Phase constitution of some intermetallics in continuous quaternary pillar phase diagrams

In order to express multicomponent phase relationships, a new type of phase diagram, named a “pillar phase diagram,” is proposed. The pillar phase diagram is a sort of quaternary and Brewertype phase diagram. A pillar phase diagram at a temperature is easily constructed by (1) composing three sides of Brewer-type ternary-phase diagrams along the periodic table and (2) piling triangles of general ternary phase diagrams along the periodic table. Using the pillar phase diagrams, systematic understandings of phase constitution and stability along the periodic table can be performed for (1) binary intermetallics containing ternary and quaternary additional elements and (2) ternary intermetallics containing quaternary elements. Thus, the diagrams are convenient in terms of alloy design of multiphase intermetallic alloys. In this paper, the concept and the construction method of the pillar phase diagrams are described, and some examples are shown for systems related with L1₂ Ni₃Al, B2 NiAl, L2₁ Ni₂AlTi, B2 NiTi, B2 FeTi, L1₀ TiAl, and L1₂ Al₃Ti alloys.     

Reassessment of Ni-Al and Ni-Fe-Al solidus temperatures

Solidus temperatures of the B2 NiAl phase have been determined by high-temperature differential thermal analysis for binary melt compositions Ni_xAl_100−x (45<x<57) and for ternary alloys Fe_yNi_50−yAl₅₀ (0≤y≤50). It was shown that the melting temperature of the stoichiometric Ni₅₀Al₅₀ phase is 1681 °C, which is 43 K higher than some literature data. The solidus line at the Ni-rich side of the Ni-Al phase diagram exhibits a steeper slope than that reported previously. Substituting Fe for Ni, the decrease of solidus temperature along the isoplethal section with 50 at.% Al of the ternary Ni-Fe-Al phase diagram exhibits a steep initial slope of −13 K/at.% Fe for small Fe-fractions, which changes into a nearly linear decrease with an average slope of −8.5 K/at.% Fe.     

Investigation of Ni-B Alloys for Joining of TiB<Subscript>2</Subscript> Ultra-High-Temperature Ceramic

Melting and wetting behavior of Ni₈₃B₁₇ and Ni₅₀B₅₀ alloys on TiB₂ ceramic are investigated upon heating to 1105 and 1050 °C, respectively, using the sessile drop technique. Both alloys show a very good wetting on the TiB₂ substrates immediately after incipient melting. Liquid Ni₅₀B₅₀ alloy is revealed not to dissolve TiB₂, but penetrates along the grain boundaries into the ceramic. Upon heating and melting of the Ni₈₃B₁₇ alloy on TiB₂, a small amount of ceramic is dissolved and the ternary Ni₂₁Ti₂B₆ phase is formed. Whereas multiple microcracks are observed at the Ni₈₃B₁₇/TiB₂ interface, the Ni₅₀B₅₀/TiB₂ couple is well bonded and free of interfacial microcracks.     

Stability and elastic properties of L12-(Al,Cu)3(Ti,Zr) phases: Ab initio calculations and experiments

The total energies and equilibrium cohesive properties of L1₂, DO₂₂ and DO₂₃ structures along Al₃Ti–Al₃Zr and Al₃X–Cu₃X (X = Ti, Zr) sections are calculated from first principles employing electronic density-functional theory (DFT), ultrasoft pseudopotentials and the generalized gradient approximation. Calculated heats of formation are consistent with a narrow field of stability of the L1₂ structure at 12.5 at.% Cu for ternary (Al,Cu)_0.75Zr_0.25 and (Al,Cu)_0.75Ti_0.25 intermetallics at low temperatures. Experimentally, samples homogenized at 1000 °C establish a more extensive stability field for the L1₂ phase in quaternary alloys with Cu concentrations ranging from 6.7 to 12.6 at.% Cu. Two L1₂ phases were observed in as-cast alloys with near equal amounts of Ti and Zr, as well as alloys homogenized at 1000 °C. Good agreement is obtained between calculated and measured values of lattice parameters and elastic moduli. These results demonstrate high accuracy of ab initio calculations for phase stability, lattice parameters and elastic constants in multicomponent trialumide intermetallics.     

Zr–Ti-based Be-bearing glasses optimized for high thermal stability and thermoplastic formability

A new class of Zr–Ti-based Be-bearing (Vitreloy) glass-forming compositions that exhibit high thermal stability and good glass-forming ability is reported. Optimized ternary compositions were obtained by re-examining the Zr–Ti–Be phase diagram for regions that produce glasses having high thermal stability and modest glass-forming ability. By incorporating a fourth element in the optimized ternary compositions, quaternary alloys were obtained having thermal stabilities twice that of Zr_41.2Ti_13.8Ni₁₀Cu_12.5Be_22.5 (Vitreloy-1) while exhibiting good glass-forming abilities. Optimized quaternary alloys exhibiting critical casting thicknesses exceeding 15 mm and thermal stabilities as high as 165 °C are reported herein. The good thermal stability of these alloys renders them attractive for forming processes that can be performed thermoplastically in the supercooled liquid region, in a manner similar to the forming of polymers.     

Reassessment of Ni-Al and Ni-Fe-Al solidus temperatures

Solidus temperatures of the B2 NiAl phase have been determined by high-temperature differential thermal analysis for binary melt compositions Ni_xAl_100?x (45<x<57) and for ternary alloys Fe_yNi_50?yAl₅₀ (0≤y≤50). It was shown that the melting temperature of the stoichiometric Ni₅₀Al₅₀ phase is 1681 °C, which is 43 K higher than some literature data. The solidus line at the Ni-rich side of the Ni-Al phase diagram exhibits a steeper slope than that reported previously. Substituting Fe for Ni, the decrease of solidus temperature along the isoplethal section with 50 at.% Al of the ternary Ni-Fe-Al phase diagram exhibits a steep initial slope of ?13 K/at.% Fe for small Fe-fractions, which changes into a nearly linear decrease with an average slope of ?8.5 K/at.% Fe.     

On the Quaternary System Ti-Fe-Ni-Al

The homogeneity ranges of the Laves phases and phase relations concerning the Laves phases in the quaternary system Ti-Fe-Ni-Al at 900 °C were defined by x-ray powder diffraction (XPD) data and electron probe microanalysis (EPMA). Although at higher temperatures the Laves phase forms a continuous solid solution, two separate homogeneity fields of TiFe₂-based (denoted by λ_Fe) and Ti(TiNiAl)₂-based (denoted by λ_Ni) Laves phases appear at 900 °C. The relative locations of Laves phases, G phase, Heusler phase, and CsCl-type phase as well as the associated tie-tetrahedra were experimentally established in the quaternary for 900 °C and presented in three-dimensional (3D) view. Furthermore, a partial isothermal section TiFe₂-TiAl₂-TiNi₂ was constructed, and a connectivity scheme, derived for equilibria involving Laves phases in the Ti-Fe-Ni-Al quaternary system at 900 °C was derived. As a characteristic feature of the quaternary phase diagram, the solid solubility of fourth elements in both the TiFe₂-based and Ti(NiAl)₂-based Laves phases is limited at 900 °C and is dependent on the ternary Laves phase composition. A maximum solubility of about 8 at.% Ni is reached for composition Ti_33.3Fe_33.3Al_33.4. Structural details have been evaluated from powder x-ray and neutron diffraction data for (i) the Ti-Fe-Ni ternary and the Ti-Fe-Ni-Al quaternary Laves phases (MgZn₂-type, space group: P6₃/mmc) and (ii) the quaternary G phase. Atom site occupation behavior for all phases from the quaternary system corresponds to that of the ternary systems. For the quaternary Laves phase, Ti occupies the 4f site and additional Ti (for compositions higher than 33.3 at.%Ti) preferably enters the 6h site. Aluminum and (Fe,Ni) share the 6h and the 2a sites. The compositional dependence of unit cell dimensions, atomic coordinates, and interatomic distances for the Laves phases from the quaternary system is discussed. For the quaternary cubic G phase, a centrosymmetric as well as a noncentrosymmetric variety was observed depending on the composition: from combined x-ray and neutron powder diffraction measurements Ti_33.33Fe_13.33Ni_10.67Al_42.67 was found to adopt the lower symmetry with space group .     

The metastable liquid miscibility gap in Cu-Co-Fe alloys

The metastable liquid-phase separation (MLPS) in the Cu-Co-Fe system was investigated using an electromagnetic levitation melting and solidification technique. It was found that when ternary alloys containing more than 10wt.% (12 at.%)Co and 10wt.% (11at.%)Fe were undercooled below a certain temperature, T _sep, the homogeneous melt separated into two liquid phases. In alloys containing more than 54 to 57wt.% (49 to 54at.%)Cu (depending on the Co and Fe content), the phase separation generally appeared as dispersed (Fe, Co)-rich droplets (L₁) in a Cu-rich matrix, whereas for alloys containing less copper, the separation resulted in Cu-rich droplets (L₂) in a (Fe, Co)-rich matrix. The metastable liquid miscibility gap boundary of the Cu-Co-Fe ternary was determined using the measured T _sep and the composition of the separated phases. The ternary liquid-phase separated boundaries were found to be consistent with a cross-sectioned phase diagram in which one axis represents pure copper and the other Fe + Co.     

Evaluation of glass forming ability in ternary Ni62(Nb,Ta)38 alloys

The parameter γ¹ we previously defined has been proved to be valid in predicting the better glass former in several binary alloy systems, but is hard to be applied in the multi-component alloys because the phase diagrams of these alloys are usually not well constructed. In the present work, we attempt to extend the application of parameter γ¹ to a ternary alloy system and predict the better glass former in the Ni₆₂Nb_38-xTa_x (x = 5, 10, 15, 20, 25, 30, 35) alloys based on the systematic investigation on the phase evolution from Ni₆₂Nb₃₈ to Ni₆₂Ta₃₈. The prediction has been confirmed by the experimental results, indicating the validity of the parameter γ¹ in the Ni₆₂(Nb, Ta)₃₈ ternary alloys.     

Ridge direction of thermal conductivity contours in ternary Ni3Ga phase

Thermal conductivity of Ni₃Ga-X ternary alloys was comprehensively surveyed for 16 kinds of ternary elements X. The direction of ridge in thermal conductivity contours in γ′ single phase field agrees with that of solubility lobe of γ′ phase in a ternary phase diagram. The ridge direction is determined by the sublattice occupation of a ternary element.     

The metastable liquid miscibility gap in Cu-Co-Fe alloys

The metastable liquid-phase separation (MLPS) in the Cu-Co-Fe system was investigated using an electromagnetic levitation melting and solidification technique. It was found that when ternary alloys containing more than 10wt.% (12 at.%)Co and 10wt.% (11at.%)Fe were undercooled below a certain temperature, T _sep, the homogeneous melt separated into two liquid phases. In alloys containing more than 54 to 57wt.% (49 to 54at.%)Cu (depending on the Co and Fe content), the phase separation generally appeared as dispersed (Fe, Co)-rich droplets (L₁) in a Cu-rich matrix, whereas for alloys containing less copper, the separation resulted in Cu-rich droplets (L₂) in a (Fe, Co)-rich matrix. The metastable liquid miscibility gap boundary of the Cu-Co-Fe ternary was determined using the measured T _sep and the composition of the separated phases. The ternary liquid-phase separated boundaries were found to be consistent with a cross-sectioned phase diagram in which one axis represents pure copper and the other Fe + Co.     

On the existence and the crystal structure of Ni4W,NiW and NiW2 compounds

The existence of the previously reported intermetallic phases NiW and NiW₂ is refuted on the basis of new experiments involving arc-melted samples. A careful study of the literature shows that these two phases were previously evidenced only in sintered alloys and in diffusion couples, both techniques being very prone to surface contamination. It is shown that the phase previously reported as NiW is in fact the low carbon containing ternary carbide Ni₆W₆C. The second phase NiW₂ is most probably the higher ternary carbide Ni₂W₄C. This study raises also the question of the existence of the equiatomic phase appearing in the Fe–W phase diagram. A crystal structure Rietveld refinement of the intermediate phase Ni₄W is also given in the present work, evidencing large substitutional disorder.     

Effect of the deviation of the chemical composition from the stoichiometric composition on the structural and phase transformations and properties of rapidly quenched Ti50 + xNi25 ? xCu25 alloys

Methods of X-ray diffraction, transmission and scanning electron microscopy, and electron diffraction have been used to study phase composition and structure of an almost stoichiometric alloy Ti₅₀Ni₂₅Cu₂₅. The alloys of the quasi-binary section TiNi-TiCu to be studied, which exhibit in the initial ascast state thermoelastic martensitic transformations B2 ↔ B19 and related shape-memory effects, have been produced by rapid quenching of the melt (melt spinning technique). The chemical composition of the Ti_{50 + x} Ni_{25 − x} Cu₂₅ alloys was varied with respect to titanium and nickel within x ≤ ±1% (from Ti₄₉Ni₂₆Cu₂₅ to Ti₅₁Ni₂₄Cu₂₅). It has been shown that the rapid quenching from the melt at a cooling rate of 106 K/s provides amorphization for all the alloys under consideration. Heating to 723 K or higher temperatures leads to the devitrification of the amorphous alloys with the formation of a polycrystalline structure of the B2 austenite. The mechanical properties of the alloys have been measured in the initial amorphous state and after subsequent heat treatment. It has been established that, depending on the degree of deviation of the alloy from the stoichiometric composition, which leads to solid solution decomposition in the process of nanocrystallization upon heat treatment, there occur regular changes in the mechanical properties and shape-memory effects of the alloys. The characteristic temperatures of the onset and finish of the process of crystallization from the amorphous and amorphous-crystalline states and the critical temperatures of the onset and finish of the forward and reverse thermoelastic martensitic transitions have been determined by measuring temperature dependences of the electrical resistivity of the alloys. The diagram of the dependence of the critical temperatures on the chemical composition of the alloy has been constructed.     

Solid State Interaction in Ni-Mo-B System During Mechanical Alloying and Annealing

This work presents the results of a study of Ni_87?x Mo _x B₁₃ alloys (x?=?7, 10 and 14?at.%), which were obtained by mechanical alloying (MA) of elemental powder mixtures in a MAPF-2M high-energy planetary ball mill. The x-ray diffraction analysis and differential scanning calorimetry measurements were used. The single-phase fcc solid solutions of Mo and B in Ni were formed by MA of Ni-Mo-B mixtures of various compositions for 6-8?h. The coherent domain sizes of solid solutions calculated from the x-ray peak widths were 12-14?nm. The exothermic effects on the DSC curves, which corresponded to the phase transformations of supersaturated Ni(Mo,B) solid solutions, were observed during heating of the synthesized alloys. After heating to 700?°C, the alloys contained a fcc Ni(Mo) phase and a metastable hexagonal MoB₄ phase. Thermodynamically stable phase composition of Ni₈₀Mo₇B₁₃ and Ni₇₇Mo₁₀B₁₃ alloys, containing three phases: fcc Ni (Mo), Ni₂₁Mo₂B₆ with cubic lattice and Ni₃B with orthorhombic lattice, was reached after the isothermal annealing at 1000?°C. The ratio between the amounts of these phases in the alloys corresponds to their location in a three-phase area of the Ni-Mo-B equilibrium phase diagram.     

The quaternary system B2O3-PbO-SiO2-ZnO: Thermodynamics and phase diagram

We evaluated the six binary phase diagrams, B₂O₃-PbO, B₂O₃-SiO₂, B₂O₃-ZnO, PbO-SiO2, PbO-ZnO, and SiO₂-ZnO, to obtain a consistent picture for the quaternary system B₂O₃-PbO-SiO₂-ZnO. We used all the available thermodynamic data: enthalpies of mixing, activity data, complete phase diagrams, and miscibility gaps. The agreement between the various sets of data is good. We also calculated the enthalpy of formation of the ternary compound 5PbO-B₂O₃-SiO₂. Δ_fH/R of 1/8 [5PbO-B₂O₃-SiO₂] =-(2.104 ± 0.057) kK.     

The quaternary system B2O3-PbO-SiO2-ZnO: Thermodynamics and phase diagram

We evaluated the six binary phase diagrams, B₂O₃-PbO, B₂O₃-SiO₂, B₂O₃-ZnO, PbO-SiO2, PbO-ZnO, and SiO₂-ZnO, to obtain a consistent picture for the quaternary system B₂O₃-PbO-SiO₂-ZnO. We used all the available thermodynamic data: enthalpies of mixing, activity data, complete phase diagrams, and miscibility gaps. The agreement between the various sets of data is good. We also calculated the enthalpy of formation of the ternary compound 5PbO-B₂O₃-SiO₂. Δ_fH/R of 1/8 [5PbO-B₂O₃-SiO₂] =-(2.104 ± 0.057) kK.     

Magnetic properties and phase diagram of Ni50Mn50−xGax ferromagnetic shape memory alloys

We present the magnetic properties and the magnetic phase diagram of Ni₅₀Mn_50?xGa_x ferromagnetic shape memory alloys across a wide concentration range. Martensitic transformation, intermediate transformation, B2–L2₁ order–disorder transformation, Néel and Curie temperatures are determined for the prepared samples. The martensitic transformation temperature decreases with increasing Ga concentration and bends two times when crossing the Curie temperature and the intermediate-phase transformation temperature. Spontaneous magnetization and its composition dependence were also investigated. Composition dependence of the transformation temperatures and the spontaneous magnetization in the martensite phase of Ni₅₀Mn_50?xGa_x are compared with those of Ni₅₀Mn_50?xIn_x and Ni₅₀Mn_50?xSn_x, revealing a similarity in the NiMn-based alloy systems.     

Amorphous phase formation in a Ni−Zr−Al−Y alloy system

Quaternary Ni-based amorphous alloys containing only metallic elements were developed through systematic alloy design. The importance of the phase equilibria information for the development of amorphous alloys was demonstrated through experimental results. Ni−Zr−Al ternary alloys having low liquidus temperature tend to have high GFA. Partial replacements of Zr with Y in the ternary alloys significantly enhanced the GFA of the quaternary alloys. The alloy Ni₆₀Zr₂₅Al₈Y₇ could be cast into a fully amorphous rod through an injection casting method. Since most Ni-based amorphous alloys reported to date contain non-metallic elements, the Ni-based amorphous alloys developed in the alloy system Ni−Zr−Al−Y are of interest.