Search

In this study, microstructural and texture development in the individual weld zone during friction stir welding (FSW) of DP780 steel at similar tool rotation speed (200 rpm) different welding speeds (200 mm/min and 400 mm/min) was investigated. Phase transformations and competition between recovery and recrystallization mechanisms in the distinct weld zones were explored by electron back scattered diffraction (EBSD). More pronounced grain refinement was observed in stir zone (SZ) of sample welded at higher speed (0.62 μm) as compared to lower welding speed (0.51 μm) which is attributed to the enhanced Zener pinning effect at higher welding speeds. Continuous dynamic recrystallization (cDRX) was found to be the dominating recrystallization mechanism in SZ of both welded samples. Orientation distribution function (ODF) based texture investigations of SZ revealed the development of D1 {1¯1¯2} and D2 {112¯} shear components along with the cube {001} texture. The lower texture intensities witnessed in SZ of higher welding speed sample was due to the accelerated recrystallization kinetics at higher welding speeds. The microstructural investigations of thermo-mechanically affected zone (TMAZ) of both welded samples revealed that cDRX was predominant recrystallization mechanism while microshear bands, grain boundary bulging and geometric DRX (gDRX) also assisted the grain refinement. Texture analysis showed the development of D2 {112¯}, J{110} and J¯{1¯1¯0} shear components in the TMAZ lower welding speed sample and D1 {1¯1¯2}, D2 {112¯}, J{110} and J¯{1¯1¯0} shear components in the TMAZ of higher welding speed sample. Moreover, heat affected zone (HAZ) of both samples showed higher evolution of low angle grain boundaries (LAGBs) indicating that the grains are in the dynamic recovery stage due to lower temperatures and strain.

Friction stir spot welding (FSSW) of similar AA5052-H32 joints has numerous benefits in shipbuilding, aerospace, and automotive structural applications. In addition, studying the role of tool rotation speed on the microstructure features, achieved textures, and joint performance of the friction stir spot-welded (FSSWed) joint still needs more systematic research. Different FSSWed AA5052-H32 lap joints of 4 mm thickness were produced at different heat inputs using three tool rotation speeds of 1500, 1000, and 500 rpm at a constant dwell time of 2 s. The applied thermal heat inputs for achieving the FSSW processes were calculated. The produced joints were characterized by their appearance, macrostructures, microstructures, and mechanical properties (hardness contour maps and maximum tensile–shear load) at room temperature. The grain structure and texture developed for all the FSSWed joints were deeply investigated using an advanced electron backscattering diffraction (EBSD) technique and compared with the base material (BM). The main results showed that the average hardness value of the stir zone (SZ) in the welded joints is higher than that in the AA5052-H32 BM for all applied rotation speeds, and it decreases as the rotation speed increases from 500 to 1000 rpm. This SZ enhancement in hardness compared to the BM cold-rolled grain structure is caused by the high grain refining due to the dynamic recrystallization associated with the FSSW. The average grain size values of the stir zones are 11, 9, and 4 µm for the FSSWed joints processed at 1500, 1000, and 500 rpm, respectively, while the BM average grain size is 40 µm. The simple shear texture with B/-B components mainly dominates the texture. Compared to the welded joints, the joint processed at 500 rpm and a 2 s duration time attains the highest tensile-shear load value of 4330 N. This value decreases with increasing rotation speed to reach 2569 N at a rotation speed of 1500. After tensile testing of the FSSWed joints, the fracture surface was also examined and discussed. [ABSTRACT FROM AUTHOR]

In metal additive manufacturing (MAM), laser direct energy deposition (L-DED) and wire arc direct energy deposition (W-DED) are commonly used methods that also possess challenges in the part quality due to the effect of different process parameters. Very little knowledge is currently available on the single-layer thermal behavior, cooling rate, melt pool dimension and their correlation with the microstructure for the DED processes (L-DED and W-DED). In this study, a comparative analysis of the microstructural characteristics along with hardness of austenitic stainless steel (SS 316L) samples is conducted to understand the variations between the L-DED and W-DED processes. It is observed that the microstructure of the W-DED samples possesses more columnar dendritic structure than the L-DED due to slower cooling rate in W-DED. It is also found that the ferrite (δ) phase fraction is 23% higher in W-DED than L-DED. There is also the formation of carbide precipitation at the fusion boundary in the L-DED samples. In L -DED, the grains are mostly oriented along the<001>/<111>direction, whereas in W-DED, the dominant orientation is<111>/<101>. The W-DED samples have significantly higher HAGB fraction (49%) than the L-DED samples. The detailed texture analysis of the samples showed that the L-DED has lower average grain misorientation than the W-DED along with ND rotated cube, twin copper, and cube structures. The hardness data reveals that the W-DED samples possess much higher hardness compared to the L-DED samples. [ABSTRACT FROM AUTHOR]

Calcite veins are widely developed in organic-rich shale, and their petrological characteristics and genetic mechanism are the focus of research. The Electron Back Scatter Diffraction (EBSD) can characterize the micro-structure and orientation of mineral crystals in situ, which has been widely used in the field of material science and has been rapidly developed in the field of geology. In order to clarify the crystal characte-ristics of fibrous calcite veins in organic-rich shale of the Longmaxi Formation in the Sichuan Basin, EBSD was used to characterize the mineralogical and crystallographic characteristics of calcite veins. The calcite veins are mainly composed of calcite and quartz. Calcite is the main body, with an average grain size of 372 μm, while quartz is mainly distributed at the interface of calcite lamina. The calcite crystals in calcite veins belong to trigonal[JP] or rhombohedral system, and the corresponding unit cell is trigonal or rhombohedral. The lattice parameters are a0=b0=4.99 Å, c0=17.061 Å, α=β=90°, γ=120°, respectively. Calcite veins have a certain preferred orientation on longitudinal section, which is due to the development of polysynthetic twin crystals in calcite grains. The adjacent twin crystal stripes have different crystal orientations, and the crystal misorientation is 75° while the alternate twin stripes have the same crystal orientation, and the crystal orientation of the same twin stripe is the same. In calcite grains, perfect cleavage occurs in groups with sharp angle with twin crystal stripes. Both cleavage and twin crystal stripes are formed by tectonic compression and shearing during the crystallization of calcite, and the maximum principal stress direction is parallel to the twin crystal stripes.

Magnanimously Aluminium metal matrix composites (MMCs) are acknowledged worldwide for keeping exceptional strength to weight ratio for which these are incorporated extensively in Aerospace and Automobile industries and gained potential limelight. Moreover, the material response outreach potential or the composite functionality potential are exclusively driven by tuning of the reinforcement materials. Herein, Al composites were concocted by introducing micro and nano Boron Carbide (B 4 C) powder into aluminium alloy AA 7075-T6 material matrix through Friction Stir Processing (FSP) with a motivation to enhance the mechanical and damping properties. Further the influence of physical structure alteration of reinforcement B 4 C from micro to nano dimension on the composites were validated through various characterizations. The microstructure of the composites was observed with optical microscope and Electron back scattered diffraction (EBSD) methods respectively. A significant grain refinement was observed with nano-reinforced composite by clinching average grain size reduced to 2.9 μm relative to base material grain size of 37 μm. The average hardness of nano-reinforced MMCs was found to be 66% higher than base material recorded a value of 141 HV. Furthermore, the AA7075-T6 composites were studied for their thermal and mechanical cyclic damping performance in the temperature range from ─ 60 to 60 °C and depicted exceptionally good damping property. [ABSTRACT FROM AUTHOR]

The change in microstructure and mechanical properties ofTi–6Al–4V alloy due to 160 MeV O6+ ion irradiation has been reported here. Detailed X-ray diffraction line profile analyses have been used to evaluate the microstructural parameters and characterize the nature of defects and their arrangements. The results indicate saturation of size of the coherent region, the dislocation density and its arrangement with dose, which points to an optimized final microstructure of irradiated material. This was also supported by the Vicker's microhardness measurements. Electron back scattered diffraction study was used to assess the changes in microstructure in terms of the evolution of misorientation boundaries within the grains due to irradiation-induced defects. All the results support the radiation resistance nature of Ti–6Al–4V alloy. Finally, comparison has been made with earlier proton irradiation results, and the difference has been related to the nature of the displacement cascade produced by light and heavy ions. [ABSTRACT FROM AUTHOR]

Aluminum metal matrix composites of the varying percentage of SiC reinforcement were welded using the tungsten inert gas welding technique. For all the conditions of the specimen, the welding parameters were kept identical. The welded composites were thermally aged to peak age-hardening conditions. Significant differences in microstructure exist between aged and non-age hardened composites in terms of misorientation, grain boundary fractions and stored energy. These differences in microstructure were seen through identical changes in the mechanical behavior of the welded composites. After aging, microstructure showed refinement in grain size and preferential orientation. Hardness and tensile strength increased at different rates with increase in SiC content indicating that hardness was a clear function of stored energy and strength had a dependence on the misorientation. EBSD measured suggests that due to age hardening, a rearrangement in dislocation substructures occurred with precipitation of Mg2Si or increasing SiC content followed by dynamic recovery of the weld metal region which leads to enhancement of hardness. The increase in tensile strength with decreased misorientation was a clear indication that the effect of annihilation of dislocations as a result of recovery was less pronounced and precipitation strengthening was dominant. The present study aims to address the role of SiC addition in aluminum metal matrix composites on the welded microstructure and finally relating the microstructural changes to the observed mechanical behavior of the welded joints. The study reveals that strength not only depends on the average value of misorientation but also on the distribution of misorientation in the microstructure.

In the present work, we report the observation of deformation kinking bands in β-treated commercial pure zirconium sheets during impact experiments. Crystallography analyses based on electron backscatter diffraction (EBSD) technique reveal that these kinking bands exhibit a common rotation axis of 〈 10 1 ¯ 0 〉 with misorientation angles varying in a wide range and are not belonging to anyone of the well-established twinning modes in Zr. Based on the combination of Schmid factor calculation and in-grain misorientation axes (IGMA) determination, the underlying mechanisms accounting for their formation are proposed and discussed. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The effect of strain path on the microstructure evolution of two different advanced high strength steel alloys (AHSS alloys) has been studied in this work. The two AHSS alloys considered are Transformation Induced Plasticity (TRIP) and Quenched and Partitioned (Q&P) steels. The formability of these AHSS was calculated at different strain paths using limit dome height (LDH) tests. Both of these AHSS show unusual formability behavior at the stretching region of the Forming Limit Diagram (FLD). A comprehensive microstructure and texture study was performed at different strain levels and near the principal strain paths to understand the effect of microstructure on the formability of these AHSS. This study clearly highlights the significance of development of α and γ fibre texture, at different strain paths, affecting the formability of AHSS steels. Additionally, the evolution of other microstructure and crystallographic texture features such as phase transformation, misorientation development, texture intensity and Taylor's factor also affect the formability of these AHSS. It has also been observed that γ fibre, maximum orientation distribution (ODF), texture intensity and misorientations are reduced in the stretching region and decrease the formability of these AHSS. [ABSTRACT FROM AUTHOR]

Fatigue crack resistance is a critical factor for the performance of aero-engine components. Deep cold rolling (DCR) is one promising surface enhancement technique, as it generates deep compressive residual stresses with the good surface finish. In this work, the influence of DCR process on the microstructure and mechanical properties of nickel-based superalloy (Udimet 720Li) was investigated. After DCR process, a deep layer of compressive residual stress up to 1mm was observed, which agrees well with the depth profile of Vickers micro-hardness. Statistical analysis of Grain Orientation Spread (GOS) in the Electron Back Scattered Diffraction (EBSD) map also shows the presence of strain hardening layer after the DCR process. Results are discussed with a focus on the strengthening mechanism through grain refinement, the addition of Low Angle Grain Boundaries (LAGBs), and intragranular deformation in the sub-surface. Overall, this fundamental understanding could shed light on a new pathway to develop nickel-based superalloys with an excellent mechanical performance for aerospace applications. [ABSTRACT FROM AUTHOR]

We introduced a strategic "Kinetic Diffusion Multiple" (KDM) that undergoes interdiffusion annealing followed by realistic thermal treatment. The blended spectra of phases and microstructures subjected to treatment in deeply grooved composition gradients enables the microstructure and micromechanical properties of structural materials to be surveyed by high-spatially resolved micro-analysis along the composition arrays. The KDM was demonstrated as a robust high-throughput methodology that enables rapid screening of the composition-microstructure-micromechanical/properties relationships for different metallic materials. It has also proven great success at elucidating the lasting effects of alloying elements and diffusion flux on microstructure, micromechanical properties, phase transformation, and their interrelationships as a whole. [ABSTRACT FROM AUTHOR]

The effect that twin activity in Magnesium alloys has in both local and global strain is investigated in this article. The need to investigate this effect is related to difficulties in associating the spatially varying twinning with both plasticity and failure of this particular class of alloys. To address this need, mechanical testing both inside and outside the Scanning Electron Microscope was conducted and it was coupled with Digital Image Correlation (DIC) deformation and Electron Backscattered Diffraction (EBSD) texture measurements. In addition volume recordings of Acoustic Emission (AE) and surface measurements of microstructural changes were used to further complement the in situ tracking of twinning activity throughout monotonic and cyclic mechanical loading experiments. The definition of appropriate monitoring regions allowed the direct correlation of evolving twin activity with associated deformation in Magnesium alloys, for the first time to the authors’ best knowledge, from which twinning contributions to strain localizations were computed. [ABSTRACT FROM AUTHOR]

In this study, the effect of ceramic nanoparticles addition on the microstructure and texture of friction stir processed (FSP) copper has been investigated. For this purpose, two pure copper plates with and without Al 2 O 3 nanoparticles were FSPed at rotational speed of 800 rpm and traverse speed of 100 mm min −1 . Electron back scattered diffraction (EBSD) technique was employed in order to study the microstructure and texture of the fabricated samples. Based on the obtained results, considerable grain refinement by dynamic recrystallization (DRX) mechanism was observed in both specimens. However, Al 2 O 3 inset led to evolution of ultrafine grained (UFG) structure with an average grain size of 0.7 µm. In addition, Al 2 O 3 addition caused formation of lower twin boundaries and stronger texture components compared with the sample without ceramic reinforcements. The presence of nanoparticles increased the proportion of the continuous DRX mechanism (CDRX) compared to the discontinuous mechanism (DDRX) during grain structure formation. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) techniques impose very high level of strains and it can enhance the strength of a material several folds. In the current work, Inconel 718 alloy was severely deformed by machining process resulting in inherently “bi-modal” grain size distribution consisting of sheared zone with nano-structured grains and moderately refined grain zone. Hardness of machined chips were found to be much higher than that of bulk and increased further upon giving heat-treatment because of precipitation of γ’’ and γ’ nano-precipitates. However, as with most severely deformed materials, ductility of the machined chip is known to be very low, primarily because of the presence of large fractions of dislocation-saturated nano-structured grains which hinder any more dislocation generation or movement. In this work, we gave short heat-treatment to these deformed samples at elevated temperature to ensue controlled recrystallization in the sheared zone. However, heat-treatment is also expected to result in coarsening of precipitates as well as the grains of the matrix. This phenomenon may, not only reduce the strength, but may also reduce the pinning ability of the precipitates which endow the microstructure with thermal stability. Hence, the specific objective of this work is to understand the interplay of grain boundary pinning and recrystallization, both of which occur at elevated temperatures. Short heat-treatment of the severely deformed samples was performed for 15 min between 700 °C to 900 °C. It was found that temperatures up to 800 °C do not lead to appreciable recrystallization, while 900 °C heat-treatment can cause appreciable recrystallization, albeit, limited to the shear zone. Size of precipitates was also found to grow with increasing temperature, nonetheless, samples heat-treated at 900 °C were found to be thermally stable with a good fraction of coincidence site lattice boundaries, low grain size and improved hardness. [ABSTRACT FROM AUTHOR]

Brandon’s criterion is frequently used to quantify distribution of coincident site lattice (CSL) boundaries in studies related to grain boundary character distribution. This criterion is based on theoretical considerations and is meant to define a range within which special boundaries may exist. Experiments have repeatedly shown that this range includes boundaries which do not show special properties. A broad aim of this study is to explore if there exists a cut-off in deviation which includes only boundaries with special properties. While most other criteria in literature are based on theoretical dependence of secondary dislocation spacing, in this work we find the cut-off deviation through experimental data of recrystallised microstructures fromin situas well asex-situheating experiments. Deviation from structure was considered in terms of both, deviation of misorientation axis-angle as well as deviation of the boundary plane from the symmetric tilt orientation. Our results indicate that the deviation in terms of misorientation angle is more important than boundary plane deviation. We also show that the limiting deviation for various orders of twin boundaries (Σ3n) in a recrystallized microstructure is a constant and approximately 1° which is significantly lower than that defined by Brandon’s criterion. We show that this constant cut-off deviation for various Σ3nCSL boundaries can also be obtained by assuming that the secondary dislocations are spaced proportional to displacement shift complete lattice vector. Similar analysis was also carried out for non-Σ3nboundaries but due to limited statistics, no cut-off value could be deduced for these boundaries. [ABSTRACT FROM PUBLISHER]

This study illustrates microstructural evolution of INCONEL 625 superalloy coatings cold-sprayed on a 4130 chrome alloy steel with medium carbon content. INCONEL 625 powder (5–25 μm) were successfully cold sprayed without any oxidation. The comprehensive microstructure analysis of the as-sprayed coatings and of the substrate-coating interface was carried out using EBSD, TEM, and XRD. The coating microstructure at the substrate-coating interface was markedly different from the microstructure away from the interface. The coating microstructure at steel-coating interface consisted of a fine layer of small grains. The microstructure beyond this fine layer can be divided into splats, inter splat and intra splat boundaries. Both splat and splat boundaries exhibited deformation induced dislocations. Dynamic recovery of dislocations-ridden regions inside the splat was responsible for the development of sub grain structure inside a splat with both low and high angle grain boundaries. Splat-splat (inter splat) boundary consisted of a relatively high density of dislocations and shear bands as a result of adiabatic shear flow localisation. This flow instability is believed to enhance the microstructural integrity by eliminating porosity at splat-splat boundaries. Based on the microstructural analysis using electron microscopy, a plausible mechanism for the development of microstructure has been proposed in this work. Cold spray technique can thus be deployed to develop high quality coatings of commercial importance. [ABSTRACT FROM AUTHOR]

Interface between ceramic particulate and matrix is known to control the response of the materials and functionality of the composite. Among numerous physical properties, grain structure of the materials has also played a significant role in defining the behaviour of metal matrix composites. Usually, silicon carbide (SiC) particles show poor interfacial wettability in aluminium melt. Herein, we were successfully synthesized magnesium oxide (MgO) and nanocrystalline magnesium aluminate (MgAl 2 O 4 ) spinel coated silicon carbide (SiC) core-shell micro-composites through sol-gel technique to improve the wettability of dispersoids. Core-shell structures of submicron size were thoroughly investigated by various characterization techniques. Further, aluminium matrix composites incorporated with pristine SiC, MgO grafted SiC and MgAl 2 O 4 grafted SiC particles were fabricated by stir casting technique, respectively. Additionally, as-cast composites were processed via friction stir processing (FSP) technique to observe the influence of grain refinement on mechanical and damping properties. Electron back scattered diffraction (EBSD), Field emission scanning electron microscopy (FE-SEM) and X-ray energy dispersion spectroscopy (EDX) analysis were conducted for investigating grain size refinement, adequate dispersion, stability and de-agglomeration of encapsulated SiC particles in aluminium matrix. The mechanical as well as thermal cyclic (from − 100 to 400 °C) damping performance of the as-cast and friction stir processed composites were studied, respectively. Finally, the enhanced properties were attributable to reduced agglomeration, stabilization and proper dispersion of the tailored SiC particles Al matrix. [ABSTRACT FROM AUTHOR]

Nitrogen alloyed austenitic stainless steels are recently developed and are finding applications in defence because of improved mechanical properties and corrosion resistance. Welding is the main fabrication technique to join the structural components. During welding, it may result in porosity, solidification cracking in weld zone, liquation cracking in heat affected zone and inferior properties compared to base metal. Selection of filler wire plays a major role to obtain a sound weld and to have a better mechanical and corrosion resistance. In the present work, gas tungsten arc welding of 5 mm thick nickel free high nitrogen stainless steels were carried out. As no suitable matching filler wires have been developed, commercially available high strength fillers of precipitation hardenable (PH) 13-8Mo filler and nickel based (MDN 250) 18Ni filler were used for welding high nitrogen stainless steel. Microstructural studies were carried out using optical microscopy and field emission scanning electron microscopy (FESEM). Electron back scattered diffraction (EBSD) technique was used to determine the grain size, phase analysis and orientation mapping. Hardness values were recorded using Vickers hardness tester. Results of the present investigation established that the weld zone/fusion zone was observed to have delta-ferrite in the austenite matrix for both the welds. Welds made with (MDN 250) 18Ni filler had an unmixed zone adjacent to the weld zone near fusion boundary. Welds made with (PH) 13-8Mo filler had high hardness which might be attributed to relatively finer grains in the weld zone. Improved pitting corrosion resistance for welds made with (PH) 13-8Mo filler might be attributed to the composition of the filler wire. The presence of chromium and molybdenum helped in enhancing the stable passive film when compared to that of welds made with MDN 250 filler. [ABSTRACT FROM AUTHOR]

One of the key aspects influencing microstructural design pathways in metallic systems is grain boundary motion. The present work introduces a method by means of which direct measurement of grain boundary mobility vs. misorientation dependence is made possible. The technique utilizes datasets acquired by means of serial electron backscatter diffraction (EBSD) measurements. The experimental EBSD measurements are collectively analyzed, whereby datasets were used to obtain grain boundary mobility and grain aspect ratio with respect to grain boundary misorientation. The proposed method is further validated using cellular automata (CA) simulations. Single crystal aluminium was cold rolled and scratched in order to nucleate random orientations. Subsequent annealing at 300 °C resulted in grains growing, in the direction normal to the scratch, into a single deformed orientation. Growth selection was observed, wherein the boundaries with misorientations close to Σ7 CSL orientation relationship (38° 〈111〉) migrated considerably faster. The obtained boundary mobility distribution exhibited a non-monotonic behavior with a maximum corresponding to misorientation of 38° ± 2° about 〈111〉 axes ± 4°, which was 10–100 times higher than the mobility values of random high angle boundaries. Correlation with the grain aspect ratio values indicated a strong growth anisotropy displayed by the fast growing grains. The observations have been discussed in terms of the influence of grain boundary character on grain boundary motion during recrystallization. [ABSTRACT FROM AUTHOR]

Two different microstructures of Ni–Ti–Fe shape memory alloys processed through different thermo-mechanical treatments with nearly similar grain size and in-grain misorientation but different crystallographic textures were subjected to series of thermal cycles without external loading. The microstructures and the phase transformation behavior of the samples were examined after every seventy cycles. The experiment involved treating the samples with liquid nitrogen (LN2) for complete martensitic (B19′) transformation and then heating it back to parent austenite (B2) condition. Thermal cycling introduced significant differences in microstructural parameters especially the grain boundary nature, stored elastic energy and the misorientation or defect densities. These microstructural alterations during thermal cycling were related to changes in transformation temperatures and enthalpy. Thermal cycling also brought out changes in crystallographic orientations of austenite grains. The present study aims to address the role of microstructure on the thermal fatigue behavior in Ni–Ti based shape memory alloys during cyclic transformations. [ABSTRACT FROM AUTHOR]

A new method based on electron back scattered diffraction (EBSD) is proposed to determine the structure of titanium oxide/MnS complex inclusion which induced the formation of intragranular acicular ferrite (IAF) in heat-affected zone (HAZ) in steel processed by oxide metallurgy route. It was found that the complex inclusion was Ti 2 O 3 /MnS, the orientation relationship between Ti 2 O 3 and MnS was also examined, and the crystallographic orientation relationship among IAF, Ti 2 O 3 /MnS complex inclusion, austenite, bainite formed at lower temperature is researched systematically. It was observed that MnS precipitated on Ti 2 O 3 at specific habit plane and direction and MnS had a specific orientation relationship ({0001} Ti 2 O 3 //{111} MnS), <10–10> Ti 2 O 3 //<110> MnS) with respect to Ti 2 O 3 . Intragranular acicular ferrite (IAF) nucleated on MnS part of the Ti 2 O 3 /MnS complex inclusion had no specific orientation relationship with MnS. IAF and the surrounding bainite had different Bain groups, so that there was an increase in high angle boundaries, which was beneficial for the toughness of HAZ. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBC) in service are prone to the attack by molten calcium–magnesium aluminosilicates (CMAS) resulting from the ingestion of siliceous minerals (dust, sand, volcanic ash) by the aeroengines. As CMAS deposits observed on ex-service parts present complex and highly variable compositions, progress in the understanding of the interaction mechanism between CMAS and TBC has been mostly obtained during laboratory experiments using simplified CMAS compositions. This paper consists in a microstructural characterization of the isothermal chemical interaction between a synthetic calcium aluminosilicate (CAS) and a standard 8YPSZ EB-PVD coating deposited on alumina substrates. The chosen CAS is the lowest melting temperature eutectic (1170°C) in the ternary (CaO–Al2O3–SiO2) system and it is prepared as a glass. The evolution of the reaction zone morphology and chemistry is studied after 1200°C treatments from 15min to 100h. The CAS/TBC interaction is governed by the classical mechanism of dissolution/reprecipitation with formation of Y-lean zirconia and Ca2Zr(Y)Si4O12. Ca2Zr(Y)Si4O12 formation induces local variation in the CAS composition leading to CaAl2Si2O8 (anorthite) precipitation. Y2O3 depletion in the YSZ regions infiltrated by CAS is attested using X-ray compositional mapping and the association of EDS and EBSD clearly illustrates that the morphological transformation from porous initial YSZ to dense globular Y-lean YSZ is associated with the structural transformation from initial tetragonal t′ to tetragonal Y-lean zirconia transforming into monoclinic during cooling. The degradation of the TBC columns increases with the duration of the 1200°C heat-treatment. The interfacial Ca2Zr(Y)Si4O12 phase forms on an increasing amount of columns and is finally observed on all the columns. Interfacial phase formation is discussed and compared to other phase assemblages reported in the literature. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mg-hybrid composites with micro-Ti and nano-SiC are developed. [•] Nano-SiC addition promoted localized DRX, and improved interfacial bonding. [•] Both Mg–5.6Ti and Mg–(5.6Ti+ x-SiC)BM composites showed similar texture. [•] The hybrid composites exhibited improved strength with retained ductility. [•] The best properties of strength and ductility were observed in Mg–(5.6Ti+1.0SiC)BM. [Copyright &y& Elsevier]

Abstract: An analysis of fatigue crack-initiation facets from the perspective of variability in lifetime of a duplex microstructure of Ti–6Al–4V is presented. Fatigue variability behavior of this alloy was marked by an increase in the lifetime variability to almost three orders in magnitude as the stress level was decreased. Crack initiation was found to occur primarily from the specimen surface with only a few exceptions where subsurface initiation was recorded. In most cases, and irrespective of lifetime, crack initiation was accompanied by crystallographic facet formation across primary-α particles. Crystallographic characterization of faceted grains and their neighborhood was conducted by sectioning across the facets using either focused ion beam or mechanical polishing, and subsequent Electron Back Scattered Diffraction analysis of the sections. The emphasis in this study was on discerning the factors that distinguish the crack-initiating microstructural arrangements and plausible mechanisms producing a life-limiting failure versus a long lifetime failure under nominally similar microstructure and applied stress level. The analyses revealed only subtle differences between the life-limiting and the long-lifetime failure in terms of deformation modes of the faceted grain(s) and their first nearest neighbors on a given section. The facets appeared to form on or near the basal plane in both the life-limiting and the long-lifetime, surface-initiated failures. In the life-limiting case, a combination of slip (in the faceted grain) and normal resolved stress across the facet plane seemed to be operational in facet formation. In the long-lifetime failure, shear along the facet plane appeared to be a more dominant deformation mode. The subtlety of differences indicates that the facet plane and the deformation modes of the faceting grain and its neighbors as determined from a 2D section may not be the most discriminating crack-initiation factors between the two lifetime regimes in this alloy. [Copyright &y& Elsevier]