Creep Properties of Directionally Solidified Nb-Modified Ni-Base Superalloy,Mar-M247

The Ni-base superalloy Mar-M247 is widely used for elevated-temperature applications in both equiaxed and directionally solidified forms. The alloy contains about 3 wt.% Ta. Due to the cost and density of Ta, an atom-for-atom substitution of Nb for Ta was investigated. The creep properties in the temperature range of 750-950?°C and stresses ranging from 200 to 1000 MPa were determined. In general, the creep properties of the Nb-modified Mar-M247 material were very similar to those of Mar-M247 samples at 750 and 850?°C. However, the Mar-M247 samples exhibited superior creep properties at 950?°C. The lower creep properties of the Nb-modified Mar-M247 are likely due to the finer starting microstructure, more rapid coarsening rate of the γ′ and reduced γ′ strengthening effect (i.e., APB energy) of Nb, compared to Ta. No evidence of TCP phases was observed in either alloy.     

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.     

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.     

Experimental Investigation and Thermodynamic Calculation of the Phase Equilibria in the Co-Cu-V Ternary System

The phase equilibria of the Co-Cu-V ternary system at 900, 1000, 1100 and 1200 °C have been experimentally determined by optical microscopy and electron probe micro-analysis of the equilibrated alloys. The phase transformations were investigated by means of the differential scanning calorimetry. Based on the experimental data of phase equilibria and thermodynamic properties, the thermodynamic assessment of the Co-Cu-V ternary system was carried out by using the calculation of phase diagrams method. A consistent set of the thermodynamic parameters leading to reasonable agreement between the calculated results and experimental data was obtained in the Co-Cu-V ternary system. Meanwhile, the calculated results show that the critical temperature of metastable magnetically induced miscibility gap of (α _f Co) and (α _p Co) phases in the Co-V system gradually decreases with increasing Cu composition in the range of 0-3 wt.% additions.     

The Microstructure and Gamma Prime Distributions in Inertia Friction Welded Joint of P/M Superalloy FGH96

A gamma prime (γ′) precipitation (~35% in volume)-hardened powder metallurgy (P/M) superalloy FGH96 was welded using inertia friction welding (IFW). The microstructure and γ′ distributions in the joints in two conditions, hot isostatic pressed state and solution-treated and aged state, were characterized. The recrystallization of grains, the dissolution and re-precipitation of γ′ in the joints were discussed in terms of the temperature evolutions which were calculated by finite element model analysis. Regardless of the initial states, fully recrystallized fine grain structure formed at welded zone. Meanwhile, very fine γ′ precipitations were re-precipitated at the welded zone. These recrystallized grain structure and fine re-precipitated γ′ resulted in increasing hardness of IFW joint while making the hardness dependent on the microstructure and γ′ precipitation.     

Composition dependences of thermodynamical properties associated with Pb-free ternary,quaternary, and quinary solder systems

In the present study, Chou’s General Solution Model (GSM) has been used to predict the enthalpy and partial enthalpies of mixing of the liquid Ag–In–Sn ternary, Ag–In–Sn–Zn quaternary, and Ag–Au–In–Sn–Zn quinary systems. These are of technical importance to optimize lead-free solder alloys, in selected cross-sections: x_In/x_Sn = 0.5/0.5 (ternary), Au–In_0.1–Sn_0.8–Zn_0.1, Ag–In_0.1–Sn_0.8–Zn_0.1 (quaternary), and t = x_Au/x_In = 1, x_In = x_Sn = x_Zn (quinary) at 1173, 773, and 773 K, respectively. Moreover, the activity of In content in the ternary alloy system Ag–In–Sn has been calculated and its result is compared with that determined from the experiment, while the activities of Ag contents associated with the alloys mentioned above have been calculated. The other traditional models such as of Colinet, Kohler, Muggianu, Toop, and Hillert are also included in calculations. Comparing those calculated from the proposed GSM with those determined from experimental measurements, it is seen that this model becomes considerably realistic in computerization for estimating thermodynamic properties in multicomponent systems.     

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.     

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.     

Influence of Zinc on Coarsening of δ-Ni<Subscript>2</Subscript>Si Particles,Aging Behavior and Hardness in a Cu-Ni-Si Alloy

In the present paper, the aging precipitation and coarsening of disk-like δ-Ni₂Si particles in Cu and Cu-10Zn alloys aged at 450 °C have been investigated by hardness, electric resistivity measurement and transmission electron microscopy observation. The coarsening dynamics of the average diameter of the δ-Ni₂Si particles coincides with the t ^1/3 time law for both alloys. The coarsening of the diminution of supersaturation related to aging time t coincides with the t ^?1/3 time rule. Adding Zn to the Cu-Ni-Si alloy increases the growth and coarsening rate of the particles mainly because of the increased diffusivity D of the δ-Ni₂Si particles in the matrix. The value of D of the δ-Ni₂Si particles in the Cu-xZn (x = 0, 10 wt.%) matrix and the Cu/δ-Ni₂Si interfacial energy γ are independently calculated by using the Lifshitz–Slyozov–Wagner theory which was extended to include disk-like particles by Boyd and Nicholson. The values of D and γ increase from 0.77 × 10^?19 to 2.21 × 10^?19 m²/s and 0.19 to 0.63 J/m², respectively, when Zn is added to the Cu-Ni-Si alloy. These calculations and the analysis show that the properties of Cu-Ni-Si-Zn alloy can significantly be enhanced by reducing the aging temperature.     

Effect of Si and Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Additions on the Oxidation Behavior of Ni–<Emphasis Type="Italic">x</Emphasis>Al (<Emphasis Type="Italic">x</Emphasis> = 5 or 10 wt%) Alloys at 1150 °C

The effect of Si and Y₂O₃ additions on the oxidation behavior of Ni–xAl (x = 5 or 10 wt%) alloys at 1150 °C was studied. The addition of Y₂O₃ accelerates oxidation rate of alloys, especially growth rate of NiO, but improves adherence of the scale to the substrate. The addition of Si facilitates the selective oxidation of Al, suppresses the formation of NiO and therefore reduces the critical Al content to form continuous layer of alumina scale. Higher Al content decreases the oxidation rate of alloys in binary Ni–Al alloys and increases the oxidation rate of alloys in ternary Ni–Al–Si alloys. The effect of third-element Si is more significant and beneficial than that of Al content in ternary Ni–Al–Si alloys.     

A Study of Tensile Flow and Work-Hardening Behavior of Alloy 617

The simple power relationship σ?=?Κε _p ⁿ satisfactorily expresses the tensile flow behavior of many metals and alloys in their uniform plastic strain regime. However, many FCC materials with low stacking fault energy have opposed such power law relationship. Alloy 617, an age-hardenable Ni-based superalloy is also observed not to obey the simple power law relationship neither in its solution-treated nor in its aged conditions. Various flow relationships were used to obtain the best fit for the tensile data, and different relationships were identified for the different aged conditions. The work-hardening rate (θ) demonstrates three distinct regions for all aged conditions, and there is an obvious change in the trend of θ versus σ. In the initial portion, θ decreases rapidly followed by a gradual increase in the second stage and again a decrease in its third stage is perceived in the Alloy 617. These three-stage characteristics are attributed to a commonly known precipitate, γ′: Ni₃(Ti, Al) which evolves during aging treatment and well recognized under transmission electron microscopy (TEM) observation. TEM results also reveal a slight degree of coarsening in γ′ over aging. The tensile flow and the work-hardening behavior are well correlated with other microstructural evolution during the aging treatments.     

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.     

Phase Equilibria in the Cu-Sn-Sb Ternary System

The phase equilibria in the Cu-Sn-Sb ternary system were investigated by means of electron-probe microanalysis and x-ray diffraction. Firstly, ternary solubilities of η-Cu₆Sn₅, δ-Cu₄₁Sn₁₁, Cu₁₁Sb₃, ε-Cu₃Sb and η-Cu₂Sb, were less than 7 at.% Sb or Sn at 400 °C. Besides, an re-stabilized ternary solubility, Cu₆(Sn,Sb)₅, was detected with a homogeneity range of Cu: 52.9-53.3 at.%, Sn: 28.4-30.9 at.%, and Sb: 15.8-18.7 at.%. Its origin was traced back to high-temperature stabilization of the binary η-Cu₆Sn₅ phase. Thirdly, the metastable phase, Cu₁₁Sb₃, was observed at 400 °C in the Cu-Sn-Sb ternary system; On raising the temperature to 500 °C, the ε-Cu₃Sn phase still retained a large solubility for Sb, at?~?16 at.%, while the ε-Cu₃Sb was replaced by β-Cu₃Sb with a dual-cornered large homogeneity range. Similarly, a ternary homogeneity range of Cu: 83.8-84.9 at.%, Sn: 2.6-6.2 at.%, and Sb: 9-12.5 at.%, was found and deduced to be the high temperature stabilization phase of γ-Cu₁₁(Sb,Sn)₂ at 500 °C.     

High Pressure Oxidation of Metals: Tantalum in Oxygen

The temperature and pressure dependence of the reaction of tantalum in oxygen were investigated from 500° to 1000°C at pressures from 10 mm Hg to 600 psi total oxygen pressure. Tantalum was found to oxidize linearly under the above conditions. Three distinct regions of temperature dependence were found with different energies of activation. From 500° to 600°C the rate of oxidation of tantalum was found to be essentially independent of the oxygen pressure at the pressure investigated. The oxidation rate increases rapidly with an increase in pressure from 600° to 800°C. The dependence of the oxidation rate on the bulk concentration may be expressed by V = k′θ, where k′ is the specific rate constant and \(\theta=k_1C_{\text{O}_{2}}/(1\;+\;k_1C_{\text{O}_{2}})\), where k₁is the equilibrium constant for the adsorption of oxygen on tantalum.     

Microstructure,Phase Occurrence,and Corrosion Behavior of As-Solidified and As-Annealed Al-Pd Alloys

In the present work, we studied the microstructure, phase constitution, and corrosion performance of Al₈₈Pd₁₂, Al₇₇Pd₂₃, Al₇₂Pd₂₈, and Al₆₇Pd₃₃ alloys (metal concentrations are given in at.%). The alloys were prepared by repeated arc melting of Al and Pd granules in argon atmosphere. The as-solidified samples were further annealed at 700 °C for 500 h. The microstructure and phase constitution of the as-solidified and as-annealed alloys were studied by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction. The alloys were found to consist of (Al), ε _n (~ Al₃Pd), and δ (Al₃Pd₂) in various fractions. The corrosion testing of the alloys was performed in aqueous NaCl (0.6 M) using a standard 3-electrode cell monitored by potentiostat. The corrosion current densities and corrosion potentials were determined by Tafel extrapolation. The corrosion potentials of the alloys were found between ? 763 and ? 841 mV versus Ag/AgCl. An active alloy dissolution has been observed, and it has been found that (Al) was excavated, whereas Al in ε _n was de-alloyed. The effects of bulk chemical composition, phase occurrence and microstructure on the corrosion behavior are evaluated. The local nobilities of ε _n and δ are discussed. Finally, the conclusions about the alloy’s corrosion resistance in saline solutions are provided.     

Analysis of Plastic Flow Instability During Superplastic Deformation of the Zn-Al Eutectoid Alloy Modified with 2 wt.% Cu

The aim of this work is to analyze the plastic flow instability in Zn-21Al-2Cu alloy deformed under 10^?3 s^?1 and 513 K, which are optimum conditions for inducing superplastic behavior in this alloy. An evaluation using the Hart and Wilkinson–Caceres criteria showed that the limited stability of plastic flow observed in this alloy is related to low values of the strain-rate sensitivity index (m) and the strain-hardening coefficient (γ), combined with the tendency of these parameters to decrease depending on true strain (ε). The reduction in m and γ values could be associated with the early onset of plastic instability and with microstructural changes observed as function of the strain. Grain growth induced by deformation seems to be important during the first stage of deformation of this alloy. However, when ε > 0.4 this growth is accompanied by other microstructural rearrangements. These results suggest that in this alloy, a grain boundary sliding mechanism acts to allow a steady superplastic flow only for ε < 0.4. For ε values between 0.4 and 0.7, observed occurrences of microstructural changes and severe neck formation lead to the supposition that there is a transition in the deformation mechanism. These changes are more evident when ε > 0.7 as another mechanism is thought to take over.     

Microstructure and Mechanical Properties of Mg-8Li-(0, 1, 2)Ca-(0, 2)Gd Alloys

A series of new Mg-8Li-xCa-yGd (x = 0, 1, 2; y = 0, 2; wt.%) alloys were prepared, and the microstructure and mechanical properties were investigated. The mechanical properties were characterized by tensile, compression and bending tests at room temperature. The results show that Mg-8Li-1Ca alloy is composed of alpha(Mg), beta(Li) and CaMg₂ phases. In addition to the same phases in Mg-8Li-1Ca, there also exists CaLi₂ phase in Mg-8Li-2Ca. In addition to the same phases in Mg-8Li-2Ca, GdMg₅ phase is also formed in Mg-8Li-1Ca-2Gd alloy due to the addition of Gd. Both Ca and Gd have refining effect in the alloys, and the refining effect of Ca is better than that of Gd. The additions of Ca and Gd can improve the tensile strength and yield strength, but decrease the elongation and the bending strength. Comparing the mechanical properties of the investigated alloys, Mg-8Li-1Ca-2Gd possesses the best mechanical properties.     

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.     

Microstructure and Room-Temperature Mechanical Properties of FeCrMoVTi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> High-Entropy Alloys

FeCrMoVTi _x (x values represent the molar ratio, where x = 0, 0.5, 1.0, 1.5, and 2.0) high-entropy alloys were prepared by a vacuum arc melting method. The effects of Ti element on the microstructure and room-temperature mechanical properties of the as-cast FeCrMoVTi _x alloys were investigated. The results show that the prepared alloys exhibited typical dendritic microstructure and the size of the microstructure became fine with increasing Ti content. The FeCrMoV alloy exhibited a single body-centered cubic structure (BCC1) and the alloys prepared with Ti element exhibited BCC1 + BCC2 mixed structure. The new BCC2 phase is considered as (Fe, Ti)-rich phase and was distributed in the dendrite region. With the increase of Ti content, the volume fraction of the BCC2 phase increased and its shape changed from a long strip to a network. For the FeCrMoV alloy, the fracture strength, plastic strain, and hardness reached as high as 2231 MPa, 28.2%, and 720 HV, respectively. The maximum hardness of 887 HV was obtained in the FeCrMoVTi alloy. However, the fracture strength, yield stress, and plastic strain of the alloys decreased continuously as Ti content increased. In the room-temperature compressive test, the alloys showed typical brittle fracture characteristics.     

Hot Deformation Mechanisms of an As-Extruded TiAl Alloy with Large Amount of Remnant Lamellae

The hot deformation mechanisms of an as-extruded Ti-44Al-5V-1Cr alloy with a large amount of remnant lamellae were investigated by hot compression tests at temperatures of 900-1250 °C and strain rates of 0.001-1 s^?1. The hot processing map of the as-extruded Ti-44Al-5V-1Cr alloy was developed on the basis of dynamic materials modeling and the Prasad criteria. There were four different domains in the hot processing map, according to the efficiency of power dissipation, η. The flow soft and hot deformation mechanisms for different domains were illustrated in the context of microstructural evolution during the process of deformation. As a result, the dynamic recrystallization and superplastic deformation occurred at 1125-1150 °C near 0.001 s^?1, and this region is suitable for superplastic forming. The α phase dynamic recrystallization and dynamic recovery occurred at 1250 °C and 0.1 s^?1. The existence of small amount of the γ and β phases effectively inhibited the growth of α grains.