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Perovskites are of great technological and geological importance, in large part, due to their considerable compositional and structural flexibility. However, the formation of perovskites with neutr...

Cubic ReO3-type fluorides often display negative or very low thermal expansion. However, they also typically undergo phase transitions upon cooling and/or modest compression, which are undesirable from the perspective of potential applications. Density measurements and total scattering data for Mg1–xZr1+xF6+2x, x = 0.15, 0.30, 0.40, and 0.50, indicate that the introduction of excess fluoride into cubic MgZrF6 is accompanied by the population of interstitial fluoride sites and the conversion of corner to edge shared coordination polyhedra. Unlike MgZrF6, no phase transitions are seen upon cooling these materials to 10 K, and the first high pressure phase transition in these compositions occurs at pressures much higher than that previously reported for MgZrF6 (0.37 GPa). The introduction of excess fluoride also provides for control of thermal expansion. For all of the compositions studied, negative thermal expansion is seen at the lowest temperature examined, and positive thermal expansion is observed at th...

Titanium alloys have a high strength-to-weight ratio, fatigue performance and excellent corrosion resistance, and therefore are widely used in the aerospace sector due to their ability to withstand severe mechanical and thermal stresses in service. There are numerous cases where it would be desirable to use different titanium alloys in defined subcomponent regions to improve performance and efficiency. Conventional processing routes do not permit components to be produced with multiple titanium alloys and thus, design efficiency and optimization of component properties is compromised or over-engineered. In this study, a hybrid solid-state consolidation route is presented whereby field assisted sintering technology (FAST) is exploited to diffusion bond (DB) dissimilar titanium alloy powders in defined regions—a process termed FAST-DB. Titanium alloy powders Ti-6Al-4V (Ti-64) and Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) were bonded using FAST in order to study the tensile deformation behavior and strain localization across a dissimilar alloy solid-state bond. FAST-DB was carried out at the sub- and super- beta transus temperatures of both alloys to generate dissimilar microstructure morphologies across the bond. In all cases, diffusion bonds showed excellent structural integrity with no defects and a smooth hardness profile across the bond. The deformation characteristics of the bonds was studied using two different tensile test approaches. The first approach used ASTM standard specimens to measure the mechanical properties of FAST-DB samples and study the location of the tensile failure. The second approach used a microtester and optical Digital Image Correlation to capture the grain interaction in the bond region under tensile loading. The work demonstrated that the diffusion bond remains intact and that tensile failure occurs in Ti-64 (i.e. the lower strength alloy) and is independent of the grain crystal orientation. The results from this study will provide materials engineers confidence in nesting FAST-DB technology in future near net shape manufacturing routes.

The governing mechanistic behaviour of Directed Energy Deposition Additive Manufacturing (DED-AM) is revealed by a combined in situ and operando synchrotron X-ray imaging and diffraction study of a nickel-base superalloy, IN718. Using a unique DAE-AM process replicator, real-space imaging enables quantification of the melt-pool boundary and flow dynamics during solidification. This imaging knowledge was also used to informed precise diffraction measurements of temporally resolved microstructural phases during transformation and stress development with a spatial resolution of 100 µm. The diffraction quantified thermal gradient enabled a dendritic solidification microstructure to be predicted and coupled to the stress orientation and magnitude. The fast cooling rate entirely suppressed the formation of secondary phases or recrystallisation in the solid-state. Upon solidification, the stresses rapidly increase to the yield strength during cooling. This insight, combined with the large solidification range of IN718 suggests that the accumulated plasticity exhausts the ductility of the alloy, causing liquation cracking. This study has revealed additional fundamental mechanisms governing the formation of highly non-equilibrium microstructures during DED-AM.

The Directed Energy Deposition Additive Manufacturing (DED-AM) of SS316L was studied using in situ and operando synchrotron X-ray imaging to quantitively understand the effect of processing parameters on the melt-pool morphology and surface quality. It was found that surface roughness of DED-AM builds can result from melt pool surface perturbations caused by changes in the melt flow and build stage motion perturbations. Process maps are developed that quantitatively correlate build quality to process parameters including powder feed rate, laser power and traverse speed. How the AM process parameters control build efficacy is clarified, and the processing conditions required to dampen surface perturbations leading to roughness were determined.

Directed energy deposition (DED) is an emerging technology with repair applications in critical aerospace components. Mechanical properties of DED components have been shown to vary significantly through a part, making it difficult to achieve the level of process control required for these applications. Using thermal data captured in-situ, cooling rates and melt pool dimensions were calculated and related to the final grain structure, captured by EBSD. The changes in cooling rate explain the microstructural variation between different processing parameters and through the build height. A new approach, using a cumulative anisotropy factor was implemented and correlates the variation in hardness with grain structure. Two regimes were found depending on the linear heat input in 316L, with high linear heat input resulting in great amounts of mechanical anisotropy on the component level. The relationships between thermal signature and mechanical properties suggest close control of anisotropy could be achieved by monitoring and controlling the melt pool size using a coaxial camera.

Porosity and high surface roughness can be detrimental to the mechanical performance of laser powder bed fusion (LPBF) additive manufactured components, potentially resulting in reduced component life. However, the link between powder layer thickness on pore formation and surface undulations in the LPBF parts remains unclear. In this paper, the influence of processing parameters on Ti-6Al-4 V additive manufactured thin-wall components are investigated for multilayer builds, using a custom-built process replicator and in situ high-speed synchrotron X-ray imaging. In addition to the formation of initial keyhole pores, the results reveal three pore phenomena in multilayer builds resulting from keyhole melting: (i) healing of the previous layers' pores via liquid filling during remelting; (ii) insufficient laser penetration depth to remelt and heal pores; and (iii) pores formed by keyholing which merge with existing pores, increasing the pore size. The results also show that the variation of powder layer thickness influences which pore formation mechanisms take place in multilayer builds. High-resolution microcomputed tomography images reveal that clusters of pores form at the ends of tracks, and variations in the layer thickness and melt flow cause irregular remelting and track height undulations. Extreme variations in height were found to lead to lack of fusion pores in the trough regions. It is hypothesised that the end of track pores were augmented by soluble gas which is partitioned into the melt pool and swept to track ends, supersaturating during end of track solidification and diffusing into pores increasing their size.

The family of additive manufacturing techniques has been attracting significant attention of manufacturers and researchers, due to its unrivalled flexibility to fabricate and repair geometrically complex objects. However, material shaping is not sufficient: wide adoption of additive manufacturing can only occur upon the achievement of satisfactory mechanical performance in terms of structural integrity. The present study exploits a wide range of micro-scale experimental techniques to shed light on fatigue failure mechanisms of Laser Metal Deposition IN718 Ni-base superalloy, and to study the effect of shot peening treatment. Thorough microstructural and fractographic analyses revealed the main deformation mechanism associated with twinning during crack propagation, while crack initiation was found to be promoted by both slip system deformation and twinning around microstructural defects, rather than at sample free-surfaces. It was found that precipitates played a major role in determining the deformation mode. It was discovered that in this case-study, shot-peening residual stresses may have a detrimental effect, in view of the presence of the largest defects within a region where tensile residual stress was present. The results presented here improve understanding of failure mechanisms and thus define future directions of development for manufacture optimisation.

It is generally recognised that electron beam melted (EBM) Ti-6Al-4V alloys exhibit a microstructural gradient along the build direction, but there have been some inconsistent experimental observations and debate as to the origin and magnitude of this effect. Here we present an unambiguous evaluation of this microstructural gradient and associated mechanical property along the EBM build direction on purpose-built round bar RB samples with build height of 380 mm and rectangular plate RP samples with build height of 120 mm. Columnar prior β grain width was found to increase (from 86 ± 38 to 154 ± 56 µm in RB and from 79 ± 34 to 122 ± 56 µm in RP samples) with the build height and the similar increase was also observed for α lath width (from 0.58 ± 24 to 0.87 ± 33 µm in RB and from 1.50 ± 45 to 1.80 ± 49 µm in RP samples). These observations can be attributed to the thermal gradient in the powder bed that produced a cooling rate gradient along the build height. The measured α lath width variation along the build height followed a log-normal distribution. The graded microstructure resulted in a decrease in micro-hardness which correlated very well with the mean α lath width by following a Hall-Petch relation.

Flexible metal-organic frameworks (MOFs) are structurally flexible, porous, crystalline solids that show a structural transition in response to a stimulus. If MOF-based solid-state and microelectronic devices are to be capable of leveraging such structural flexibility, then the integration of MOF thin films into a device configuration is crucial. Here we report the targeted and precise anchoring of Cu-based alkylether-functionalised layered-pillared MOF crystallites onto substrates via stepwise liquid-phase epitaxy. The structural transformation during methanol sorption is monitored by in-situ grazing incidence X-ray diffraction. Interestingly, spatially-controlled anchoring of the flexible MOFs on the surface induces a distinct structural responsiveness which is different from the bulk powder and can be systematically controlled by varying the crystallite characteristics, for instance dimensions and orientation. This fundamental understanding of thin-film flexibility is of paramount importance for the rational design of MOF-based devices utilising the structural flexibility in specific applications such as selective sensors., Understanding the structural dynamics of flexible metal-organic frameworks at a thin-film level is key if they are to be implemented in devices. Here, Fischer and colleagues anchor flexible MOF crystallites onto substrates and identify a structural responsiveness that is distinct to that of the bulk.

Flexible metal-organic frameworks (MOFs) exhibit large potential as next-generation materials in areas such as gas sensing, gas separation and mechanical damping. By using a mixed metal approach, we report how the stimuli reponsive phase transition of flexible pillared-layered MOFs can be tuned over a wide range. Different Cu2+ to Zn2+ metal ratios are incorporated into the materials by using a simple solvothermal approach. The properties of the obtained materials are probed by differential scanning calorimetry and CO2 sorption measurements, revealing stimuli responsive behaviour as a function of metal ratio. Pair distribution functions derived from X-ray total scattering experiments suggest a distortion of the M2 paddlewheel as a function of the Cu content. We rationalize these phenomena by the different distortion energies of Cu2+ and Zn2+ ions to deviate from the square pyramidal structure of the relaxed paddlewheel node. Our work follows on from the large interest in tuning and understanding the materials properties of flexible MOFs, highlighting the large number of parameters that can be used for the targeted manipulation and design of properties of these fascinating materials.

Additive Layer Manufacturing (ALM) technologies, such as Powder Bed Direct Laser Deposition (PB-DLD), have gained increasing popularity within the aerospace industry due to the advantages they hold over conventional processing routes. Among the advantages are the ability to produce more sophisticated cross-sectional geometries, a decrease in production lead times and an improvement to the buy-to-fly ratio. However, build quality and microstructural characteristics have a dependency on the process variables such as build direction. In order to understand the influence of grain size and build orientation on tensile behaviour, the Small Punch Tensile (SPT) testing technique has been applied to variants of the nickel based superalloy C263, manufactured using the PB-DLD method. The test technique utilises miniaturised samples, requiring only small volumes of material and is therefore a desirable test method to employ. SPT testing has characterised the mechanical properties between vertically and horizontally built PB-DLD C263 in comparison with the cast material derivative. Differences in mechanical performance between each variant have been revealed and found to be associated with microstructural variations. The deformation behaviour across each material variant have been exposed by interrupted tests. SPT results have also been accompanied by fractography, fracture energy calculations along with comparisons with uniaxial data.

Small punch (SP) tensile testing provides several advantages over conventional test techniques for mechanical property characterisation of components produced using novel manufacturing processes. Additive layer manufacturing (ALM) is becoming more widespread, particularly in high value manufacturing sectors such as the gas turbine industry as it allows near net shape manufacture of near fully dense components with complex geometries. One such ALM process which is receiving attention from the gas turbine industry is electron beam melting (EBM), a powder bed process which uses an electron beam energy source. The additive nature of ALM processes including EBM results in the microstructures produced differing significantly to those produced by conventional processing techniques. As well as being influenced by the input parameters, the microstructure and hence mechanical properties are also affected by the geometry of the component being manufactured, primarily due to the effect this has on the cooling characteristics. SP testing of material manufactured by EBM allows the mechanical property characterisation of local component representative geometries which wouldn’t be possible using conventional uniaxial testing techniques. This work is aimed towards developing and validating the SP tensile technique for this application; different Ti-6Al-4V material variants manufactured using EBM as well as conventional methods have been characterised with a range of test conditions.

The governing mechanistic behaviour of Directed Energy Deposition Additive Manufacturing (DED-AM) is revealed by a combined in situ and operando synchrotron X-ray imaging and diffraction study of a nickel-base superalloy, IN718. Using a unique process replicator, real-space phase-contrast imaging enables quantification of the melt-pool boundary and flow dynamics during solidification. This imaging knowledge informed precise diffraction measurements of temporally resolved microstructural phases with unprecedented precision during transformation and stress development with a spatial resolution of 100 µm. The diffraction quantified thermal gradient enabled a dendritic solidification microstructure to be predicted and coupled to the stress orientation and magnitude. The fast cooling rate entirely suppressed the formation of secondary phases or recrystallisation in the solid-state. Upon solidification, the stresses rapidly increase to the yield strength during cooling. This insight, combined with IN718’s large solidification range suggests that the accumulated plasticity exhausts the alloy’s ductility, causing liquation cracking. This study has revealed additional fundamental mechanisms governing the formation of highly non-equilibrium microstructures during DED-AM.

Negative thermal expansion materials are of interest for an array of composite material applications whereby they can compensate for the behavior of a positive thermal expansion matrix. In this work, various design strategies for systematically tuning the coefficient of thermal expansion in a diverse series of metal-organic frameworks (MOFs) are demonstrated. By independently varying the metal, ligand, topology, and guest environment of representative MOFs, a range of negative and positive thermal expansion behaviors are experimentally achieved. Insights into the origin of these behaviors are obtained through an analysis of synchrotron-radiation total scattering and diffraction experiments, as well as complementary molecular simulations. The implications of these findings on the prospects for MOFs as an emergent negative thermal expansion material class are also discussed.

Additive manufacturing (AM) is a novel near net shape manufacturing technology that joins metallic powders layer upon layer in conjunction with 3D model data and as such offers tremendous potential to a wide range of industrial sectors given its ability to produce highly intricate components with very little material wastage. Subsequently, the aerospace industry has become particularly interested in utilising AM as a means of manufacturing nickel-based superalloys for high-temperature applications, such as non-rotating components within gas turbine engines, which are traditionally fabricated through traditional cast and wrought methodologies. As a result of this, a detailed understanding of the influence of key process variables on the structural integrity of the different experimental builds is required. A semi-empirical quantitative approach for melt track analysis has been conducted and the impact on melt track sizing and defect forming mechanisms in the as-built and heat-treated condition is investigated.

Directed Energy Deposition Additive Manufacturing (DED-AM) is transformative for the production of larger, geometrically complex metallic components. However, the mechanical properties of titanium alloy DED-AM components do not always reach their full potential due to microstructural features including porosity and regions of lack of fusion. Using in situ and operando synchrotron X-ray imaging we gain insights into key laser-matter interaction and microstructural feature formation mechanisms during DED-AM of Ti-6242. Analysis of the process conditions reveals that laser power is dominant for build efficiency while higher traverse speed can effectively reduce lack of fusion regions. We also elucidate the mechanisms underlying several physical phenomena occurring during the deposition of titanium alloys, including the formation of a saddle-shaped melt pool and pore pushing. The findings of this work clarify the transient kinetics behind the DED-AM of titanium alloys and can be used as a guide for optimising industrial additive manufacturing processes.

In recent years the use of Additive Manufacturing (AM) has become increasingly widespread with numerous industries now moving towards large scale manufacture of structurally integral components. The nature of AM offers the ability to manufacture more complex and optimised geometries, such as cooling channels and honeycomb structures, which would not be possible or economically viable to manufacture using more traditional fabrication processes. However, the layer by layer build structure of AM components also introduces a complex and component specific microstructure arising from the rapid cooling rates resulting from the build parameters and geometries, which hence influence the mechanical properties. Therefore, the use of conventional mechanical test approaches to assess the performance of these materials can be limited. This paper will extend upon some of the recent research at Swansea University in applying the innovative small punch fatigue (SPF) experiment to characterise the mechanical performance of AM materials and how they compare to traditionally manufactured variants of the same alloys. Results show excellent agreement with the microstructural morphologies of the different materials, with supporting fractography evidencing the contrasting failure modes.

The microstructure of direct laser deposited (DLD) IN718 has been investigated in detail using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results confirm that the dendrite core microstructure can be linked to the cooling rate experienced during the deposition. A ~ 100 μm wide δ partially dissolved region in the IN718 substrate was observed close to the substrate/deposit boundary. In the deposited IN718, γ/Laves eutectic constituent is the predominant minor microconstituent. Irregular and regular (small) (Nb,Ti)C carbides and a mixture of the carbides and Laves were observed. Most M3B2 borides were nucleated around a (Nb,Ti)C carbide. Needles of δ phase precipitated from the Laves phase were also observed. A complex constituent (of Laves, δ, α-Cr, γ″, and γ matrix) is reported in IN718 for the first time. The formation of α-Cr particles could be related to Cr rejection during the formation and growth of Cr-depleted δ phase.

Numerical modelling of the residual stresses and strains within mechanical components is of great importance for improving the quality and reliability of design for structural integrity. A particularly versatile and powerful approach is offered by direct and inverse eigenstrain modelling. The nature of the eigenstrain modelling approach is that it not only generates an efficient parametric representation of the residual stress field, but also ensures consistency by enforcing stress equilibrium and strain compatibility. In the present study we propose a particular way of prescribing the eigenstrain field due to surface treatment such as shot peening. Eigenstrain variation is described by a continuous function of the distance from the boundary of the object in a two-dimensional model of its cross-section. The procedure is compatible with the use of commercial numerical simulation software, and allows correct assignment of all eigenstrain components. We apply the technique to the evaluation of residual strain within an additively manufactured nickel superalloy compressor blade that was subsequently subjected to shot peening treatment. Two experimental techniques are used to validate the model, namely, Focused Ion Beam ring core milling (FIB-DIC) and synchrotron X-ray Powder Diffraction (SXRPD). Consistency between model prediction and experimental measurements provides verification of the suitability of eigenstrain modelling as consistent basis for the incorporation of residual stress effects on the deformation behaviour of manufactured components.

Titanium alloys are used extensively in the aerospace sector due to the good combination of high strength-to-weight ratio and corrosive resistance. Many aerospace components are exposed to extreme service stress states and temperatures, which in some applications could compromise the component’s performance if a single titanium alloy is used. A potential solution to this issue could be the combination of dissimilar titanium alloys in subcomponent regions, achieved through consolidating powders via field assisted sintering technology (FAST-DB) and subsequent hot forging (FAST-forge). In this paper, near net shape titanium-titanium alloy demonstrator components are produced from oversized AM powders in just two hybrid solid-state steps; FAST-DB and hot forging.

A micro-tensile testing system coupled with focussed ion beam (FIB) machining was used to characterise the micro-mechanical properties of the weld from a turbine disc alloy. The strength variations between the weld and the base alloy are rationalised via the microstructure obtained.

Additive Layer Manufacturing (ALM) is an innovative net shape manufacturing technology that offers the ability to produce highly intricate components not possible through traditional wrought and cast procedures. Consequently, the aerospace industry is becoming ever more attentive in exploiting such technology for the fabrication of nickel-based superalloys in an attempt to drive further advancements within the holistic gas turbine. Given this, the requirement for the mechanical characterisation of such material is rising in parallel, with limitations in the availability of material processed restricting conventional mechanical testing, particularly with the abundance of process parameters to evaluate. As such, the Small Punch Creep (SPC) test method has been deemed an effective tool to rank the elevated temperature performance of alloys processed through ALM, credited to the small volumes of material utilised in each test and the ability to sample material from discrete locations. In this research, the SPC test will be used to assess the influence of a number of key process variables on the mechanical performance of Laser Powder Bed Fused (LPBF) Ni-based superalloy CM247LC. This will also include an investigation into the influence of build orientation and post-build treatment on creep performance, whilst considering the structural integrity of the different experimental builds.

Oxide intrusions which formed ahead of the crack tip in an advanced nickel-based superalloy after exposure to air at 650 °C have been investigated by (scanning) transmission electron microscopy equipped with energy-dispersive X-ray spectrometry. Three different cases were considered: (i) a fast growing crack; (ii) a stationary crack exposed to a 5 h period under load; and (iii) a stationary crack exposed to a 5 h period but held at zero mechanical applied load. The intrusions formed during both hold periods were much longer than those present ahead of the (growing) dynamic crack (∼1.5 μm) and consisted of layered oxides in the thermodynamic sequence of CoO, NiO, Cr 2 O 3 , TiO 2 and Al 2 O 3 . The last three of these oxides appeared to form protective layers along the flanks and, for the stationary cracks, at the intrusion tip. Calculations of the oxygen partial pressure both across the width and along the length of the oxide intrusions have been undertaken assuming such protective conditions. Significant quantities of oxygen are thus not expected to exist in the alloy ahead of intrusions which are sealed by protective oxide layers.

Machining, surface treatment, plastic forming and stretching, welding, and other manufacturing processes introduce residual stresses and distortion into work pieces and engineering components. These phenomena exert a significant influence on the behaviour of components affecting the response to thermal/mechanical in-service loading, e.g. in terms of crack initiation and propagation under the conditions of creep and fatigue, thus ultimately affecting their durability. In the present study, the inertia friction welding process is considered that is used for butt joining of hollow cylindrical components, such as shafts and drums. An inverse eigenstrain framework is used for the interpretation of neutron diffraction measurements in terms of the underlying eigenstrain distributions. Eigenstrain distributions that describe the nature of permanent inelastic deformation are found by minimizing the sum-of-squares measure of the disagreement between model prediction and experimental measurements of residual elastic strains. Experimental data obtained from neutron diffraction measurements are used in an inverse solution scheme in order to determine the underlying eigenstrain (strains permanently ‘locked in’) that give rise to the residual stress state. Once these are found, approximate reconstruction of the complete stress tensor within the entire component becomes straightforward. Eigenstrain distributions are first obtained for reduced size test specimens which have been characterized in detail using neutron diffraction. Subsequently, the eigenstrain distributions are scaled and applied to more complex, full-size real engine components, with scaling factors adjusted to match surface hole drilling measurements.

A thorough investigation has been performed to assess the microstructural properties, mechanical properties (hardness and elastic modulus), and residual stress development in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) inertia friction welds in the as-welded and postweld heat-treated conditions. It was evident that the thermomechanical deformation in the weld region occurred above the β transus, forming dynamically recrystallized β grains and precipitating acicular α within the β grains, which resulted in a localized hardness increase. In the heat-affected zone, a ghost microstructure of the base metal formed because of the absence of sufficient time for diffusion, resulting in Mo segregation in the prior primary α plates. Energy-dispersive synchrotron X-ray diffraction and neutron diffraction were used to assess the residual stress development in the three principal directions. The variation in the unstrained lattice parameters across the weld regions was established by imposing a stress balance on the axial stress component in the radial direction. It was found that the maximum stresses occurred in the hoop direction, with significantly lower stresses present in the radial and axial directions. The maximum tensile hoop stresses were located at ~4 mm from the weld centerline and not at the dynamically recrystallized β-rich weld zone. This was associated with the α → β phase transformation and the subsequent acicular α precipitation within the region surrounding the weld centerline.

Microstructure in the weld line (WL) zone produced by inertial friction welding has been studied for a series of RR1000–RR1000 welds using transmission electron and scanning electron microscopy. A fully recrystallised fine grain structure was found to form throughout the WL zone, characterized by straight and smooth grain boundaries, high energy status and modified grain boundary chemistry due to very fast cooling after welding. Very fine γ′ particles with unimodal size distribution were reprecipitated in the WL zone. The fine γ′ particles are spherical in shape, high in number density and characterized by an imbalanced chemistry, containing less Al, Ti, Ni, Ta γ′-forming elements but more Cr, Co, Mo γ-forming elements than all types of parent γ′ particles. As a result, a hard and strong WL zone was produced by the inertial friction welding.

The effect of the base material microstructure on the development of residual stresses across the weld line in inertia friction welds (IFWs) of high-strength nickel-base superalloy RR1000 was studied using neutron diffraction. A comparison was carried out between tubular IFW specimens generated from RR1000 heat treated below (fine grain (FG) structure) and above (coarse grain (CG) structure) the γ′-solvus. Residual stresses were mapped in the as-welded (AW) condition and, after a postweld heat treatment (PWHT), optimized for maximum alloy strength. The highest tensile stresses were generally found in the hoop direction at the weld line near the inner diameter of the tubular-shaped specimens. A comparison between the residual stresses generated in FG and CG RR1000 suggests that the starting microstructure has little influence on the maximum residual stresses generated in the weld even though different levels of energy must be input to achieve a successful weld in each case. The residual stresses in the postweld heat treated samples were about 35 pct less than for the AW condition. Despite the fact that the high-temperature properties of the two parent microstructures are different, no significant differences in terms of stress relief were found between the FG and CG RR1000 IFWs. Since the actual weld microstructures of FG and CG RR1000 inertia welds are very similar, the results suggest that it is the weld microstructure and its associated high-temperature properties rather than the parent material that affects the overall weld stress distribution and its subsequent stress relief.

This article describes an experimental study aimed at characterizing the extent of residual stress relaxation during thermal treatment of inertia friction-welded alloy 720Li nickel-based superalloy welded tubular rings. In the as-welded condition, yield level tensile hoop stresses were found by neutron diffraction in the weld region along with axial bending stresses (tensile toward the inner diameter (ID)/compressive toward the outer). The evolution of these residual stress levels during postweld heat treatment (PWHT) was mapped experimentally over the weld cross section. After 8 hours of PWHT, the axial stresses relaxed by 70 pct, whereas the hoop stresses reduced by only 50 pct. Some scatter of residual stress evolution was found between samples, particularly for the axial stress direction. This was attributed to substandard tooling to grip the rings. The results on subscale samples were transferred to a full-scale aeroengine (650-mm diameter) compressor drum assembly that was postweld heat treated for 8 hours. It was found that the residual stresses, particularly in the axial direction, were noticeably lower in this full-scale weld component compared to the subscale weld heat treated for the same time. The differences seem to be best rationalized by the different standards of jigging used during joining these two types of welds.

Nickel based superalloys have been utilised within numerous industrial sectors from power generation to chemical processing plants for over four decades as a result of their ability to retain mechanical properties at arduous temperatures alongside excellent oxidation and corrosion resistance. Within the aerospace industry, they have been primarily used within regions of the gas turbine engine where metal temperatures can often exceed 1000°C and high temperature deformation mechanics are prominent. Although typically manufactured using traditional wrought and casting methodologies, the aerospace industry has become increasingly interested in the use of Additive Layer Manufacturing (ALM) as a means of fabrication to take advantage of the numerous benefits that ALM has to offer. Detailed characterisation of the structural integrity of components processed via additive processes is a key requirement of the understanding. In this paper, the small punch creep (SPC) test has been applied to samples of a high gamma prime containing nickel-based superalloy manufactured using the laser powder bed fusion (LPBF) process. Several different builds are investigated and ranked, with ALM builds provided in different epitaxial orientations and with contrasting process parameters to help determine the optimal process parameters.

Miniaturised mechanical test approaches, specifically small punch testing, are now widely recognised as a means of obtaining useful mechanical properties to characterise the creep, tensile and fracture characteristics of numerous material systems from a range of industrial applications. Limited success has been found in replicating fatigue properties through the use of a small punch disc. This paper will discuss the ongoing research and progress in developing a novel small punch fatigue testing facility at the Institute of Structural Materials at Swansea University. Experiments have been performed on the nickel superalloy C263 at ambient room temperature, investigating three different alloy variants; two orientations produced through additive manufacturing and the cast equivalent. Fractographic analysis has been completed to interpret the complex damage mechanisms in the test method along with the differences in performance amongst the alloy variants.

A sequentially coupled thermal and mechanical finite element (FE) model has been developed to describe inertia friction welding (IFW) using the DEFORM 8.2 package. All modelling and experimental work was undertaken on inertia friction welds made from RR1000, which is an advanced high γ′ content nickel-based superalloy. The accuracy of the thermal predictions has been assessed by an analysis of γ′ distribution across the weld region as compared to those recorded during prescribed thermal simulations, while the mechanical model has been validated by comparing predicted and measured upsets and weld pressures. Finally the residual stress predictions have been compared against measurements (by neutron diffraction). In all cases excellent agreement was found between predicted and experimental data. This exercise revealed that the clamping forces applied during the welding process may have a strong influence on the axial stress field. The validated model was then used to study the effect of welding pressure on material flow, thermal history and residual stresses. The work shows that with increasing weld pressure the width of the heat-affected zone (HAZ) is reduced, while the peak temperature and strain rate is increased. In addition the peak stresses in the hoop direction near the weldline were found to be largely unaffected by the weld pressure. However, for lower welding pressures a broader high tensile hoop stress region was found in accordance with the increased HAZ.

The high temperature fatigue performance of two dissimilar material joints made by inertia friction welding and linear friction welding is assessed in the present study. The fatigue strength of the welded joints is found to be comparable to that of the weaker parent material for the plainsided specimens. However, the fatigue crack growth resistance within the weld zone of both material systems is found to be reduced compared to that of parent material. This effect is more pronounced for high temperature Ni alloys than for the lower temperature nickel alloy. Environmental attack is confirmed to be the controlling failure mechanism for acceleration of crack growth, but the extent to which it is observed is sensitive to local microstructure, i.e. to grain size, redistribution of the main strengthening phase γ′, and to the grain boundary carbide morphology. Such local microstructural variations are the result of welding and subsequent post-weld heat treatment procedures.

In the present study inertia friction welded RR1000 to IN718 joints have been investigated. Crack growth tests within 0·3 mm of the weld interface, conducted in air at 500 and 650°C, have shown that there is no difference in crack growth rate due to three different sets of welding parameters applied. The cracks were found to propagate from RR1000 through the weld line into IN718. In RR1000 the cracks pass a zone within 15–30 μm from the weld interface, allowing higher crack growth rates. Fractographic studies have shown that these higher crack growth rates are caused by a higher tendency to intergranular cracking, most likely due to oxidation damage along grain boundaries. The similar properties of the welds tested can be related to a similar weld process characteristic during the last second of the welding cycle for all three sets of welding parameters applied.

This article describes a comprehensive microstructural characterization of an inertia friction welded joint between nickel-based superalloys 720Li and IN718. The investigation has been carried out on both as-welded and postweld heat-treated conditions. The detailed metallographic analysis has enabled the relation of hardness profiles across inertia-welded alloy 720Li to IN718 and morphological changes of the precipitates present. The work demonstrates that inertia friction welding (IFW) 720Li to IN718 results in a weld free of micropores and microcracks and no significant chemical migration across the weld line. However, substantial differences in terms of grain structure and precipitation phase distribution variations are observed on each side of the dissimilar weld. The high γ′ volume fraction alloy 720Li exhibits a wider heat-affected zone than the mainly γ′′ strengthened IN718. Alloy 720Li displays only a small hardness trough near the weld line in the as-welded condition due to the depletion of γ′, while γ″-strengthened IN718 shows a soft precipitation-free weld region. Postweld heat treatment (PWHT) of the dissimilar weld at 760 °C, a typical annealing temperature for alloy 720Li, results in an overmatch of the heat-affected zone in both sides of the weld. The comparison of the as-welded and postweld heat-treated condition also reveals that IN718 is in an overaged condition after the stress relief treatment.

In this paper the microstructure, mechanical properties and residual stresses are compared for three inertia friction welded nickel-base superalloys. In contrast to alloy 720Li and RR1000, for Inconel 718 welding produces a precipitation free region leading to significantly reduced strength near the weld line. As a result, for alloy 720Li the hoop stresses are 1.5 times, and in RR1000 two times, higher than the tensile hoop stresses for Inconel 718. The maximum tensile weld stresses in Inconel 718 and RR1000 are yield stress limited in the weld region. That stresses significantly below the yield stress are found near the weld for alloy 720Li may be because the inferior creep properties of alloy 720Li compared to RR1000 result in stress relief during cooling after welding. Post weld heat treatment at the standard maximum aging temperature for Inconel 718 (732 °C), relieved residual hoop stresses to below 400 MPa. To achieve a similar level of residual hoop stress, Alloy 720Li must be stress relieved at least 30 °C and RR1000 about 80 °C hotter.

A coupled thermal and mechanical finite-element (FE) model has been developed to describe the inertia welding of RR1000 nickel-base superalloy tubes using the DEFORM 7.2 FE package. The energy input rate is derived from measurements of torque, angular rotation speed, and upset taken from actual inertia welding trials. The model predicts the thermal history of the joint as well as the deformation pattern and final residual stresses. The thermal variation has been validated by a microstructural study of the weld region of the trial joints. Thermal profile predictions have been made for three welds having the same initial kinetic rotational energy but different levels of flywheel inertia and rotational velocity. The concomitant residual stress predictions have been compared with nondestructive neutron diffraction residual stress measurements. The implications of the results for inertia welding are discussed.

The description of particulate degradation using a matrix equation is a potentially useful tool in modelling degradation processes. One of the main constraints in adopting this approach is measuring the relevant breakage matrix, especially where degradation of particles in a given size class is influenced by the presence of particles in other size classes. This paper describes a technique for quantifying such intra-mixture interactions in degradation processes, hence calculating the full breakage matrix for interacting mixtures, for a relatively modest increase in necessary observational effort. The result indicates that the breakage matrix approach may be more useful and versatile than previously realised.

Corrosion resistance has been examined for composites in the AlN – SiC – TiB2 ternary system. They have high corrosion resistance in air up to 1500°C because mullite and β-tialite are formed in the outer layer of scale. Their corrosion resistance substantially exceeds that of other ceramic materials because of the formation of the mullite phase on prolonged exposure (up to 200 h) to gaseous combustion products from kerosene and diesel fuel in the presence of sea salt at 900 and 1000°C. Also, AlN – SiC – TiB2 ceramics have higher bending strength than does AlN – TiB2 ceramic.

Predictions of residual stresses in inertia friction welded Ni-base superalloys have been carried out using a commercial finite element code (DEFORM) combined with an energy balance approach and a 2D axisymmetric formulation. A coupled thermal and mechanical finite element model has been created. During inertia welding trials of RR1000, a high γ ′ Ni-base superalloy, the rotational velocity and upset history curves were recorded. From these data the heat flux (the rate of energy input) through the weld interface was inferred and together with the upsetting rate input into the model as evolving boundary conditions. The coupled thermal and mechanical analysis leads to the prediction of the thermal history and the residual stresses generated during cooling. The validation of the model has been undertaken by comparing the predicted residual stresses with those measured using neutron diffraction. The comparison between predicted and measured stresses is in good agreement.

Recent advances, accelerated by the application of computer technology, allow numerical characterization of particle shape in two dimensions. However, characterization of three-dimensional (3D) particle shapes is still largely an unresolved problem. Here, 3D pseudo-shape descriptors are proposed for characterising the particle shapes. The microscopic characteristics are recorded using a computer-based image analysis system to assess particle shape. The particle shapes are based on the complete coverage by a set of images of the particle projections in three mutually perpendicular directions. The circularity of particle projections in each plane was measured in turn and found to be suitable for particle shape estimation. Analogues of the resulting 3D pseudo-shapes are constructed for the purposes of computer simulation of non-spherical particulate assemblies. Preliminary results of the simulation work are illustrated.

Neutron diffraction residual strain measurements have been made on a tubular structure formed by joining two nickel-based superalloy RR1000 parts by inertia welding. Residual strains in the radial, hoop and axial directions of the tube cross-section have been measured. The corresponding residual stress field has been calculated accounting for the stress-free lattice parameter variations in the region close to the weld line. Tensile residual stresses were observed near the inner diameter of the tube with magnitudes of the order of +500, +1100 and +1300 MPa in the radial, axial and hoop directions, respectively. By comparison near the outer diameter (OD) of the weld the corresponding stresses are of the order of −200, −1000 and 150 MPa. The final stress state reflects the influence of the gripping fixture tooling and thermal gradients during inertia welding. Additional X-ray (at the surface) and hole-drilling (at the near surface) measurements show a steep residual stress gradient in the near surface region. Tensile hoop and axial machining stresses at the surface indicate the potential for improving the inertia weld tooling and the machining parameters used when removing the flash.

The fatigue performance of Kaowool fiber reinforced 339 aluminum composites at 300°C is limited by spherical thin walled hollow Kaowool shot particles. These act as crack initiation sites particularly when located at the surface. This problem does not occur for thick walled particles or particles filled with the aluminum matrix. The effect of wall thickness (t) is evaluated from finite element analysis of both 2D and 3D models, with and without plasticity. Both models predict that hollow thin walled particles act as defects, while thick walled particles act as reinforcements, this transition being defined by a critical wall thickness (tc). The 3D model is preferred in that it predicts more accurate and smaller values of tc. Specifically, the 3D elastic/plastic model predicts that the largest stress concentration occurs for a fractional surface particle and that in this condition tc = 0.18a, where a is the particle radius. This value agrees with our experimental observation that particles with t > 0.2a do not initiate failures.

The e/ects of deposition noise on two-dimensional mound coarsening with slope selection are studied using both continuum and discrete models. Our continuum model may also be considered as a model of two-dimensional polycrystalline growth with a preferred facet orientation. In agreement with recent scaling arguments, we 3nd n = � = 1 , where n is the mound coarsening exponent andis the surface roughening exponent. We also 3nd � = 1 whereis the facet length coarsening exponent. These results are compared with simulation results obtained using a discrete model in which deposition noise and di/usion have been included, but island nucleation and mass transfer between mounds are assumed to be negligible. In the presence of an interfacet di/usion barrier, the surface exhibits a self-a6ne morphology and Edwards-Wilkinson scaling behavior (� = 1 ) while the average facet length is constant (� = 0). However, inthe absen ce of a barrier to interfacet di/usion, we again 3nd a mound-like morphology and coarsening with n = � = 1 , while the average facet length increases logarithmically with 3lm thickness. The slow growth of the facet length in this case may also explain the absence of island nucleation in polycrystalline growth. Our results may also be useful in the development of improved continuum and discrete models of polycrystalline growth. c

The next generation of Ni-based alloys for aeroengines are richer in γ′ than existing alloys and are more difficult to weld by conventional means. Inertia welding is currently being developed as a joining technique for these alloys. Steep microstructural gradients have been observed in nickel-based superalloy RR1000 tube structures welded by inertia friction welding,[1] and in this article, the concomitant residual stresses are mapped at depth using neutron diffraction. One tube in the aswelded and two in the postweld heat-treated (PWHT) condition have been investigated. In the case of the as-welded specimen, it was necessary to establish the variation of the stress-free lattice parameter, a0, across the weld line to infer elastic strain from lattice spacing changes. A biaxial sin2ψ measurement on thin slices was used to determine a0 as a function of the axial position from the weld line. This was in excellent agreement with the variation inferred by imposing a stress balance on the axial measurements. The change of a0 across the weld line can be rationalized in terms of the observed variation in the element partitioning effect between the matrix (γ) and the precipitates (γ′). It was found that the residual stresses in the weld and heat-affected zone generated by the welding process are large, especially close to the inner diameter of the welded ring. The experimental results have shown that, in order to relax the residual stresses sufficiently, the heat-treatment temperature must be increased by 50 °C over the conventional heat-treatment temperature. This is due to the high γ′ content of RR1000.

This article describes a quantitative study of the microstructure of nickel-based superalloy RR1000 tube structures joined by inertia welding. One as-welded and three post weld heat-treated (PWHT) conditions have been investigated. The samples were characterized mechanically by measuring the hardness profiles and microstructurally in terms of γ grain size, γ′ precipitate size and volume fraction, stored energy, and microtexture. Electron backscatter diffraction (EBSD) was used to characterize high-angle grain boundaries (HAGB) and the variation of microtexture across the weld line. The coherent γ′ precipitates were investigated over a range of scales on etched samples in a field emission gun scanning electron microscope (FEGSEM), using carbon replicas in a transmission electron microscope (TEM) and from thin slices by means of high-energy synchrotron X-rays. Dramatic changes in the microstructure were observed within 2 mm of the weld line. In this region, the hardness profile is influenced by changes in grain size, γ′ volume fraction, γ′ particle size, and the work stored in the material. Further away, the observed hardness variation is still significant although only minor microstructural changes could be observed. In this region, the correlation of microstructure and hardness is less straightforward. Here, a combination of small microstructural changes appears to give rise to a significant change in strength. No significant texture or grain distortion was observed in the extensively plastically deformed region due to recrystallization.

Thin films of a benzylic amide macrocycle, the common component of a wide class of mechanically interlocked molecules, are prepared by vapor deposition on Au(111). The films are characterized by monochromated X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS). The relative amounts of carbon, nitrogen, and oxygen are consistent with the formation of intact molecular species. At monolayer coverage, the relative intensity of out-of-plane to in-plane phenyl ring vibrational modes indicates that the macrocycle adopts a nearly flat-lying conformation. The formation of a chemisorption bond is evidenced by the presence of a Au-O stretching vibration and a low binding energy component in the O 1s core level region assigned to interfacial bonding. A decrease in film order and the absence of a preferred molecular orientation is observed at higher coverages. Computer modeling of the adsorption of the macrocycle on the surface rationalizes the experimental observations.