Search

Vacuum induction melted equi-atomic NiMn alloy has been studied through x-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern of the as-solidified alloy may be matched with the tI2 η′-NiMn phase and the cF4 Ni3Mn phase simultaneously. In the TEM bright field image of the same alloy, alternating bright and dark contrast with chessboard-like appearance is observed. Electron diffraction patterns from the bright phase match with the tI2 NiMn phase. The electron diffraction patterns from the dark phase are related to the tetragonal phase with additional superlattice reflection along [110] and [112]. The crystal structure of the new phase has been found to be polymorphically related mP8 phase with space group P 2/m (a = 5.02 Å, b = 5.16 Å, c = 3.61 Å). The phase has not been reported so far in the Ni–Mn system. The chessboard-like morphology between a tetragonal and monoclinic phase is being reported for the first time.

Synthesis of Cu–In–S (CIS) nanoparticles by hot injection method using a mixed solution of Cu(acac), In(acac) and DDT in solvents OAm and trioctylphosphine oxide (TOPO), was carried in nitrogen atmosphere. Phase and crystallographic structure evolution were evaluated by extracting samples at intermediate synthesis stages and was characterized by X-ray diffraction and transmission electron microscopy. Ex-situ observation of phases indicated the formation and growth of Cu2S at the earlier stages. With further increase in temperature, CIS formed with the diffusion of In3+ ion. Wurtzite CIS nanoparticles preferentially grew along a length (from ~42 to 62 nm) while the width nearly remained constant to about ~32 nm. The preferential growth took place along [0002] while the particle width was oriented along [10 1 ‾ 0], which resulted in nearly oval-shaped nanoparticles. FTIR spectra recorded at different stages of synthesis (50–310 °C) pointed towards the ligand exchange mechanism after the addition of sulfur source at (160 °C).

Atomic arrangements in the nanostructured grains and interfaces of thermally evaporated Au/Cu multilayer thin films on polycrystalline Si substrate have been explored through GIXRD, HRTEM, simulation, and direct structure imaging. GIXRD pattern conforms to cF4 solid solution of Au and Cu with peak broadening and shift. Comparative analysis with simulation indicated the presence of cP4, tP4, oP8, and oI40 phases in the multilayer. The Cu layer is amorphous. Localized amorphous phase forms at the Cu–Si interface due to the impingement of Cu atoms during deposition. Interfaces of Au–Cu are wavy. The Au layer is polycrystalline and columnar with some twin-like defects present in them. At the Cu–Au interface, diffusionally grown cP4, tP4, oI40, and oP8 phases could be observed. Adatom mobility, concurrent growth, and coalescence of growth islands lead to columnar growth. Ordered intermetallic phases could be related with the cF4 solid solution phase through polymorphism. The strain associated with the polymorphs and the solid solution phase is quite small. Faceted semi-coherent interfaces of the ordered phases with the solid solution phase have been resolved. The ordered phases grow into the solid solution matrix by homogeneous transformation. Structure imaging of the ordered phases indicated that most of the time a cluster of atoms is imaged in these structures. The interfaces are likely to be chemically diffused in nature. Polymorphism and homogeneous nature of the transformation at low temperature allows local transformation to ordered phases, that explain the phase field ambiguity in the binary phase diagram. Such structural details are critical in understanding the novel properties in these nanostructured alloys.

A newly designed composition of non-equiatomic Fe40Cr25Ni15Al15Co5 medium-entropy alloy (MEA) was produced by induction melting (IM). The as-cast alloy was found to consist of a two-phase microstructure of BCC (2.87 ± 0.01 A) and ordered B2 (2.88 ± 0.02 A) type phases. The structures of these phases were confirmed through X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It was observed that the Ni-Al-enriched ordered B2 phase of cuboidal shapes (~ 100 to 200 nm) is homogeneously distributed in Fe-Cr-rich BCC matrix with a cube-on-cube orientation relationship. The formation of the columnar dendrites (width 50 to 100 μm) was identified through optical microscopy (OM). The structural and microstructural stability of the alloy was investigated by heat-treating the alloy through different schedules. Heat-treated samples at different temperatures (< 1273 K) exhibit a similar type of two-phase microstructure with columnar dendrites. However, compositional rearrangement takes place during long time exposure to develop polymorphically related phases. The alloy was observed to possess a high compressive yield strength and hardness, i.e., ~ 1047 MPa and 391 ± 9 HV, respectively, at room temperature. Heat-treated samples at 600 °C and 900 °C (873 K and 1173 K) showed an increase in yield strength and ultimate strength with a significant increase in plasticity due to the increase in volume fraction of B2 phase and softening of the BCC matrix phase. The thermal stability and high strength of this alloy may open new avenues for high-temperature applications.

An equiatomic quinary MgAlMnFeCu high-entropy alloy (HEA) has been synthesized successfully by mechanical alloying (MA). Phase evolution of MgAlMnFeCu HEA has been studied using X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS/XEDS). Milling up to 60 h leads to the formation of a mixture of two phases consisting of a BCC phase (a = 2.87 ± 0.02 A) and ϒ-brass-type phase (a = 8.92 ± 0.03 A), with ~ 2 μm powder particle size. The as-milled alloy after spark plasma sintering (SPS) at 900 °C exhibits an experimental density of 4.946 ± 0.13 g cc−1, which is 99.80% of the theoretical density. SPS leads to the formation of C15 Laves phase (MgCu2-type; a = 7.034 ± 0.02 A) and B2 (AlFe-type; (a = 2.89 ± 0.02 A) intermetallic along with the ϒ-brass-type phase. The SPSed sample has exceptional hardness value (~ 5.06 GPa), high compressive strength (~ 1612 MPa) and appreciable failure strain (~ 6.4%) coupled with relatively low density. Various thermodynamic parameters have been considered for understanding the phase evolution and their stability during MA.

It has earlier been reported that that the gallium incorporation in wurtzite CuInS2 (CIS) results in structural distortion, non-homogeneous shape, and distribution of particles. However, a detailed study of the effect of Ga substitution on the structure and morphology has not been reported. Here, we report the synthesis of nanocrystalline CuInxGa1−xS2 (x = 1, 0.7, 0.5, 0.3, and 0) wurtzite particles by solution processing in a nitrogen atmosphere. Structural analyses by X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the as-synthesized CuInS2 (CIS) and CuGaS2 (CGS) nanoparticle were single-phase wurtzite structures, whereas CuIn0.7Ga0.3S2, CuIn0.5Ga0.5S2, and CuIn0.3Ga0.7S2 had three wurtzite phases having In-rich, In–Ga, and Ga-rich compositions. The shape of the resulting nanoparticles was either elongated, polygonal, or tadpole depending on the phase composition. In-rich particles had elongated rod-like morphology, the In–Ga particles were irregular hexagonal/equiaxed, while the Ga-rich phase formed with a tadpole morphology. The bandgap of the wurtzite-CuInxGa1−xS2 increased with Ga substitution: from 1.49 eV for CIS to 2.0 eV for CGS.

In this paper, we investigate the impact of rice-starch stabilization of gold nanoparticles (AuNPs) on their catalytic and surface-enhanced Raman spectroscopy (SERS) activities. A typical green synthesis protocol was used to prepare AuNPs with rice-starch functioning as the reductant and the stabilizer. The localized surface plasmon resonance (LSPR) of the starch-stabilized AuNPs is pH-sensitive and got red-shifted with the medium’s pH. The average size of the AuNPs formed decreased with the amount of rice-starch up to a certain level. TEM result shows that the polymeric behavior of starch extract may help synthesize the Au nanorod morphologies. AuNPs stabilized by different amounts of rice-starch were applied as the catalysts for the model [Formula: see text]-nitrophenol reduction reaction. For all AuNP catalysts used, the reaction followed pseudo-first-order kinetics. The catalyst turnover frequencies increased up to a certain level of starch functionalization. Further increase in starch led to a fall in the activity of AuNPs catalyst. The evidence on rate kinetics, induction times, activation energies, and turnover frequencies is combined to explain this phenomenon in terms of starch content. The SERS response of these AuNPs as substrates has also been investigated for methylene blue as the target molecules. AuNP substrates with an excess amount of starch weaken the SERS response and it can be ascribed to decreased light scattering efficiency of NPs as well as reduced interactions of methylene blue molecules with the NP surface.

In this work, nanocrystalline tungsten oxide (WO3) powder was obtained by high energy ball milling (HEBM) followed by heat treatment of tungsten (W) powder. HEBM significantly influenced the oxidation behavior by reducing the crystallite size and inducing lattice strain in W powder. The resultant nanocrystalline WO3 shows variation in the optical bandgap with respect to the bulk counterparts. The alteration in the bandgap of WO3 is ascribed to the changes in crystallite size and the unit cell volume. In the end, a thorough correlation between fundamental interactions of these changes was succinctly highlighted.

Intermetallic phases in Au-Cu nanoparticles has been synthesized chemically in liquid phase. The heat-treatment of these nanoparticles at 180 °C for 1 h in solution phase led to the formation of Au-Cu alloy nanoparticles with nearly spherical shapes and monodispersed size of ∼10 nm. Subsequent heat-treatment at 300 °C for 30 min of these Au-Cu alloy nanoparticles not only revealed structural transformation to intermetallic phases (tetragonal AuCu (tP4) and cubic Cu3Au (cP4)) but also shape change occurs from spherical to rods having average aspect ratio ∼3.0. The structural determination at the particle has been carried out through nano-beam electron diffraction coupled with simulation of electron diffraction patterns and high resolution phase contrast images. These Au–Cu intermetallic nanoparticles exhibit an excellent surface enhanced Raman spectroscopic activity with methylene blue compared to that of Au-Cu alloy nanoparticles.

Alloyed nanostructures of Au Cu in varying compositions were synthesized by wet chemistry routes. Synthetic products in all the compositions are FCC solid solutions of Au Cu with slightly varying lattice parameter. Variation in shape, size, and nature of attachment has been studied through electron microscopy and localized surface plasmon resonance measurements. FCC solid solutions upon heat-treatment at ~400 °C for 1 h under N2 atmosphere, transform to orthorhombic AuCu (oP8) and many superlattice structures based on it. Nano-beam electron diffraction reveals multiplication of periodicities along [3 1 ¯ 0], [210] and [201] directions, mostly originating due to the chemical or vacancy ordering. Symmetry breaking transitions of orthorhombic AuCu (oP8) from Pbam to P21212 has been observed. The phase with P21212 space group also shows polymorphic transition to P21221. All these transitions have been confirmed through nano-beam electron diffraction coupled with computed diffraction patterns based on Wyckoff positions. Commonly observed orthorhombic (oI40) AuCu upon heat-treatment has not been found. The multiplication of lattice periodicity along certain crystallographic directions, symmetry breaking transition and polymorphism in the same sub-group are important findings of this work. These might have far-reaching implications in electron transport properties of such nanostructures.

The influence of mechanical milling (MM), primarily on microstructure and phase evolution in Al62.5Cu25Fe12.5 (at%) quasicrystalline (IQC) matrix reinforced with varying volume fraction of Sn has been investigated by means of X-ray diffraction (XRD), scanning & transmission electron microscopy (SEM and TEM) and differential scanning calorimetry (DSC) methods. It was observed that with increasing the milling duration, the IQC phase transforms to crystalline B2 phase [Al (Cu, Fe) and Pm3 m, a = 0.29 nm]. In SEM and TEM analysis, it was found that both IQC and Sn particles are refined during MM. The XRD and TEM results confirm the formation nanostructured matrix consisting of nanocrystalline B2 phase along with minor IQC phase reinforced with ultrafine grained Sn particles after 40 h of MM. The STEM-EDS results show a homogenous distribution of elements (Al, Cu, Fe). The Sn particles were immiscible in a matrix consisting of B2 and IQC phase as indicated by XRD and TEM investigations.

Materials science and engineering / A 802, 140687 (2021). doi:10.1016/j.msea.2020.140687, The present investigation studied the influence of initial texture on large strain deformation behavior of hexagonal close packed (HCP) titanium in high pressure torsion (HPT). Discs of two distinct initial textures comprising of near basal and near prismatic-pyramidal orientations were subjected to HPT at room temperature. X-ray diffraction (XRD) revealed the formation of omega phase in HPT processed samples with the fraction of omega phase increasing with increase in strain. Transmission electron microscopy and precession electron diffraction showed the formation of nanocrystalline grains of alpha and omega phases in 5 turns samples for both the orientations. Although omega transformation initiated first in the prismatic-pyramidal textured sample, the basal textured sample showed higher omega volume fraction at higher strain. The mechanical response based on micro-hardness measurements is different for the aforementioned two different initial textures. This is because hardness depends not only on the omega phase fraction, but also on the grain size and distribution of the nanocrystalline omega phase. Further, the relative contributions of strengthening imparted by the omega phase and hardening caused by the accumulated strain component determines the overall hardness profile. Also, synchrotron XRD measurements were performed to estimate crystallite size, microstrain and dislocation densities. The latter analysis coupled with the microstructural analysis indicates that initial texture and crystallographic orientation relationships of omega transformation influence the distribution of omega phase and strain partitioning between the alpha and omega phases, resulting in a strong texture dependence of hardness response., Published by Elsevier, Amsterdam

In this investigation, we have reported the alloying behavior, phase evolution, and thermal stability of equiatomic AlCoCrFeNiTi high-entropy alloy (HEA). The 40 h milled powder shows good chemical homogeneity with agglomerated particles varying in the range of ∼3–18 μm. The formation of a nanostructured single-phase BCC (a = 2.85 ± 0.01 A) was observed along with the minor tungsten carbide (WC) phase that formed due to contamination during milling. Thermal stability of the alloy has been studied using dynamic differential scanning calorimetry (DSC) thermogram and in situ X-ray diffraction. It has been found that this HEA is stable up to 600 °C (873 K). Consolidated samples at 1000 °C (1273 K) showed the transformation of body centered cubic (BCC) phase into the B2 (a = 2.87 ± 0.03 A) phase co-existing with minor hexagonal WC (a = 2.90 A, c = 2.83 A) phase.

An equiatomic quinary AlCoCrFeNi high entropy alloy (HEA) has been synthesized by mechanical alloying. Milled powder after 30 h shows good chemical homogeneity and refined morphology with a mean particle size of ∼4 μm. Solid solution phase with BCC crystal structure (a = 2.89 ± 0.02 A) has been confirmed from XRD and transmission electron microscopy in the as-synthesized high entropy alloy. The milled alloy powder is not thermally stable. Differential scanning calorimetric (DSC) thermogram of 30 h milled powder exhibits the presence of a small peak at ∼600 °C (873 K) with a thermal shift near the peak. This thermal shift indicates the diffusive type of phase transformation in this alloy while heating. The analysis of the in-situ heating X-ray diffraction patterns at various temperatures extends support to the diffusive nature of the phase transformation. Upon heat treatment, the disordered BCC solid solution phase partially transforms to Ni3Al prototype L12 phase which precipitates at a lower temperature (350 °C (623 K)) as observed by in-situ XRD experiments. However, at high temperature annealing (575–800 °C (848–1073 K)) the evolution of a partially ordered BCC phase (B2) with lattice parameter (a = 2.87 ± 0.02 A), and L12 phase (a = 3.58 ± 0.05 A), along with tetragonal σ phase (a = 8.8 A and c = 4.53 A) are observed. Similar types of phases have also been identified after annealing and microwave sintering at 800 °C (1073 K) & 900 °C (1173 K) respectively. The transformation of ordered BCC phases along with two intermetallics such as L12 phase and σ phase suggests that the evolution of the high entropy phase in the milled condition leads to a combination of high entropy and medium entropy phases in the annealed condition.

An equiatomic AlCoCrFeNiMn hexanary high entropy alloy (HEA) was successfully synthesized by mechanical alloying. The 40 h milled powder exhibits chemical homogeneity with an average particle size of less than 3 μm. This alloy, after 40 h of milling produces a solid solution BCC phase (a = 2.89 ± 0.03 A), the lattice parameter of which is very close to the lattice parameter of Fe and Cr. Similar BCC solid solution phase is also obtained by following a two different milling schedule containing 3 elements i.e., AlCoCr & FeMnNi separately. Dynamic DSC thermogram of the hexanary alloy powder shows two exothermic peaks. The peak temperatures and heat evolution corresponding to each peak are sensitive to heating rates, indicating that the transformations are diffusional in nature. Phase evolution at these heat events was confirmed through high-temperature XRD and TEM study. It has been found that this alloy is stable upto 500 °C (773 K). Heat treatment at higher temperatures leads to the formation of a FCC phase closely related to Ni3Al type and Mn3Co7 type intermetallic phase. Microwave sintered samples show the similar kind of behaviour as in heat-treated powder. The BCC phase along with ordered Ni3Al type (L12) phase was observed in the bulk consolidated high entropy alloy. Thermo-physical properties of this alloy have been studied in order to elucidate its classification as high entropy alloy and to understand the essential differences with multicomponent glass forming alloys.

The metastable ω phase stabilizes either in hexagonal (P6/mmm) or trigonal ( $$ P\overline{3} m1 $$ ) structures depending upon the extent of collapse of the atomic planes. The stability between these two structures depends on the atomic scale shear mechanism of the ω formation and also on the relative composition of the bcc stabilizer. Detailed interpretation of the bcc → ω phase transformation demands understanding of structure, chemistry and interface of ω phase along with the bcc matrix down to the atomic level. Present paper deals with the structural imaging of partially collapsed ω structure and its lattice correspondence with the bcc phase in a phase-separated V–Ti alloy. High-resolution TEM characterization with the aid of phase-contrast image simulation and atomic structure modeling has been systematically carried out to study the structural aspects of the nanostructured ω. The contrast of the collapsed atoms and the corner atoms are understood through systematic studies of the experimental images and their corresponding column intensities, as seen along simulated exit waves and their phase and amplitude parts along different zone axis. Attempts have also been made to understand the qualitative nature of the electron channeling behavior along the different atomic positions of the ω structure.

We report the formation of new phases in bimetallic Au–Cu nanoparticles. These phases were observed in nanoparticle synthesised by adopting a three-step protocol in a single pot. Nanoparticles at 180°C for 1 h led to the formation of single-phase solid solution of Cu in Au. Subsequent heat treatment at 290°C for 2 h of these Au–Cu nanoparticles revealed three new phases. One of them relates to the modification of occupancy of Cu in an ordered AuCu tetragonal phase (tP4). This cell although retains tetragonal symmetry but displays metrical properties akin to that of a cube. The other two relates to vacancy ordering along directions in the {111} planes of an ordered AuCu3 cubic phase (cP4). On the one hand, statistical occupancy of vacancy on Cu site in this cell leads to the reduction of cell size from ∼3.75 Å to ∼3.5 Å whereas ordering of vacant layer on the other hand gives rise to symmetry breaking. Former continues to display cubic symmetry whereas latter transforms to a trigonal cell.

Thermal stability of CoCrFeNi high entropy alloy in as-milled and sintered conditions was investigated using X-ray diffraction, differential scanning calorimetry, transmission electron microscopy, and atom probe tomography. Composite microstructure consists of FCC and carbide with a fine dispersion of oxide was observed in the sintered condition. Unsolicited contamination of carbon and oxygen in the as-milled powder due to the milling medium had led to the formation of composite microstructure. An exceptional thermal stability was observed upon exposure of sintered compact to higher temperatures (0.56 Tm to 0.68 Tm) for the prolonged duration of 600 h. Sintered compact exposed to 700 °C (0.56 Tm) for 600 h showed negligible change in hardness and grain size. Analysis based on the modified Hall-Petch model for two phase alloy indicates the phase boundaries act as a strong obstacle while the major contribution to strengthening comes from grain boundaries. Keywords: High entropy alloy, Thermal stability, Atom probe tomography, Grain growth, strengthening

Understanding the structural characteristics in bulk metallic glass forming alloys is important in order to understand the atomic origin of its high glass forming ability and associated physio-chemical properties. Zr 60 Cu 10 Al 15 Ni 15 alloy was cast in a water cooled copper mold. Due to difference in cooling rate the bottom regions of the cast rod shows amorphous phase with randomly oriented short range ordered domains while in the top part of the cast rod having faceted or dentritic crystals of cF96 Zr 2 Ni and tP20 Zr 3 Al 2 phases were observed. The size of the short/medium range ordered domains is ~ 0.3 nm. Complete structural analysis of the crystalline phases indicates that complex interconnected polyhedral order exists in the crystalline phases which are related to Bernal deltahedra and Frank-Kasper polyhedra. Correlation with the size of short range ordered regions indicates that similar polyhedra may also exist in the liquid, the specific interaction of which leads to the formation of short range ordered domains and crystal nuclei. Morphology of the crystalline phases indicates strong interplay of solid-liquid interfacial energy; break down of solid-liquid planar interface and solute segregation during solidification and crystal nucleation.

Isothermal cross sections of the ternary phase diagram of Bi-Cr-O system have been established at 500 and 750 °C. Existence of a new compound Bi 22 Cr 18 O 60 was identified and it was characterized by XRD, SEM and TEM. Ternary phase diagram at 500 °C shows that no ternary compounds would coexist with liquid Bi at 500 °C. Only Cr 2 O 3 and Bi 2 O 3 would coexist with liquid Bi at this temperature. Equilibrations at 750 °C show that two ternary compounds, namely Bi 22 Cr 18 O 60 and Bi 38 CrO 60 can coexist with liquid Bi at this temperature and no other ternary compound would be stable in liquid Bi.

Over the last couple of decades vanadium and V-based alloys have received significant attention as a potential structural material for fusion power applications because of their favourable mechanical properties under irradiation and at elevated temperatures. They are also considered as the advanced options of storage materials for hydrogen and its isotopes. However, the higher affinity of V for O, C and N poses critical challenges in its engineering applications since they lead to degradation of mechanical properties. They can further interact with the matrix to produce metallic oxy-carbo-nitride precipitates. To a certain limit, these precipitates are beneficial and can be exploited to enhance the mechanical behaviour of the alloy through suitable microstructural design. However, this requires a prior knowledge of the interaction between the alloy and the impurity solutes. In the present work vanadium specific experiments have been designed and carried out to bring out the V-interstitial solute interaction by charging oxygen in the near surface region of vanadium. Microstructural and microchemical behaviour of the V-O solid solution has been studied through HRTEM (high resolution transmission electron microscopy) and HAADF (high angle annular dark field) coupled with EELS. Quantitative electron microscopy has been carried out to study structural modification of the alloy in atomic level caused by O charging.

V-Ti-Cr alloys have emerged as the potential candidate for many advanced engineering applications e.g. first wall blanket for fusion reactors, alternative energy technologies and hydrogen storage. Phase transformation behaviour of these alloys is not completely understood and the binary V-Ti phase diagram is still debated. The system becomes even more complicated with the addition of Cr as a ternary addition. Thermodynamic calculations indicate that within certain composition range in the V-Ti system, a prominent miscibility gap exists and the propensity for phase separation decreases with the addition of Cr in the binary system. Alloys with nominal composition of V-50Ti and V-40Ti-20Cr have been prepared through vacuum arc melting and detailed microstructural and microchemical studies have been carried out. Diffraction contrast and phase contrast microscopy studies confirm the occurrence of phase separation in both the alloys. The lamellar and interconnected nanostructured domains with coherent interfaces as seen in the phase contrast mode are indicative of possible phase separation in the alloys. It has further been confirmed by High-angle annular dark field (HAADF) studies associated with STEM-XEDS and STEM-EELS. Further, microscopic studies on the as melted and the heat treated alloys confirm that the phase separation propagates through a spinodal decomposition mechanism in this alloy and is not limited by nucleation and growth kinetics. Another interesting aspect of this study is the formation of nanostructured ω phase in the phase separated regions. Phase contrast microscopy studies in selected orientations confirm the presence of distorted hexagonal zones of ω phase in the phase separated domains of the alloys.

The present paper reports the growth and branching mechanism of W 18 O 49 nanowires grown on nanocrystalline tungsten (W) surfaces. Nanocrystalline W powder was prepared using high energy ball milling. The nanopowder was non-isothermally heat-treated up to 1400 °C in argon atmosphere. The nanowires of 30–50 nm diameter were observed on nanopowder surfaces after the heat-treatment. A model based on crystallographic shear phase formation to accommodate the oxygen deficiency during the reduction of WO 3 is discussed to explain the growth and branching mechanism of these nanowires which correlates well with the observed angle for the branching.

Low cycle fatigue (LCF) behavior of the AA7075 was studied in the solution treated-ultrasonic shot peened and the peak aged (ST-USSP-PA) condition and was compared with that of the peak aged and ultrasonic shot peened (PA-USSP) as well the peak aged-ultrasonic shot peened and stress relieved (PA-USSP-SR) condition, studied earlier. LCF tests were carried out under fully reversed axial strain control at different total strain amplitudes (Δet/2) from ±0.38% to ±0.60%. LCF life was highest in the ST-USSP-PA followed by the PA-USSP and PA-USSP-SR conditions. It was found that nanostructure of comparable size (~22 nm) was developed up to a depth of ~50 μm in all the three conditions, however, there was much variation in the type, size, distribution and number density of the metastable of η precipitates in the three conditions. While the size of the strengthening precipitates η′ was ~20 nm in the ST-USSP-PA, it was much smaller (~10 nm) in the other two conditions. High resolution TEM examination revealed high density of dislocations in the matrix and also within the equilibrium η precipitates in the PA-USSP condition whereas dislocations were not observed in η precipitates of the PA-USSP-SR and ST-USSP-PA conditions. Highest fatigue life in the ST-USSP-PA condition is attributed to more homogeneous distribution, larger size and higher volume fraction of the strengthening precipitates η′ and consequent increase in the resistance against fatigue crack initiation.

Cadmium Sulfide thin films were deposited on soda-lime glass substrates by chemical bath deposition technique at bath pH varying from 8 to 11. The films were annealed at temperature 120 °C for 5 min using radiative annealing. The best film coverage at thickness ~ 99 nm, with bandgap 2.15 eV and resistivity of 0.5x101 Ωcm was obtained at a bath pH 10.

In the present investigation efforts were made to study mechanically driven structural transformation in Sn reinforced Al–Cu–Fe icosahedral quasicrystalline (IQC) matrix nanocomposites. The sequence of structural transformation, phase composition, thermal stability and hardness of mechanically milled IQC-Sn nanocomposite powder were studied through X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning caloriemtery (DSC) and nanoindentation techniques. The XRD result suggests the formation of nano-structured composites. The IQC phase co-existed with monoclinic Al13Fe4 (a = 1.549 nm, b = 0.808 nm, c = 1.248 nm, α = β = 90°, γ = 107.72°; mC102) and B2-type Al (Cu, Fe) (a = 0.29 nm; cP2) phase in IQC-Sn nanocomposite powder subjected to mechanical milling for 40 h. The structural transformation and fraction of IQC, Al13Fe4 and B2–Al (Cu, Fe) phase depends upon the volume fraction of Sn and duration of milling. The crystalline phases formed during milling transformed to a stable IQC phase along with the other crystalline phases during subsequent annealing treatment. The structural transformations occurring during milling have a remarkable effect on indentation hardness, which is in the range of ∼ 4–7 GPa. This suggests that IQC-Sn nanocomposite produced through milling with desirable mechanical properties may be used as potential coating materials for engineering applications.

AlCoCrFeNi high entropy alloy (HEA) was synthesized by mechanical alloying (MA). Formation of single-phase solid solution of body centered cubic (BCC) structure (a = 2.88 ± 0.01 A) was confirmed from x-ray diffraction (XRD) and high-resolution synchrotron XRD. The nanostructure nature of the milled powder was observed through transmission electron microscopy (TEM). The milled powder was consolidated through conventional sintering at 900 °C (1173 K) for 2 h. The microstructure of the sintered AlCoCrFeNi HEA showed two types of grain distribution. Coarser size of grains varied in the range of ∼18–22 μm and finer grains of ∼ 2–10 μm sizes that are homogeneously distributed in the matrix. Detailed analysis of the x-ray diffraction pattern of sintered HEA showed the phase transition from parent BCC phase to Al–Ni type B2 phase (cP2) (a = 2.91 ± 0.02 A) and Ni3Al type L12 phase (cP4) (a = 3.56 ± 0.01 A) along with Co–Cr type σ phase (tP30) (a = 8.8 A, c = 4.53 A). The sintered samples showed high value of microhardness, i.e. 919 ± 18 HV at 300 g load. Alloy shows fascinating soft magnetic property with saturation magnetization of 70.05 A m2/kg (emu/gm) along with effective Curie temperature (TC) of ∼617 °C (890 K).

In the present investigation, attempts were made to study the effect of Al–Cu–Fe (40 vol%) quasicrystalline (QC) reinforcement on the structure, morphology and phase composition of 6082 Al matrix nanocomposites (AMCs) processed through mechanical milling (MM) and spark plasma sintering (SPS). The characterization of these MM and SPSed AMCs was done through X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM). The MM induces microstructural refinement of matrix and partial structural transformation of QC phase to Al13Fe4 approximant phase (a = 1.549 nm, b = 0.808 nm, c = 1.248 nm, α = β = 90°, γ = 107.72°; mC102; C2/m). The presence of (311111) diffraction peak of the QC phase in AMCs confirms the existence of face-centred QC phase even after 50 h of MM. The consolidation of Al-QC at 450 °C (723 K) and 550 °C (823 K) results in the fabrication of AMCs having a density of 2.921 and 3.319 g cm−3 respectively. The compressive yield strength and ultimate strength of these AMCs is ∼519 MPa and 639 MPa respectively. The enhancement in the mechanical properties may be attributed to strong interfacial bonding of the Al matrix and QC reinforcement due to interfacial reactions.

Precipitation of Laves phase in steels is often identified as the primary cause for the degradation of mechanical properties. Analytical electron microscopy and thermodynamic modelling have been used in this study to understand the Lave phase precipitation induced damage initiation process in modified 9Cr–1Mo steel, exposed to high temperature for 10,000 h. The results have suggested that in addition to void nucleation at the interface and de-cohesion, the limited plasticity of the Laves phase is also a predominant mechanism for crack initiation in this material. The thermodynamic propensity of Laves phase precipitation around the carbides and the underlying role of local chemistry have also been studied. Binary Laves phases have been found to be stabilized by ternary additions.

V-Ti-Cr alloys are the potential candidates for advanced high temperature structural applications, alternative energy research and improved hydrogen storage capacity. In the present work, Miedema model has been used to predict the phase stability of V-Ti-Cr/W systems. Alloys of selected compositions were prepared by arc melting the highly pure V, Ti and Cr. Microstructural and microchemical characterizations were carried out on two selected alloy compositions, one nearby the Ti-Cr rich side of the ternary enthalpy-composition diagram and the other from the binary V-Ti alloy. TEM characterizations confirmed the phase evolution in these two alloys as predicted by Miedema’s model.

The structural characteristics of NiO–YSZ (YSZ: Yttria-stabilized zirconia) composites and the redox stability of NiO have been explored by in-situ and high-resolution transmission electron microscopy (TEM). NiO has been reduced on alumina support while doing in-situ microscopy, and the observations on redox instability and microstructural changes have been extrapolated to understand the behavior of NiO/Ni–YSZ system. In the composite, the NiO and YSZ grains are strain free and no reaction product is observed at the grain boundaries after long term annealing. Under a low partial pressure of oxygen, NiO may begin to reduce to metallic Ni at temperatures as low as ~200 °C. The volume change associated with such a reduction process is ~40.3%. Although metallic Ni nucleates in NiO coherently, such a huge volume contraction may lead to porosity generation and mechanical instability. Long term exposure of metallic Ni to high temperatures leads to coarsening, which reduces the available surface area. This in turn has a direct, negative consequence on the catalytic properties of the metallic Ni particles. The coarsened particles may even undergo faceting, and the facets may not be the most active catalytically. Synthesis of finely dispersed and percolatively connected Ni–YSZ anodes for SOFCs and core–shell or compositionally graded electrodes for batteries may be viable solutions to enhance the lifetime and structural integrity of such electrodes.

The energetics behind transformation of liquid structure into subsequent intermediate phases during solidification is expected to play a decisive role in glass/crystal formation. A great deal of experimental and simulation work on supercooled liquids has indicated that, there exists a close link between the liquid structure and icosahedral clusters, especially for bulk metallic glass forming liquids. Pertinently, icosahedral clusters are also found to be energetically favorable to form upon devitrification of Zr60Cu10Al15Ni15 glassy alloy. Such evolution of icosahedral clusters upon devitrification in this alloy invariably proves their manifestation at the intermediate stage during transition of supercooled liquid into glass. Hence understanding the energetics behind restructuring of these clusters into glass or crystal during solidification, aids in microstructure optimization of glass/crystal composites for structural and functional applications. In this paper, it has been attempted to investigate the energetics behind the evolution of Zr�Ni and Zr�Al binary intermetallic phases during crystallization of Zr60Cu10Al15Ni15 glassy alloy. Ascalaph Designer Molecular Modeling Suite is used to generate different models of clusters to understand the formation of Zr�Ni and Zr�Al phases. We propose solidification mechanism in this alloy via two steps, namely, formation of intermediate Zr�Cu icosahedral clusters which is structurally restricted process and precipitation of crystalline phases as thermodynamically favorable process. � 2015, The Indian Institute of Metals - IIM.

V-alloys in combination with Ti and Cr have been identified as potential candidate materials for various energy technologies as an alternative to fossil fuel based technologies. Phase formation and microstructural evolution in ternary V–Ti–Cr alloys along with the constituent binaries have been studied by Miedema approach and the selected binary and ternary alloy compositions have been studied experimentally in order to validate the results obtained from Miedema's model. According to Miedema's model V–Ti–Cr ternary alloys in the V-rich side of the phase diagram should form a solid solution phase and the ternary alloy composition in the vicinity of binary TiCr 2 Laves phase should form amorphous or intermetallic phase. The expected solid solution phase in binary V–Ti and V–Ti–20Cr alloy system may undergo phase separation. Four alloy compositions, as identified by the Miedema approach e.g., V–4Ti–4Cr, V–39Ti–54Cr, V–50Ti and V–40Ti–20Cr, have been studied experimentally. V–4Ti–4Cr alloy forms BCC solid solution phase upon solidification. In V–39Ti–54Cr alloy, V-substituted cubic TiCr 2 Laves phase is seen upon solidification. The BCC solid solution phase in binary V–50Ti and ternary V–40Ti–20Cr alloys undergoes phase separation giving rise to V-rich and V-poor domains. In the ternary V–40Ti–20Cr alloy, the phase separation is essentially binary as Cr is distributed homogeneously in the phase separated domains. Interesting possibilities exist for V–Ti–Cr alloys so far as phase transformation, microstructural evolution and tailoring of properties are concerned. Moreover, Miedema's approach could be used to design alloys in this system.

Properties of Laves phase compounds can be tailored by alloying and microstructural engineering. V-substituted cubic TiCr2 Laves phase has been studied to understand the location of V atoms in the lattice, by structural imaging and first-principle computations. Even though Ti, V and Cr appear next to each other in the periodic table, V preferentially replaces the Ti lattice producing anti-site defects. The defect formation energy for V substitution in Ti and in Cr lattice is 0.29 and 0.40 eV, respectively. V replacement in the Ti lattice generates atomic scale strain. Atomic numbers of V, Ti and Cr being very close, this phase is not quite suitable for incoherent imaging for understanding the structure and the chemistry. Instead, difference in channelling behaviour of electron waves along the Ti columns and along the Cr columns could be exploited to preferentially image the individual atom columns. Nature of the exit phase wave, phase and amplitude has been used to understand the contrast qualitatively. T...

After publication of the paper, the authors realized that the affiliation of the fourth author (Tiberiu Esanu) was given incorrectly. Its correct version appears above. Moreover, a second funding grant was missed in the acknowledgements. We give their complete correct version below.