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The directional spectral emissivity of a Ti–48Al–2Nb–2Cr alloy (in at.%), 4822 alloy, and a Ti-43.5Al–4Nb–1Mo-0.1B alloy (in at.%),TNM alloy, used in the aeronautical industry, are measured between 150 and 850 °C. The differences in the emissivity values between both alloys at the lowest temperatures, indicates that the βo phase, only present in TNM, exhibit higher emissivity values. By numerical integration of the measured data, the total directional and hemispherical emissivity have been calculated. At 850 °C the total hemispherical emissivity in vacuum are nearly identical with 0.274 ± 0.006 for the 4822 alloy and 0.273 ± 0.007 for the TNM alloy. The lower emissivity change with temperature measured in TNM alloys is related with the deconvolution of βo phase by diffusion processes. Afterwards, near-normal spectral emissivity measurements are performed in both alloys during isothermal oxidation treatments at 750 °C and 850 °C for 120 h. The emissivity data reveal that the TNM alloy exhibits higher oxidation resistance especially at 750 °C. In parallel, microstructural characterization has been performed before the measurements, after the directional emissivity measurements prior to oxidation and after isothermal oxidations. The formed oxide scale is composed of four layers that coincide with those reported in the literature: an outer layer of TiO2 contiguous with a layer of Al2O3, followed by a TiO2/Al2O3 mixed layer and finally a thin layer of Nb-rich nitride. This mixed layer governs the interferential part of the alloys’ emissivity spectra, which, in combination with the background, determines the overall radiative behavior of the alloys under service conditions.

It is commonly agreed that the α 2 phase in γ(TiAl)-based alloys is quite difficult to deform plastically especially by order twinning. In the present study, for the first time we report deformation twinning in the α 2 phase in a nearly-lamellar two-phase γ-TiAl alloy investigated by electron microscopy. Diffraction pattern and high-resolution images indicate that the twinning plane is (20 2 ¯ 1) and the twinning direction is [ 10 14 ¯ ] , which is essentially analogous to what has been observed in disordered hexagonal structures. The twinning and anti-twinning mechanisms are interpreted. The twinning is a combined result of superpartial dislocation glide activated by the dissociation of <2 c + a > type superdislocation, accompanied by atomic shuffling and short-range diffusion which is facilitated by the anti-structural bridges diffusion mechanism during high-temperature compression. The appearance of deformation twinning in the α 2 phase can play an important role for the excellent mechanical properties of high Nb containing TiAl alloys, which is of great importance for the further development of γ-TiAl alloys. • Deformation twinning of α 2 phase is firstly observed in a two-phase γ-TiAl alloy. • The twinning system is similar to that observed in disordered α structure. • Twinning and anti-twinning elements are revealed. • Atomic shuffling and short-range diffusion are responsible for deformation twins. [ABSTRACT FROM AUTHOR]

For the manufacturing of low pressure turbine blades, titanium aluminides are used as structural materials, among them the alloy Ti-43.5Al-4Nb-1Mo-0.1B (at.-%) known as TNM™ alloy. In this study, laser metal deposition (LMD) was investigated as a potential technology to repair defective, damaged or worn blades, and process conditions were successfully optimized. However, post-process heat treatment is required to optimize the microstructure. In this work, different annealing treatments and the resulting microstructures were characterized for bulk LMD samples as well as for investment cast reference samples. Annealing temperatures were selected from 1245 to 1290 °C. The results show that annealing at 1290 °C for a duration of 60 min with subsequent furnace cooling can be used so that the LMD and cast micro-hardness nearly match, albeit with significant differences in microstructure. Nonetheless, yield strength mismatch can be mitigated and LMD can qualify as prospective additive repair technology, but also as a manufacturing technology for functional TiAl parts. [ABSTRACT FROM AUTHOR]

Phase stability information regarding the formation of the topologically close packed (TCP) phases is critical for the design of advanced Ni-based and Co-based superalloys that contain high concentrations of refractory elements. Isothermal sections of the Co-Ni-W, Co-Ni-Mo, Co-Ni-Nb and Co-Ni-Ta systems at both 900 °C and 800 °C were constructed for the first time from electron probe microanalysis (EPMA) and electron backscatter diffraction (EBSD) measurements on two Co-CoAl-Cr-Mo-Ni-Nb-Ta-W diffusion multiples. The new data will serve as experimental input to future thermodynamic assessments of the Co-Ni-X ternary systems in order to improve the thermodynamic databases for the design and development of advanced Ni-based and Co-based superalloys. [ABSTRACT FROM AUTHOR]

Pure Sn solder balls of initial diameter of 2 mm, having been reflow soldered on Cu substrate at 573.15 K for 1, 2 and 5 min, were subjected to furnace cooling. Upon the start of reflow, the initially spherical solder balls underwent a rapid radial spreading and wetting on Cu substrate and thus attained non-spherical geometry with a maximum height at the center whereas a minimum one at the periphery. The wetting or interfacial reaction, that would produce an even scalloped intermetallic compounds (IMCs) during isothermal reflow, resulted in the growth of dense prismatic IMC rods at the central region during cooling whereas the peripheral scalloped IMCs were not overriden by the faceted or prismatic rods during the temperature reduction procedure. Reduced interfacial heat transfer at the central interface, existence of radial isotherms and lowered supply of Cu precipitates at the peripheral interface owing to the compromised solder height have been discussed as the factors responsible for the segregated IMC morphology. The abundant precipitation of Cu and the presence of thermal gradient, sustain a screw dislocation based growth of hexagonal IMC whiskers. The increase in reflow duration is associated with the enhanced tubularity of the rods. Finite element method has been utilized to accomplish numerical simulations for heat and mass transfer in solder phase as well as for anisotropic thermal conduction at the dislocation in evolving IMC. [ABSTRACT FROM AUTHOR]

In this study, the solidification behavior of an intermetallic γ-TiAl based alloy, the so-called β-solidifying TNM alloy, Ti-43.5Al-4Nb-1Mo-0.1B [at.%], was investigated regarding the evolving phases, morphology and microstructure as a result of the high solidification rate during gas-atomization. By means of X-ray diffraction combined with electron back-scatter diffraction as well as at a higher resolution by transmission electron microscopy and transmission Kikuchi diffraction, conclusions regarding the ongoing processes during cooling were withdrawn. Furthermore, differential scanning calorimetry measurements on the powder condition served as supportive tool for the understanding of the microstructural development during heating of the initial state of disequilibrium. The investigations revealed a cellular/dendritic structure of the primary solidified β-grains and microsegregations along the former solidification front. The former β-grains, examined by energy dispersive X-ray spectroscopy and atom probe tomography, showed an increasing Al-content and a depletion of refractory metals when moving from the center toward the interface. Depending on the local chemical composition, the high cooling rate results in a massive type transformation of α-Ti(Al)/α 2 -Ti 3 Al- and γ-TiAl phase in the Al enriched areas, and to a martensitic transformation in the center of the retained β-phase. Furthermore, a partial suppression of the ordering reaction of the majority α-phase is detected. During annealing the microstructure evolves toward equilibrium condition, i.e. the ordering of the retained α-phase and the formation of nanolamellar γ-phase are observed. [ABSTRACT FROM AUTHOR]

A Ti 5 Si 3 -containing multiphase MoSiBTiC alloy with a composition of 38Mo–30Ti–17Si–10C–5B (at.%) was designed and produced by arc-melting. The alloy was composed of five phases—Mo solid solution (Mo ss ), Mo 3 Si, Mo 5 SiB 2 (T 2 ), Ti 5 Si 3 and TiC—and consistently has good thermal stability at least up to 1700 °C. The density of the alloy was ∼7.0 g/cm 3 , which is considerably smaller than that of Ni-base superalloys. Microstructure was carefully examined and microstructural anisotropy was confirmed. The anisotropy was considered to be generated by thermal gradient during the solidification process. Microcracking was remarkable across the primary Ti 5 Si 3 phase, which was caused by thermal expansion anisotropy of the Ti 5 Si 3 phase. High-temperature deformability was examined by high-temperature compression tests at 1500 °C. Two kinds of loading axes were chosen for the compression tests with respect to the microstructural anisotropy. The alloy exhibited a peak stress of 450–550 MPa, followed by good deformability at the testing temperature. Microstructure refinement and reduction in microcrack density were observed after hot working. Oxidation tests were conducted on the alloy at 1100 °C and 1300 °C for 24 h. The oxidation curves demonstrated that rapid mass loss finished within several minutes. After that, the mass loss began to slow down and then the specimens' mass decreased almost linearly with increasing testing time. Cross-section observation indicated that oxygen propagated through Mo ss , whereas T 2 and Ti 5 Si 3 phases acted as barriers against oxygen attack during the tests. In addition, it was found that the alloy gained better oxidation resistance after high-temperature deformation, suggesting a positive effect of phase refinement on its high-temperature oxidation resistance. [ABSTRACT FROM AUTHOR]

Growth directions (GD) variation of α phase in Ti-49Al (at.%) alloy with solidification parameters were studied by using directional solidification technology. GD of the primary phase (α phase) changed with growth rate ( V ) and temperature gradient ( G ). Evolutions of Θ (the angle between the preferred growth direction (PG) and heat flow direction (HD) and Ψ (the angle between GD and HD) with V and G are presented. By controlling the solidification parameters accurately, the grains of α solidified TiAl alloy can grow with < 11 2 ¯ 0 > direction or close to this direction during directional solidification, which is beneficial to the lamellar orientation control of TiAl alloys. For present experimental conditions, the feasible solidification condition for the lamellar orientation control of TiAl alloy by the seeding technology is: V = 10 μm/s∼20 μm/s and G = 10 K/mm∼12.1 K/mm. [ABSTRACT FROM AUTHOR]

The precipitation of γ phase and heterogeneous nucleation of ω o phase within β o phase areas are common phenomena in TiAl alloys. However, detailed explanation on the corresponding phase transformation mechanisms is still lacking. In this study, the precipitation behaviors of γ and ω o phases in a quenched Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy are investigated. The results show that large γ grains form after quenching whereas small γ particles can directly nucleate within the remaining β o phase during annealing. Semi-coherent interfaces are observed between γ and β o phases and the average distance between dislocations is evaluated. The heterogeneous nucleation of ω o phase at the lamellar colony boundary is imaged by HRTEM. Edge-to-edge method is used to calculate the orientation relationship between γ and ω o phases. The γ phase grows up faster than ω o phase within the β o phase areas during annealing at 800 °C. [ABSTRACT FROM AUTHOR]

In order to clarify the controversy in the literature reports, we studied the thermal stability of the ternary compound Al 13 CeMg 6 by integrating X-ray powder diffraction, electron probe microanalyzer and differential scanning calorimetry techniques. It was found that the compound Al 13 CeMg 6 decomposes at a certain temperature between 320 and 400 °C with a eutectoid reaction: Al 13 CeMg 6 → Al 11 Ce 3 +Al 3 Mg 2 , and melts at 492 °C via a peritectic reaction: Liquid + Al 11 Ce 3 → Al 13 CeMg 6 . Moreover, the crystal structure of Al 13 CeMg 6 compound was successfully determined by X-ray powder diffraction using the Rietveld method. The compound crystallizes in the hexagonal, space group P 63/ mmc (No. 194) with the structure type of MgNi 2 and lattice parameters of a = 0.5525(9) and b = 1.7866(2) nm. [ABSTRACT FROM AUTHOR]

A polycrystalline Ni 3 Al-based intermetallic alloy was successfully prepared via vacuum induction melting processing. Next, the microstructural evolution and mechanical properties of the intermetallic alloy were investigated by solution treatments at temperatures ranging from 1230 to 1290 °C. The results showed that the as-cast polycrystalline Ni 3 Al-based intermetallic alloy consisted of dendrite γ+γ′ with interdendritic distribution, matrix γ′ phase, and eutectic γ–γ′, and the total volume fraction of γ′ phase was ∼83.2%. After solution treatment at 1270 °C, the size and morphology of the γ′ phase changed and the secondary γ′ phase precipitated in the γ channel. The maximum room temperature yield strength, tensile strength and elongation reached 488 MPa, 686 MPa, and 5.2%, respectively. At 1100 °C, the high-temperature tensile strength of sample subjected to solution treatment at 1250 °C reached 203 MPa. It was found that solution treatment did not eliminate the incipient γ′ m , resulting in the weaker interdendritic boundary area in the alloy. Moreover, noteworthy, α-Cr particles were found in the γ′ m of the polycrystalline Ni 3 Al-based intermetallic alloy, revealing an orientation relationship such as [123] α-Cr ∥[123] γ' and (1–21) α-Cr ∥(11–1) γ'. The α-Cr particles have the strengthening effect of second-phase particles through pinning dislocations, which can improve the high-temperature creep performance of the alloy. • A vacuum induction melting polycrystalline Ni 3 Al-based intermetallic alloy was investigated for its room temperature and 1100 °C high temperature mechanical properties, and microstructure. • Nano-sized α-Cr particles formed in the γ′ phase on the Al-rich and Ni-poor side, the orientation relationship of [123] α-Cr ∥[123] γ' and (1–21) α-Cr ∥(11–1) γ' between the precipitates α-Cr and γ′-matrix. • The inter-dendrite boundary is the weakest point of the alloy. [ABSTRACT FROM AUTHOR]

We prepared Nb–16Si ingot via the laser directed energy deposition (L-DED) using mixed pure Nb and Nb 5 Si 3 alloy powders, and investigated the microstructure and fracture behaviour of the L-DEDed samples along directions that were parallel and perpendicular to the built direction, as well as the fracture behavior of the arc melting Nb–16Si sample for comparison. The L-DED molten pool approximately showed a scaly-like morphology, and the fine microstructure containing primary dendritic Nb SS arm and eutectic colony of Nb SS + Nb 3 Si was obtained, which oriented to the built direction and the scanning direction. The multiformity of orientation relationships (ORs) with the small Miller indices in the Nb SS /Nb 3 Si couple was confirmed, while the ORs, such as (0 1 1 ‾) Nb SS //(0 2 0) Nb 3 Si, [0 1 1] Nb SS //[0 0 1] Nb 3 Si, and (1 ‾ 1 0) Nb SS //(2 0 0) Nb 3 Si, [1 1 2] Nb SS //[0 0 1] Nb 3 Si were the dominant. The fine Nb phase in the L-DEDed sample fractured in a mixed dimple, tear and cleavage mode, resulting in higher fracture toughness K Q of approximately 7.6–8.6 MPa m1/2. As for the arc-melting Nb–16Si sample with coarsened microstructure, the Nb SS phase usually failed in a single cleavage mode, leading to a low K Q value of 6.8 MPa m1/2. [Display omitted] • Dense Nb–16Si ingot has been successfully fabricated by laser melting deposition (LMD). • LMD melted pool approximately shows a scale-like morphology. • LMD ingot shows fine orientated microstructure containing dendritic Nb SS and Nb SS + Nb 3 Si eutectic. • Orientation relationships with small Miller indices exist between Nb SS and Nb 3 Si. • Higher K Q of 7.6–8.6 MPa m1/2 is attributed to mixed dimple, tear and cleavage failure of fine Nb SS. [ABSTRACT FROM AUTHOR]

A series of Mn 1-x Ni 1-x Fe 2x Si 0.95 Al 0.05 MM'X-type compounds (with x = 0.28, 0.3, 0.32 and 0.35) were investigated for their potential as magnetocaloric materials. Structural and magnetic properties were studied by magnetometry, microscopy and X-ray diffraction. Double substitution of Fe in Mn and Ni sites allowed to tune martensitic transition temperatures between low temperature orthorhombic and high temperature hexagonal structures from 373 K in x = 0.28–183 K in x = 0.35 during cooling. Transition temperatures occur around room temperature for x = 0.30 (300 K for cooling transformation) and 0.32 (270 for heating transformation). Isothermal entropy changes of −8, −19 and −26 J/kg.K were calculated for field changes of μ 0 H = 0–2, 0–5 and 0–7 T for x = 0.30. The values are comparable to those reported for MnNi(SiAl)-based compounds with single site substitutions (Mn and Ni) by Fe. Further analyses show that high magnetic fields are necessary to induce the magnetostructural transition in all studied compounds, which can be attributed to the presence of secondary phases and/or disorder at a local level. • Novel MnNiSi intermetallics with low-cost Fe and Al substitutions are reported. • Compounds feature magnetostructural transitions at room temperature. • Structural, microstructural, caloric and magnetic properties are evaluated. [ABSTRACT FROM AUTHOR]

We have shown in a previous paper that twin boundary area fraction in lamellar γ-TiAl based alloys depends on collective or correlated nucleation induced by long-range elastic interactions among nucleating precipitates or between pre-existing and nucleating precipitates. In this study we investigate the effects of applied stresses on γ nucleation and evolution by elastic interaction energy calculations and phase field simulations. It is found that the elastic interaction energy reaches minimum when two variants are twin related because of their self-accommodation of the coherency strain. When external stresses are present, such autocatalysis during nucleation could be either enhanced or suppressed. Compression perpendicular or tension parallel to the basal plane of the α phase is found to enhance the internal elastic interactions between nucleating precipitates, promote twin variant selection and reduce the overall nucleation rate, while isostatic pressing, compression parallel, tension perpendicular to the basal plane does the opposite. Shear along the interface always reduce the twin boundary area fraction, regardless of the shear direction. These findings could shed light on optimizing processing routes to increase twin boundary area fraction in lamellar microstructures of γ-TiAl based alloys. [ABSTRACT FROM AUTHOR]

The oxidation resistance of MSi 2 compounds with M = V, Ti, Cr was investigated from 450 to 950 °C in air under isothermal and cyclic conditions. Vanadium, chromium and titanium disilicide were not subjected to the pest phenomenon at 650 °C over 800 1-h cycles. The results demonstrated very low weight gains regardless of the testing conditions. Oxidation tests were also performed over long duration (1000 h) to identify the oxidation products. The MSi 2 compounds were all subjected to the simultaneous oxidation of M and Si despite the formation of a protective silica scale. Increasing the duration of oxidation enhanced the protective properties of the silica scale. Therefore, short-term measurements (by thermogravimetry) did not allow an extrapolation of the MSi 2 lifetime. The formation of molten V 2 O 5 induced a higher oxidation rate of VSi 2 and delayed the establishment of the protective silica scale compared with CrSi 2 and TiSi 2 . [ABSTRACT FROM AUTHOR]

Ruthenium addition was found to be beneficial in inhibiting the formation of the detrimental topologically closed-packed (TCP) phases in Ni-based single crystal superalloys; thus, the Ni–Cr–Ru phase stability is very valuable for better understanding of the constitutional effects of Ru in multicomponent Ni-base superalloys. Four isothermal sections of the Ni–Cr–Ru system at 800 °C, 900 °C, 1000 °C and 1200 °C were constructed from results obtained from diffusion multiples using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The measured phase equilibria together with prior experimental results were used to optimize a CALPHAD thermodynamic description of the Ni–Cr–Ru ternary system using thermodynamic parameters of the Ni–Cr and Ni–Ru systems published in the literature and modified Cr–Ru parameters from the current study. The intermetallic compound sigma phase in the Cr–Ru system was described with a simplified two-sublattice model, (Cr,Ru) 20 (Cr,Ru) 10 , by taking into account future extension of the model into higher order systems. Comparison between the calculated results and the experimental measurements was made to demonstrate the reliability of the current thermodynamic parameters for the Ni–Cr–Ru system. For easy implementation of the thermodynamic parameters into some existing thermodynamic databases, a version of the thermodynamic description of the Ni–Cr–Ru system with an older sublattice model, (Cr,Ni,Ru) 10 (Cr) 4 (Cr,Ni,Ru) 16 , for the sigma phase was also developed. [ABSTRACT FROM AUTHOR]

Directional solidification (DS) experiments with thermal stabilization (TS) treatments were performed on Ti–46Al–5Nb (at.%) alloys in a Bridgman-type furnace using a quenching technology. Influence of the TS treatment on mushy zone and directional growth afterwards were investigated. The results show that the length of the mushy zone decreases but the β dendrite spacing in directional growth significantly increases with increasing TS time. During the DS process, β dendrite spacing is more homogeneous and its growth direction is more inclined to parallel to the axial direction with increase of the TS time. Al solute concentration in the mushy zone in a steady-state is always lower than that in original as-cast alloys. The mushy zone with the columnar β and α grains is easily produced after TS treatment on the alloys with microstructures of the directional dendrite segregation morphology before DS starting. TS treatment results in the redistribute of solute Al thus changes the phase constituent in the mushy zone. An appropriate TS is necessary to produce the L + β + α region in the mushy zone, which is of great benefit to control DS microstructures of TiAl peritectic alloys. [ABSTRACT FROM AUTHOR]

Micrometer-sized γ−Ni dendrite reinforced nanoeutectic matrix composites have been developed in (Ni 0.92 Zr 0.08 ) 100– x Al x (0 ≤ x ≤ 4) by arc melting. The eutectic matrix is composed of alternate nano-lamellae of intermetallic Ni 5 Zr and fcc–Ni solid solution phases. All these composites exhibit very high strength, large compressive plasticity ∼25% and strain-hardening up to 1780 MPa. Al dissolves in γ−Ni(Zr) solid solution phase, decreases its hardness/strength, and increases the volume % of γ−Ni dendrite from 20% ( x = 0) to 29% ( x = 4). Whereas, refinement of the eutectic lamellae thickness from 275 nm ( x = 0) to 160 nm ( x = 4) increases the matrix hardness and retains the global strength of the composites. The effect of Al addition on the microstructure formation, volume fraction as well as the length scale of the constituent phases, and mechanical properties, have been discussed using an analytical model. [ABSTRACT FROM AUTHOR]

Vacuum induction melting device combined with temperature control system was employed to investigate the effect of isothermal heat treatment (IHT) during solidification process on the microstructure evolution of a high Nb containing TiAl alloy. The microstructures of the alloy in as-cast condition and after IHT were studied. The results show that the as-cast microstructures exhibit a significant microstructural inhomogeneity with fine grains in dendrite core and coarse grains in interdendritic region. A new treatment approach by means of a short-term IHT within the β phase field during solidification process is proposed to obtain a uniform and refined microstructure. Compared with the as-cast alloy, IHT can reduce the tendency for crack. This phenomenon is attributed to the improvement of microstructural homogeneity by the elimination of peritectic α phase and the microstructure refinement by β → α transformation. [ABSTRACT FROM AUTHOR]

Carbon, Mo and Si represent promising alloying elements with respect to increase the operating temperature of intermetallic titanium aluminides. The influence of these elements on microstructural stability and creep properties is investigated on a β-solidifying γ-TiAl based alloy, named TNM, with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at.%) in two different microstructural conditions. The first condition after casting and hot isostatic pressing has a coarse “nearly lamellar γ” microstructure. The second condition is adjusted by a subsequent heat treatment and shows a “nearly lamellar β” microstructure with finely spaced α 2 and γ lamellae and areas of discontinuous precipitation (cellular reaction) in the α 2 /γ-colonies. Creep tests were carried out at 815 °C and 150 MPa to examine the influence of microstructure and its change on and during creep. Alloying of C and Si or Mo to the TNM based material led to improved creep properties and microstructural stability by inhibiting the progress of discontinuous precipitation. [ABSTRACT FROM AUTHOR]

In situ time-resolved X-ray diffraction by synchrotron radiation was used to monitor the phase transformations and grain-refining processes during laser-beam welding of a γ-TiAl-based alloy. The heating rate plays an important role of grain refinement. A high heating rate suppresses solid–solid phase transformations. The superheated γ grains serve as heterogeneous nuclei for β grains on subsequent solidification and refine the lamellar colonies. At low heating rate, diffusion-based transformations are observed on heating and coarse lamellae are formed after welding. The refined lamellar colonies improve the mechanical properties. [ABSTRACT FROM AUTHOR]

The morphology and growth behavior of Ni 3 Sn 4 grains at the Sn/Ni interface during soldering were systematically investigated. Sn/Ni reaction samples were examined in three electroplated Sn thicknesses, 5 μm, 10 μm and 100 μm. In soldering at 280 °C, the formed Ni 3 Sn 4 grains exhibit two kinds of morphologies, needle-like grains and larger chunk-type grains. Experimental observations reveal that the amount of the chunk-type grains increased as the Sn layer thickness was decreased, which is attributed to the Ni content in molten Sn. Moreover, needle-like grains display a hexagonal columnar structure with (100) and (110) facets. With the reaction proceeding, the needle-like grains coarsen with cube root of reaction time. The faceted chunk-type grains are transformed from the boomerang-shaped grains, consisting of two inverted triangular plates sharing an edge. The crystal plane orientations of the chunk-type Ni 3 Sn 4 grains were also analyzed based on its crystalline structure. Additionally, the Sn/Ni reactions at 250 °C indicate that the morphology of the chunk-type grains is also affected by the reaction temperature. [ABSTRACT FROM AUTHOR]

The paper focuses on the phase transformation of undercooled Ti–48Al (at.%) droplets atomized by high pressure gas. The microstructural evolution was analyzed using the transient nucleation theory in combination with the microstructural examinations. The primary phase, final phase volume fraction and the hardness are related to the droplets size to provide fundamental understanding. The competitive formation of the primary phases α and β are strongly controlled by the droplets size, and a critical diameter of about 25 μm was identified corresponding to an undercooling of 102 K. The final phase volume fraction of γ increased with the increase of powder size from 12% to 85%. The highest hardness with the value of 652 HV was obtained for powder of 50 μm in diameter. [ABSTRACT FROM AUTHOR]

Drop-tube processing was used to rapidly solidify droplets of Ni 64.7 Fe 10 Si 25.3 and Ni 59.7 Fe 15 Si 25.3 alloys. In the larger droplets, and therefore at low cooling rates, only two phases, γ-Ni 31 Si 12 and β 1 -Ni 3 Si were observed. Conversely, in the smaller droplets, and therefore at higher cooling rates, the metastable phase Ni 25 Si 9 was also observed. The critical cooling rate for the formation of Ni 25 Si 9 was estimated as 5 × 10 3 K s −1 . SEM and TEM analysis reveals three typical microstructures: (I) a regular structure, comprising single-phase γ-Ni 31 Si 12 and a eutectic structure between γ-Ni 31 Si 12 and β 1 -Ni 3 Si; (II) a refined lamellar structure with a lamellar spacing <50 nm comprising γ-Ni 31 Si 12 and β 1 -Ni 3 Si; (III) an anomalous structure with a matrix of Ni 25 Si 9 and only a very small proportion of a second, and as yet unidentified, phase. These results indicate that there is an extended stability field for Ni 25 Si 9 in the Ni-rich part of the Ni–Fe–Si ternary system in comparison to the Ni–Si binary system. With an increase of cooling rate, an increasing fraction of small droplets experience high undercoolings and, therefore, can be undercooled into the Ni 25 Si 9 stability field forming droplets consisting of only the anomalous structure (III). The Fe atoms are found to occupy different substitutional sites in different phase, i.e. Fe substitutes for Ni in the γ phase and Si in the L1 2 (β 1 ) phase respectively. [ABSTRACT FROM AUTHOR]

This study investigated the effects of Zn contents on the reaction products and microstructural evolution in the liquid/solid Sn–Zn/Pd interfacial reactions at 260 °C. A uniform Pd 2 Zn 9 layer was formed at the Sn–9 wt.%Zn/Pd interface. The reaction phase transited from Pd 2 Zn 9 to PdSn 4 when the Zn content decreased from 2 wt.% to 1 wt.%. The most striking feature is that the PdSn 4 growth was greatly suppressed with only 0.5 wt.% Zn addition in solders. Additionally, a drastic microstructural evolution was observed in the Sn–1.5 wt.%Zn/Pd reaction. The Pd 2 Zn 9 layer was initially formed and then it was detached from the interface due to the decrease in the Zn content. Subsequently, the dominant phase changed to the PdSn 4 phase. Furthermore, a partial isothermal section in the Sn–Zn–Pd ternary system (less than 20 at.%Pd) at 260 °C was experimentally determined. The liquid apex of the liquid + PdSn 4 + Pd 2 Zn 9 tie-triangle was located at Sn–2.7 at.%Zn–1.0 at.%Pd. The phase transition from Pd 2 Zn 9 to PdSn 4 in the interfacial reactions was in good agreement with the phase equilibria relationship. [ABSTRACT FROM AUTHOR]

The paper presents new results concerning the influence of nickel addition (1 and 5 at.%) into tin on the development of the Cu/(Sn,Ni) interface area in diffusion couple experiment. The morphology and chemical composition of the intermetallic phases growing in the Cu/(Sn,Ni) diffusion couples were examined by means of the scanning (SEM) and transmission (TEM) electron microscopy after annealing at 215 °C in vacuum for different period time. It was shown that even 1 at.% of nickel addition into tin resulted in formation of intermetallics of complex microstructure. The presence of (Cu 1− x Ni x ) 6 Sn 5 in two morphological and compositional variants was noted. The discontinuous layer consisting up to 7.2 at.% of Ni closer to copper end-member coexisted with needle-like and faceted precipitates with even 22.3 at.% of Ni, which intensively detached from the interface. At the Cu/(Cu 1− x Ni x ) 6 Sn 5 interface the formation of Cu 3 Sn wavy layer compound was observed in all examined diffusion couples which became thicker with time. The porosity within the both formed intermetallic phases existed irrespective of the amount of added nickel. [ABSTRACT FROM AUTHOR]

The effect of changes in the composition and microstructure of the Ni 3 V–Ni 3 Al pseudo-binary alloys on their thermal conductivity has been investigated. For Ni 3 V and Ni 3 Al-based single-phase alloys, the thermal conductivity shows a maximum value at the stoichiometric compositions, and it decreases as the V (or Al) content of the Ni 3 Al (or Ni 3 V) alloy increases, following the Nordheim rule. For Ni 3 V–Ni 3 Al two-phase alloys, the thermal conductivity of the constituent Ni 3 Al phase exhibits a smaller value than that of the Ni 3 V phase. Eventually, the thermal conductivity of the two-phase alloys decreases as the Al content increases because of the increase in the volume fraction of the Ni 3 Al phase with low conductivity. As the temperature increases from 293 K to 1073 K, the conductivity increases for all of the alloys but not for stoichiometric Ni 3 V. However, the dependence of the thermal conductivity on the alloy composition between 293 K and 1073 K is similar. Hence, it is confirmed that the thermal conductivity of the Ni 3 V–Ni 3 Al pseudo-binary alloys is controlled by the composition and volume fraction of the constituent phase. [ABSTRACT FROM AUTHOR]

Columnar-to-Equiaxed Transition (CET) of binary Ti–Al alloys and multi-component Ti–48Al–2Cr–2Nb alloys is studied using Bridgman solidification technique. The effect of aluminum concentration and growth rate on CET is determined. It is found in Ti–46Al and Ti–50Al alloy ingots equiaxed grains develop ahead of the moving solid–liquid interface with a growth rate of 500 μm/s; microstructures in Ti–49Al alloy stay columnar dendrites with the same growth rate. CET in Ti–Al alloys are not only influenced by growth rate, but also by the solidification path that is related to alloying composition. CET in Ti–Al alloys is predicted using the dendritic growth model based on the criterion of growth at marginal stability. According to the calculated results and directionally solidified microstructures, values of the nucleation undercooling for α and β phases are given. The growth rates to avoid CET in Ti–48Al–2Cr–2Nb alloy are suggested. [ABSTRACT FROM AUTHOR]

With respect to the wrought processing of γ-TiAl alloys, the hot forging processes for ingot-breakdown is one of the most important steps. To obtain a billet with fine and uniform microstructure and excellent mechanical performances, an understanding of the strictly controlled forging processes and microstructure evolution are necessary. The hot forging processes and microstructure evolution of a high Nb containing TiAl alloy with nominal composition of Ti–43Al–8Nb–0.2W–0.1Y (at.%) were investigated in this paper. Three forging routes, one-step canned forging (OCF), one-step non-canned forging (ONF) and multi-step non-canned forging (MNF), were designed to study their effect on microstructure evolution of as-forged materials. Results showed that OCF and ONF produced nonuniform microstructures due to inhomogeneous deformation, while the specifically designed MNF process yielded fine and uniform grains, indicating that it is an effective and economic approach for ingot break-down of the present alloy. Besides, it is also found that forging at (α + β) phase region can retain large amount of β/B2 phase due to the strain-induced segregation of Nb and W, which is beneficial to the workability, and thus enables the use of near-conventional forging operations for the present alloy. The proposed multi-step forging in the present work may yield important information for the development of hot-deformation techniques and new alloy design strategies of γ-TiAl alloys. [ABSTRACT FROM AUTHOR]

High resolution time-resolved X-ray imaging with synchrotron radiation has been used to in situ observe the growth behavior of Cu 6 Sn 5 intermetallic compounds (IMCs) during solidification in Sn–6.5 Cu and Sn–6.5 Cu–0.2 Al (wt. %) solders under applied direct current (DC) field. The morphological evolution of Cu 6 Sn 5 with I-like, X-like, Y-like and bird-like shapes is directly observed. It is shown that trace levels of Al have a marked effect on the solder microstructures and refining the size of the primary Cu 6 Sn 5 . The solidification pathway leading to the refinement is observed in real time using synchrotron microradiography. After adding the trace Al, I-like shapes bifurcate into X-like shapes. Furthermore, when DC field with 10 A/cm 2 is applied, both the growth rate and the mean size of Cu 6 Sn 5 are increased but decreased when 100 A/cm 2 is applied. Meanwhile, the effect of thermodynamic potential barrier caused by DC field on the growth behavior of Cu 6 Sn 5 is discussed. [ABSTRACT FROM AUTHOR]

The evolution of microstructure and grain boundaries were investigated in coarse-grained Ni–48Al intermetallics during plastic deformation at 1075 °C with the initial strain rate of 1.5 × 10 −3 s −1 using electron backscatter diffraction (EBSD) technique. Before deformation, most grain boundaries were high-angled (HAGBs), with several particular angles being predominant. During initial deformation, low-angle grain boundaries (LAGBs) with misorientation less than 5° began to evolve. The misorientation of the newly-formed LAGBs increased with the increase of deformation, meanwhile, grain boundaries with misorientations between 6 and 15° were gradually observed, and finally transformed into HAGBs (misorientation angle > 15°). There appeared a steady state transition from the formation of new LAGBs to the transformation into high-angle grain boundaries. As a result, the grain size was refined continuously with the deformation strain. [ABSTRACT FROM AUTHOR]

In this work, the B2 phase precipitation behavior in Ti–40Al–8Nb alloys with a (α 2 +γ) duplex microstructure during the hot deformation process was investigated. Results showed that even if the deformation temperatures, 1000 °C and 1050 °C, were much lower than the B2 phase precipitation temperature (1160 °C), obvious B2 precipitates were observed in the compressed samples. The characteristics of B2 precipitates were significantly dependent on the deformation condition, i.e., its grain size and phase content increased with the rise of deformation temperature and decrease of strain rate. The detailed analysis indicated that the B2 phase was derived from the α 2 →B2 phase transition under the mechanical-thermal coupling effect. The applied stress provides a driving force for the redistribution of Nb element in the deformed α 2 phase and the preferable thermal conditions with an enhanced diffusion accelerate the enrichment of Nb element in local regions. Moreover, the precipitated B2 phase was thermodynamically unstable, and an inverse transition B2→α 2 occurred during the post-annealing at 1050 °C. • B2 precipitates appear below its precipitation temperature during hot deformation process. • B2 phase is derived from α 2 phase following the Burgers orientation relationships. • Mechanical-thermal coupling effect is responsible for the B2 phase precipitation. • B2 phase is thermodynamically unstable, and B2.→α 2 transition occurs during the post-annealing process. [ABSTRACT FROM AUTHOR]

CoSn 3 is the major reaction product in Sn/Co interfacial reactions. Compared with other substrate materials, e.g., Cu and Ni, the CoSn 3 growth is much faster during reflow soldering and thermal aging. However, excessive formation of intermetallic compound (IMC) layer might deteriorate the reliability of solder joints. This study demonstrated that the CoSn 3 growth was effectively slowed down by adding minor amounts of Zn in Sn solder. The solder reactions between Co and Sn with addition of various Zn contents (0.05 wt% ∼ 2 wt%) were systematically examined in liquid-state and solid-state reactions. For liquid-state reactions at 240 °C–260 °C, the CoSn 3 growth rate was decreased by 50% with 0.1 wt%Zn addition, and further decreased by 75% with 0.5 wt%Zn. Moreover, the growth kinetics of CoSn 3 was investigated with various Zn additions. The CoSn 3 growth was found to be proportional with reaction time, and their apparent activation energies were very close (between 105 kJ/mol ∼ 110 kJ/mol). For solid-state reactions, the effect of Zn addition on the inhibition of CoSn 3 growth was more significant. The growth rate was greatly reduced by 75% with only 0.05 wt%Zn addition. The possible inhibition mechanism was discussed. [ABSTRACT FROM AUTHOR]

Arc-melting (AC) and directional solidification (DS) techniques were used to prepare Nb-15Si-22Ti-2Al-2Hf-2V-(2, 14) Cr alloys (hereafter referred as to 2Cr and 14Cr alloys, respectively), and the microstructural evolution and mechanical properties, including Vickers hardness, room temperature fracture toughness and high temperature strength, of the two AC and DS alloys were compared. The results showed that with heat-treatment at 1350 °C for 50 h, the AC-2Cr alloy composed of Nb solid solution (Nb SS ) and α-Nb 5 Si 3 silicide, while Laves C15-Cr 2 Nb phase arose in the 14Cr alloy. With two-phase Nb SS /α-Nb 5 Si 3 microstructure, the AC-2Cr alloy showed excellent room-temperature fracture toughness ( K Q : 14.2 MPa m 1/2 ) and 0.2% yield strength at 1250 °C ( σ 0.2 : 315 MPa) and 1350 °C ( σ 0.2 : 294 MPa), better than the AC-14Cr alloy with tri-phase Nb SS /α-Nb 5 Si 3 /C15-Cr 2 Nb microstructure ( K Q : 9.4 MPa m 1/2 , σ 0.2 : 189 MPa at 1250 °C and 87 MPa at 1350 °C). The DS technique was found not to change the phase constituent of each alloy, but it made the microstructure slightly orient to the growth direction, resulting in a significant improvement in room-temperature fracture toughness (by ∼43%) and high-temperature yield strength σ 0.2 (by ∼55%), as compared with the AC samples. [ABSTRACT FROM AUTHOR]

Sn-40 at.%Mn peritectic alloys in which both primary and peritectic phase are intermetallic compounds were directionally solidified at different growth rates (1 μm/s∼100 μm/s). Dendritic growth of primary phase has been observed even at low growth rate, and dependence of microstructural characteristic length scales on growth rate has been investigated. Liquidus slope is the dominating factor in determining non-faceted/faceted solid/liquid morphology. Experimental results show that: λ 1 = 229.64 v −0.20 , λ 2 = 33.337 v −0.34 , λ 3 = 39.90 v −0.378 , R = 16.90 v −0.384 . Besides, both λ 1 / λ 2 and λ 1 / λ 3 vary greatly with increasing growth rates while λ 2 / R ranges from 2 to 2.3 with increasing growth rate. Both the peritectic reaction and solute distribution of intermetallic compounds during solidification influence these length scales. A modified solute distribution coefficient which is appropriate for intermetallic compounds makes calculation agree reasonably well with experimental results. The value of λ 1 is influenced more by solute distribution of intermetallic compounds, while growth of λ 2 , λ 3 and R are more significantly influenced by the peritectic reaction. [ABSTRACT FROM AUTHOR]

A Mg–Y–Zn alloy composed almost completely of the Long-Period-Stacking-Ordered (LPSO) phase has been prepared by casting and extrusion to flat bar. An elongated microstructure is obtained with different grain orientations along the extrusion, transverse and normal directions, leading to a strong orientation dependence of strength. Differences of tensile and compressive stress are also noted. The importance of basal slip and other dislocation-dependent deformation mechanisms is discussed. The large tension-compression strength differences are considered to imply that twinning plays an important role in determining strength. The analysis of deformation mechanisms and strengthening is supported by metallographic studies of surface slip bands and dislocation distributions. [ABSTRACT FROM AUTHOR]

The strain in different regions of the pancake was different during isothermal forging process. Different strain could greatly influenced the forged microstructure. In the present work, the relationships between strain, dynamic recrystallization (DRX) and microstructure in different regions of powder metallurgy Ti–45Al–10Nb alloy during isothermal forging were investigated. The results show that the microstructure from the center to edge of the forged pancake was inhomogeneous due to the degree of DRX. And DRX was related with the degree of strain, large strain can promote DRX. [ABSTRACT FROM AUTHOR]

Sixty nine Nb–Si based alloys with Al, B, Cr, Fe, Ge, Hf, Mo, Sn, Ta, Ti, V, W, Zr additions that were produced using cold hearth based solidification processing were used to study the macrosegregation of Si. The study used chemical analysis data for the compositions of the cast alloys and phases present in their microstructures to calculate various material parameters and the partitioning of solutes. The material parameters were based on the melting temperatures and enthalpies of melting of sd and sp electronic configuration alloying elements in Nb. The key material parameters controlling the macrosegregation of Si were the alloy melting temperature T m , the melting temperature of the sd elements of the alloy T m sd , the enthalpy of melting of the sd elements Δ H m sd , the ratio of the melting temperatures of the sd and sp elements in the alloys T m sd / T m sp and the “alloy entropy of fusion” Δ H m / T m . The macrosegregation of Si was explained using the concepts of “alloy entropy of fusion”, and “alloy enthalpy of melting” Δ H m and T m and by considering (i) the stability of S/L interfaces in terms of constitutional supercooling theory and the growth of S/L interfaces in terms of their structure and (ii) the partitioning of solutes between the Nb ss and the intermetallics present in the microstructures of the alloys. High Si macrosegregation was observed in alloys that had high Δ H m / T m and T m sp values and low T m sd / T m sp and T m . [ABSTRACT FROM AUTHOR]

Phase equilibria in the Ir–W, Ir–Al and Ir–W–Al systems at temperatures between 1100 °C and 1600 °C were experimentally investigated using diffusion couples and two- or three-phase alloys, and the mechanical properties of γ ′ (L1 2 ) strengthened Ir–W–Al alloys were examined by hardness and compression tests at room and elevated temperatures. The phase boundaries between the γ (A1)/ ε ′(D0 19 ), ε ′/ ε (A3) and ε / ε ″(B19) in the Ir–W system at 1400 °C–1600 °C and those between the γ/ β (B2) and β /Al 2.7 Ir in the Ir–Al system at 1100 °C–1400 °C were determined. The phase diagrams in the Ir-rich corner of the Ir–W–Al ternary system at 1300 °C and 1400 °C were also determined. The existence of the γ ′ phase of the Ir 3 (W,Al) ternary compound was confirmed, and this system was found to consist of the γ , γ ′, ε , ε ′ and β phases in the Ir-rich portion. It was also found from hardness and compression tests up to 1200 °C that Ir–Al–W alloys having the γ + γ ′ structure with a small lattice misfit show high hardness and strength at room and high temperatures. [ABSTRACT FROM AUTHOR]

In this work, high Nb-containing TiAl alloy sheets were hot rolled starting from powder metallurgical billets. The prealloyed powder prepared by the plasma rotation electrode process (PREP) was characterized. Results show that there are two typical morphologies of powders: martensitic (M) and dendritic (D) powders, which are formed due to different local cooling conditions. The two PREPed powders lead to the formation of different microstructures in HIPing. The coarse D powder will introduce defects, such as residual primary particle boundaries and interfacial porosity in the as-HIPed microstructures. The deformation behavior of PM high-Nb TiAl alloys largely depends on γ phase. Besides the dynamic recrystallization and the superplastic deformation, due to the large amount of the γ phase in PM high-Nb TiAl alloy and the high rolling rate, the mechanical twinning in γ phase plays a critical role in the hot rolling process. The mechanical properties of high-Nb TiAl alloys can be significantly improved by the hot rolling, through the refinement of microstructures and the elimination of primary particle boundaries. However, a large deformation may introduce defects and coarsened microstructures, and thus 60% deformation may be suitable for the purpose of improving mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution scanning transmission electron microscopy was used to investigate the core structure of a metadislocation in a plastically deformed sample of the complex metallic alloy ε 6-Al–Pd–Mn. The atomic-level characterization of a metadislocation with 16 associated phason planes showed dissociation into metadislocations with 6 and 10 phason planes. A structural model of the dissociated core region was developed. The Burgers vector of the dislocation = −0.07 nm [001] splits up into = −0.183 nm [001] and = 0.113 nm [001] increasing the strain at the metadislocation cores. Although unfavourable with respect to an increasing elastic strain energy the dissociation is realized due to a decrease in fault-plane energy. The latter arises from a size reduction of the ξ-phase area that is required to accommodate the metadislocation in the structure. A careful inspection of several exemplary metadislocations with 16 phason planes using electron microscopy indicates their dissociated structure which casts doubt on the stability of elementary metadislocations with 16 phason planes. The study includes a detailed analysis of the structure of a metadislocation core with 6 associated phason planes. [Copyright &y& Elsevier]

The creep properties of K5 (Ti-46Al-3Nb-2Cr-0.2W) based alloys were analyzed in wrought processed microstructure forms. The brittle–ductile-transition-temperature (BDTT) depends distinctly on microstructure as well as strain rate, with the minimum value for each microstructure achieved at ∼10−6/s being about 680 °C and 780 °C, respectively. The greatest creep resistance is achieved in coarse-grained fully lamellar (FL) material and is related to the strong anisotropy of lath structure, large grain size and consequently high BDTT. Additional significant resistance improvement is realized with additions or increases of refractory elements (Nb or W) and decrease in Al content. The most remarkable improvements in primary as well as the minimum creep resistance are realized when small amounts of C or C + Si are added to generate incoherent (to gamma) carbide and silicide particles along γ/γT interfaces. The significance of primary creep is assessed for controlling subsequent creep behavior and discussed for its crucial role in satisfying the stringent design creep requirements for advanced rotational components. The accelerated or tertiary creep is used to explain the high temperature (870 °C) high cycle fatigue deformation that exhibits two-stage SN curves with the rapidly softening second stage. [ABSTRACT FROM AUTHOR]

Pack aluminization – a chemical vapor deposition process widely used to form protective coatings on Ni-based superalloy components – was used to form shells of Ni2Al3, NiAl and/or γ′-Ni3Al on the surface of γ-Ni wires with diameters of 127 μm. The growth kinetics of these Al-rich intermetallic shells are studied as a function of aluminization time and pack activity at 1000 °C. Similar kinetics but additional phases (Cr/Ni two-phase shell, Cr silicide particles and Al-rich particles distributed in Ni2Al3) are found in the shells of pack-aluminized Ni–20 wt.% Cr wires with similar diameters. Fully homogenous Ni–Al and Ni–Cr–Al wires are achieved by interdiffusion at 1200 °C between the deposited Al-rich intermetallic shells and the Ni-rich core of both types of wires. Upon subsequent aging at 900 °C, wires with γ/γ′ structure and high hardness indicative of precipitation strengthening are obtained. [ABSTRACT FROM AUTHOR]

A new method of melt cyclical superheating combined with the control of solidification and cooling process as well as appropriate heat treatment was proposed to prepare bulk β-FeSi2. FeSi2 precursor of φ18 × 17 mm in size was obtained under the conditions of melt superheating temperature 1550 °C, superheating time 10 min, recycling times 3, solidification rate 30 °C/s, cooling rate 12 °C/min from solidification temperature to 700 °C and cooling naturally from 700 °C to room temperature. The precursor had homogeneous and complete α + ε eutectic structure, with the rod-like ε phase of 1–2 μm in diameter. After the precursor with complete α + ε eutectic structure were annealed at 900 °C for 150 h, both the α and ε phases totally disappeared and were transformed into β-FeSi2 except few residual Si-rich phase. [ABSTRACT FROM AUTHOR]

Abstract: In the present work the effect of Cu/Zr atomic ratio on structural and calorimetric properties of this high temperature shape memory alloy (HTSMA) is studied. It has been discussed the changes induced by Cu/Zr ratio on the martensitic transformation temperatures and the corresponding transformation heats coupled with the phases microstructure. The modification of the Cu content in the range ±2% at, around the equiatomic composition, does not drastically change the thermal properties of the alloys. Moreover, the Cu/Zr ratio strongly influences the microstructure in terms of the presence and amount of the other characteristic phases, Cu10Zr7 and CuZr2, in the place of the CuZr phase. The understanding of the basic properties of the binary system can be of great help for further investigations on CuZr based systems with other alloying elements. [Copyright &y& Elsevier]

Abstract: This paper deals with phase constitutions, microstructural evolutions, and mechanical properties of Nb–16Si–xFe in-situ composites (where x = 2, 4, 6 at.%, referred as to 2Fe, 4Fe and 6Fe alloys, hereafter) prepared by arc-melting. It is found that with additions of Fe, Nb4FeSi silicide arises and microstructures of as-cast samples are consisted of dendritic-like NbSS phase, Nb3Si block, and Nb4FeSi matrix in the 2Fe and 4Fe alloys, and of the dendritic-like NbSS phase and Nb4FeSi matrix in the 6Fe alloy. When heat-treated at 1350 °C for 100 h, part of the Nb3Si phase decomposes in the 2Fe and 4Fe alloys, and the 6Fe alloy shows no change in microstructure as compared with the as-cast one. The Nb4FeSi silicide is found to be brittle, its fracture toughness and elastic modulus are first obtained, having values about 1.22 MPa m1/2, and 310 GPa, respectively. The fracture toughness of the bulk as-cast and heat-treated Nb–16Si–xFe samples are changed slightly by the Fe additions, which is in a range of 9.03–10.19 MPa m1/2. It is interesting that at room temperature, strength is improved by the Fe additions, whereas at 1250 °C and 1350 °C the strength decreases. As the Fe content increased from 2 at.% to 6 at.%, for example, the 0.2% yield strength increases from 1410 MPa to 1580 MPa at room temperature, decreases from 479 MPa to 385 MPa at 1250 °C. [Copyright &y& Elsevier]

Abstract: This paper investigates the strength response of Ir-xHf-yNb alloys (x = 3, 4, 5, 8, 9, 10 at.%, and y = 5, 6, 7, 11, 13, 15 at.%) with a dual-phase fcc/L12 microstructure at room and high temperatures. The experimental strength at 1950 °C was compared with that obtained by the rule of mixture. The results showed that in the fcc/L12 structure the fcc phase always shows higher strength than the L12 phase, at both room and high temperatures. A dual-phase fcc/L12 microstructure with different fcc to L12 fraction ratio formed when Hf and Nb contents in the Ir-xHf-yNb ternary alloys were larger than 3 at.% and 5 at.%, respectively, and the pure L12 microstructure was obtained at 10 at.% Hf and 15 at.% Nb. The Ir-5Hf-7Nb alloy, possessing an fcc-dominant microstructure in which the optimization fcc fraction is about 78%, has an outstanding 0.2% yield compressive strength of 270 MPa even at 1950 °C. This ultra-high strength is attributed to strong interface hardening by the large lattice misfit between the fcc and L12 phases. The failure mode of the Ir–Hf–Nb ternary alloys is by debonding of the grain boundary. [Copyright &y& Elsevier]

Abstract: Single phase Bi85Sb15 bulk materials were prepared by a melt spinning (MS) combined with subsequent spark plasma sintering (SPS) technique (MS + SPS). The effects of cooling rate in MS process on the microstructure and low temperature thermoelectric properties (10–300 K) of bulk Bi85Sb15 have been systematically investigated. With increasing the cooling rate, the increase of constituents homogeneity and corresponding increase in actual energy gap give rise to a significant improvement of electron mobility and decrease in electron concentration, resulting in an optimized power factor with a highest value of 7.9 mW m K−2 for the sample with highest cooling rate. Meanwhile, the thermal conductivity retains a very low value due to the intensified phonon scattering by alloying and interfaces. Consequently, the sample with highest cooling rate exhibits a highest Z value of 2.74 × 10−3 K−1 at 120 K which is superior to most of polycrystalline sintered samples, mainly benefiting from its relatively higher power factor. In addition, the utilization of the rapid and energy-saving MS + SPS technique along with improved thermoelectric and mechanical performances is very promising for the cryogenic application of BiSb alloy. [Copyright &y& Elsevier]

Abstract: The soldering of eutectic Sn3.0Ag0.5Cu solder on an electroplating Ni is carried out at 250 °C for 5 s followed by rapid quench with liquid nitrogen. During soldering, metastable NiSn compound formed in contact with Ni layer because Ni dissolves into the liquid solder to react with Sn. The formation of Sn–Cu–Ni ternary amorphous diffusion zone is observed between NiSn nucleation zone and solder. In this ternary amorphous diffusion zone, different types of structures are formed such as base structure, atomic clusters, short-range order structure formations and nucleation of nanocrystalline NiSn and Cu6Sn5 compounds. The long-range order structures of nano cells consist of the short-range order and base structures. The atoms within an atomic cluster which is composed of several base structures tend to arrange to form the short-range order. The atomic clusters and short-range order may be the intermediate state during the nucleation of intermetallic compunds. [Copyright &y& Elsevier]

Abstract: Directional solidification experiments were performed on intermetallic Ti-46Al-0.5W-0.5Si (at. %) alloy using a Bridgman-type furnace. Lamellar orientation and growth direction of α phase under different growth rates were studied. The hexagonal α phase is the primary phase of the alloy. The lamellar orientations are inclined at the angles of 80°–90° to the growth direction at growth rates below 10 μm/s. With increasing growth rate, the lamellar orientations are changed and not perpendicular to growth direction. When growth rates are below 10 μm/s, the preferred growth direction (PGD) of α dendrites is <0001> direction. The PGD of α phase changes into direction when growth rate increasing to 20 μm/s. Besides, The PGD of α phase is changed into direction at growth rates of 30 μm/s and 50 μm/s. The lamellar orientation can be aligned to the growth direction when the PGD of α phase is direction. [Copyright &y& Elsevier]