.

This is a pre-copyedited version of a contribution published in Gdoutos E. (eds) Proceedings of the First International Conference on Theoretical, Applied and Experimental Mechanics. ICTAEM 2018 published by Springer The definitive authenticated version is available online via https://doi.org/10.1007/978-3-319-91989-8_38

Grade 91 steel has been widely utilized in power plants over the last 20 years. Its specification for worldwide power plant construction has dramatically increased since the acceptance of Code Case 1943 for this material in 1983. Recent evaluation of a combination of ex-service Grade 91 steel components and virgin material has provided a unique opportunity to independently assess the performance of a combination of base metals and weldments. This approach has been grounded in the fundamental objective of identifying and quantifying metallurgical risk factors in 9%Cr creep strength enhanced ferritic (CSEF) steels and in Grade 91 steel in particular. Identification of metallurgical risk factors is essential in the integration of a meaningful life management strategy for complex 9%Cr CSEF steels. In particular, there is a need to link the damage developed either in-service or through well-controlled testing to features in the material. These features may include, but not be limited to, carbonitride precipitates (and distribution of these phases along grain boundaries, e.g. M23C6 and MX-type), inclusions developed as a consequence of the steel making process (such as MnS, Al-rich or complex Ca-modified) and intermetallic phases which evolve in-service (Laves or Z-phase) or through product forming (AlN or BN). Identification and linking of these particles to damage is considered a critical need for widely used 9%Cr CSEF steels as Grade 91 steel can show widely variable behavior with respect to creep ductility whilst Grade 92 shows a marked and consistent trend to low creep ductility. In this study, the evaluation of damage is detailed for an ex-service Grade 91 steel heat which exhibited a marked susceptibility to the evolution of in-service damage. This evaluation focuses on the evolution of HAZ damage under well-controlled, uniaxial creep test conditions using feature, cross-weld creep tests. For interrupted and failed samples, evaluation of damage was performed using state-of-the-art scanning electron microscopy (SEM) based techniques. Particular emphasis was made to link the post-test condition with the as-fabricated weldment and the parent material condition. It will be shown that there is a significant population of cavities associated with second phase particles, and particularly inclusions and intermetallic phases resulting from steel making and product manufacturing processes.

Functionally graded, multi-layered coatings are designed to provide corrosion protection over a range of operating conditions typically found in industrial gas turbines. A model incorporating diffusion, equilibrium thermodynamics and oxidation has been developed to simulate the microstructural evolution within a multi-layered coating system. The phase and concentration profiles predicted by the model have been compared with an experimental multi-layered system containing an Al-rich outer layer, a Cr-enriched middle layer and an MCrAlY-type inner layer deposited on a superalloy substrate. The concentration distribution and many microstructural features observed experimentally can be predicted by the model. The model is expected to be useful for assessing the microstructural evolution of multilayer coated systems which can be potentially used on industrial gas turbine aerofoils.

The gamma prime (γ′) distribution in the Ni based superalloy, CMSX-4, has been examined in detail using a field emission gun scanning electron microscope and a transmission electron microscope after high temperature degradation and the subsequent application of a number of rejuvenation heat treatments. The observed microstructures have been studied in order to explain the observed mechanical properties of the material and also to assess the effectiveness of the heat treatment procedures and their effect on the subsequent mechanical performance. It is shown that there are significant differences in the rafting behaviour and the size of the channels between the γ′ particles and the size of the tertiary γ′ particles in each of the different microstructural conditions. The aim of this research is to provide greater understanding of the suitability of rejuvenation heat treatments and their role in the extension of component life in power plant applications.

B and N can be used to increase the creep strength of advanced 9Cr power plant steels by means of microstructural stabilization and precipitation strengthening; however, the formation of boron nitride (BN) particles removes B and N from solution and reduces the strengthening effect of B and N simultaneously. In the current study, the BN precipitation/dissolution conditions in 9Cr-3W-3Co-V-Nb steels have been investigated to understand how to prevent the formation of BN. A series of austenitizing heat treatments have been designed using thermodynamic predictions as a guide in an attempt to dissolve the BN present after the production of 9Cr-3W-3Co-V-Nb type steels and to prevent also the precipitation of BN during the subsequent heat treatments. Advanced electron microscopy has been carried out to investigate the evolution of the BN particles in relation to the austenitization temperature. Energy Dispersive X-ray spectroscopy (EDS) has been used to identify the B-containing phases, and a method has been developed using secondary electron images to quantify the amount of BN present within the microstructure. It has been found that BN solubility is sensitive to the B and N levels in the steel composition, as indicated by thermodynamic calculations. However, it is proposed that austenitizing heat treatments at temperatures ranging from 1448 K to 1473 K (from 1175 °C to 1200 °C) with durations from 1 to 7 hours can effectively prevent the precipitation of BN as well as dissolving most of the BN particles formed during initial steel manufacture.

The nickel based alloys IN617 and IN625 that have been selected for their candidacy in the construction of the hottest regions of the supercritical steam cycle have been oxidised under isothermal conditions at 750 °C and atmospheric pressure in atmospheres of 100 % steam, 50/50 % steam/argon and air for up to 4,200 h. Both alloys developed a thin protective oxide under each condition. Scale thickness measurements using SEM micrographs were performed and showed that exposures in steam exhibited a higher rate of scale formation than exposures in air in both alloys. IN617 developed an extensive internal network of alumina which resulted in the formation of alloy protrusions into the scale altering scale growth kinetics, IN625 also formed alumina to a lesser extent. Voids formed in the matrix below the scale in both alloys in each environment. The extent of alumina formation alters the void morphology which eventually impacts the scale growth rate as inward scale growth occurred into the voids in IN625 but not in IN617.

The microstructural evolution of IN617 subjected to oxidising atmospheres of 100% steam, 50% steamyargon and air in the temperature range 700 – 750°C for exposures times up to 4000 h at atmospheric pressure has been investigated using a range of analytical electron microscopy techniques. It has been found that for this alloy the presence of steam in the atmosphere has an effect on the oxidation kinetics, and influences the nature of the scale. It has also been shown that there are differences in the volume and nature of voids formed, and that the voids are often associated with an internal structure of alumina. Significant internal oxidation was observed, particularly in the presence of steam, and a 3D reconstruction of the microstructure using FIBSEM techniques showed that this comprised interconnected alumina plates that followed the grain boundaries into the substrate.

Multiple three-dimensional reconstructions of a γ/γ′ phase structure in Alloy 720Li have been carried out by employing a serial milling technique with simultaneous electron backscatter diffraction (EBSD) and energy dispersive x-ray (EDX) analysis data collection. Combining EBSD data with EDX is critical in obtaining maps to distinguish between the chemically differing, but crystallographically similar γ and γ′ phases present in the alloy studied. EDX is shown to allow the differentiation of γ and γ′ phases, with EBSD providing increased grain shape accuracy. The combination of data sources also allowed identification of coherent γ/γ′ phase interfaces that would not be identified using solely EBSD or EDX. The study identifies a region of grain banding within the alloy, which provides the basis for a three-dimensional comparison and discussion of γ′ phase size between coarse and fine grain regions, whilst also identifying coherent γ′ phase interfaces, possible only using both EDX and EBSD systems simultaneously. The majority of the γ′ phase lies in the range of 1–10 μm in non-banded regions, with a detectable particle size limit of 500 nm being established. The validity of the reconstruction has been demonstrated using an electron interaction volumes model, and an assessment of the validity of EBSD and EDX data sources is discussed showing γ′ phase connectivity in all dimensions.

In this paper, an in-depth study of steam oxidation of two 9Cr ferritic-martensitic steels (P91 and P92), for advanced power plant, has been carried out. The steels investigated were exposed to a 100% flowing steam environment at 650°C for 1,000 – 3,000 hours. Metallographic analysis showed a multilayered scale was formed on both substrates consisting of an outer Fe-rich phase and inner Fe – Cr spinel, of varying oxide stoichiometry, as well as Cr –Mn-rich bands. The results of scale thickness measurements showed that the oxide formed on the P92 steel was thicker compared to that on the P91 steel. Crystallographic analysis showed that the P91 steel exhibited a martensite to ferrite transformation adjacent to scale – substrate interface which was not observed on the P92 steel. The outer oxide layer on both substrates exhibited a region of equiaxed grains followed by a region of columnar crystal growth. However, on the P91 steel the longer exposure time (3,000 hours) resulted in the outer layer havi...

A multicomponent, one-dimensional diffusion model that was developed for simulating microstructure evolution in coated gas turbine blade systems has been used to compare the phase structures of three MCrAlY coated superalloy systems. The model is based on finite differences and incorporates oxidation and equilibrium thermodynamic computations. The superalloy substrates considered were the nickel-based superalloy CMSX-4, a high-Cr single-crystal superalloy, and a cobalt-based MAR-M509, and these were all coated with an MCrAlY bond coat of similar composition. The results predicted by the model have been compared with similar experimental systems. The model can predict many features observed experimentally and therefore can be expected to be a useful tool in lifetime prediction and microstructural assessment of turbine blade systems based on superalloys. The work also highlighted the fact that for a given coating, the phase evolution within system is dependent on the substrate material.

An electron backscatter diffraction (EBSD)-based tool is described to assess the depth of strain-hardening effects of shot-peening treatments applied to the Ni-based superalloy, Udimet© alloy 720Li. The method consists of a statistical analysis of a number of data points from each grain scanned based on the grain orientation spread and their relative position from the shot-peened edge. The output is a quantitative measure of the depth of strain-hardening effects. The tool is used at various shot-peening intensities to demonstrate the ability to distinguish between these changes, using a range of intensities from 4 to 10 Almen. An increase in shot-peening intensity is observed to increase the depth of strain-hardening effects in the alloy. A comparison with residual stress measurements using X-ray diffraction for the same material shows that the strain-hardened depth determined by EBSD extends to approximately half the distance of the residual stress present due to shot peening. A comparison is also made with predicted profiles from the PeenstressSM model and subsequent microhardness testing. A positive correlation is observed between strained hardened depth and surface roughness of the peened samples. In each case, the increases in surface roughness and strain-hardened depth diminish toward the upper end of the shot-peening intensity range studied for this alloy.

The coefficients of thermal expansion of intermetallic phases in multicomponent Al–Si casting alloys were measured by high temperature X-ray diffraction. The measured coefficient of thermal expansion (CTE) values ranged from 10 to 23 ppm/°C for the intermetallic phases. The large thermal expansion mismatch between the Al matrix and the Si particles resulted in cracks being observed in all alloys after quenching. The lattice parameters generally changed linearly with increasing temperature for all phases apart from the monoclinic Al 9 FeNi phase, along the a- and c-axes, which also demonstrated anisotropic behaviour and microcracking. The α-AlFeMnSi particle cracking is mainly dominated by its intrinsic brittleness and is not due to large thermal expansion misfit. No cracks were observed in Al 2 Cu particles due to a combined effect of reduced brittleness and a small thermal misfit.

Multi-component Al–Si alloys are important for the engineering applications such as automotive pistons. The presence of additional elements in the Al–Si alloy system allows many complex intermetallic phases to form. The mechanical properties of different intermetallic phases have been investigated as a function of temperature using hot-stage nanoindentation. In particular, the hardness and modulus of a number of phases have been established for a range of alloy compositions. In this study, the results show that both hardness and reduced modulus increase as the Ni ratio (Ni/(Ni + Cu)) of the AlCuNi phases increases (Al3Ni2 > Al7Cu4Ni > Al2Cu) up to 350 °C. The creep effect of the intermetallic phases has also been investigated with a heating stage and indicated that the hardness strongly depends on the creep rate of the phase, particularly in the Al2Cu phase. The Ni containing phases (Al3Ni2 and Al7Cu4Ni) have a good high temperature stability up to 200 °C; however, they drop significantly at 350 °C due to the fact that the frequent jumps of Cu and Ni atoms cause disordered structures. The Si and α-AlFeMnSi phases have good mechanical properties up to 350 °C corresponding to their good creep resistance. Al5Cu2Mg8Si6 with a lower hardness and elastic modulus exhibits the most stable phase at elevated temperatures, which is correlated with its good creep resistance.

Multicomponent Al–Si based casting alloys are used for a variety of engineering applications, including for example, piston alloys. Properties include good castability, high strength, light weight, good wear resistance and low thermal expansion. In order for such alloys to continue operation to increasingly higher temperatures, alloy element modifications are continually being made to further enhance the properties. Improved mechanical and physical properties are strongly dependent upon the morphologies, type and distribution of the second phases, which are in turn a function of alloy composition and cooling rate. The presence of additional elements in the Al–Si alloy system allows many complex intermetallic phases to form, which make characterisation non-trivial. These include, for example, CuAl2, Al3Ni2, Al7Cu4Ni, Al9FeNi and Al5Cu2Mg8Si6 phases, all of which may have some solubility for additional elements. Identification is often non-trivial due to the fact that some of the phases have either similar crystal structures or only subtle changes in their chemistries. A combination of electron backscatter diffraction (EBSD) and energy dispersive X-ray analysis (EDX) has therefore been used for the identification of the various phases. This paper will present comparisons of phase identification methodologies using EBSD alone, and in combination with chemical information, either directly or through post processing.

Setting conditions for the avoidance of in-service crack growth in aggressive corroding environments has long been a major challenge owing to the number of variables that have a significant effect on material behaviour. The fatigue behaviour of API 5L X65 pipeline steel parent material tested in a sour environment has been investigated. Fatigue crack growth rate (FCGR) tests have been performed to evaluate the influence of crack depth on crack growth rate (da/dN), over the range 2–10 mm. The results obtained showed crack growth rates for deep flaws to be a factor of 5–30 higher in the sour environment than in air, dependent on the applied stress intensity factor range (ΔK). Shallow flaws have been shown to grow up to an order of magnitude faster than deep flaws in a sour environment at the same value of ΔK. The results highlight a potential non-conservatism associated with using deep-crack data to predict the behaviour of shallow flaws. The observed behaviour is attributed to the uptake of hydrogen at specimen surfaces exposed to the sour environment.

Thermal barrier coatings (TBCs) are used to allow higher gas temperatures (and hence greater efficiencies) in power generation gas turbines and/or to lengthen blade lifetimes, by reducing the heat transfer from the combustion gases to the blade substrate materials. However, the lives of TBC coated components tend to be limited by the growth of an oxide layer between the thermally insulating top coat and the MCrAlY coated superalloy substrate; this results in stresses which can lead to spallation (flaking-off) of the top coat. The present paper gives an overview of a recent programme of modelling work undertaken to understand the development of stresses due to the growth of the oxide layer. Typical examples of the rough interface between top coat and bond coat are characterised in terms of their aspect ratios. Representative geometries are then studied using a series of 2D finite element models of the interface layer. Initial models assumed a simple parabolic growth law for the oxide layer; the mod...

The presence of additional elements in a multi-component Al–Si alloy system allows many complex intermetallic phases to form. The mechanical properties of different intermetallic phases have been investigated using nanoindentation. In particular, the hardness and modulus of a number of phases have been established for a range of alloy compositions. The results show that both hardness and reduced modulus increase as the Ni ratio of the Al–Cu–Ni phases increases. The elastic modulus can be correlated with the formation temperature of the intermetallic phases. The intermetallic phases with a high heat of formation have a strong binding between atoms and therefore, their elastic modulus is also higher.

Thermal barrier coatings provide a means of thermal insulation of gas turbine components exposed to elevated temperatures. They undergo severe microstructural changes and material degradation, which have been implemented in this work by means of a sequentially coupled microstructural mechanical calculation that made use of a self-consistent constitutive model within finite element calculations. Analyses for different temperatures and bond coat compositions were run, which reproduced the trends reported in previous research and identified the accumulation of high out-of-plane tensile stresses within the alumina layer as an additional phenomenon that could drive high temperature crack nucleation.

Nickel-based superalloys are commonly used in industrial gas turbine engines for power generation due to their ability to withstand the arduous environments. Coating systems are employed to increase the service life of components by increasing the oxidation\corrosion resistance and high temperature capabilities. MCrAlY coatings are a common coating system used, not only to protect the substrate from oxidation and corrosion but also to act as a bond coat for thermally insulating coatings. The ‘M’ in the MCrAlY coatings is generally Ni, Co or a mixture of the two, with Co being added to improve the hot corrosion resistance (in conjunction with Cr) and to make the coatings more ductile. These coatings work by forming oxides that act as protective layers against further oxidation (known as the thermally grown oxide, TGO). Alumina is most commonly formed oxide from the MCrAlY bond coat, which acts as a reservoir of elements for the oxide formation.It is necessary to understand the formation and nature ...

Steel catenary risers (SCR) are used in deepwater oil and gas developments to transfer produced fluids from the seabed to surface facilities. SCRs can be subject to fatigue loading from a variety of sources including wave and tidal motion, vortex induced vibration (VIV) and operating loads. When the produced fluids are sour (ie contain water and H2S) higher fatigue crack growth rates (FCGR) are expected, and this can have a significant effect on defect tolerance. The aim of this paper is to provide guidance on the current best practice methods for performing engineering critical assessments (ECA) on internal surface breaking defects in SCRs operating in a sour environment and subject to VIV fatigue loads. Example ECA calculations are presented for circumferential girth weld flaws, based on the failure assessment diagram (FAD) approach within the framework of BS 7910 [1]. The influence of certain key input variables is demonstrated, including the FCGR, determined from recent sour test data generated as part of this research.

Ni based superalloy systems are used in gas turbine engines for power generation because of their ability to function at high temperature and pressure in oxidative and often corrosive environments for prolonged time periods. A superalloy system is usually composed of a substrate (either conventionally cast, directionally solidified or single crystal), a coating (either overlay or diffusion) to maximise either oxidation and/or corrosion resistance and a ceramic thermal barrier coating to reduce the temperature experienced by the superalloy. Under service conditions the microstructure of the superalloy system evolves, which is often accompanied by a gradual degradation in mechanical properties of the material. It is highly desirable to be able to predict how a particular system would evolve in a given environment so that the part can be replaced before failure. In order to understand the changes that occur in systems with such microstructural complexity, advanced characterisation techniques are requ...

A multicomponent model which can simulate the microstructural evolution of a coated Ni based superalloy system has been developed. The model consists of a one-dimensional finite difference diffusion solver to calculate the component distribution, a power law based model for predicting surface oxidation and a thermodynamic calculation routine for determining the phase evolution. Apart from forecasting concentration and phase profiles after a given thermal history, the model can estimate the losses due to oxidation and the remaining life of a coating based on a concentration and/or phase fraction dependent failure criteria. The phase constitution and concentration profiles predicted by the model have been compared with an experimental NiCoCrAlY coated CMSX-4 system, aged for times up to 10 000 h between 850 and 1050°C, and many experimental features can be predicted successfully by the model. The model is expected to be useful for assessing microstructural evolution of coated turbine blade systems.

The MCrAlY bond coats (BCs) used in thermal barrier coatings (TBCs) undergo severe microstructural changes that affect their creep behaviour. One method to take into account the effect of the high-temperature degradation in the creep properties of these alloys is by means of unit cell calculations that reproduce the microstructure present in the alloy. However, this method is not suitable to be included in large-scale calculations and a self-consistent constitutive model, based on Eshelby's inclusion technique, is presented for that purpose, showing good numerical agreement. Results are compared with experimental data obtained for several MCrAlY BCs.

The mechanical properties of individually pure and intermetallic phases of typical Al–Ni–Si piston alloys are investigated at different temperatures using hot stage nanoindentation. The hardness and the indentation modulus of a number of phases are determined at room temperature, 500 K and 650 K. Both, hardness and reduced modulus drop with increasing temperature in different ratios for the various phases. Increasing Ni content in the grains improves the mechanical stability of the material at elevated temperatures in general. The indentation patterns are studied using atomic force microscopy with particular reference to the indentation depths and pile-up effects. Site-specific samples from the material surrounding the nanoindents are prepared using a focussed ion beam field emission gun for examination in the transmission electron microscope. This allows direct observation of material changes as a result of the indentation process in the different phases within the alloy system. Corresponding linked atomistic finite element calculations have been carried out for Si and Ni–Al systems as a function of increasing Ni content at various temperatures. The results show only a small difference in the mechanical behaviour of Si between 300 K and 650 K as observed in the experiments. Large differences for Al at both temperatures studied result in an increase of plasticity with rising temperature and atomic motion that changes from slip in well-defined planes to a viscous fluid-like behaviour. The formation of dislocations and slip bands during indentation for the Ni–Al systems is studied.

A novel computational interface between a thermodynamic calculations software MTDATA and a scientific computing software MATLAB is developed utilising the MATLAB interface to generic dynamic link libraries (DLLs). As such, runtine thermodynamic calculations can be performed in MATLAB environment with extended flexibility. In addition, combined thermodynamic-kinetic models developed in MATLAB can have a seamless link to MTDATA whenever thermodynamic parameters are required. Further extension of the interface to a multiphysics modelling software, COMSOL Multiphysics, is also introduced. The interface extends the capabilities of these three software packages and provides a methodology for sophisticated and even three dimensional combined thermodynamic-kinetic modelling. Applications of the interface in equilibrium thermodynamic calculation, nonequilibrium Scheil calculation, and diffusion in a multicomponent multiphase system are presented.

As solder joints become increasingly miniaturised to meet the challenging demands of future electronic packaging, it is vitally important to consider whether the solder joint size and geometry could become a reliability issue and thereby affect the implementation of the Pb-free solders. In this study, different bumping techniques, e.g. solder dipping, stencil printing followed by solder reflow, and electroplating of solders and subsequent reflow, were used to investigate the microstructure and interfacial interactions of molten Sn and Sn-based Pb-free solders on different metallizations, e.g. copper and electroless nickel immersion gold (ENIG). The resultant microstructures from a variety of pad sizes, ranging from 1 mm down to 25 mum, and representing different solder bump geometries have been investigated. In addition, thermodynamic and combined thermodynamic-kinetic modelling has been used to assist the understanding of the microstructure of Pb-free solders, the kinetics of dissolution of the metallizations and the formation of interfacial intermetallic compounds (IMCs). Both the experimental results and theoretical predictions suggest that the solder bump size and geometry can influence the as-soldered microstructure. In the light of the increasing importance of the microstructural features of the ultrafine solder joint in determining its long term reliability, a novel computational interface between software for thermodynamic calculations, high level scientific computing and multiphysics modelling, is introduced. This modelling methodology provides a potential platform for microstrucrure-based finite element (FE) reliability modelling of ultrafine interconnects for future microelectronic products