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A novel polycrystalline Ni 3 Al-based intermetallic alloy was prepared using the vacuum induction melting process. Subsequently, the alloy was subjected to the solution-treatment underwent two different aging processes: 870 °C for 24 h in air cooling, referred to as AT 1, and 1060 °C for 4 h in air cooling followed by 870 °C for 24 h in air cooling, referred to as AT 2. The effects of different aging processes on the microstructure and mechanical properties of the polycrystalline Ni 3 Al-based intermetallic alloys were analyzed. Results indicated the cubicity of the primary γ′ phase within the dendritic γ+γ′ structure of the AT 2 sample was significantly enhanced, yielding the best overall mechanical properties for the alloy. The percentage elongation increased from less than 3 % for the AT 1 sample to about 4.5 %, highlighting a notable enhancement in room temperature tensile plasticity. The creep rupture time at 1100 °C/30 MPa reached 113 h. The α-Cr particles in the As-cast and solid solution alloy gradually transformed into Cr 23 C 6 during the aging process, exhibiting the orientation relationships of (020) Cr23C6 ||(010) γ' and [103] Cr23C6 ||[103] γ'. High-temperature aging treatments resulted in Cr 23 C 6 particles that provided enhanced precipitation strengthening effects, thereby improving the creep rupture performance of the Ni 3 Al-based intermetallic alloys. Following high-temperature aging, a four-layer interface structure formed around the blocky γ′ matrix phase, which altered the alloy's fracture mechanism from a brittle intergranular fracture to a ductile transgranular fracture. • The orientation relationship of (020) Cr23C6.||(010) γ' and [103] Cr23C6 ||[103] γ' between the precipitates Cr 23 C 6 and γ′-matrix • A four-layer interface structure formed around the blocky matrix γ′ phase after high-temperature aging process. • The unique interface structure causes the fracture mechanism of the alloy to transition from brittle transgranular fracture to ductile intergranular fracture. [ABSTRACT FROM AUTHOR] more...

The early oxidation behaviors of complex Al–Cr compositional gradient coatings on a novel Co–Al–W substrate prepared by multi-arc ion plating technology (MIPT) at 1000 °C for 20–60 min were rapidly characterized. The as-deposited coatings with compositions ranging from (55%–90%Al, 45%–10%Cr) exhibited the laminated structure α-Al + Al 80 Cr 20 +Al 8 Cr 5 +α-Cr. After annealing at 640 °C for 40 h, a two-layered coating composed of (Co(Al, Cr) + Al 8 Co 18 Cr 4) and IRL formed, and the thickness of the coating increased from the 14–18 μm of the as-deposited state to 25–35 μm. During oxidation at 1000 °C for 20–60 min, a three-layer structure consisting of an outer α-Al 2 O 3 +α-Cr 2 O 3 +CoCr 2 O 4 layer, a central unoxidized Al–Cr layer, and an inner μ-Co 7 (W 0.55 Cr 0.45) 6 +B 2 –CoAl layer formed on the substrate. The Al–Cr coatings with higher Cr content had a looser oxide layer due to the CoCr 2 O 4 phase, which might degrade the intended protective effect of the Al–Cr coatings. Thus, the Al–Cr coatings with higher Al content were suitable for preventing oxidation behavior. This work proposes a high-throughput screening method for rapid characterization of the early oxidation mechanism of the complex Al–Cr compositional gradient coatings. [Display omitted] • Compositional gradient Al–Cr coatings were prepared on Co–Al–W alloy by MAIP. • Annealed Al–Cr coatings contained (Co(Al, Cr) + Al 8 Co 18 Cr 4) layer and innermost reaction layer (IRL). • Quick oxidation behaviors at 1000 °C for 20–60 min were first investigated. • Oxidation layer composed of out (α-Al 2 O 3 +α-Cr 2 O 3 +CoCr 2 O 4) layer, Al–Cr layer and IRL. • Al–Cr coating with higher Al was proposed to be optimized composition. [ABSTRACT FROM AUTHOR] more...

In this study, we analysed the effect of Fe, Mn, or Fe and Mn additions (5 or 10 at%) on the structure, mechanical properties, deformation behaviour, including microstructure evolution, and oxidation resistance of a lightweight (density of 3.92 g/cm3) intermetallic Al 55 Cr 23 Ti 22 complex concentrated alloy (CCA) with a L1 2 + C11 b structure. The additions of Fe, Mn, or Fe and Mn (at the expense of Cr) retained the density below 4 g/cm3 and resulted in forming a D8 a phase (Th 6 Mn 23 -prototype; cF120; Fm-3m) in all the alloys, except for the Al 55 Cr 18 Ti 22 Mn 5 alloy. The D8 a phase nucleated with a different morphology within or adjacent to the C11 b phase, and adopted an orientation relationship of (110) C11b || (4 ‾ 4 ‾ 0) D8a , [3 3 ‾ 1] C11b || [ 1 ‾ 1 1 ‾ ] D8a , which provided coherent C11 b /D8 a interfaces. Alloying with Mn or Fe and Mn had either neutral or negative effect on the mechanical properties, while the Fe additions boosted the strength along with some decrease in the compressive plasticity at room temperature. Specifically, the Al 55 Cr 13 Ti 22 Fe 10 alloy showed a yield strength of 250 MPa at 1000°С, which was 60 % higher compared to the Al 55 Cr 23 Ti 22 alloy. During plastic deformation, all the alloys demonstrated pronounced strain hardening at T ≤ 800 °C and steady state flow at 1000 °C. Post-deformation observation of the microstructure of the Al 55 Cr 13 Ti 22 Fe 10 alloy showed the inhomogeneous distribution of the strain-induced defects between the L1 2 matrix and (C11 b + D8 a) regions at 800 °C and partial recrystallisation of these phases at 1000 °C. All the alloys exhibited complex oxidation behaviour with multistage oxidation kinetics. The addition of 5 at% of Fe or Mn was beneficial for the oxidation resistance, while the further increase in their contents intensified the mass gain after a certain time. The latter effect was more pronounced in the Al 55 Cr 13 Ti 22 Mn 10 alloy than in the Al 55 Cr 13 Ti 22 Fe 10 alloy, because of forming a loose Al 2 O 3 oxide layer. All the alloys investigated exhibited a superior synergy of 1000°C-specific yield strength and compressive plasticity at room temperature, as well as a lower mass gain after 100 h at 1000 °C, compared to both lightweight and the most oxidation-resistant refractory CCAs. • Effect of Fe, Mn, or Fe and Mn additions on the Al 55 Cr 23 Ti 22 CCA were studied. • The alloying resulted in the precipitation of D8 a phase with coherent interfaces. • Fe increased the strength at 22–1000 °C, while Mn or Fe and Mn had neutral effects. • Addition of 5 at% of Fe or Mn reduced the mass gain at 1000 °C. • All the alloys were stronger and more oxidation-resistant at 1000 °C than other CCAs. [ABSTRACT FROM AUTHOR] more...

The diffusion multiple containing Ni–NiAl–Co alloys was fabricated using spark plasma sintering technique. The microstructure, mechanical properties and diffusion behavior were evaluated under annealing conditions of 1100 °C and 800 °C. The results suggest that spark plasma sintering proves to be an efficient processing approach in producing well-welded diffusion multiples in Al–Co–Ni based alloys. Nano-indentation tests were employed to quantify specific hardness and modulus values of the γ′, β and γ phases on a micro-scale level. Additionally, the diffusion path was determined through correlated compositional analysis, aligning well with existing phase equilibria data. [Display omitted] • SPS proves to be an efficient method in producing well-welded diffusion multiples. • The phase equilibria can be determined using the Ni–Co–NiAl diffusion multiple. • Nano-indentation quantifies the hardness and modulus values of γ′, β and γ phases. • The diffusion path can be determined via correlated compositional analysis. [ABSTRACT FROM AUTHOR] more...

Due to the low production cost and light weight, copper-clad aluminum conductors show great potential value in the field of power transmission, while the phase structure and organizational changes at the Cu–Al interface in high-temperature environments have a great impact on the electrical and mechanical properties. In this paper, Cu–Al diffusion couples are prepared to study the diffusion process, microstructure, and growth kinetics of intermetallic compounds (IMCs) in Cu–Al interface during heating from 600 °C to 800 °C, and the mechanical and electrical properties of Cu–Al diffusion couples are discussed. The results show that after heat treatment, IMC layers are formed at the Cu–Al interface and the Al-side is composed of CuAl and CuAl 2 , in which the CuAl phase transforms from long to thick dendrites with the increase of temperature, and finally grows into a "popcorn" form. The IMCs at the Cu–Al interface from the Cu side to the Al side are in the order of Cu 3 Al layer, Cu 9 Al 4 layer, Cu 3 Al 2 layer and CuAl layer, among which the Cu 3 Al 2 layer is the thickest (168.42 μm at 700 °C), while the Cu 3 Al layer is the thinnest (37.32 μm at 700 °C). The kinetic calculations show that the diffusion layer grows up rapidly, which is caused by the generation of liquid-phase during the heating process, leading to the acceleration of the diffusion of Cu and Al. The kinetic factor of the Cu 3 Al 2 layer is the largest (n = 0.69), causing the fastest growth rate of the Cu 3 Al 2 layer, while the Cu 3 Al layer shows the largest activation energy for diffusion and the smallest diffusion rate (Q = 9.48 kJ/mol, D 0 = 2.06 × 10−1 m2/s), therefore its growth rate is the slowest. Based on the thermodynamic calculations and the Cu–Al phase diagram, a growth mechanism of the Cu–Al interface is proposed, the formation sequence of IMCs at the Cu–Al interface is Cu 9 Al 4 , CuAl, Cu 3 Al 2 and Cu 3 Al. The formation of IMCs layer at the Cu–Al interface leads to a significant increase in the hardness of Cu–Al samples (the hardness of the Cu 3 Al 2 is 10 times higher than that of Cu) and an obvious decrease in electrical conductivity (the electrical resistivity of Cu–Al is 5 orders of magnitude higher than that of Cu), affecting its application in the electrical industry. • Cu 3 Al, Cu 9 Al 4 , Cu 3 Al 2 , and CuAl were formed in the Cu–Al interface at 600°C–800 °C. • Cu 3 Al 2 layer has the excellent kinetic factor (n = 0.69) and the growth rate. • The formation mechanism of IMCs in the Cu–Al interface at 600°C–800 °C is proposed. [ABSTRACT FROM AUTHOR] more...

The preparation of efficient and long-lasting electrocatalysts with low cost is crucial for hydrogen production by water electrolysis. Here, a series of high-entropy alloys (HEAs) of FeCoCrNiMo x (x = 0, 0.5, 1, 1.5, and 2) were created by arc melting method and enhanced by heat treatment according to various schedules. The microstructure transitioned from the FCC phase to the FCC + σ phase and finally to the FCC + σ + μ phase with the increase of Mo content. The FeCoCrNiMo 1.5 HEAs performed superior catalytic properties, which could be further modified by solution and aging treatment. As-cast FeCoCrNiMo 1.5 alloy showed a HER overpotential of 344 mV at the current density of 10 mA/cm2. After age treated at 800°Cthe overpotential decreased to 260 mV. According to the findings of SEM and TEM, the electrocatalytic activity performance of FeCoCrNiMo 1.5 HEAs after aged at 800 °C might be related to the precipitation of micro/nano-scale FCC phases inside μ phases. This work demonstrates the feasibility of non-noble metal-based HEAs (excluding platinum group metals) for hydrogen evolution and proposes a possible way to further enhance the electrocatalytic performance through heat treatment. • High-entropy alloys with good HER efficiency were prepared free of precious metals. • The feasibility of heat treatment for enhancing the HER properties was proved. • Superior HER activity was achieved at FeCoCrNiMo 1.5. • Quenching and 800 °C aging treatment further enhanced the catalytic properties. • Enhanced HER properties are related to the transition of IMC phase based on TEM data. [ABSTRACT FROM AUTHOR] more...

The Ni–Al–Zr system offers a variety of intermetallic eutectic combinations. Here, we demonstrate complex eutectic microstructures consisting of intermetallic i.e. Ni 3 Al–Ni 7 Zr 2 , NiAl–Ni 7 Zr 2 , and Ni 3 Al–NiAl–Ni 7 Zr 2. We also developed alloys with different fractions of two eutectics i.e. Ni 3 Al–Ni 7 Zr 2 , NiAl–Ni 7 Zr 2. These microstructures result in attractive combinations of ultra-high tensile strength of more than 1.5 GPa and are combined with 3–4% ductility and strength retention till 700 °C, which is better than most of the state of art super-alloys. The deformation behaviour along with fracture studies shows the role of individual intermetallic phases in the overall mechanical properties of the alloys. The transmission electron microscopy studies of the deformed samples show unique twinning in Ni 7 Zr 2 intermetallic. • A unique microstructure consisting of Ni 3 Al + Ni 7 Zr 2 and NiAl + Ni 7 Zr 2 intermetallic-intermetallic eutectic composites. • The exceptional strength of these alloys is derived from the constituent eutectics and is greater than 1.5 GPa with 3–4% tensile ductility at room temperature. • The alloys retain strength to 700 °C and their strength is significantly greater than many current Ni-base alloys. • The alloys deform by dislocation-based plasticity in Ni 3 Al and NiAl and twinning of Ni 7 Zr 2. • The fracture resistance is derived from scaling effects that restrict cleavage cracks to submicron eutectic lamellar thicknesses. • The brittle Ni 7 Zr 2 phase, enveloped by ductile Ni 3 Al or NiAl both of which fail by void nucleation and growth. [ABSTRACT FROM AUTHOR] more...

Ni 3 Al-based alloy joints were fabricated by transient liquid phase (TLP) bonding with Ni/Ti composite interlayer. The typical interfacial microstructure of the bonded joint was primarily composed of three zones: isothermal solidification zone, athermal solidification zone and base metal. Various reaction products were observed in the bonded joint, including γ′-Ni 3 (Al, Ti), TiNi 3 , Cr-Mo-Fe rich precipitates and β-Ti. The TiNi 3 phase in the athermal solidification zone was gradually reduced and eventually vanished by increasing the bonding parameters. The maximum room temperature shear strength of 828 MPa was obtained when the joint was bonded at 1220 °C for 60 min, while it was 625 MPa and 533 MPa at 650 °C and 800 °C, respectively. Cracks propagated primarily along the Ni 3 Al base metal and partially at the bonding interface when the joint was bonded at 1220 °C for 60 min, indicating the shear strength of the joint was almost equal to that of the base metal. • TLP bonding of Ni 3 Al-based alloy with Ni/Ti composite interlayer was achieved. • Ni 3 Al-based alloy joints had excellent room and high temperature strength. • Correlation between the joint microstructure and properties was established. [ABSTRACT FROM AUTHOR] more...

Mechanical properties of Ni-based superalloys strongly depend on phase and site preferences of alloying elements which influence bonding strength within γ′-Ni 3 Al precipitates and microstructural characteristics of these unique class of materials. In the current work, therefore, besides disclosure of the phase partitioning behaviours of alloying X elements (i.e. X = Co, Cr, Nb, Ta or Ti) among γ′ and γ phases, their site occupancy tendencies in γ′ precipitates (determined via first-principles ab initio calculations at 0 K) and effects on the microstructural evolution of Ni 80 Al 15 X 5 alloy systems (exposed to aging at 800 °C for 4, 16, 64 and 256 h, respectively) have been examined. Bonding features of Ni-Al, Ni-X and Al-X atomic pairs within Ni 3 Al-X intermetallics have been simulated by utilizing charge density difference (CDD) method, which reveals site preferences of alloying X elements as well. Present theoretical and experimental investigations have shown that mechanical strength of Ni-based superalloys is predominantly affected by bonding properties within γ′ precipitates. As atomic radii of alloying X elements become closer to that of Al atom, energy change parameter, E N i → A l X , values decrease and more Al sublattice sites are preferentially occupied in γ′ precipitates. Correspondingly, bonding strength of Ni-X atomic pairs along <110> directions of Ni 3 Al-X phases and micro-hardness properties of both as-cast and pre-aged Ni 80 Al 15 X 5 alloy systems enhance in the order of X = Co < Cr < Ti < Nb < Ta additions. Nevertheless, with increasing aging time, mechanical strength of alloys weakens in parallel with increasing size of γ′ precipitates simultaneously evolved from near-spherical to irregular forms. • Mechanical strength of superalloys mainly depends on bonding strength in γ′ phase. • Micro-hardness properties of alloys worsen with increasing size of γ′ precipitates. • Phase and site preferences are affected by atomic size of alloying elements. [ABSTRACT FROM AUTHOR] more...

In present work, a multiphase Ni 3 Al-based intermetallic alloy with complex components of γ'+γ dendrite comprising extremely high volume fraction (81 vol %) of γ′ phase and interdendritic β phase is investigated, the microstructure evolution and phase transformation behavior tailored by different solution cooling rates are studied by applying different cooling methods of water cooling (WC, 138 °C/s), air cooling (AC, 72 °C/s), and furnace cooling (FC, 0.05 °C/s) after solution treatment at 1200 °C for 10 h. Results show that the cubic degree, size and volume fraction of cuboidal primary γ′ as well as size of spherical secondary γ′ particles in the γ'+γ dendrite are improved by decreasing cooling rates, and the average sizes of the primary and secondary γ′ particles are found to meet logarithmic relationships with cooling rates. There are three kinds of precipitates in the interdendritic β phase resulted from different cooling methods, i.e., the rod-like Cr 3 C 2 carbides, the semi-spherical α-Cr particles, and the long acicular γ′ precipitates. The lower cooling rate decreases the number of rod-like Cr 3 C 2 carbides, increases the number and size of the semi-spherical α-Cr particles, and promotes the formation of long acicular γ′ precipitates in the interdendritic β-matrix. The semi-spherical α-Cr particles play the role of pinning dislocations in the β-matrix and have the orientation relationship of [‾110] α-Cr //[‾110] β-matrix. In addition, the precipitation of semi-spherical α-Cr particles in β-matrix is observed to accomplish in two sequential stages and grow in an onion-like ordered way. Stacking faults existed in partial of α-Cr particles due to the nanotwins in β-matrix. Microtwins are observed in the interdendritic β-matrix after water cooling, which have a bimodal configuration of nanotwins at the microtwinning boundaries and interior stacking faults. Besides, γ′-envelope formed between the γ'+γ dendrite and interdendritic β phase dependent on the solution cooling processes. Image 1 • Re-precipitation sizes of primary and secondary γ′ particles have the logarithmic relationship with solution cooling rates. • Microtwins in the β-matrix have a bimodal configuration of nanotwins at their boundary and interior stacking faults. • Precipitation pattern and growth mode of semi-spherical α-Cr particles in β-matrix phase after air cooling. • Precipitation behaviors influenced by solution cooling rates of precipitates in the interdendritic β. [ABSTRACT FROM AUTHOR] more...

Abstract The grain orientation dependence of stress-induced ω phase transformation during tensile deformation was investigated in the ordered body-centered cubic (B2) NiTi based single crystal alloys fabricated by directional solidification. The results show that the alloy with [102] orientation plastically deforms via {112}<111> mechanical twinning and stress-induced ω phase transformation at the twin boundary, while the same alloy with [001] orientation only generates brittle fracture without plastic deformation. The [102] oriented alloy has a much higher Young's modulus and better ductility compared with the [001] oriented alloy. Orientation plays a significant role in {112}<111> mechanical twinning and stress-induced ω phase transformation at the twin boundary, which governs the mechanical properties of the B2 NiTi based single crystal alloys. Graphical abstract Image 1 Highlights • The NiTi based single crystal alloy with [102] orientation plastically deforms via {112}<111> mechanical twinning and stress-induced ω phase transformation at the twin boundary. • The same alloy with [001] orientation only generates brittle fracture without plastic deformation. • The [102] oriented alloy has a much higher Young's modulus and better ductility. • Orientation plays a significant role in deformation behaviors of the NiTi based single crystal alloys. [ABSTRACT FROM AUTHOR] more...

Abstract First principles pseudopotential calculations have been performed to explore the effect of spin-orbit coupling on the electronic, elastic, mechanical, vibrational and electron-phonon interaction properties of noncentrosymmetric BaPtSb crystallizing in the hexagonal SrPtSb-type. This coupling makes only moderate changes to the elastic and mechanical properties but significant changes to the phonon spectrum in the acoustic range. Analysis of the Eliashberg spectral function reveals that these low-frequency phonon modes originate from the vibrations of Pt and Sb atoms and couple strongly to their d and p electronic states at the Fermi level. The spin-orbit coupling has a significant effect on the electron-phonon interaction properties by decreasing the frequencies of some phonon modes and increasing the strength of the most dominant peak of the Eliashberg spectral function. The average electron-phonon coupling increases from 0.617 without spin-orbit coupling to 0.629 with spin-orbit coupling, resulting in the corresponding changes to the superconducting transition temperature from 1.46 to 1.54 K. The latter value of superconducting transition temperature compares very well with its experimental value of 1.64 K. Highlights • Elastic and electronic properties of BaPtSb are investigated by using ab initio pseudopotential method. • Phonons and electron-phonon interaction in BaPtSb are studied using a linear response theory. • The superconductivity in observed BaPtSb appears to be an intrinsic property of the PtSb honeycomb lattice. • The electron-phonon coupling increases from 0.617 to 0.629 when SOC included. • The calculated Tc of BaPtSb with SOC is 1.54 K which coincides with the experimental value of 1.64 K. [ABSTRACT FROM AUTHOR] more...

Abstract The intermetallic compounds Zr 2 Pd and ZrPd 2 have been investigated by perturbed angular correlation (PAC) spectroscopy considering anomalies in their hydrogen absorption properties. It is known that both these compounds have same crystal structure, but Zr 2 Pd forms an excellent hydride while ZrPd 2 does not, even at high pressure. From PAC measurement at room temperature in annealed ZrPd 2 sample, this phase is found as a minor component (∼27%) while the dominating phase is identified to be the ZrPd 3 (∼73%). In Zr 2 Pd, this phase has been found to be predominant (∼86%) along with a minor phase (∼14%) due to ZrPd. In ZrPd 2 , unlike Zr 2 Pd, a weak temperature dependence of electric field gradient (EFG) has been found from present PAC measurements. Also, site occupancies for both Zr and Pd atoms by the Ta-probe atoms have been found in ZrPd 2 and ZrPd 3 (formed in ZrPd 2). In ZrPd 3 , Pd site occupancy by the probe is found to be maximum while a small fraction for Zr site occupancy has been found. But, in case of Zr 2 Pd and ZrPd, no Pd site occupancy of the probe is observed. Calculation of electric field gradients at 181Ta impurity atom for different phases have been performed by density functional theory based on the all electron full potential linearized augmented plane wave plus local orbitals (FP-(L)APW + lo) method to assign the different components observed from PAC measurements. Measurements by XRD have also been carried out to confirm the presence of component phases in the samples. [ABSTRACT FROM AUTHOR] more...

In this paper, porous NiTi intermetallic was synthesized via a modified thermal explosion (TE) method, utilizing Ni (74 μm, 38 μm, 5 μm, 100–200 nm) and Al element powders as raw material. The exothermic behavior and phase transition of porous NiTi intermetallic compounds were studied. The results showed that with the refinement of Ni particle size, the heat release decreased, and the Ti-74 μm sample was the product of two eutectic reactions. Their mechanical properties were verified by the Vickers hardness tester and universal testing machine, and the corrosion behavior of porous NiTi intermetallic compounds in phosphate-buffered saline (PBS) solution was studied by electrochemical tests. Among them, Ti-5 μm exhibits the most homogeneous microstructure and favorable mechanical properties, which has a porosity of 31.7 % and a compressive strength of 321.71 MPa. However, corrosion resistance is sacrificed due to the high open porosity. This study holds great promise for precise control microstructural characteristics and optimization of mechanical and electrochemical properties of porous NiTi intermetallics. • Porous NiTi intermetallic compounds were sintered by a rapid TE method. • The refinement of the particle size will limit the heat release of the TE reaction. • The prepared NiTi has a porosity of 31.7 % and a compressive strength of 321.71 MPa. • Reducing porosity contribute to improving corrosion resistance. [ABSTRACT FROM AUTHOR] more...

New ternary intermetallic Pt 5 Mn 2 Si was obtained in the form of single crystals and phase-pure polycrystalline bulk samples. This compound is only the second one found in the Pt–Mn–Si system. Pt 5 Mn 2 Si (space group Pbam , a = 5.4355(3) Å, b = 10.5955(7) Å, c = 4.0024(3) Å, Z = 2) is isotypic with the Rh 5 Ga 2 As structure, an ordered ternary variation of the Rh 5 Ge 3 structure type. This structure type is fairly rare, and Pt 5 Mn 2 Si is only the second ternary intermetallic adopting this structure. Magnetic measurements show that the compound has magnetic transition at ca. 80 K, most likely attributed to ferrimagnetic ordering of manganese spins. DFT calculations predict Pt 5 Mn 2 Si to be a metallic conductor. Chemical bonding analysis shows a pattern of localized pairwise-like Pt–Mn and Pt–Si bonds. [Display omitted] • Ternary intermetallic Pt 5 Mn 2 Si was obtained as single crystals and bulk. • Its crystal structure was determined from X-ray diffraction data. • Pt 5 Mn 2 Si belongs to the rare subtype of the Rh 5 Ge 3 structure type. • DFT calculations indicate metallic properties and localized bonding. • Pt 5 Mn 2 Si has a transition to ferrimagnetic state at ca. 80 K. [ABSTRACT FROM AUTHOR] more...

We have applied a universal geometrical-topological approach to analyze 23507 robust crystal structures of intermetallic compounds, which are deposited in the Inorganic Crystal Structure Database. All the structures were represented as three-periodic nets and arranged into 2551 topological types each of which possesses a unique system of interatomic bonds. For all 104309 topologically different atoms in these structures their environments (local atomic configurations, LACs) were explored within the first and second coordination shells. In total, 5251 topologically distinct types of coordination polyhedra and 21450 types of two-shell LACs were distinguished and deposited into our interactive database system TopCryst. We have found that the local density of the nearest environment of an atom naturally depends on its coordination number (CN) with a maximum at CN = 9. It was shown that LACs at CN ≥ 9 follow the close packing model of hard balls with Slater's atomic radii. At lower CNs, covalent interactions make a significant contribution that results in a decrease of the local density. Resting upon the dependence between the local density and CN we have proposed criteria for the estimation of the geometric instability (disbalance) of both a separate LAC and the whole intermetallic structure. We have revealed that strong geometric disbalance can be caused by errors in the structural data, incorrect description of the crystal structure, non-metallic nature of the chemical bonding or metastability of the crystalline phase. Thus the instability criteria can serve as important indicators of the structure inconsistency that is especially useful for checking crystallographic information on intermetallics or validating the structural models predicted by theoretical methods. • Intermetallic crystal structures are analyzed by geometrical-topological methods. • All coordination polyhedra and two-shell clusters are topologically classified. • Dependence of local density on coordination number is constructed. • Local and overall structure instability (disbalance) criteria are proposed. • An interactive database on topological types of metal clusters is developed. [ABSTRACT FROM AUTHOR] more...

We report the formation of large and highly twinned dendrites of the Al 13 Fe 4 approximant phase embedded in an fcc Al-rich matrix. Using a rapid cooling technique, the approximant appears as a 10-fold dendrite. Within each arm, all grains share a common [010] direction. The grain distributions within the arm are quite complex and a single dendrite arm can contain up to four different orientations. Using several techniques, including Electron Back-Scattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM), it has been possible to identify three types of twins, namely {100}, {001} and {20 1 ̄ } twins. From these observations and previous reports, we propose a growth mechanism to explain the formation of such specific 10-fold motifs. It corresponds to the heteroepitaxial growth of the Al 13 Fe 4 approximant from a well-facetted decagonal Al–Fe quasicrystalline seed. [Display omitted] • Growth of Al 13 Fe 4 approximant precipitates in an Al fcc matrix with 10-fold dendritic structure. • Repetitive occurrence of three types of twins to maintain rapid dendrite growth. • Evidence for grain orientation relationships among symmetrically opposite dendrite. • Heteroepitaxial growth of a decagonal approximant on a quasicrystalline template. [ABSTRACT FROM AUTHOR] more...

The growth kinetic behaviors of the Cu/Al system under current were investigated. The current was shown to significantly promote the growth of the intermetallic (IMC) layer. The growth rate constant of the Al 4 Cu 9 layer under current was approximately 3.26 times higher than that processed without current. Moreover, the current direction leads to a significant difference in the growth rate of the IMC layer, which was attributed to the electromigration effect. Based on the traditional thermal-activated theory and electromigration theory, an electromigration and thermal dual-activated growth kinetic model incorporating the contributions of Joule heat and the nonthermal effect was constructed. The growth kinetic behaviors of the Al 4 Cu 9 layer were investigated by applying this model. The calculated growth activation energies under different current densities were almost constant and close to 130 kJ/mol. The experimental data were applied to verify the model, and the results showed that the model was in good agreement with the experimental results. • 1. The current was shown to significantly promote the growth of the IMC layer. • 2. The current direction leads to a significant difference in the growth rate of the IMC layer. • 3.An IMC growth kinetic model incorporating the contributions of Joule heat and electromigration was constructed. [ABSTRACT FROM AUTHOR] more...

Abstract We have aimed to explore the influence of spin orbit coupling (SOC) on the electronic, elastic, mechanical, lattice dynamical and electron-phonon interaction properties of the simple orthorhombic IrGe using first principles density functional calculations within the generalized gradient approximation. The effect of SOC on the above properties of IrGe is mainly associated with Ir atom which possesses a 5d orbital and much heavier mass than that of Ge atom. The calculated values of nine independent elastic constants satisfy all the stability criteria, indicating that IrGe is mechanically stable in its MnP-type crystal structure. Also, no imaginary phonon frequencies are found in the phonon dispersion curves, indicating the dynamical stability of IrGe in its orthorhombic structure. Inclusion of SOC leads to the hardening of some low-frequency phonon modes which influences the electron-phonon interaction. Furthermore, inclusion of SOC leads to a decrease in dominant peaks of the Eliashberg function, and thus decrease in the values of the electron-phonon scattering parameter λ as well as the superconducting transition temperature T c . Using the calculated value of λ with SOC, the value of T c is obtained to be 5.09 K which compares very well with the recent measured value of 5.17 K. Highlights • Ab initio pseudopotential method is used to examine the effect of SOC on the physical properties of IrGe superconductor. • The inclusion of SOC causes to the splitting of some electronic bands. • Ir-related vibrations couple strongly with electrons. • The inclusion of SOC decreases the value of _ from 0.953 to 0.785. • The calculated TC of 5.087 with SOC consistent very well with its measured value of 5.17 K. [ABSTRACT FROM AUTHOR] more...

Abstract As a potential material used in aero-engine, a γ-TiAl/Ti 2 AlNb dual alloy was fabricated by depositing γ-TiAl alloy on a Ti 2 AlNb alloy plate using direct metal deposition (DMD) technique. Due to re-melting of previous layer during DMD, a transition zone with gradual change of compositions and microstructures was generated between γ-TiAl and Ti 2 AlNb alloy. In this paper, formation mechanism of the transition zone was analyzed after considering solidification route and compositional variations. Results reveal that the transition zone mainly consists of three layers, and compositions are comparatively uniform in layers but change stepwise between each other. Microstructures of layers are dominantly controlled by their compositions and cooling schedules, and the first layer possesses columnar grains with α 2 phase and γ phase dispreading in B2 matrix. While for the second layer, a mixed microstructure of (α 2 +γ) lamella, B2 phase and γ phase is formed. The third layer exhibits equiaxial (α 2 +γ) colony with fully lamellar microstructure, which is similar to microstructure of γ-TiAl alloy but without elemental segregations. Results of room temperature tensile test indicate that fracture takes place at γ-TiAl alloy side, and the fracture morphology is a mixture of interlamellar fracture and translamellar fracture. Highlights • A γ-TiAl/Ti 2 AlNb dual alloy was fabricated using direct metal deposition. • Transition zone contains three layers with different microstructures. • Composition in transition zone changes stepwise. • Fracture surface of the dual alloy is located at γ-TiAl alloy side. [ABSTRACT FROM AUTHOR] more...

Abstract The high Nb-containing γ-TiAl alloy Ti-45Al-5Nb-0.2B-0.2C (in at. %) was successfully brazed by transient liquid phase (TLP) bonding using two brazing solders with different melting point depressing elements (MPD): Ti-24Ni and Ti-29Fe (in at. %). The brazing process was executed for 24 h at 1110 °C. An additional annealing was performed for 168 h at 1000 °C for a better homogenization. The joints were characterized with high-energy X-ray diffraction (HEXRD) and scanning electron microscopy (SEM) using energy dispersive X-ray spectroscopy (EDX). Depending on the MPD and if the specimens were annealed two to three symmetrically arranged transition zones developed between the substrate and the middle of the joint with different microstructures, phase compositions, and chemical compositions. Beside α 2 and γ which have been present in the substrate additional phases as β, β o , ω o , τ 3 , and τ 2 were identified in the joints. We discuss the different solidification paths and the following solid-state transformations. The Fe-containing joint solidified via a single β o phase field leading to large β o grains. In contrast, the Ni-containing joint solidified via a two-phase field resulting in a finer grained microstructure. Graphical abstract Image 1 Highlights • A γ-TiAl alloy was successfully brazed by transient liquid phase bonding comparing two different brazing solders. • The joint region was investigated space-resolved with high-energy X-ray diffraction. • Solidification and solid-state transformation paths for both systems are presented space-resolved. [ABSTRACT FROM AUTHOR] more...

Abstract Porous Ni 3 Al intermetallic is successfully fabricated through elemental powder metallurgy of Ni-25 at% Al samples. The influences of sintering parameters, such as heating rate, isothermal treatment on the sintering behaviors of the samples are investigated. When the samples are heated continuously from room temperature to 1000 °C at a relatively high rate (>5 °C/min), the reaction between Ni and Al happens in an intense way. The heat suddenly released by the reaction produces liquid phase in the material, which facilitates the reaction significantly. Therefore, a sudden expansion (∼6%) occurs, resulting in severe deformation of the samples. The shape retention ability of the sample can be improved by isothermally treating the sample at a proper temperature (470–490 °C) for prolonged time or heating it up at a low heating rate. Under these sintering conditions, the reaction between Ni and Al happens in a much more controllable solid-state way. Therefore, the abrupt expansion can be decreased to ∼0.5%. During the solid-state reaction, imbalanced diffusion between Al and Ni results in more Al diffusing into Ni than the other way around, therefore creating pores on the Al side. As a result, homogeneous porous Ni 3 Al intermetallic samples can be fabricated and the regular shape of the sample can be well preserved. Highlights • The first systematic investigation of the kinetics of porous intermetallics fabricated by the Kirkendall effect. • Revealing the effects of heating rate and isothermal treatment on the sintering behavior of Ni-25 at% Al samples. • Revealing the relationship of shape retention ability of sintered Ni-25 at% Al samples and sintering parameters. [ABSTRACT FROM AUTHOR] more...

Abstract Room temperature mechanical behaviour of cast in-situ TiAl matrix composite reinforced with carbide particles was studied using hardness, tensile, compression, and three-point bending tests. The initial microstructure of the in-situ composite consists of TiAl matrix reinforced with coarse primary (H Ti 2 AlC and TiC) and fine secondary (H Ti 2 AlC and P Ti 3 AlC) particles. The in-situ composite shows plastic deformation of TiAl matrix and limited plastic deformation of primary Ti 2 AlC particles during the compression test. The compressive work hardening behaviour is affected by the plastic deformation of the matrix, plastic deformation of primary carbide particles and formation of cracks. The local equivalent strains in the compression specimens are numerically calculated using finite element analysis (FEA) and related to the size of primary carbide particles. The in-situ composite specimens show brittle fracture behaviour during tensile and three-point bending tests. The numerically calculated critical stress leading to a crack initiation in the notch tip region of three-point bending specimen is comparable with the ultimate tensile strength. The brittle fracture of the in-situ composite includes crack deviation, zone shielding by microcrack toughening, carbide fragmentation, delamination on the matrix-carbide interfaces and pull-out of the carbide particles from the matrix. Highlights • The hardness, fracture toughness, tensile and compressive properties are characterised. • The effect of matrix and carbide particles on compressive work hardening behaviour is described. • The compressive strains calculated by FEA are related to size of fragmented carbide particles. • The critical stress leading to a crack initiation in notched specimen is calculated by FEA. • The effect of coarse carbide particles on crack initiation and propagation is discussed. [ABSTRACT FROM AUTHOR] more...

Abstract In this work, the compressive deformation behavior and the microstructure evolution of bonding interface of TiAl/Ti 2 AlNb dual-alloy joint were investigated comprehensively. An Arrhenius-type serial constitutive model was developed to describe the hot deformation behavior of TiAl/Ti 2 AlNb joint. Based on the microstructure characterizations and composition analysis, it is found that small particles of Ti 3 Al 2 Nb intermetallics precipitated at the bonding interface adjacent to the Ti 2 AlNb base material after hot compression. During hot compressing at 900 °C, the dominant deformation mechanism is demonstrated to be a dislocation-mediated creep accompanied by the decomposition and the reprecipitation of O phase in Ti 2 AlNb. Moreover, O phase decomposition occurs in Ti 2 AlNb when deforming at 1000 °C. The (α 2 + Ti 3 Al 2 Nb) grains layer and the α 2 phase transformation were captured at bonding interface. At the temperature of 950 °C and 1000 °C, it is revealed that the strain rate sensitivity parameter (m) tends to be 0.2 with the increase of deformation even though deforming at the strain rates of 0.1s−1, 0.01s−1, and 0.001s−1, indicating a similar mechanism at large strain conditions under those various conditions. This work provides a strategy not only contributing to control the structure of bonding interface but also improving the processability of TiAl/Ti 2 AlNb joints. Highlights • The Arrhenius-type serial constitutive equation was developed to describe the deformation behavior of TiAl/Ti 2 AlNb joint. • The Ti 3 Al 2 Nb grains were found at the bonding interface adjacent to the Ti 2 AlNb after hot compression. • The diffusion interface has little effect on the hot deformation behavior of TiAl/Ti 2 AlNb joint. • The deformation mechanism of TiAl/Ti 2 AlNb joint was revealed. [ABSTRACT FROM AUTHOR] more...

Abstract The MoSiBTiC alloy is one promising candidate for ultrahigh–temperature materials. However, it faces severe challenges in the machining of complex shapes because of its significant brittleness, high melting point, and stiffness. To overcome this challenge, we have successfully fabricated MoSiBTiC alloy parts via laser powder bed fusion (L-PBF). A combination of arc-melting and controllable high-energy ball milling (HEBM) was employed to prepare suitable MoSiBTiC powders for L-PBF. The evolution of powder morphology, constituent phases, and laser absorptivity, as well as particle size and distribution during HEBM, was investigated. Moreover, the effects of L-PBF parameters on the densification, microstructure, and mechanical performance of MoSiBTiC alloy builds were studied. A dense MoSiBTiC alloy, mainly consisting of a Mo solid-solution, Mo 5 SiB 2 , Mo 2 C, and TiC phases, was obtained at an energy density of 156 J mm−3 using the laser power of 70 W. Compared to the as-cast alloy, the L-PBF-processed MoSiBTiC alloy possessed more uniform and finer grain structures, while exhibiting a lower Vickers hardness due to the existence of internal microcracks. It was also proved that the small quantity of ZrO 2 particles from HEBM processing was uniformly imbedded in L-PBF builds. This work may offer significant guidance for designing and producing complexly shaped refractory intermetallics with unique microstructures in ultrahigh–temperature applications. Graphical abstract Image 1 Highlights • Additive manufacturing of MoSiBTiC alloy for ultrahigh–temperature material was firstly attempted. • An effective approach was developed and optimized for large-scale production of starting MoSiBTiC powders. • High-density MoSiBTiC alloy (∼99.8%) was produced via optimizing laser processing conditions. • Additive-manufactured MoSiBTiC alloy had more uniform and finer grain structures than as-cast one. [ABSTRACT FROM AUTHOR] more...

Abstract Plenty of papers with regard to the processing of TiAl alloys via investment casting, forging, rolling, extrusion pressing as well as mechanical machining have been published, whereas the manufacturing of gamma-TiAl based alloys and corresponding semi-finished products has not been entirely described so far. The aim of this paper is to review and evaluate the present technologies of TiAl alloy production on an industrial scale. Metallurgical alloying techniques such as vacuum arc remelting (VAR), plasma arc melting (PAM) and electron beam melting (EBM) are being shortly described and evaluated with regard to their advantages and disadvantages from both technical and economical point of view. Particular focus is set on some specifics in metallurgical processing of TiAl alloys compared to Ti and Ti alloys. Outstanding requests on the accuracy of chemical composition, microstructural homogeneity, acceptable local deviations of alloying elements, small sizes of the products, and, additionally, the very limited wrought processing capability of TiAl alloys require a set of adjusted metallurgical technologies for the manufacturing of semi-finished products. With this regard, the production of small sized semi-finished parts via skull melting technologies and subsequent centrifugal casting in permanent moulds have been successfully developed and industrialized. Both, VAR skull melting (VAR SM) for ingot conversion and induction skull melting (ISM) for the conversion of valuable revert materials result in technically indistinguishable products due to the application of a consistent centrifugal casting technology. Both procedures offer the highest flexibility on product shapes and dimensions for minimizing the specific materials usage, which has a direct positive influence on final component costs. Resulting materials properties of the semi-finished products meet entirely the different (customer related) specification requirements. There are basically no technical limitations with regard to TiAl alloy compositions as it is the case for TiAl alloy manufacturing via other technologies. [ABSTRACT FROM AUTHOR] more...

Abstract The deformation microstructure of an interdendritic18 R long-period stacking ordered (LPSO) phase in an Mg-Zn-Y alloy subjected to shock loading was investigated by transmission electron microscopy. It was found that kink banding, the key deformation mode of LPSO phases under quasi-static loading, is suppressed by shock loading. Instead, second-order pyramidal slip by dislocations, which has not been observed in LPSO before, contributes to the plastic deformation of LPSO, in addition to the dislocations. The rate-dependent deformation modes of LPSO have an important implication in understanding the mechanical behaviour of LPSO strengthened Mg alloys under extreme loading conditions. Graphical abstract Image 1 Highlights • Shock deformation of interdendritic18 R LPSO phase in an Mg-Zn-Y alloy was investigated by TEM. • The deformation behaviour of LPSO under shock loading shows obvious difference from that under quasi-static conditions. • Shock loading suppresses kink banding in the LPSO phase while quasi-static compression favours kink band formation. • Shock loading activates an unusual second-order pyramidal slip by dislocations in the 18 R LPSO phase. [ABSTRACT FROM AUTHOR] more...

The effect of yttrium on the microstructure and high-temperature oxidation performance of Nb-15Si-24Ti-4Cr-2Al-2Hf (at.%) alloys was investigated. Alloys containing different yttrium contents were designed, aiming at maximizing the beneficial effect of yttrium addition and avoiding the possible adverse effect of over-doped yttrium. Results showed that Y was primarily partitioned in γ-Nb 5 Si 3 , relative to Nb solid solution (Nbss), Nb 3 Si and α-Nb 5 Si 3 . Microstructural refinement and oxidation resistance enhancement were achieved by yttrium addition up to 0.3 at.%, accompanied by the transition towards parabolic oxidation kinetics. An adverse effect of over-doped yttrium (0.5 at.% addition) by coarsening the microstructure and deteriorating the oxidation resistance was confirmed. A relatively continuous glassy SiO 2 layer was generated in the oxide scale formed on the Y-containing alloys with enhanced oxidation resistance. [ABSTRACT FROM AUTHOR] more...

60NiTi is a Ni-rich NiTi alloy containing ∼55 at.% (60 wt%) Ni and ∼45 at.% (40 wt%) Ti. This paper covers the use of Ni and Ti blends to fabricate porous 60NiTi parts by conventional press-and-sinter method. In this study, critical processing parameters such as heating rate and sintering holding time were altered to process porous parts with different open porosity levels. In the next step, as-sintered samples were heated at ∼1050 °C and then quenched (solutionized) to obtain hard and homogenized 60NiTi parts. Effects of these processing factors on the microstructure and mechanical properties of porous 60NiTi parts were investigated. It was found that processing the parts under a faster heating rate or a shorter sintering holding time resulted in as-sintered and solutionized samples with lower relative density and a higher amount of open porosity volume. However, a lower hardness and compressive strength was achieved as compared to the situations where a slower heating rate or a longer sintering holding time was applied. It was observed that the effect of heating rate is more pronounced compared to the sintering holding time. Final solutionizing treatment resulted in solution of soft Ni-rich phases such as Ni 3 Ti and Ni 3 Ti 2 in the parent NiTi phase. This consequently resulted in a drop of austenite-martensite phase transformation to well below room temperature. This final heat treatment was beneficial in terms of increasing the amount of open porosity. Solutionized parts exhibited higher hardness, approximately the same compressive strength but more embrittlement compared to as-sintered specimens. [ABSTRACT FROM AUTHOR] more...

A-T-Al family of alloys (where A = actinides, lanthanides or rare earth elements; T = transitional metals) has unique physical properties. AT 2 Al 20 phases are of particular importance since they have exhibited superconductivity properties. Understanding the reasons for the formation of the AT 2 Al 20 structures in various A-T-Al alloys is the objective of current study, since it will allow formulation of rule for prediction of stable structures in these alloys. Such rule will shorten the research time because usually the search for these phases (although is based on some criteria) performed by serendipity. Formerly we proposed that type of transition metal dictates the symmetry of the ternary phases' structure formed in the AT 2 Al 20 systems, while symmetry breakage point was found to be in T = Mn. Here, AMn 2 Al 20 alloys were studied with a purpose to understand the influence of A type atoms on the stable ternary aluminide formed. Despite adequate amount of Al provided in these alloys, cubic AMn 2 Al 20 phase did not formed in any of the studied compounds besides A = U. The results of Density Functional Theory calculations were in excellent agreement with the experimental ones. It was found that proposed earlier rule for the prediction of the stable structure in these systems using the minimal magnetic moment of the transition metal works as long as A type atoms do not have 5 f -electrons. Otherwise, the stable structure in these systems can be assessed by the minimal average energy of the transitional metal 3 d -electrons participating in bonding. [ABSTRACT FROM AUTHOR] more...

The addition of carbon in TiAl alloys can improve the mechanical properties by precipitate hardening through the perovskite Ti 3 AlC carbide. Usually precipitates coarsen during continuous annealing. However, in the Ti-45Al-5Nb-0.75C alloy a splitting of the perovskite carbides was observed in later stages of annealing. By investigation with transmission electron microscopy the details of this splitting process are revealed after annealing at 900 °C. The results show that the re-orientation of the γ phase regions between sub-particles is associated with the splitting step from carbide needles into small sub-particles. γ domains with a different orientation with respect to the γ matrix nucleate and gradually replace the γ matrix phase in regions between the carbide sub-particles. The progress of the splitting process is locally different in different carbides and also in one individual carbide. By increasing the temperature from 800 to 900 °C the growth of the emerging carbide conglomerates and the splitting process of the carbides are greatly accelerated. It is found that both are diffusion-controlled processes. [ABSTRACT FROM AUTHOR] more...

In order to give an insight into the formation mechanism of γ lamellae during α to γ phase transformation, surface reliefs produced by precipitation of γ lamellae on pre-polished specimen surface in Ti48Al2Cr2Nb alloy were systematically investigated. The results show that the surface reliefs are of single-tilt type and terraces and step risers can be observed on the surface relief. The height of the surface relief is closely related to the width of the γ lamella and each surface relief of regular γ lamellae consists of γ lamella and accommodated matrix. Terraces of the surface relief actually have needle-tooth shaped interfaces in atomic scale and step risers consist of nano-sized steps. These indicate that the initial stage of the precipitation of γ lamellae involves in a shear process and the increase in width of γ lamellae is achieved in a diffusional process by the motion of growth steps. The shear and diffusional processes finally induce an accommodation of the matrix near the specimen surface, resulting in the formation of abnormal structure layer and surface relief. [ABSTRACT FROM AUTHOR] more...

Based on its excellent high-temperature performances, polycrystalline Ni 3 Al-based alloys have attracted more and more attention. In this work, different thermal cycle aging treatments (TCAT) were applied to investigate microstructure evolution behavior of Ni 3 Al (γ′) phase in eutectic γ-γ′ area of JG4246A alloy. SEM equipped with energy dispersive X-ray spectrometer (EDS) and high-resolution transmission electron microscopy (HRTEM) were used for microstructure observation and mechanism analysis. The results showed that plate-like Ni 3 Al (γ′) phase and twinning Ni 3 Al (γ′) formed in eutectic γ-γ′ area due to its initial state of the alloy and thermal cyclic aging treatment conditions. Meanwhile, blocky Ni 3 Al (γ′) phase precipitated along eutectic γ-γ′ area and dual phase (γ+γ′) area ((γ-γ′)/(γ+γ′)) interfaces. Vacancies and dislocations generated during short-term TCAT were responsible for the formation of plate-like Ni 3 Al (γ′) phases in eutectic γ-γ′ area of as-cast alloy. While, for the solution-treated alloy, dislocations and internal stress generated during long-term TCAT led to the formation of twinning Ni 3 Al (γ′) in eutectic γ-γ′ area and blocky Ni 3 Al (γ′) phase along (γ-γ′)/(γ+γ′) interface. [ABSTRACT FROM AUTHOR] more...

A new intermetallic compound, ternary antimonide Eu 7 Cu 44 Sb 23-δ [ Fm -3m, a  = 17.4346(1)Å, δ = 0.5(1)] is reported. The compound forms a continuous substitutional solid solution with its Eu 7 Cu 44 As 23 archetype. The gradual substitution of Sb for As evokes partial disorder in the copper–pnictogen framework that becomes more pronounced with an increase of the Sb content and changes magnetic properties. Whereas Eu 7 Cu 44 As 23 is metallic ferromagnet below 17 K, Eu 7 Cu 44 Sb 23-δ shows paramagnetic behavior down to 1.8 K according to the magnetic measurements, while retaining metallic properties according to the DFT calculations. The origin of the disorder, the structure-property relationships, as well as prospects of further substitution in the anionic sublattice are discussed. [ABSTRACT FROM AUTHOR] more...

Hexagonal γNb 5 Si 3 plates have precipitated from Nb solid solution in heat-treated Nb-Si based ultrahigh temperature alloys. The orientation relationships (ORs) and interfacial structures between γNb 5 Si 3 precipitates and Nb solid solution matrix have been investigated by high-resolution transmission electron microscopy (HRTEM). The ORs have been determined as [ 111 ] N b / / [ 0001 ] γ and ( 10 1 ¯ ) N b / / ( 1 1 ¯ 00 ) γ with a near coherent interface. The interfacial structure has been interpreted with the Coincidence site lattice/Displacement shift complete lattice (CSL/DSC) model, forming an array of phase boundary dislocations (PBDs) on the interface. PBDs with Burgers vectors of b → = 1 3 < 1 ¯ 2 1 ¯ > N b on (111) Nb plane might promote the precipitation of γNb 5 Si 3 . [ABSTRACT FROM AUTHOR] more...

We report results of ab-initio studies for the structural, electronic, lattice dynamical and electron-phonon interaction properties of cubic and tetragonal phases of V 3 Si by using the plane-wave pseudopotential method, the density-functional theory, and a linear-response technique. Our total energy results propose that the martensitic transition from cubic to a tetragonal variant of the A15 structure takes place with a very little change in the unit cell volume and total energy. Thus, the electronic and lattice dynamical properties of both phases look like similar to each other. Our electron-phonon interaction calculations reveal that the phonon properties of V lattice considerably enter into electron-phonon interaction calculations due to noteworthy presence of transition metal d electrons at the Fermi level. Using the calculated value of 1.15 for the average electron-phonon coupling parameter of both phases, the superconducting critical temperature and the electronic specific heat coefficient are evaluated to be 17.3 K and 54.5 m J / ( mol K 2 ) , respectively, in gratifying agreement with their measured values of 17 K and 53 m J / ( mol K 2 ) . [ABSTRACT FROM AUTHOR] more...

The site occupy behaviors of NbCr 2 -based C15 Laves phase alloyed with M (M = Ti, V, Mo and W) and Hf 0.25 V 0.6 Nb 0.15 C15 Laves phases at finite temperature were predicted using sublattice model, where the Gibbs free energies at finite temperature were obtained by quasi-harmonic approximation(QHA) model. The predicted results were compared with the available experimental results and other calculated results. The prediction was improved compared with early thermodynamic model, where the enthalpies of formation of the end-members at 0 K were accounted only. For NbCr 2 -based C15 Laves phases, Nb atom prefers to occupy 8a subattices, Cr atom prefers to occupy 16d subattices, and the third alloying element Ti prefers to occupy 8a subattices, which is not affected by the chemical composition and temperature, on the contrary, the site preferences of the third alloying elements Mo, V and W depend sensitively on the chemical composition and temperature. For the selected ternary Hf 0.25 V 0.6 Nb 0.15 C15 phase with available experimental data, the site fraction of Nb element occupying the 8a sublattices decreases slowly with the increase of temperature, the calculated site occupying configuration at 1473 K is (Hf 0.750 Nb 0.240 V 0.001 ) 8a (Nb 0.105 V 0.895 ) 16d , which is close to the available experimental result. [ABSTRACT FROM AUTHOR] more...

Sixteen new intermetallic aluminum compounds with RE 4 T Al ( RE  = Y, Sm, Gd–Tm, Lu; T  = Pd, Pt) composition have been prepared by arc-melting of the elements followed by subsequent annealing. The samples were characterized by powder X-ray diffraction. All compounds crystallize isostructural in the cubic Gd 4 RhIn type structure ( F 4 ¯ 3 m ) with lattice parameters ranging from a  = 1369-1323 pm for Pd and a  = 1377-1323 pm for Pt. In the crystal structure, the transition metal atoms have a trigonal prismatic rare earth coordination. Condensation of these T@RE 6 prisms leads to a three-dimensional network in which large voids are present that are filled by tetrahedral Al 4 entities. The aluminum atoms themselves have twelve nearest neighbors (3 × Al and 9 ×  RE ) in a slightly distorted icosahedral coordination. For the compounds of the Pt series the magnetic properties have been investigated by means of magnetic susceptibility measurements. Gd 4 PtAl and Tb 4 PtAl order antiferromagnetically at Néel temperatures of T N  = 63.8(1) and 45.9(1) K, while Dy 4 PtAl and Ho 4 PtAl order ferromagnetically with Curie temperatures T C  = 32.6(1) and 23.8(1) K. For the Pd series finally, the RE Al impurities dominate, hence magnetic measurements were not conducted. [ABSTRACT FROM AUTHOR] more...

We designed two types of Al-based alloy composites reinforced by η-Zn 2 Mg (hexagonal) and T-Al 6 Mg 11 Zn 11 (cubic) intermetallic phases using monovariant eutectic reactions in the Al–Mg–Zn ternary system and then attempted to fabricate them using solidification. Thermodynamic assessment revealed two alloy compositions of Al–18Mg–36Zn and Al–22.5Mg–23.5Zn (at%) with the α-Al (fcc) phase reinforced with high fractions (>50%) of the η and T phases. Both alloys exhibited fine two-phase eutectic microstructures consisting of α/η and α/T phases, respectively. The morphology of the α-Al phase in the eutectic colonies varied from lamellae to fibers upon changing the neighboring intermetallic phase. These eutectic microstructures exhibit high stability at an elevated temperature of 300 °C. In addition, the size and spacing of the α-Al phase could be controlled by changing the cooling rate during solidification. The fabricated composites exhibited high hardness values exceeding 220 HV, which were much superior to those of conventional Al alloys. The calculated solidification path and component partitioning in the liquid phase during solidification provided insights into the solidification segregation of Zn element in the Al–18Mg–36Zn alloy. The Zn-enriched regions would enhance the local microstructural change at elevated temperatures, which confirmed by the microstructural observations of the alloy exposed at 300 °C. [ABSTRACT FROM AUTHOR] more...

High porosity of porous TiAl 3 intermetallics were prepared from Ti-75Al at.% elemental powders by NaCl as temporary space holder, combining with multilayer stacking technology and thermal explosion reaction. Results showed that space holder particles in green compact were completely removed before sintering and only single TiAl 3 phases were synthesized in sintered product. The porosity (>70%) can be easily obtained when adding 0, 30 or 50 vol.% NaCl in designed layers. SEM image indicated that the distribution of small pores (<80 μm) was uniform and embedded in pore walls of the skeleton without NaCl space holder. Large pores (300–500 μm) began to appear when added the NaCl particles and the number of large pores improved with the increase of space holder content. The sintered discs with three or five sintered layers exhibited a symmetrical graded pore size distribution: large pores replicating from space holder and small pores generated during the sintering process. The graded pore-structure can be designed by adjusting the compact structure in each layer, allowing for a widespread applications in specific filtration units and liquid-gas separation. [ABSTRACT FROM AUTHOR] more...

In this work, double wire arc addictive manufacturing (WAAM) of Fe 3 Al parts was implemented and high-temperature properties of produced structures were studied. In-situ fabrication of several wall-shaped intermetallic structures was performed using a dual wire feeding system, designed for unsymmetrical transfer of Fe- and Al-based wires. Mechanical properties, such as strength and ductility, as well as phase composition and microstructure of produced material were studied. Enhanced ductility at room temperatures and superplastic behavior at high temperatures were revealed by tensile tests. Furthermore, anomaly in temperature dependance of ultimate tensile strength has been revealed and discussed. Wear properties analysis demonstrated higher friction coefficient with lower wear rate for Fe 3 Al than for stainless steel. • Double WAAM with unsymmetrical transfer of the wires was used for Fe3Al intermetallic alloy synthesis. • Tensile and wear tests presented sufficient results, making Fe3Al double WAAM feasibility promising. • Superplastic behavior of Fe 3 Al-alloy at high temperatures is governed by dynamic strain aging. • Anomaly in tensile strength was observed: ultimate tensile strength increases with a temperature rise from 20 °C to 550 °C. [ABSTRACT FROM AUTHOR] more...

Intermetallic compounds of beryllium with refractory materials (niobium, tantalum, zirconium, etc.) possess exceptional characteristics, such as high-temperature strength, excellent corrosion resistance, and high hardness. However, despite the impressive physical and mechanical properties of beryllides, the current manufacturing methods for producing components from these materials have not yet reached industrial maturity. The main producers of beryllides in the global market are Brush Wellman Inc. (USA) and Ulba Metallurgical Plant (UMP) JSC (Kazakhstan). In this study, niobium beryllides manufactured by UMP JSC were chosen as the object of research. Specifically, this work focuses on studying the synthesis process of the binary intermetallic compound of niobium beryllide NbBe 3. The current study presents the results of determining the type and quantity of intermetallic pairs of niobium beryllides during the synthesis of the binary intermetallic compound NbBe 3 from a compacted mixture of beryllium and niobium powders in the temperature range of 800 °C–1300 °C. • Synthesis process of the monophasic compound NbBe3 was investigated. • The results of qualitative X-ray phase analysis and quantitative evaluations of the phases formed in each temperature-time range are presented. • The transformation of Nb and Be powders into NbBe3 compound occurs in temperature between 900°C and 1300°C through a series of intermediate intermetallic compounds. [ABSTRACT FROM AUTHOR] more...

To ensure optimal working conditions for the next-generation power modules, a comprehensive understanding of the thermo-mechanical properties of the joint layer between the chip and substrate is essential. The Ag 9 In 4 intermetallic compound is a promising candidate for the joint layer; however, related material data are not available. This study proposes a straightforward method to fabricate densified and pure Ag 9 In 4 bulk samples. Bulk Ag 9 In 4 with less than 0.1% porosity was fabricated by pouring molten alloy into the water-cooled mold, followed by a two-step heat treatment at 520 °C and 250 °C for 40 h each. Properties, including Young's modulus, hardness, creep behavior, and coefficient of thermal expansion, were measured from 30 °C to 250 °C. As the temperature increased, the Young's modulus of Ag 9 In 4 decreased linearly from approximately 117.9 GPa–95.9 GPa. Correspondingly, the coefficient of thermal expansion increased linearly from 19.2 μm/m/°C to 22.69 μm/m/°C, with an average value of 20.58 μm/m/°C. Moreover, the hardness decreased from 4.1 GPa to 1.7 GPa following an exponential relationship with temperature. At 250 °C, a significant creep phenomenon was detected in Ag 9 In 4. The creep mechanism changed from dislocation climb to dislocation diffusion, with creep stress exponents of 33.1 and 10.6 at 30 °C and 250 °C, respectively. • A simple fabrication method for densified and pure Ag 9 In 4 bulk was proposed. • Thermo-mechanical properties of the Ag 9 In 4 intermetallic compound were studied. • Young's modulus and CTE of Ag 9 In 4 decreased linearly as temperature increased. • Hardness exponentially decreased from 4.1 GPa to 1.7 GPa with temperature. • Creep mechanism shifted from dislocation climb to dislocation diffusion from 30 °C to 250 °C. [ABSTRACT FROM AUTHOR] more...

In this work, the structure and hydrogen storage properties of the TiVFeZr multicomponent alloy with C14-type Laves phase structure was comprehensively investigated. This alloy presents fast hydrogen storage kinetics at room temperature with high hydrogen storage capacity, absorbing H/M = 1.5 (2.41 wt%) in less than 100 s under initial hydrogen pressure of 20 bar. This is one of the highest hydrogen storage capacities among the Laves phase alloys reported to date. The formed hydride is highly stable, which needs temperatures above to 550 °C to completely desorb hydrogen. The high hydrogen storage capacity of this alloy as well as the high stability of the formed hydride are discussed in terms of the high fraction of hydride forming elements in the C14-type Laves phase structure. • TiVFeZr alloy solidifies with single C14-type Laves phase structure. • TiVFeZr alloy has a fast hydrogen storage kinetics at room temperature. • TiVFeZr alloys presents high hydrogen storage capacity (H/M = 1.5 and 2.41 wt%). • TiVFeZr alloy for a highly stable hydride, needing temperatures above to 550 °C to fully desorb hydrogen. [ABSTRACT FROM AUTHOR] more...

Developing a new ordered single-phase TiAl alloy, with no solid-state transformation operated at a long-term high temperature, is important in the aerospace industry. Here, the preparation of newly Ti-55Al-7.5Nb alloy via direct laser deposition (DLD) is proposed and studied. The oriented grain growth in Ti-55Al-7.5Nb alloy is successfully achieved by using laser additive manufacturing (AM) without interlayer pause during the laser scaning back and forth. AM features a rapid cooling rate while Ti-55Al-7.5Nb alloy owns a narrow L → α and α → γ phase transformation temperature window, and then enabling the TiAl liquid phase directly transform into a γ single-phase, which is confirmed by the combination of experiments and thermodynamic calculations. The heat treatment in the AM thermal cycles induces a thermal gradient, promoting the new recrystallized grains growing base on the preferred growth of [111]γ along the heat flow during the DLD solidification stage. The AM Ti-55Al-7.5Nb alloy exhibits continuous γ single-phase columnar grains, meanwhile, accompanied by the twins growing along the building direction. [Display omitted] • A novel single-phase γ-TiAl alloy with columnar structure was successfully fabricated by additive manufacturing. • Ti-55Al-7.5Nb alloy owns narrow L.→ α and α → γ phase transformation temperature window. • AM featureing a rapid cooling rate enables the TiAl liquid phase directly transform into γ single-phase. • The AM thermal cycles promote the grains growing base on the preferred growth of [111]γ along the heat flow. [ABSTRACT FROM AUTHOR] more...

The precipitation and growth morphology of topologically close-packed (TCP) phases in a Re-containing Ni-based single crystal superalloy during thermal exposure were studied. The alloy was found to develop acicular-shaped coherent μ phase particles along <110> γ directions of the matrix after exposure at 950 °C. P phase precipitates were found to form with increased time and at higher temperatures, and in different morphologies, including acicular shaped particles along <112> γ and <110> γ directions, and plate-like particles in {110} γ planes of the matrix. The different P phase precipitates were found to have different lattice constants and different lattice correspondences with the matrix. The μ phase precipitate was also found to have different lattice correspondences with those reported in the literature. The multiplicity of lattice correspondences for the same TCP phase is attributed to the different lattice parameters, which render the precipitates to have different coherency relationships with the matrix. [ABSTRACT FROM AUTHOR] more...

An Nb-Silicide in situ composite with a nominal composition of Nb-16Si-10Ti-10Mo-5Hf (at. %) was fabricated by mechanical alloying followed by hot-pressing sintering. The microstructure consisted of an Nb solid solution, Nb 5 Si 3 and a small amount of Nb 3 Si. This in-situ composite exhibited good balance of strength between ambient temperature and high temperatures; the ultimate tensile strength was 413 and 496 MPa at room temperature and 1200 °C, respectively. The tensile fracture behavior was dominated by cleavage of the Nbss and Nb 5 Si 3 at 1200 °C and lower temperatures. However, the fracture behavior was governed by ductile rupture of Nbss at 1300 °C and higher temperature, which was ascribed to both the increased ductility of Nbss and the decreased interface strength. At 1400 °C and higher temperature, the material exhibited extensive plasticity or superplasticity; the dominant deformation mechanism was grain boundary sliding at 1400 °C and higher temperature. [ABSTRACT FROM AUTHOR] more...

The goal of this work was to understand the effects of aging at 800 °C on the microstructures and mechanical properties of two recently-developed AFA stainless steels based on Fe-14Cr-32Ni-3Nb-3Al-2Ti (wt.%), one of which contained small additions of boron and carbon. To that end both the size distributions and growth kinetics of the B2, Laves phase, L1 2 precipitates present were quantified. While the lattice parameter, morphology, size and coarsening behavior of the L1 2 precipitates was the same in both AFA alloys, the B and C enhanced the grain boundary coverage by both Laves phase and B2-NiAl precipitates, but suppressed their coarsening. These interstitial additions also suppressed the formation of twins and discontinuous precipitation, which were observed in the B and C-free material. It is shown that the yield strength at 700 °C is largely controlled by the size of the L1 2 precipitates, with the largest strengthening effect obtained after aging for 2.4 h for both AFA alloys. Longer aging time led to a loss of strength mainly due to the coarsening of the L1 2 precipitates. [ABSTRACT FROM AUTHOR] more...