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.     

The Fe–Ni–Al phase diagram in the Al-rich (>50 at.% Al) corner

The ternary Fe–Ni–Al phase diagram between 50 and 100 at.% Al was investigated by a combination of powder X-ray diffraction (XRD), differential thermal analysis (DTA) and electron probe microanalysis (EPMA). Ternary phase equilibria and accurate phase compositions of the respective equilibrium phases were determined within the isothermal section at 850 °C. The crystal structure of τ1 (Fe_4−xNi_xAl₁₀) and τ2 (Fe_2−xNi_xAl₉) was determined by means of single crystal X-ray diffraction. The decagonal quasi-crystalline phase q (Fe_4.9Ni_23.4Al_71.7) was found to be stable between 850 °C and 930 °C. All experimental data were combined to yield a ternary reaction scheme (Scheil diagram) involving 10 ternary invariant reactions in the investigated composition range, and a liquidus surface projection was constructed based on DTA results.     

Measurement of phase equilibria in Ti-Ni-Sn system

Phase relations of the Ti-Ni-Sn ternary system were investigated via alloy sampling assisted with X-ray diffractometry (XRD) and electron probe micro-analysis (EPMA). A new binary phase with composition of TiSn₄ (molar fraction, %) was detected at 508 K. In addition, a supplementary phase (Ti_1–x–yNi_xSn_y)Ni₃ (τ, AuCu₃-type) was observed at 873 and 973 K. According to the characterised microscopic structure in various annealed alloys, four ternary phases were detected in Ti-Ni-Sn ternary system: TiNiSn, TiNi₂Sn, Ti₂Ni₂Sn and (Ti_1–x–yNi_xSn_y)Ni₃. Additionally, isothermal sections of Ti-Ni-Sn ternary system at 508, 873 and 973 K were constructed. By comparing three isothermal sections, a peri-eutectic reaction, L+TiNi₂Sn→Ni₃Sn₄+TiNiSn, was deduced, which occurs at a temperature between 873 and 973 K. Furthermore, the solubility of Sn in TiNi and Ni in Ti₅Sn₃ was detected.     

Ni radiotracer diffusion in B2 ordered NiFeAl alloys

Ni bulk diffusion was measured in the B2 ordered NiFeAl alloys with a constant Al content of approximately 50 at.%. The ⁶³Ni radioisotope in combination with the radiotracer serial sectioning technique was applied at higher temperatures and the secondary ion mass spectrometry (⁶⁴Ni isotope) was used in a low temperature range. Arrhenius-type temperature dependencies were established for all studied compositions in the temperature interval from 1050 to 1500 K. As the Fe content x in the Ni_50−xFe_xAl₅₀ ternary alloys increases, the Ni diffusivity generally increases along the quasi-binary section between stoichiometric NiAl and FeAl. The activation enthalpy Q of Ni diffusion changes strongly non-monotonically in the ternary alloys between the binary end-members NiAl and FeAl revealing a pronounced minimum at the Ni₄₀Fe₁₀Al₅₀ composition and a conspicuous maximum around the Ni₂₅Fe₂₅Al₅₀ composition.     

Effects of annealing at 800 and 1000 °C on phase precipitates and hardness of Al7Cr20FexNi73−x alloys

The effects of Fe content on the microstructure, phase constituents and microhardness of the as-cast, 800 °C- or 1000 °C-annealed Al₇Cr₂₀Fe_xNi_73?x (x=13?66) alloys were investigated. Not all these alloys are composed of the single FCC phase. The BCC and B2 phases are found. It is confirmed that the BCC phase in the Al₇Cr₂₀Fe₆₆Ni₇ alloy is transformed from the FCC phase at about 900 °C during cooling. While in the 800 °C-annealed Al₇Cr₂₀Fe₆₀Ni₁₃ alloy, the FCC phase is stable and the hardness decreases. After annealing at 1000 °C, for the precipitation of the B2 particles, the Al content in the FCC phase decreases, which results in decreasing of the alloy hardness. Moreover, after annealing at 800 °C, a small amount of Al-rich B2 particles precipitate at the phase boundary and some nanocrystal BCC phase precipitates in the FCC matrix, which increases the hardness of the Al₇Cr₂₀Fe_xNi_73?x (x=41?49) alloys. These results will help to the composition design and processing design of the Al?Cr?Fe?Ni based high-entropy alloys.     

Microstructures,Martensitic Transformation,and Mechanical Behavior of Rapidly Solidified Ti-Ni-Hf and Ti-Ni-Si Shape Memory Alloys

In this work, the microstructure and mechanical properties of rapidly solidified Ti_50?x/2Ni_50?x/2Hf _x (x = 0, 2, 4, 6, 8, 10, and 12 at.%) and Ti_50?y/2Ni_50?y/2Si _y (y = 1, 2, 3, 5, 7, and 10 at.%) shape memory alloys (SMAs) were investigated. The sequence of the phase formation and transformations in dependence on the chemical composition is established. Rapidly solidified Ti-Ni-Hf or Ti-Ni-Si SMAs are found to show relatively high yield strength and large ductility for specific Hf or Si concentrations, which is due to the gradual disappearance of the phase transformation from austenite to twinned martensite and the predominance of the phase transformation from twinned martensite to detwinned martensite during deformation as well as to the refinement of dendrites and the precipitation of brittle intermetallic compounds.     

Experimental Investigation on Phase Equilibria of Al-Fe-Y System at 773 K

The phase diagram determination of Al-Fe-Y is helpful for development of magnetic and amorphous materials. The entire isothermal section of Al-Fe-Y at 773 K has been determined by means of x-ray powder diffraction, scanning electron microscopy with energy dispersive analysis and optical microscopy. The existences of 14 binary compounds in the Al-Fe, Al-Y and Fe-Y binary systems were confirmed. The binary phases Al₂Y, Fe₂Y, Al₂Y₃, Fe₂₃Y₆ and Fe₁₇Y₂ in this study present appreciable ternary solubility: Fe_17?x Al _x Y₂ (0 ≤ x ≤ 8.5), Y(Fe_1?x Al _x )₂ (0 ≤ x ≤ 1), Al₂(Fe _x Y_1?x )₃ (0 ≤ x ≤ 0.3), and (Fe,Al)₂₃Y₆ with Al up to 22 at.%. The ternary compounds: τ₁-Al₁₀Fe₂Y, τ₂-Al_8?x Fe_4+x Y (0 ≤ x ≤ 2) were confirmed. The isothermal section consists of 19 single-phase regions, 33 two-phase regions and 17 three-phase regions.     

Stability of B2 phase in Ti–Ni–Fe alloys against MeV electron-irradiation-induced solid-state amorphization and martensite transformation

The amorphization tendency of a B2 phase in Ti₅₀Ni_50?xFe_x (x = 2 to 40 at%) intermetallic compound was investigated in order to determine the relationship between solid-state amorphization (SSA) and martensite transformation. SSA was observed in the B2 phase at 103 K and 298 K by high-voltage electron microscopy (HVEM). The total dose required for the amorphization increased with the Fe content. The replacement of Ni by Fe increased the phase stability of the B2 phase in Ti–Ni–Fe intermetallic compound and suppressed SSA as well as martensite transformation.     

Microstructure and plastic deformation behavior of Ni3(Ti,X) (X = Nb,Al) single crystals with long-period geometrically closely packed crystal structures

The crystal structure, phase stability and plastic deformation behavior of Ni₃(Ti_1−xNb_x) [x = 0, 0.01, 0.03, 0.05 or 0.10] and Ni₃(Ti_1−yAl_y) [y = 0.16 or 0.28] single crystals were investigated. The substitution of Ti by Nb in Ni₃Ti induced the formation of various long-period stacking ordered (LPSO) structures with 18-fold, 10-fold or 9-fold stacking sequences of closely packed plane (CPP) depending on the Nb content. In compression tests, the yield stress anomaly (YSA) appeared in ternary LPSO crystals as well as in binary Ni₃Ti by slip on the CPP. The change in stacking sequence of CPP in the LPSO phases strongly affects the YSA behavior due to the change in APB energy on the non-closely packed plane.     

Effect of Ti content on the microstructure and mechanical behavior of (Fe36Ni18Mn33Al13)100−xTix high entropy alloys

The microstructure and mechanical properties studies of a series of two-phase f.c.c./B2 (ordered b.c.c.) lamellar-structured, high entropy alloys (HEA) Fe₃₆Ni₁₈Mn₃₃Al₁₃Ti_x with x up to 6 at. % Ti have been investigated. X-ray microanalysis in a TEM showed that the Ti resided mostly in the B2 phase. The lamellar spacing decreased significantly with increasing Ti content from 1.56 μm for the undoped alloy to 155 nm with an addition of 4 at. % Ti, leading to a sharp increase in room-temperature yield strength,σ_y, from 270 MPa to 953 MPa, but with a concomitant decrease in ductility from 22% elongation to 2.3%. Annealing at 1173 K for 20 h greatly increased the lamellar spacing of Fe₃₆Ni₁₈Mn₃₃Al₁₃Ti₄ to 577 nm, producing a corresponding decrease in σ_y to 511 MPa. The yield strengths of all the doped alloys decreased significantly when tensile tested at 973 K with a concomitant increase in ductility due to softening of the B2 phase. The fracture mode changed from cleavage at room temperature to a ductile dimple-type rupture at 973 K. The results are discussed in terms of the Hall-Petch-type relationship.     

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.     

Thermal stability and crystallization of Zr–Al–Cu–Ni based amorphous alloy added with boron and silicon

The amorphous Zr_65−x−yAl_7.5 Cu_17.5Ni₁₀Si_xB_y alloy ribbons, x=1–4 and y=1–2, with 0.1 mm thickness were prepared by melt spinning. The thermal properties and microstructure development during the annealing of amorphous alloys were investigated by the combination of differential thermal analysis, differential scanning calorimetry, X-ray diffractometry, and TEM. Both of the glass transition temperature and the crystallization temperature for Zr_65−x−yAl_7.5 Cu_17.5Ni₁₀Si_xB_y alloys increases with the silicon and boron additions and reaches 674 and 754 K, respectively for Zr₆₀Al_7.5 Cu_17.5Ni₁₀Si₄B₁ alloy. The highest T_rg (0.62) and γ value (0.43) occurred at the Zr₆₀Al_7.5Cu_17.5Ni₁₀Si₄B₁ alloy. In addition, the Zr₆₀Al_7.5Cu_17.5Ni₁₀Si₄B₁ alloy was revealed to have the highest activation energy of crystallization (about 370 kJ/mol as determined by the Kissinger plot). This value is about 20% higher than the activation energy of crystallization for the Zr₆₅Al_7.5Cu_17.5Ni₁₀ based alloy (314 kJ/mol). In parallel, the alloy 4Si1B also performs a longer incubation time at higher isothermally annealing temperature. All of the evidence implies that Zr₆₀Al_7.5 Cu_17.5Ni₁₀Si₄B₁ alloy exhibits the highest thermal stability among those alloys in this study. The crystallization behavior for the alloy 4Si1B isothermally annealed at the supercooled temperature region for different time has also been examined by TEM and discussed.     

Isothermal section of the Al-Dy-Ge ternary system at 673 K

The isothermal section of the phase diagram of the Al-Dy-Ge ternary system at 673 K has been investigated by X-ray powder diffraction and scanning electron microscope equipped with energy dispersive X-ray spectroscopy in backscattered electron imaging modes. The existence of thirteen binary compounds including Dy₃Ge₄ in the system Dy-Ge has been confirmed. Four ternary compounds, namely AlDyGe, Al₃Dy₂Ge₄, AlDy₂Ge₃, and AlDy₂Ge₂ were observed, and five new ternary compounds, i.e., Al_0.33DyGe₂, AlDy₂Ge₆, Al₂DyGe₂, AlDy₃Ge₃, and Al_3−xDy₁₁Ge_7+x (x ≤ 0.7), and one pseudo-binary compound Al_3−xDyGe_x were found in this system at 673 K. The maximum solid solubility of Ge in the pseudo-binary compounds Al_3−xDyGe_x is about 7.5 at.% with x = 0.3 at 673 K.     

Phase equilibria and structural investigations in the system Al–Fe–Si

The Al–Fe–Si system was studied for an isothermal section at 800 °C in the Al-rich part and at 900 °C in the Fe-rich part, and for half a dozen vertical sections at 27, 35, 40, 50 and 60 at.% Fe and 5 at.% Al. Optical microscopy and powder X-ray diffraction (XRD) was used for initial sample characterization, and Electron Probe Microanalysis (EPMA) and Scanning Electron Microscopy (SEM) of the annealed samples was used to determine the exact phase compositions. Thermal reactions were studied by Differential Thermal Analysis (DTA). Our experimental results are generally in good agreement with the most recent phase diagram versions of the system Al–Fe–Si. A new ternary high-temperature phase τ₁₂ (cF96, NiTi₂-type) with the composition Al₄₈Fe₃₆Si₁₆ was discovered and was structurally characterized by means of single-crystal and powder XRD. The variation of the lattice parameters of the triclinic phase τ₁ with the composition Al_2+xFe₃Si_3?x (?0.3 < x < 1.3) was studied in detail. For the binary phase FeSi₂ only small solubility of Al was found in the low-temperature modification LT-FeSi₂ (ζ_β) but significant solubility in the high-temperature modification HT-FeSi₂ (ζ_α) (8.5 at.% Al). It was found that the high-temperature modification of FeSi₂ is stabilized down to much lower temperature in the ternary, confirming earlier literature suggestions on this issue. DTA results in four selected vertical sections were compared with calculated sections based on a recent CALPHAD assessment. The deviations of liquidus values are significant suggesting the need for improvement of the thermodynamic models.     

Isothermal Section of Al-Si-Ce Ternary System at 1073 K

The phase equilibria in the Al-Si-Ce ternary system at 1073 K is investigated by means of x-ray diffraction and scanning electron microscope coupled with energy dispersive spectroscopy. There exist 12 three-phase regions exist in this system and one can be deduced. One ternary compound T (Ce(Al _x Si_1?x )₂) found in the isothermal section at 1073 K has the LaPtSi structure with a lattice parameter a = 0.4242 nm which composition span ranges from 32.1-47.8 at.%Al, 17.9-33.7 at.% Si, 33.4-34.0 at.% Ce. The maximum solubility of Al (in at.%) in CeSi_2?α, CeSi, Ce₅Si₄, Ce₃Si₂ and Ce₅Si₃ at 1073 K is 29.3, 23.8, 2.8, 13.6 and 6.5 respectively, and the maximum solubility of Si (in at.%) in Al₄Ce, Al₃Ce, Al₂Ce and AlCe at 1073 K is 1.4, 1.7, 1.8 and 2.1 respectively.     

An experimental investigation of the Fe-Ni-Sb ternary phase diagram

The ternary system Fe-Ni-Sb has been investigated in the region between 42 and 100 at. % Sb using conventional methods including DTA, X-ray techniques, metallography, and electron probe mi-croanalysis (EPMA). A continuous solid solution was found to exist between the NiAs(B8)-type phases Fe _1+x Sb and Ni _1±x Sb, whereas the marcasite-type phase Fe _x Ni _1-xS b ₂ is only stable in the ranges 0.50 ≤x≤ 1.00 and 0.00 ≤x ≤ 0.03, respectively. A skutterudite-type compound FeNiSb ₆ —isotypic with CoSb ₃ —was found to decompose peritectically at 642 ‡C. An isothermal sec-tion of the phase diagram was studied at 600 ‡C by X-ray powder diffraction using the Guinier tech-nique, and the lattice parameters of Fe _x Ni _1-x Sb ₂ and (Fe _y Ni _1-y ) _1±x Sb were determined as a function of composition. Several samples were investigated by microprobe analysis to fix the phase bounda-ries of the (Fe _y Ni _1-y Sb-phase. Four invariant ternary reactions were found in the Sb-rich part of the phase diagram, all of them within the narrow temperature range between 615 and 642 ‡C. The results of the DTA measure-ments were also used to construct the liquidus surface in the entire composition range investigated. All experimental information was combined with literature data to yield a complete ternary phase diagram in the composition range between 42 and 100 at. % Sb.     

Experimental Investigation of the Al-Fe-Nd System at 773 K

The phase diagram of Al-Fe-Nd is helpful for development of the magnetic and amorphous materials based on this system. The entire isothermal section of Al-Fe-Nd at 773 K was determined by means of x-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive analysis (EDX) and optical microscopy (OM). The existences of 12 binary compounds of the Al-Fe, Al-Nd and Fe-Nd systems were confirmed, and binary phases Al₂Nd and Fe₁₇Nd₂ demonstrated appreciable ternary solubility. The ternary compounds: τ₁-Al₁₀Fe₂Nd, τ₂-Al_8+x Fe_4?x Nd (0 < x < 0.7) and λ-Nd₃₀Fe_62?x Al_8+x (0 < x < 17) were confirmed in the present work. The isothermal section consists of 18 single-phase regions, 36 two-phase regions and 19 three-phase regions.     

Ternary Sm–Al–Ni bulk metallic glasses

The present paper is concerned with the formation of the ternary Sm-based Sm–Al–Ni bulk metallic glasses. Composition design is carried out using our e/a- and cluster-related criteria. Three bulk metallic glasses, Sm₅₄Al₂₃Ni₂₃, Sm₅₆Al₂₂Ni₂₂ and Sm₅₈Al₂₁Ni₂₁, are obtained by suction casting into rods with diameter of 3 mm. All of them share a constant e/a = 1.5 and fall along the e/a-constant composition line in the ternary composition diagram. The Sm₅₄Al₂₃Ni₂₃ BMG exhibits the best thermal stability and glass-forming ability, which is located at the intersecting point of the e/a-constant line and the Sm₇Ni₃–Al cluster line.     

A wide temperature window for the magnetostructural transformation in Mn50Ni50-x-ySnxCoy alloys

In order to open a wide temperature window for a magnetostructural transformation, Sn–Co co-doping was explored in the Mn₅₀Ni₅₀ alloy. The experimental results show that doping with Sn and doping with Co have different effects on the martensitic and austenitic structures, the martensitic transformation, the thermal hysteresis and the magnetic properties of the martensitic and austenitic phases. By tuning the Sn and Co content in Mn₅₀Ni_50−x−ySn_xCo_y from x = 11, y = 0 to x = 6, y = 14, the martensitic transformation temperature, T_m, could be adjusted over the range from 99 K to 450 K, with the condition that T_m remains lower than the Curie temperature of the austenitic phase, Tc^a, which varied from 288 K to 565 K. Thus, a 351 K temperature window for the magnetostructural transformation was established and a series of ferromagnetic shape memory alloys was identified.     

Experimental Investigation of the Al-Fe-Gd System at 773 K

The phase equilibrium of the Al-Fe-Gd plays an important role of development of bulk amorphous alloys and magnetocaloric materials. The entire isothermal section of the phase diagram for Al-Fe-Gd ternary system at 773 K has been investigated by means of x-ray powder diffraction, scanning electron microscopy with energy dispersive analysis, and optical microscopy. The existences of 13 binary compounds for the Al-Fe, Al-Gd, and Fe-Gd binary systems were confirmed. The binary phases, i.e., Al₂Gd, Fe₂Gd, and α-Fe₁₇Gd₂ present appreciable ternary solubility. Three ternary compounds: τ₁-Al₁₀Fe₂Gd, τ₂-Al_8+x Fe_4-x Gd (0 ≤ x ≤ 2), and λ-Al_2?x Fe _x Gd (0.951 ≤ x ≤ 1.245) were determined. The isothermal section consists of 19 single-phase regions, 40 binary-phase regions, and 20 ternary-phase regions.