Precipitation mechanism of an MoNi type intermetallic phase in W–27.0at.%Mo–35.6at.%Ni–17.6at.%Fe

For W–27.0Mo–35.6Ni–17.6Fe (at.%) sintered at 1500 °C for 240 min, an MoNi type intermetallic phase was formed during cooling, when either a water-quenching or furnace-cooling practice was employed. For the water-quenched specimen, a quasi-eutectic reaction took place, wherein the intermetallic phase precipitated directly from a eutectic liquid phase, which was super-saturated with W and Mo, in the form of a lamellar structure along with the Ni-based matrix phase. Accordingly, the intermetallic phase was located primarily in the interstices between the grains of the Ni-based matrix phase. On the other hand, for the furnace-cooled specimen, the intermetallic phase was formed by the peritectoid reaction between the Ni-based matrix phase and the W–Mo grains. The intermetallic phase thus existed primarily at the boundaries between the Ni-based matrix phase and the W–Mo grains.     

Evolution of the fine structure of Pd–5.3 at % Ιn–0.5 at % Ru solid solution after hydrogenation

Fine-structure parameters, such as the effective coherent domain size D_hkl and microstrain ε_hkl, of Ρd–5.3 at % Ιn–0.5 at % Ru alloy foil, which was subjected to electrolytic hydrogenation and subsequent prolonged (for 55000 h) relaxation, have been determined using X-ray diffraction data. The hydrogenation and subsequent relaxation of the alloy have been found to result in the refinement of coherent domains CD(hkl) and increase in the microstrains ε_hkl.     

Air Oxidation of Ni–Ti Alloys at 650–850°C

The oxidation of pure Ni and three Ni–Ti alloys containing 5, 10, and 15 wt.% Ti over the temperature range 650–850°C in air was studied to examine the effect of titanium on the oxidation resistance of pure nickel. Ni–5Ti is a single-phase solid solution, while the other two alloys consisted of nickel solid solution (-Ni) and TiNi₃. The oxidation of Ni–Ti alloys at 650°C follows an approximately parabolic rate law and produces a decrease in the oxidation rate of pure Ni by forming an almost pure TiO₂ scale. At higher temperatures, Ni–Ti alloys also follow an approximately parabolic oxidation, and their oxidation rates are close to or faster than those of pure Ni. Duplex scales containing NiO, NiTiO₃ and TiO₂ formed. Some internal oxides of titanium formed, especially at 850°C. In addition, the two-phase structure of Ni–10Ti and Ni–15Ti was transformed into a single-phase structure beneath the scales.     

Isothermal section of Al–Ti–Zr ternary system at 1073 K

Through alloy sampling combined with diffusion triple technique, phase equilibria in Al–Ti–Zr ternary system at 1073 K were experimentally determined with electron probe microanalysis (EPMA). Experimental results show that there is a solid solution β(Ti,Zr) which dissolves Al up to 16.3% (mole fraction). Ti and Zr can substitute each other in most Ti–Al and Al–Zr binary intermediate phases to a certain degree while the maximum solubility of Zr in Ti₃Al and TiAl reaches up to 17.9% and 4.0% (mole fraction), respectively. The isothermal section consists of 16 single-phased regions, 27 two-phased regions and 14 three-phased regions. No ternary phase was detected.     

Role of vacancies in the relaxation of Pd–5.3 at % In–0.5 at % Ru alloy foil after hydrogen desorption

The Pd–5.3 at % In–0.5 at % Ru foil subjected to electrolytic hydrogenation and subsequent prolonged relaxation (for 55 000 h) has been studied by X-ray diffraction analysis. Diffraction reflections belonging to phases with different indium concentrations and palladium phases enriched in vacancies were found. Phase transformations observed in the absence of hydrogen occur mainly due to the vacancy migration; the vacancies formed during hydrogenation and remained in vacancy complexes and alloy matrix up to the moment of the study.     

An investigation of Harper–Dorn creep at large strains

Harper–Dorn creep in Al was investigated under the condition of large strains (more than 0.1). In performing the investigation, two Al grades were creep tested at 923 K. The first grade is of 99.9995% purity (99.9995 Al) whereas the second grade is of 99.99% purity (99.99 Al). The results show that 99.99 Al, unlike 99.9995 Al, does not exhibit the Harper–Dorn creep at low stresses; and that the creep curves associated with Harper–Dorn creep in 99.9995 Al exhibit regular, periodic accelerations. An examination of the substructure developed during creep reveals that the details of the substructure in 99.99 Al are significantly different from those characterizing Harper–Dorn creep in 99.9995 Al. In 99.99 Al, an extensive, regular array of equiaxed subgrains is formed. By contrast, in 99.9995 Al, a wide range of substructural features including new grains, boundaries with high and low dislocation densities on opposite sides of the boundary, and localized regions of very high dislocation density, are observed. Consideration of the present data leads to three important findings. First, dynamic recovery is the dominant restoration mechanism during the creep of 99.99 Al, while dynamic recrystallization is the dominant restoration mechanism during the creep of 99.9995 Al. Second, the occurrence of Harper–Dorn creep in Al requires that two conditions be satisfied: high purity Al and very low dislocation density in the annealed samples (10³–3×10⁴ cm⁻²). Third, while the results verify the Newtonian nature of Harper–Dorn creep at small strains (less than 0.01), they indicate that under the condition of large strains (more than 0.1), the stress exponent is more than 2.     

Equilibrium phases at the Ir-rich corner of the Ir–Nb–Ni–Al quaternary system

The equilibrium phases of three Ir–Nb–Ni–Al quaternary alloys at the Ir-rich corner were investigated in some detail. The phases were determined by X-ray profile as well as microstructure observation. Three phases of fcc/L1₂-Ir₃Nb/B2-IrAl were found in two samples, and four phases of fcc/L1₂-Ir₃Nb/L1₂-Ni₃Al/B2-IrAl were characterized in one sample. The electron probe microanalysis (EPMA) technique was applied for analyzing the phase composition of this quaternary system. A partial quaternary phase diagram at the Ir-rich side was plotted according to the EPMA results.     

Constitution of the Mn–H system at high hydrogen pressures

The structure of Mn–H alloys was determined by X-ray diffraction under high hydrogen pressures and high temperatures, and a phase diagram was established over a wide range of p(H₂), T conditions. A new phase having a dhcp structure was found, and the stability of various phases was examined in particular relation to superabundant vacancy formation.     

Hydrogen embrittlement of Ti–49Al at various strain rates

The mechanical properties of a Ti–49Al alloy were investigated by tensile tests at different strain rates in vacuum, air, or a flowing hydrogen gas, before or after the specimens were exposed to a high temperature hydrogen gas. The results indicate that the strain rate hardly affect the tensile properties in a strain rate range of 5.6×10⁻⁶ to 2×10⁻⁴ s⁻¹. A large amount of the internal hydrogen decreases the ductility more than the external hydrogen. The internal hydrogen induces embrittlement by decreasing the cohesive strength of the lattice, whereas the external hydrogen embrittlement may be attributed to hydrogen-enhanced localized plastic deformation. The presence of a large amount of internal hydrogen increases the width of the stacking fault; that is, it decreases the stacking fault energy.     

Tensile Deformation of Iron Oxides at 600–1250°C

Tensile tests of virtually pure FeO, -Fe₃O₄, and -Fe₂O₃ were performed at 600–1250°C at strain rates of 2.0×10^–3–6.7×10^–5 s^–1 under controlled gas atmospheres. Mechanical properties and deformation/fracture behavior were investigated. For -Fe₂O₃, brittle fracture resulted at 1150–1250°C and the fracture strain was below 4.0% at a strain rate of 2.0×10^–4 s^–1. -Fe₃O₄ deformed plastically above 800°C. Steady-state deformation was indicated at 1200°C; elongation of 110% was obtained. Plastic deformation observed at 800 to 1100°C was considered to result from dislocation glide. Using TEM, the Burgers vector of dislocations observed in deformed -Fe₃O₄ was determined to be <110>, its slip system was estimated to be {111}<110>. FeO deformed plastically above 700°C. Steady-state deformation became predominant above 1000°C. Elongation of 160% was obtained at 1200°C. Strain rates of FeO at 1000°C and 1200°C were proportional to the fourth power of the saturated stress, indicating that plastic deformation was affected by dislocation climb.     

Creep- and coarsening properties of Al–0.06 at.% Sc–0.06 at.% Ti at 300–450 °C

Upon aging at 300–450 °C, nanosize, coherent Al₃(Sc_1−xTi_x) precipitates are formed in pure aluminum micro-alloyed with 0.06 at.% Sc and 0.06 at.% Ti. The outstanding coarsening resistance of these precipitates at these elevated temperatures (61–77% of the melting temperature of aluminum) is explained by the significantly smaller diffusivity of Ti in Al when compared to that of Sc in Al. Furthermore, this coarse-grained alloy exhibits good compressive creep resistance for a castable, heat-treatable aluminum alloy: the creep threshold stress varies from 17 MPa at 300 °C to 7 MPa at 425 °C, as expected if the climb bypass by dislocations of the mismatching precipitates is hindered by their elastic stress fields.     

Kinetics of the hydration reaction at the electrolyte–insulator interface

The instability of the dc operating point in the pH-sensitive ion-selective field effect transistors (ISFETs) has been ascribed to a chemical ageing at the electrolyte–insulator. This instability, commonly referred to as a drift, is believed to involve formation of a chemically-modified insulator surface layer as a result of hydration of the insulator material. A kinetic model for hydration of the amorphous insulator material is presented. The kinetics of hydration is limited by the hopping and/or trap-limited transport mechanism known as dispersive transport, the key characteristic of which is a power-law time dependence of the diffusion coefficient. The power-law time dependence of the diffusion coefficient will be shown to lead to a stretchedexponential decay in the form exp[–(t/τ)^β] for the excess density of sites or traps occupied by the hydrating chemical species undergoing dispersive diffusion, where τ is the time constant associated with a structural relaxation and β is the dispersion parameter satisfying 0 < β < 1. The kinetics associated with a hydration reaction limited by the dispersive diffusion has been shown to lead to a hydrated layer thickness exhibiting a time dependence in the form {1–exp[–(t/τ)^β]}. The first order rate equation describing the kinetics of the hydration reaction is characterized by the time-dependent rate coefficient.     

Experimental Investigation of the Mg–Zn–Zr Isothermal Section at 400 °C

Mg-Zn-Zr series Mg alloys(ZK) are one of the most important commercial Mg alloys due to their good comprehensive mechanical properties. The phase equilibria of the Mg-Zn-Zr system at 400 ℃ covering the overall composition range were investigated by X-ray diffraction and electron probe microanalyses on thirteen ternary alloys. Three ternary compounds, τ_1, τ_2 and τ_3, were detected to be thermodynamically stable at 400 ℃, and their homogeneity range was determined to be Mg_((7-17))Zn_((80-88))Zr_((4-6)), Mg_((15-22))Zn_((66-65))Zr_((9-16)) and Mg_9 Zn_(68)Zr_(23)(in at.%), respectively. Eight three-phase regions and four two-phase regions were observed. The maximum solubility of Mg in Zn_(22) Zr, Zn_(39) Zr_5 and Zn_3 Zr phases was measured to be 0.52, 0.37 and 0.99 at.%, respectively, while the solubility of Zr in MgZn_2 and Mg_2 Zn_3 phases is negligible. The isothermal section of the Mg-Zn-Zr system at 400 ℃ was then constructed based on the present experimental data.     

Air Oxidation of Two Nanophase Ni–Ag Alloys at 600–700°C

Two nanophase Ni-base alloys containing 50 and 25 at.% Ag prepared by mechanical alloying, denoted Ni–50Ag and Ni–25Ag were oxidized in air at 600 and 700°C for 24 hr. Ni–50Ag underwent internal oxidation of nickel, associated with the formation of a continuous outermost layer of silver metal with scaling rates larger than those for pure nickel. On the contrary, Ni–25Ag formed a continuous NiO layer surmounted by a discontinuous silver layer and internal oxidation was suppressed. The oxidation rate of Ni–25Ag decreased with time much more rapidly than predicted by the parabolic rate law during the initial stage and eventually became parabolic, with rate constants much lower than those for the oxidation of pure nickel. These results are attributed to the two-phase nature and, particularly, to the very small grain size of the two alloys.     

Aging precipitation behavior and properties of Al–Zn–Mg–Cu–Zr–Er alloy at different quenching rates

The effect of quenching rate on the aging precipitation behavior and properties of Al–Zn–Mg–Cu–Zr–Er alloy was investigated. The scanning electron microscopy, transmission electron microscopy, and atom probe tomography were used to study the characteristics of clusters and precipitates in the alloy. The quench-induced η phase and a large number of clusters are formed in the air-cooled alloy with the slowest cooling rate, which contributes to an increment of hardness by 24% (HV 26) compared with that of the water-quenched one. However, the aging hardening response speed and peak-aged hardness of the alloy increase with the increase of quenching rate. Meanwhile, the water-quenched alloy after peak aging also has the highest strength, elongation, and corrosion resistance, which is due to the high driving force and increased number density of aging precipitates, and the narrowed precipitate free zones.     

Formation of nanoquasicrystalline Al–Cu–Fe coatings at electron beam physical vapour deposition

Coatings with a quasicrystalline Al–Cu–Fe structure were formed during high rate (∼100 nm/s) electron beam deposition of the vapour phase at substrate temperatures in a range of 100–800 °C. Features of the structure and some mechanical properties of quasicrystalline coatings obtained at the reducing of substrate temperature were studied.     

The isothermal section at 450°C of the Yb–Pr–Mg system

In the framework of a systematic investigation of the ternary alloys formed by magnesium with two different metals of the rare earth family, data obtained in a study of the Yb–Pr–Mg system are presented. In the isothermal section at 450°C, phases have been identified which are based on the ternary extensions of the binary compounds PrMg, PrMg₃, Pr₅Mg₄₁ and YbMg₂. The PrMg₁₂ compound on the contrary shows very small ternary solid solubility. Two ternary compounds have also been identified: τ₁, (Yb_xPr_1-x)Mg₂ (0.15⩽x⩽0.48), cF24–MgCu₂ Laves type and τ₂,≈(Yb_xPr_1-x)Mg_4.5 (0.12⩽x⩽0.40), cF440–GdMg₅ type. The trends of the lattice parameters and the general features of the isothermal section are discussed and compared with those of other magnesium ternary alloys with rare earth elements. The behaviour of the different MeMg₂ Laves phases is particularly highlighted.     

Deformation of a multiphase Mo–9.4Si–13.8B alloy at elevated temperatures

A 3-phase silicide alloy, Mo–9.4Si–13.8B (at.%), was prepared via powder metallurgy techniques. The tensile properties of the alloy at elevated temperatures were evaluated in vacuum at temperatures ranging from 1350 to 1550°C and strain rates ranging from 5.0×10⁻⁴ to 1×10⁻³ s⁻¹. The alloy was found to exhibit a stress exponent of about 2.8 and relatively a high activation energy 740 kJ/mol. Also, it displayed unusually large tensile ductility (>100%) at T>1400°C. The deformation mechanism as well as large ductility are discussed in the light of the microstructural observations. The alloy has a very good mechanical strength at elevated temperatures, comparable to some of the most advanced tungsten-based alloys.     

Cyclic-Oxidation Behavior of Fe–20Cr–4Al Alloys with Small Amounts of Sulfur at High Temperatures

The cyclic-oxidation behavior of Fe–20Cr–4Al alloys with 3, 35, 53, 104, and 171 ppm sulfur was studied in oxygen at 1273, 1373, 1473, 1573, and 1673 K by mass-change measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron-probe microanalysis (EPMA). The cyclic oxidation consisted of an 18.0 ksec exposure that was repeated up to five times. Amounts of spalled oxides of the alloys with 35 and 53 ppm sulfur increased after one and two oxidation cycles, and then decreased after three or more oxidation cycles at 1473 and 1573 K. On the other hand, spalling of oxide scales on the alloys with 3 and 171 ppm sulfur was scarcely recognized after all cycles used in this study. SEM observations of both sides of the spalled oxides indicated that spallation was related to the morphology of the surface oxides and to the morphology and volume of cavities at the oxide–alloy interface.     

The isothermal section of the phase diagram of the Dy–Mn–Ni ternary system at 803 K

The isothermal section of the phase diagram of the ternary system Dy–Mn–Ni system at 803 K was investigated by powder X-ray diffraction (XRD), differential thermal analysis (DTA), optical microanalysis and electron probe microanalysis techniques. It consists of 13 single-phase regions, 22 two-phase regions and 10 three-phase regions. At 803 K, the maximum solid solubilities of Mn in Ni, Dy₂Ni₁₇, DyNi₅, Dy₂Ni₇, DyNi₃, DyNi, Dy₃Ni₂ and Dy₃Ni are about 31at.% Mn, 6 at.% Mn, 5.5 at.% Mn, 3 at.% Mn, 5 at% Mn, 5 at.% Mn, 3 at.% Mn and 1.5 at.% Mn, respectively. The maximum solid solubilities of Ni in Mn, DyMn₁₂ and Dy₆Mn₂₃ are about 2.6 at.% Ni, 2 at.% Ni and 4 at.% Ni, respectively. DyMn₂ and DyNi₂ form a continous solid solution in this system. The binary compounds DyNi₄ and Dy₄Ni₁₇ were not observed in this work. The existence of any ternary compound was not observed.