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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.

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.

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.

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.

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.

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).

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 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.

Au–Cu alloy nanostructures have been synthesized in aqueous phase through co-reduction of HAuCl4.3H2O and CuCl2.2H2O by glucose in presence of hexadecylamine at ∼80 °C. By changing the synthesis conditions, nanostructures of various shapes such as nanowires, multiply twinned tripod, tetrapod, etc were observed. Systematic variation of the synthesis condition not only leads to change in size and particle morphology but also develops various other crystallographic characters in the nanoparticles. Alloying behavior of Au–Cu has been examined through transmission electron microscope operating in its conventional and analytical modes coupled with high resolution phase contrast microscopy. These results suggested that nanostructures are composed of homogeneous Au–Cu alloy. Preferential attachment along {111} and {100} crystallographic facets of Au–Cu alloy nanoparticles led to the formation of nanowires. Multiply twinned branched shape Au–Cu (width of branch ∼30 nm) nanostructures exhibit localized surface plasmon resonance maxima in the near-infrared region. The branched shape Au–Cu alloy nanostructures display better surface enhanced Raman scattering response in the detection of methylene blue as compared to spherical Au nanoparticles.

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.

V–(4–10)Ti–(4–5)Cr alloys are the potential candidate materials for the high performance structural applications in fusion power systems due to their favorable mechanical and physical properties. In the present study, the alloy design has been attempted through model based approach for pre mentioned composition range. Thermodynamic calculations have been carried out through Miedema model for this alloy system. The enthalpy difference—composition plot for the ternary V–Ti–Cr system indicate the stability of the solid solution phase in this composition range, which is also in agreement with the atomic size variation which is well within the 15 % size variation limit. Based on these plots, an alloy with a composition of V–4Ti–4Cr is considered as the reference composition for our study. The alloys have been prepared by melting the desired compositions of highly pure metals in a water cooled vacuum arc melting unit. For structural information, X-ray diffraction experiment has been carried out. The XRD pattern does not contain any signature for the secondary phase formation. The structure is bcc structure with small variation in lattice parameter from that of pure vanadium. Transmission electron microscopy characterization has also been carried out, which confirms the absence of fine secondary phases and the crystal structure as b.c.c.

In the present investigation, deformation behavior of melt spun glassy ribbon of Cu 60 Zr 20 Ti 20 has been studied using microhardness test. Further, the glassy ribbon was annealed at supercooled liquid region (Δ T x ), offset of first crystallization ( T x 1 ) and offset of second crystallization temperature ( T x 2 ). X-ray diffraction and transmission electron microscopy has been used to understand the crystallization behavior of the glass and to correlate its microstructural evolution with the mechanical properties. The glassy alloy initially undergoes phase separation during annealing which transforms into a totally crystalline structure after annealing at T x 2 temperature. It has been observed that at any particular load, the hardness of the alloy increases with the progress of phase separation and partial crystallization. After complete crystallization the hardness drops off. This leaves behind the scope of microstructural engineering of metallic glasses and composites for best enhancement of properties. Further the role of phase separation on the indentation behavior of this glassy alloy has been explored. The role of relaxation and crystallization on hardness and deformation behavior of glassy ribbon alloy is examined by observing the indentations under scanning electron microscopy. Results indicate that the composite structure formed during annealing at T x 1 has superior hardness in comparison to other microstructures.

Alloying behavior and phase stability of nine Fe-ETM (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W) binary, five ternary (Fe–Zr–Nb, Fe–Ti–Nb, Fe–Cr–Zr, Fe–Cr–Ti, Fe–V–Ti) alloy systems have been analyzed by Miedema's model. It is observed that Fe with V, Cr, Mo, W would tend to form solid solutions over entire composition range when the molten alloy is supercooled to a large extend below its melting point. With Ti, Zr, Hf, Ta and Nb there exists a terminal solid solubility beyond which liquid alloy will tend to freeze in the glassy state than crystallizing as a solid solution phase. The composition where glassy state will be most stable compared to the solid solution phase coincides with that of the Laves phase as reported in the equilibrium phase diagram. In ternary systems also similar trend is observed. Independent calculation of elastic and chemical enthalpy for all the systems indicates that low contribution of the enthalpies favors solid solution formation. Whereas, highly negative chemical and the positive elastic energy contribution tends to destabilize the parent lattice favoring intermetallics and amorphous phase formation. This leads to a theoretical convergence of Hume-Rothery rule and Inoue's empirical criteria of amorphous phase formation. Laves phase being a Frank-Kasper phase, further structural similarity could be drawn between complex crystalline and liquid phases. This opens up new possibilities in alloy design of glasses and predicting phase stability, which is extended to microstructure analysis in Fe based binary and multicomponent systems.

An α-β alloy (β~8% in the stress relieved condition) of Ti-5Ta-1.8Nb has been subjected to severe plastic deformation (SPD) by cryo-rolling. The grain size of α-Ti could be reduced significantly from ~ 8µm to 100 nm and less by cryo-rolling. Extensive plastic deformation leads to grain fragmentation through the formation of defect clusters. The fragmented grains exhibit deformation texture. High resolution transmission electron microscopy (HRTEM) confirmed the presence of low and high angle grain boundaries. The role of substitutional atoms (Ta, Nb) in producing lattice strains and altering the projected potential from the atomic columns has been discussed. Although, the minor phase, β (bcc-Ti) is evident in the starting alloy, it was not observed after SPD, possibly due to extended solid solution formation (Gibbs–Thomson effect) in the fine grains or due to the stress induced transformation of the α-Ti phase.

Transparent conductive nanofibrous membranes have been successfully fabricated by sputter-coating a metal (Au, Pd, Pt, Ni, Ag, or Au/Pd alloy) onto a water-soluble-polymer nanofibrous template, followed by the dissolution of the template in a water bath. The size of the conductive nanofibers can be facilely controlled by adjusting the diameter of the polymer nanofibers as well as the sputter-coating time. The as-prepared samples were characterized by SEM, TEM, FTIR, and TGA, and the results reveal that the as-prepared conductive nanofibers consist of many metal nanoparticles held together after the dissolution of the polymer template, which is likely due to the coalescence of the metal nanoparticles as well as the bridging effect of the polymer chains between the adjoining metal nanoparticles. The transmittance of the film decreases but the conductivity of the film increases with the time of sputter-coating. The as-prepared transparent nanofibrous membrane also shows good mechanical and metallic propertie...

Four Ni-bearing Ti, Zr and Hf ternary alloys of nominal composition $Zr_{41.5}Ti_{41.5}Ni_{17}$, $Zr_{25}Ti_{25}Ni_{50}$, $Zr_{41.5}Hf_{41.5}Ni_{17}$ and $Ti_{41.5}Hf_{41.5}Ni_{17}$ were rapidly solidified in order to produce ribbons. The Zr–Ti–Ni and Ti–Hf–Ni alloys become amorphous, whereas the Zr–Hf–Ni alloy shows precipitation of a cubic phase. The devitrification of all three alloys was followed and the relative tendency to form nanoquasicrystals and cF96 phases analysed. The relative glass-forming ability of the alloys can be explained by taking into account their atomic size difference. Addition of Ni often leads to quasicrystallisation or quasicrystal-related phases. This can be explained by the atomic radius and heat of mixing of the constituent elements. The phases precipitated at the initial stages of crystallisation indicate the possible presence of Frank–Kasper polyhedral structure in the amorphous alloys. Structural analysis reveals that the Laves and the anti-Laves phases have the same polyhedral structural unit, which is similar to the structural characteristics of glass.

Two alloys of nominal compositions $Zr_{41.5}Ti_{41.5}Ni_{17}$ and $Zr_{41.5}Hf_{41.5}Ni_{17}$ have been melt spun at $40 ms^{-1}$ wheel speed. Under this processing condition Zr–Ti–Ni alloy becomes amorphous and the Zr–Hf–Ni alloy precipitates a cubic phase with 4.95 \AA lattice parameter in the amorphous matrix. The Zr–Ti–Ni alloy, upon annealing, precipitates a nanoquasicrystalline phase, which at the later stages of crystallisation transforms into cF96 $NiZr_2$ phase. The amorphous phase in Zr–Hf–Ni alloy upon annealing precipitates the same cubic phase with 4.95 \AA lattice parameter. The lower glass forming ability of Zr–Hf–Ni compared to Zr–Ti–Ni and nanoquasicrystallisation in Zr–Ti–Ni alloy can be explained by taking into consideration the atomic size differences among Ti, Zr and Hf.

Four Cu bearing alloys of nominal composition Zr25Ti25Cu50, Zr34Ti16Cu50, Zr25Hf25Cu50 and Ti25Hf25Cu50 have been rapidly solidified in order to produce ribbons. All the alloys become amorphous after meltspinning. In the Zr34Ti16Cu50 alloy localized precipitation of cF24 Cu5Zr phase can be observed in the amorphous matrix. The alloys show a tendency of phase separation at the initial stages of crystallization. The difference in crystallization behavior of these alloys with Ni bearing ternary alloys can be explained by atomic size, binary heat of mixing and Mendeleev number. It has been observed that both Laves and Anti-Laves phase forming compositions are suitable for glass formation. The structures of the phases, precipitated during rapid solidification and crystallization can be viewed in terms of Bernal deltahedra and Frank-Kasper polyhedra.

Miedema's approach has been useful in determining the glass forming composition range for a particular alloy system. The concept of mixing enthalpy and mismatch entropy can be used in order to quantify Inoue's criteria of bulk metallic glass formation. In the present study, glass forming composition range has been determined for different binary and ternary (Zr, Ti, Hf)-(Cu, Ni) alloys based on the mixing enthalpy and mismatch entropy calculations. Though copper and nickel appear next to each other in the periodic table, the glass forming ability of the copper and nickel bearing alloys is different. Thermodynamic analysis reveals that the glass forming behaviour of Zr and Hf is similar, whereas it is different from that of Ti. The smaller atomic size of Ti and the difference in the heat of mixing of Ti, Zr, Hf with Cu and Ni leads to the observed changes in the glass forming behaviour. Enthalpy contour plots can be used to distinguish the glass forming compositions on the basis of the increasing negative enthalpy of the composition. This method reveals the high glass forming ability of binary Zr-Cu, Hf-Cu, Hf-Ni systems over a narrow composition range. � 2007 Elsevier B.V. All rights reserved.

The addition of early and late transition metals to Al–La alloys has a strong influence on the glass forming ability and the subsequent devitrification route. Four quaternary alloys of nominal composition $Al_{87}Fe_5Ni_5La_3,$ $Al_{88}Fe_3Ni_3La_6,$ $Al_{82}Fe_4Ni_4La_{10},$ $Al_{75}Ti_{10}Ni_{10}La_5$ and a ternary alloy of nominal composition $Al_{75}Ti_{10}Ni_{15}$ have been melt spun at 10, 20, 30 and 40 $m s^{-1}$ wheel speed. Amorphous alloys thus secured have been annealed at the peak temperatures as indicated by the DSC thermograms from 10 min to 2 h. The $Al_{87}Fe_5Ni_5La_3$ alloy showed in the melt-spun state precipitates of $\alpha-Al,$ a FCC phase with $12.5 \AA$ lattice parameter. The $Al_{88}Fe_3Ni_3La_6$ alloy in the melt-spun state shows nano-sized precipitate of $\alpha-Al$ in the amorphous matrix. The $Al_{82}Fe_4Ni_4La_{10}$ alloy after melt-spinning at 40, 30, 20 $m s^{-1}$ wheel speed becomes amorphous and shows precipitates of $\alpha-Al$ in the amorphous matrix when melt spun at 10 $m s^{-1}$ wheel speed. The amorphous phase in the $Al_{82}Fe_4Ni_4La_{10}$ alloy is stable up to 625 K and crystallises in three exothermic heat events. After heat treatment at the first crystallisation peak temperature and below the first crystallisation temperature precipitation of $\alpha-Al$ in the amorphous matrix can be observed. At the end of the crystallisation process very fine precipitates of $Al_3La$ and LaNi can be seen at the $\alpha-Al$ grain boundaries. Activation energy of crystallisation has been calculated by Kissinger and Ozawa method. Al–Ti–Ni–La becomes partially amorphous after melt-spinning. Al–Ti–Ni alloy does not produce amorphous phase after melt-spinning. Precipitation of $Al_3Ti$ phase can be observed in both the alloys. The development of different microstructures, effect of La on the glass forming ability and the stabilisation of the glassy matrix with enrichment of La and with the progress of crystallisation, establishes a possible link between Al based metallic glasses and La based bulk metallic glasses.

Bulk glass-forming alloys have emerged over the past fifteen years with attractive properties and technological promise. A number of alloy systems based on lanthanum, magnesium, zirconium, palladium, iron, cobalt and nickel have been discovered. Glass-forming ability depends on various factors like enthalpy of mixing, atomic size and multicomponent alloying. A number of processes is available to synthesise bulk metallic glasses. The crystallisation behaviour and mechanical properties of these alloys pose interesting scientific questions. Upon crystallisation many of these glasses transform to bulk nanocrystals and nanoquasicrystals. A detailed study of the structure and the crystallisation behaviour of glasses has enabled the elucidation of the possible atomic configuration in liquid alloys. Their crystallisation behaviour can be exploited to synthesise novel nanocomposite microstructures and their mechanical properties can be enhanced. A broad overview of the present status of the science and technology of bulk metallic glasses and their potential technological uses is presented.

The applicability of the confusion principle and size factor in glass formation has been explored by following different combinations of isoelectronic Ti, Zr and Hf metals. Four alloys of nominal composition Zr41.5Ti41.5Ni17, Zr41.5Hf41.5Ni17, Zr25Ti25Cu50 and Zr34Ti16Cu50 have been rapidly solidified to obtain an amorphous phase and their crystallisation behaviour has been studied. The Ti-Zr-Ni alloy crystallises in three steps. Initially this alloy precipitates icosahedral quasicrystalline phase, which on further heat treatment precipitates cF96 Zr2Ni phase. The Zr-Hf-Ni alloy can not be amorphised under the same experimental conditions. The amorphous Zr-Ti-Cu alloys at the initial stages of crystallisation phase-separateinto two amorphous phases and then on further heat treatment cF24 Cu5Zr and oC68 Cu10Zr7 phase are precipitated. The lower glass-forming abilityof Zr-Hf-Ni alloy and the crystallisation behaviour of the above alloys has been studied. The rationale behind nanoquasicrystallisation and the formation of other intermetallic phases has been explained.