Phase Equilibria of the Co-Mo-Zr Ternary System at 1000 °C

The isothermal section of the Co-Mo-Zr ternary system at 1000 °C was investigated by using 29 alloys. The annealed alloys were examined by means of x-ray diffraction, optical microscopy, and electron probe microanalysis. It was confirmed that three ternary phases, λ₁ (Co_0.5-1.5Mo_1.5-0.5Zr, hP12-MgZn₂), ω (CoMoZr₄) and κ (CoMo₄Zr₉, hP28-Hf₉Mo₄B), exist in the Co-Mo-Zr ternary system at 1000 °C. And the experimental results also indicated that there are sixteen three-phase regions at 1000 °C. Thirteen of them were well determined in the present work: (1) (γCo)?+?Co₁₁Zr₂?+?Co₂₃Zr₆, (2) (γCo)?+?Co₂₃Zr₆?+?ε-Co₃Mo, (3) Co₂₃Zr₆?+?ε-Co₃Mo?+?μ-Co₇Mo₆, (4) (Mo)?+?μ-Co₇Mo₆?+?Co₂Zr, (5) (Mo)?+?Co₂Zr?+?λ₁, (6) (Mo)?+?Mo₂Zr?+?λ₁, (7) λ₁?+?Mo₂Zr?+?CoZr, (8) Co₂Zr?+?CoZr?+?λ₁, (9) Mo₂Zr?+?CoZr₂?+?ω, (10) κ?+?Mo₂Zr?+?ω, (11) CoZr₂?+?liquid?+?ω, (12) (βZr)?+?liquid?+?ω and (13) (βZr)?+?κ?+?ω. The homogeneity of λ₁ spans in the range of 28.66-50.77 at.% Co and 15.71-37.03 at.% Mo, and that for ω is within the range of 18.66-23.64 at.% Co and 8.53-14.68 at.% Mo. The homogeneity range for κ is from 8.09 at.% to 9.94 at.% Co and 23.13 at.% to 25.58 at.% Mo. The maximum solubility of Zr in μ-Co₇Mo₆ phase, Mo in Co₂Zr phase and Co in Mo₂Zr phase were determined to be 6.17, 11.27 and 9.14 at.%, respectively. While the solubility of Zr in ε-Co₃Mo and (γCo) phases, Mo in Co₁₁Zr₂ and CoZr phases were detected to be extremely small. According to this work, the Co₂₃Zr₆ phase contained 15.61 at.% Mo and 12.7 at.% Zr. In addition, the maximum solubility of Co and Zr in (Mo) phase and Mo in (γCo) phase were measured to be 3.50, 5.44 and 7.40 at.%, respectively.     

Effect of nitrogen on sigma formation in Cr-Ni steels at 1200°F (650°C)

The addition of nitrogen (0.10 to 0.20 pct) to Fe-Cr-Ni alloys of simulated commercial purity results in a real displacement of the σ phase boundaries to higher chromium contents. The effect is small for the (γ + σ)/γ boundary, but is pronounced for the (γ + α + σ)/(γ + α) boundary. Although there is an indication of an exceptionally large shift of the σ boundaries to higher chromium contents, especially in steels with nitrogen over 0.2 pct, the major portion of this apparent shift results from the fact that carbide and nitride precipitation cause “chromium impoverishment” of the matrices. The effect of combined additions of nitrogen and silicon to the Fe-Cr-Ni phase diagram is demonstrated also. Nitrogen can nullify the effect of about 1 pct Si in shifting the (γ + σ)/γ phase boundary to lower values of chromium at all nickel levels from 8 to 20 pct. Nitrogen can nullify this σ-forming effect of about 2 pct Si at the 8 pct Ni level, but not at the 20 pct Ni level. The alloys studied were in both the cast and the wrought conditions. There are indications that the σ phase forms more slowly in the cast alloys than in the wrought alloys if both are in the completely austenitic state. The presence of δ ferrite in the cast alloys accelerates the formation of σ. Cold working increases the rate of σ formation in both cast and wrought alloys.     

Beta-Omega Age Hardening Means Stronger Zirconium Alloys

The β-ω phase transformation, important in many titanium alloys, has been revealed in zirconium alloys. Hitherto unattainable tensile strength with adequate ductility is now feasible for certain zirconium alloys. It is expected that many new applications will result from this discovery.     

Structure of the transition phase omega in Ti-Cr alloys

Ti-Cr alloys age harden after β-quenching by formation of an ω-phase. The structure and orientation of this transition phase have been determined. The hardness appears to be caused by strain in the β-matrix produced by concurrent enrichment of alloy content in the ω-phase.     

System Zirconium-Nitrogen

Iodide zirconium was combined with calculated amounts of nitrided zirconium sponge and arc melted to prepare alloys in the 0 to 6 wt pet N region. Annealing treatments were carried out at 21 temperature levels. Metallographic examination of the heat-treated specimens permitted construction of the binary phase diagram from 0 to 6 pet N. Features of the diagram include the peritectic formation of both a and β solid solutions. The maximum solubility of nitrogen is 0.8 pet in β zirconium and 4.8 pet in a zirconium. An X-ray study of nitrided materials was made in the range 6 to 13 wt pet N region because serious nitrogen losses were experienced when attempts were made to arc melt these high nitrogen alloys.     

Normal state of metallic hydrogen sulfide

A generalized theory of the normal properties of metals in the case of electron–phonon (EP) systems with a nonconstant density of electron states has been used to study the normal state of the SH₃ and SH₂ phases of hydrogen sulfide at different pressures. The frequency dependence of the real Re Σ (ω) and imaginary ImΣ (ω) parts of the self-energy Σ (ω) part (SEP) of the Green’s function of the electron Σ (ω), real part Re Z (ω), and imaginary part Im Z (ω) of the complex renormalization of the mass of the electron; the real part Re χ (ω) and the imaginary part Imχ (ω) of the complex renormalization of the chemical potential; and the density of electron states N (ε) renormalized by strong electron–phonon interaction have been calculated. Calculations have been carried out for the stable orthorhombic structure (space group Im3?m) of the hydrogen sulfide SH₃ for three values of the pressure P = 170, 180, and 225 GPa; and for an SH₂ structure with a symmetry of I4/mmm (D4h1?7) for three values of pressure P = 150, 180, and 225 GP at temperature T = 200 K.     

Phase Equilibria and Microhardness of As-Cast and Annealed Ni-Al-Os Alloys in Ni-Rich Region

In this paper, the isothermal section at 1273 K and liquidus projection of ternary Ni-Al-Os system in Ni-rich region were firstly measured by using 6 annealed and 6 as-cast Ni-Al-Os alloys with 65 at.% Ni in combination with x-ray diffraction, optical microscopy and electron probe microanalysis techniques. For the determined partial isothermal section at 1273 K, 2 single-phase, 4 two-phase and 2 three-phase regions were observed. The solubilities of Os in both γ and γ′ phases were also determined. For the proposed liquidus projection, four primary surfaces of γ′, γ, β and δ, and two invariant reactions were identified. Secondly, the microhardness of both as-cast and annealed alloys were measured. The evolution trend of microhardness in both as-cast and annealed alloys with Os addition generally increases first, and then decreases. Thirdly, the further comprehensive discussion on possible substitution of Re by Os in new-generation nickel-based single-crystal superalloys were performed in terms of strengthening degree, high-temperature creep resistance, and possibility for formation of harmful topologically close-packed phases. It was finally concluded that Os may be used as a new additional element to replace or partly replace Re in Ni-based single crystal superalloys.     

Structure and Thermoelastic Martensitic Transformations in Ternary Ni–Ti–Zr Alloys with High-Temperature Shape Memory Effects

X-ray diffraction analysis and transmission electron and scanning electron microscopies were used to study the effect of alloying with zirconium (0–20 at %) on the phase composition and structural and morphological features of thermoelastic martensitic transformations in ternary Ni–Ti–Zr alloys. The electrical resistivity of alloys has been measured in a wide range of temperatures, the critical temperatures have been determined, and a complete diagram of the high-temperature thermoelastic forward and reverse martensitic transformations B2 ? B19' occurring with a hysteresis in the range of 32–50 K has been constructed based on XRD data. The intercritical range of the temperatures of transformations increases as the zirconium content increases within the indicated limits. The lattice parameters of the monoclinic crystal lattice of the B19' martensite have been measured at room temperature. The twinning types most frequently observed in B19' martensite have been found as follows: I-(011), \(\left( {11\;\bar 1} \right)\) and (001), II-(011).     

The Effect of Oxygen on Phase Equilibria in the Ti-V System: Impacts on the AM Processing of Ti Alloys

Oxygen is always a constituent in “real” titanium alloys including titanium alloy powders used for powder-based additive manufacturing (AM). In addition, oxygen uptake during powder handling and printing is hard to control and, hence, it is important to understand and predict how oxygen is affecting the microstructure. Therefore, oxygen is included in the evaluation of the thermodynamic properties of the titanium-vanadium system employing the CALculation of PHAse Diagrams method and a complete model of the O-Ti-V system is presented. The β-transus temperature is calculated to increase with increasing oxygen content whereas the extension of the α-Ti phase field into the binary is calculated to decrease, which explains the low vanadium solubilities measured in some experimental works. In addition, the critical temperature of the metastable miscibility gap of the β-phase is calculated to increase to above room temperature when oxygen is added. The effects of oxygen additions on phase fractions, martensite and ω formation temperatures are discussed, along with the impacts these changes may have on AM of titanium alloys.     

Phase Equilibria of the Ternary Al-Cu-Zn Alloys on Al-Zn Rich Side

Phase equilibria of the Al-Cu-Zn system on Al-Zn rich side was experimentally determined with 16 alloys annealed at 360 °C. The annealed alloys were examined by means of x-ray diffraction, electron probe microanalysis and differential scanning calorimetry. Five single-phase regions and seven two-phase regions as well as three three-phase regions, i.e. α-(Al)?+?θ-Al₂Cu?+?τ′-Al₄Cu₃Zn, α-(Al)?+?τ′-Al₄Cu₃Zn?+?ε-CuZn₄ and α-(Al)?+?ε-CuZn₄?+?(Zn), were determined. The partial isothermal section of the Al-Cu-Zn system on Al-Zn rich side at 360 °C was constructed based on the obtained experimental data in this work. It was observed that the solid solution phase α-(Al) would easily decompose into ε-CuZn₄, (Zn) and α′-(Al) at the ambient temperature in the early stages. The ternary phase τ′-Al₄Cu₃Zn would form and ε-CuZn₄ would disappear gradually along with the extension of aging time.     

Structure,magnetic and magnetocaloric properties of nonstoichiometric TbCo<Subscript>2</Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> compounds

The structure and magnetic and magnetocaloric properties of new nonstoichiometric TbCo₂Ni _x compounds (0 ≤ x ≤ 0.4) have been studied. The alloys with х ≤ 0.1 have been shown to be single-phase with the MgCu₂-type structure; in alloys with х > 0.1, an additional phase with a PuNi₃-type structure has been formed. It has been found that the concentration dependences of the Curie temperature and magnetic moment of the 3d-metal sublattice have a maximum at x = 0.025. The magnetocaloric effect magnitude for the TbCo2Nix compounds has been estimated using the results of magnetic and heat-capacity measurements.     

Effect of Cu and Mo Additions on the Crystallization Behavior and Magnetic Properties of Fe<Subscript>80</Subscript>Zr<Subscript>10</Subscript>B<Subscript>10</Subscript> Alloy

Fe₈₀Zr₁₀B₁₀, Fe₈₀Zr₁₀B₉Cu₁, and Fe₈₀Zr₈Mo₂B₁₀ amorphous alloys were prepared by melt-spinning and annealed at various temperatures. The effect of Cu and Mo additions on the thermal property, microstructure and magnetic properties of Fe₈₀Zr₁₀B₁₀ alloy is studied. Both Cu and Mo additions decrease the crystallization activation energy. The crystallization process of Fe₈₀Zr₁₀B₁₀ alloy is very complex. Both Cu and Mo additions simplify the crystallization process. But a few α-Mn-type phase is still observed in the initial crystallization stage of Mo-containing alloy. Both Cu and Mo additions increase saturation magnetization (M _s) and decrease coercivity (H _c) of alloys. The addition of Cu is beneficial to decrease H _c in the initial crystallization stage, and the addition of Mo is beneficial to decrease H _c at high temperatures.     

Effect of Testing Variables on the Hydrogen Embrittlement of Titanium and a Ti-8 pct Mn Alloy

The effects of increasing hydrogen content, introducing a notch, and changing the strain rate on properties of titanium and one of its alloys were investigated over a range of testing temperatures from —196° to 200°C. Both high purity and commercial purity A-55 titanium were used as representative a materials, while a commercial Ti-8 pct Mn alloy was used for an α-β alloy. It was found possible to analyze the data, using the ductile-to-brittle transition temperature concept. Increasing hydrogen, the presence of a notch, and increasing the testing speed raised the transition temperature for the a materials. The presence of hydrogen and notches raised the transition temperature of the α-β alloy also. However, increasing the testing speed generally decreased the transition temperature of the α-β alloy.     

Prediction of Martensite Start Temperature for Lightweight Fe-Mn-Al-C Steels

A tailor-made thermodynamic database of the Fe-Mn-Al-C system was developed using the CALPHAD approach. The database enables predicting phase equilibria and thereby assessing the resulting microstructures of Fe-Mn-Al-C alloys. Available information on the martensite start (M_s) temperature was reviewed. By employing the M_s property model in the Thermo-Calc software together with the new thermodynamic database and experimental M_s temperatures, a set of model parameters for the Fe-Mn-Al-C system in the M_s model was optimised. Employing the newly evaluated parameters, the calculated M_s temperatures of the alloys in the Fe-Mn-Al-C system were compared with the available measured M_s temperatures. Predictions of M_s temperatures were performed for the alloys, Fe-10, 15 and 20 wt.% Mn-xAl-yC. The predictability of the M_s model can be further validated when new experimental M_s temperatures of the Fe-Mn-Al-C system are available.     

Evolution of structural changes in nanocrystalline alloys with temperature

Structural features of the NANOPERM-type alloys Fe_{91 ? x} Mo₈Cu₁B _x with x = 12, 15, and 17 have been investigated by Mössbauer spectroscopy. The room-temperature Mössbauer spectra of the as-quenched alloys are characteristic of disordered structural arrangement, but traces of bcc-Fe(Mo) as well as a FeMo₂B₂ phase have been revealed by X-ray diffraction in all the samples. These results have been confirmed by conversion-electron Mössbauer spectroscopy. The differences between the opposite sides of the ribbon-shaped samples have been shown to stem from structural distinctions. From the point of view of hyperfine interactions, the x = 12 sample exhibits paramagnetic behavior. With increasing x, a contribution from ferromagnetic regions appears gradually, thus leading to an increase in the magnetic ordering temperature in the as-quenched state. Partially crystallized samples have been prepared by controlled annealing of the original precursors for one hour at temperatures ranging from 330 to 650°C in a vacuum. The temperature of the onset of crystallization has been determined to be of 430, 450, and 470°C for x = 12, 15, and 17, respectively. During the first step of crystallization, bcc-Fe(Mo) nanosized grains are formed. Surface features of the samples investigated have also been characterized by using atomic force microscopy.     

Improved High-Temperature Microstructural Stability and Creep Property of Novel Co-Base Single-Crystal Alloys Containing Ta and Ti

The influence of Ta and Ti additions on microstructural stability and creep behavior in novel Co-Al-W base single-crystal alloys has been investigated. Compared to the ternary alloy, the γ′ solvus temperature and γ′ volume fraction were raised by individual additions of Ta and Ti, and increased further in the quinary alloy containing both alloying additions. In contrast to ternary and quaternary alloys, an improved microstructural stability with the stable γ–γ′ two-phase microstructure and more than 60% γ′ volume fraction existed in the quinary alloy after prolonged aging treatment at 1050°C for 1000 h. The creep behavior at 900°C revealed lower creep rates and longer rupture lives in the quaternary alloys compared to the ternary alloy, whereas the quinary alloy exhibited even better creep resistance. When the creep temperature was elevated to about 1000°C, the creep resistance of the quinary alloy exceeded the previously reported Co-Al-W-base alloys and first-generation Ni-base single-crystal superalloys. The improved creep resistance at approximately 1000°C was considered to be associated with high γ′ volume fraction, γ′ directional coarsening, and dislocation substructure, which included γ–γ′ interfacial dislocation networks and the sheared γ′ precipitates containing stacking faults and anti-phase boundaries.     

Phase transformations during deformation of Fe-Ni and Fe-Mn alloys produced by mechanical alloying

Compositions of Fe_{(100 ? x)}Mn _x (x = 10 and 12 at. %) and Fe_{(100 ? y)}Ni _y (y = 18 and 20 at. %) were produced by combined mechanical alloying of pure-metal powders and annealed in the austenitic field. After annealing and cooling to room temperature, the alloys had a single-phase austenitic structure. During deformation, the γ phase partially transforms into the α ₂ phase (and/or ? phase in Fe-Mn alloys). The phase composition of the alloys after deformation depends on the amount of alloying elements and the predeformation annealing regime. The amount of martensite in the structure of a bulk alloy obtained by powder compacting grows proportionally to the degree of deformation of the sample.     

Structure,Magnetic and Magnetocaloric Properties of Nonstoichiometric TbCo<Subscript>2</Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Compounds

TbCo₂Mn_x (x ≤ 1) alloys were synthesized and their crystal structure, heat capacity, magnetic and magnetocaloric properties were studied. Single-phase compounds with the MgCu₂-type structure were formed at х < 0.4. In alloys with х > 0.4, additional phases with the PuNi₃- and Th₆Mn₂₃-type structures form. It was shown that there is a substantial increase in the Curie temperature and magnetic moment of 3d?metal sublattice of the nonstoichiometric compounds when compared to those of the TbCo₂ binary compound. The magnetocaloric effect of single- and multiphase alloys were estimated based on magnetic and heat capacity measurements.     

Self-Diffusion of Iron in Molten Fe-C Alloys

Self-diffusion coefficients of iron in molten Fe-C alloys have been measured by using the capillary method. In addition, the samples have been autoradiographed and sectioned to insure that no significant convection has occurred during the diffusion. The results can be represented by the equation D = 4.3×10^?3 exp (—12.200/RT) for carbon = 4.6 pct and T = 1513° to 1633°K; and D = 1.0×10^?2 exp (—15,700/RT) for carbon = 2.5 pct and T = 1613° to 1673°K. The D values are higher and the heat of activation for diffusion lower in alloys containing more carbon. Calculation based on the Einstein-Stokes equation indicates that the diffusing species is iron ion.     

Properties of the Ti<Subscript>40</Subscript>Zr<Subscript>10</Subscript>Cu<Subscript>36</Subscript>Pd<Subscript>14</Subscript> BMG Modified by Sn and Nb Additions

The results of investigation of the influence of additions of 2 and 3 at.% of Sn and simultaneously of Sn and 3 at.% Nb on microstructure and properties of the bulk metallic glasses of composition (Ti₄₀Cu_36?x Zr₁₀Pd₁₄Sn _x )_100?y Nb _y are reported. It was found that the additions of Sn increased the temperatures of glass transition (T _g), primary crystallization (T _x ), melting, and liquidus as well as supercooled liquid range (ΔT) and glass forming ability (GFA). The nanohardness and elastic modulus decreased in alloys with 2 and 3 at.% Sn additions, revealing similar values. The 3 at.% Nb addition to the Sn-containing amorphous phase decreased as well all the T _g, T _x , T _L, and T _m temperatures as ΔT and GFA; however, relatively larger values of this parameters in alloys containing larger Sn content were preserved. In difference to the previously published results, in the case of the amorphous alloys containing small Nb and Sn additions, a noticeable amount of the quenched-in crystalline phases was not confirmed, at least of the micrometric sizes. In the case of the alloys containing Sn or both Sn and Nb, two slightly different amorphous phase compositions were detected, suggesting separation in the liquid phase. Phase composition of the alloys determined after amorphous phase crystallization was similar for all compositions. The phases Cu₈Zr_3, CuTiZr, and Pd₃Zr were mainly identified in the proportions dependent on the alloy compositions.