Atom probe tomography of the evolution of the nanostructure of oxide dispersion strengthened steels under ion irradiation

The atom probe tomography of the nanostructure evolution in ODS¹ Eurofer, ODS 13.5Cr, and ODS 13.5Cr–0.3Ti steels under heavy ion irradiation at 300 and 573 K is performed. The samples were irradiated by 5.6 MeV Fe²⁺ ions and 4.8 MeV Ti²⁺ ions to a fluence of ~10¹⁵ cm^–2. It is shown that the number of nanoclusters increases by a factor of 2–3 after irradiation. The chemical composition of the clusters in the steels changes after irradiation at 300 K, whereas the chemical composition of the clusters in the 13.5Cr–0.3Ti ODS steel remains the same after irradiation at 573 K.     

Transmission electron microscopy study of the heavy-ion-irradiation-induced changes in the nanostructure of oxide dispersion strengthened steels

Transmission electron microscopy was used to study the effect of heavy-ion irradiation on the structure and the phase state of three oxide dispersion strengthened (ODS) steels: ODS Eurofer, ODS 13.5Cr, and ODS 13.5Cr–0.3Ti (wt %). Samples were irradiated with iron and titanium ions to fluences of 10¹⁵ and ~3 × 10¹⁵ cm^–2 at 300, 573, and 773 K. The study of the region of maximum radiation damage shows that irradiation increases the number density of oxide particles in all samples. The fraction of fine inclusions increases in the particle size distribution. This effect is most pronounced in the ODS 13.5Cr steel irradiated with titanium ions at 300 K to a fluence of 3 × 10¹⁵ cm^–2. It is demonstrated that oxide inclusions in ODS 13.5Cr–0.3Ti and ODS 13.5Cr steels are more stable upon irradiation at 573 and 773 K than upon irradiation at 300 K.     

Low temperature dielectric study on swift heavy ion irradiated 6H-SiC crystals

The effect of 150 MeV Ag¹²⁺ ion irradiation on the electrical behavior of 6H-SiC crystals has been studied by impedance spectroscopy. The study was carried out on the pristine, 8 ′ 10¹² ions/cm² and irradiated at 300 K and 80 K respectively. The present study elucidates the divergence of defect introduction due to irradiation at different temperatures through the electric polarizability and conductivity. The frequency and temperature dependent dielectric dispersions observed for the sample irradiated with 8 × 10¹² ions/cm² at 300 K are observed to be more than those of the sample irradiated at 80 K. The study reflects that more defects are produced in the case of 8 × 10¹² ions/cm² at 300 K irradiated sample than the sample irradiated with 8 × 10¹² ions/cm² at 80 K. The ac conductivity measured at 1 kHz over a temperature range from 100 – 300 K showed that complex defects are produced at 300 K for the swift heavy ion irradiated samples.     

Thermodynamic aspects of the selection of sulfur-containing collectors during flotation of sulfide ores

Investigations into the complexing ability of sulfur-containing collectors relative to metal ions (Cu²⁺, Ni²⁺, Fe²⁺, Co²⁺) at 298 K and an ion force of 0.075–0.75 mol/L (NaNO₃) are carried out. It is established that potassium dibutyl dithiophosphate possesses the largest affinity to metal ions among phosphorus-containing collectors, while the maximal complexing ability is characteristic of the Co²⁺ ion. Series of thermal stability are found; the variations in enthalpy, entropy, and the Gibbs energy, as well as temperature-dependent and temperature-independent contributions of complexes of metal ions with collector anions into ΔG ⁰, are calculated.     

Nano-scale Mechanical Properties and Microstructure of Irradiated X-750 Ni-Based Superalloy

This study investigates the effect of irradiation on the mechanical properties of a Ni-based superalloy, X-750. 40 MeV Ni⁺ ions were used to irradiate the X-750 up to 1 dpa with and without 5000 appm helium pre-implantation at room temperature and 400 °C. Nano-indentation hardness tests were carried out at room temperature in the depth range of 200 to 1400 nm before and after irradiation. Cross-sectional TEM observations were performed on the irradiated materials to correlate the mechanical results with the microstructural evolution. The results show that helium pre-implantation enhances the irradiation-induced hardening due to generating a high density of small cavities and promoting the formation of larger Frank loops. In addition, nano-scale mechanical tests reveal that changing the subsequent Ni ion irradiation temperature from room temperature to 400 °C, leads to changing of the mechanical response from a softening behavior to an irradiation-induced hardening. The γ′ precipitates became disordered after irradiation at room temperature, whereas the γ′-phase remained ordered during irradiation at 400 °C. The softening effect of the γ′ instability outweighed the hardening impact of irradiation-induced defects such as cavities and Frank loops, leading to a hardness reduction for the room-temperature-irradiated material. Three different obstacle-hardening models were employed to assess the individual impact of each type of defect on the material’s overall strength enhancement. Furthermore, the superposition principle was used for each model to estimate the overall irradiation-induced strengthening, which is compared to the results from the nano-hardness measurements.     

Order-disorder transformations in Ni4Mo under self ion irradiation

The order-disorder transformation has been studied in Ni₄Mo under cascade forming 300 keV Ni⁺ ion irradiation in the temperature range 300–1050 K. The progressive changes in the short range ordered (SRO) and the long range ordered (LRO) structures and the steady state structures developed at different temperatures have been characterized by electron diffraction and imaging. At temperatures below 450 K, both SRO and LRO completely disorders, between 450 and 1000 K LRO is destroyed but SRO survives and above 1000 K LRO persists. Based on these observations a steady state diagram is constructed and compared with that reported for electron irradiation. The essential difference between the influence of cascade forming and non cascade forming irradiation on the order-disorder transformation has been discussed.     

Lead and nickel distribution in the Cup-PbO-SiO2 and the Cup-NiO-SiO2 Systems equilibrated with liquid copper

The distribution of lead and of nickel between molten copper and a ternary cuprous oxide-metal oxide-silica saturated slag was measured at 1498 K. The results are correlated using ion fractions, calculated either according to Temkin’s method, or as electrically equivalent ion fractions. The simpler method suggested by Temkin correlates slightly better than the other giving the following relations between the ionic concentration quotients and impurity concentration in the metal: logN _Pb ⁺⁺/N ² _Cu ⁺ = logX _Pb + 2.40 ± 0.05, valid up toX _Pb = 0.003 logN _Ni ⁺⁺/N ² _Cu ⁺ = 0.44 logX _Pb + 0.15 ± 0.07, valid up toX _Ni = 0.004. In the nickel systems, an Ni rich phase, identified as NiO, separates from the metal at X_Ni = 0.04 (0.4 wt pct). A tentative phase diagram of the Cu₂O-NiO-SiO₂ system at 1498 K is presented. The data found in this investigation explain why the impurities Pb or Ni cannot be practically reduced to low levels by oxidation. This results from the large amounts of copper that are oxidized in going to low impurity levels. Use of a two-slag refining process is shown to cut slag losses of copper to less than half those encountered with a single slag operation.     

Transformation to Ni5Al3 in a 63.0 At. Pct Ni-Al alloy

Microstructures in a 63 at. pct Ni-Al alloy, produced by a powder metallurgy process, have been investigated in detail in as-quenched and aged (823 to 923 K) conditions. The parent L1₀ martensite plus B₂ NiAl microstructure in the as-quenched state transformed nearly completely to the orthorhombic Ni₅Al₃ phase upon aging at 823 K for 720 hours. The volume fraction of Ni₅Al₃ formed as a function of aging time at 823 K was observed to obey cellular reaction kinetic behavior. The specimens aged at 823 K for short times indicated that nucleation of the Ni₅Al₃ phase occurred preferentially at grain boundaries. Transmission electron microscopy (TEM) observations of short-time aged specimens revealed a complex microstructure consisting of shortrange ordered domains of Ni₂Al in a matrix of 7R martensite, in addition to new variants of 3R martensite and Ni₅Al₃. Aging at 873 and 923 K for 720 hours produced a stable two-phase microstructure consisting of NiAl and Ni₅Al₃. A quantitative phase analysis was carried out to calculate the (NiAl + Ni₅Al₃)/Ni₅Al₃ phase boundary locations. The measured lattice parameters of Ni₅Al₃ formed at 823, 873, and 923 K indicated an increase in tetragonality of the phase with increasing nickel content. Formerly with Case Western Reserve University Formerly with Case Western Reserve University     

Nickel and nitrogen ion irradiation induced void swelling and defect microstructures in Ni-Al,Ni-Cr and Ni-Ti solid solutions

The effects of solute content, temperature, and irradiation dose on the void swelling characteristics of pure nickel and several nickel base solid solutions (Ni-Al and Ni-Ti containing up to 8 at. pct solute and Ni-Cr containing up to 16 pct Cr) have been iN_vesti-gated. Samples were irradiated in the temperature range 400 to 650°C to a maximum dose of 70 dpa using 3.5 MeV⁵⁸Ni⁺, 400 keV¹⁴N⁺ and 400 keV¹⁴N⁺ ₂ ions. The irradiation in-duced microstructures were studied using transmission electron microscopy. In general, the addition of Al, Cr or Ti to Ni is found to decrease the void swelling and mean void diameter and to increase the dislocation density. The behavior of the void number den-sity, N_v, as a function of solute content is found to be dependent upon the irradiation con-ditions as well as the particular solute addition. N_v passes through a maximum at approxi-mately 2 pct solute content for Ni-AI and Ni-Cr alloys irradiated at 550°C, but through a minimum at 4 pct for Ni-Ti alloys irradiated at 550 and 600°C. N_v decreases monotoni-cally as a function of Al content at 600 and 650°C. The results are discussed in terms of recent theories of void swelling suppression due to impurity or solute additions and in light of several correlations between void swelling and material parameters. The be-havior of N_v is found to be best described by the actions of two compcting processes. The first enhances void nucleation, is not strongly temperature dependent and is dominant at low solute contents. The second suppresses void swelling, is probably diffusion con-trolled and dominates in the more concentrated alloys. R.F.PINIZZOTTO, JR., formerly Graduate student, UCLA, This paper is based on a presentation made at a symposium on “Radiation Induced Atomic Rearrangements in Ordering and Clustering Alloys” held at the annual meeting of the AIME, Atlanta, Georgia, March 7 to 8, 1977, under the sponsorship of the Physical Metallurgy and Nuclear Metallurgy Committees of     

Microstructural evolution in high energy helium implanted nickel—I. Room temperature (t − 100°c) implantation

Nickel foils of about 12 μm thickness have been homogeneously implanted with 0 to 6 MeV He ions at room temperature. For helium concentrations ranging between 0.1 and 5 at.% the implantation induced changes of the microstructure have been investigated by measurements of the electrical resistivity, the length and the lattice parameter and by transmission electron microscopy (TEM). Beginning from the lowest implantation dose clustering of irradiation induced vacancies and self-interstitial atoms leads to the formation of stacking fault tetrahedra (SFT), dislocation loops and of a dislocation network. In addition a large number of small He-vacancy complexes is present that are invisible in the TEM at low He concentrations, c_He, and can be identified as small cavities for c_He ≳ 0.7 at.%. The He-vacancy complexes are characterized by a He-density that is rather low compared to the density necessary to activate the loop punching mechanism for bubble growth: i.e. c_He is about one half of the vacancy concentration c_V for c_He ≲ 0.8 at.%. At higher implantation doses the ratio c_He/c_V increases slowly up to a value of 1.4. Hence, the limiting pressure for loop punching may be obtained only for c_He ≈ 8 at.%. A “model” is proposed that describes this microstructural evolution by the continuous nucleation of stable He-vacancy complexes as a result of high energy collision cascades. This model directly explains the low average helium density observed during the early stages as well as the coexistence of small cavities and SFT's. A saturation of the bubble density at high doses and the slow increase of the He density in bubbles might be understood by cascade overlap.     

The precipitation of Ni3S2 from sulfate solutions

The formation conditions for the recovery of nickel from sulfate solutions as Ni3S2 have been investigated; this sulfide is more reactive than NiS in subsequent leaching operations. Hydrogen sulfide gas at atmospheric pressure is introduced into a NiSO4-Na2SO4-MgSO4-Al2(SO4)3 solution in the presence of reduced iron powder. Although the formation of Ni3S2 is compctitive with that of NiS, the nickel precipitation efficiency and the ratio of nickel as Ni3S2 to the total nickel precipitated reached 99.5 to 99.9 and 90 to 95 pct, respectively, under the following conditions: 363 K, Ph2s 31 kPa, Ni²⁺ 4.0 g · dm^-3, 3[Fe^o]/[Ni²⁺] 1.25 to 1.5, H2S flow rate 70 to 100 cm³ · min^-1, and 45 to 60 minutes retention time. Selective formation of Ni3S2 is achieved within 10 minutes, and a reaction on the surface of the iron is rate-determining during the early stages of precipitation. Since the iron is almost totally consumed after 1 to 2 hours of reaction, the precipitated Ni₃S₂ is gradually converted to NiS. Calculations considering the buffer action of sulfate ion and sulfate complex formation with polyvalent metal cations as well as with nickel ions confirmed that significant nickel precipitation as Ni₃S₂ should occur under the test conditions.     

Comparison of Properties of Pristine and 200 MeV Ag15+ Ions Irradiated ‘Li’ 3 wt% Doped V2O5 Thin Films

Lithium (3 wt%) doped V₂O₅ thin film of thickness 97 nm was spray deposited over an ITO coated glass substrate at 450 °C. The deposited film was irradiated with 200 MeV Ag¹⁵⁺ swift heavy ions (SHI) at a fluence of 5 × 10¹² ions/cm². X-ray diffraction reveals the pristine and irradiated films to have an orthorhombic phase. The SHI irradiation induced thermal spike lead to texturing along the (400) direction along with partial amorphization. The 394 cm^?1 O–V–O Raman bending deformation is suppressed due to SHI irradiation induced oxygen vacancies. Optical transparency decreased from 80 to 50 % and the direct and indirect band gaps showed red shift upon SHI irradiation. Hall effect study revealed marginal variation in transport parameters upon SHI irradiation. The results are discussed.     

Helium ion irradiation effects on neodymium and cerium co-doped Gd2Zr2O7 pyrochlore ceramic

This paper studies the helium ions irradiation effects on Nd and Ce co-doped Gd_2 Zr_2 O_7 ceramics. where Nd replaces the Gd site and Ce replaces the Zr site respectively. A series of(Gd_(1-x)Nd_x)_2(Zr_(1-y)Ce_y)_2 O_7(0 ≤ x, y ≤ 1) ceramics were irradiated with a 500 keV He ions at room temperature at fluences ranging from 1 × 10~(15) to 1 × 10~(17) ions/cm~2. The irradiated samples were characterized using GIXRD, Raman and SEM measurements. From the GIXRD and Raman observations, the results indicate that all the samples display a deficient fluorite structure after irradiation. The irradiation toleration increases with the irradiation depth increasing under experimental conditions, and Nd_2 Ce_2 O_7 has the best irradiation stability in the(Gd_(1-x)Nd_x)_2(Zr_(1-y)Ce_y)_2 O_7(0≤ x. y≤1). Based on SEM results, the irradiated samples are still relatively dense and uniform, and no second phase exists.     

Electrochemistry of samarium in lithium-beryllium fluoride salt mixture

The electrochemical behaviour of samarium was investigated in LiF-BeF2 system on an inert (Mo) electrode by cyclic voltammetry and chronopotentiometry at 804, 833, 847 and 872 K. Redox process Sm3++e-→Sm2+ was recognized and analysed. Cyclic voltammetry data suggested that at potential sweep rates lower than 0.25 V/s, the reduction was limited by the diffusion of Sm3+ ions. It was not possible to observe reduction process of Sm2++2e-→Sm0 due to insufficient electrochemical stability of LiF-BeF2. Diffusion coefficients of Sm3+ ions in LiF-BeF2 were calculated from voltammetric and chronopotentiometric data in the temperature range 804-872 K. Diffusion coefficient values obeyed Arrhenius law. Activation energy was calculated to be 102.5 kJ/mol.     

Effects of electron and ion irradiation on the dislocation structure of [001] twist boundaries in FeS alloys

Previous work has demonstrated that the dislocation structures of small and large angle [100] twist boundaries in FeS alloys are changed as S is implanted. It was not clear from that work, however, to what extent the radiation damage accompanying the implantation played a role in the change of boundary structure. In the present work the influence of irradiation on the dislocation structures of small angle and large angle (near Σ = 5) twist boundaries in the FeS system was studied using 80 keV S⁺ ions, 80 keV Ar⁺ ions, 1.5 and 0.8 MeV Ne⁺ ions and 800 keV electrons. Electron irradiation produced no change in structure of the boundary in the irradiated region. However, a neighboring region showed a change of structure which is due possibly to diffusion of S related to the high concentration of point defects produced by the electron irradiation (radiation-induced segregation). Ne⁺ ion irradiation also had no effect on the dislocation structure of the boundaries. With a similar mass as S, Ar⁺ ions create a defect structure very similar to that of implanted S⁺. Ar⁺ ion implantation caused no change in the structure of the large angle boundary, but did transform small areas of the small angle grain boundary. This is substantially different behavior from that caused by S⁺ ion implantation. These results lead to the conclusion that the observed change of structure as a result of implantation of S in the vicinity of [001] twist boundaries in FeS alloys is due primarily to the presence of the S, and that the point defects which are a product of the irradiation may affect only the kinetics of the structural transformation.     

Reduction kinetics of Ni(OH)2 to nickel powder preparation under hydrothermal conditions

The reduction kinetics from Ni(OH)₂ to fine Ni metal powder under hydrothermal and H₂ pressure conditions using anthraquinon as an activator were investigated. The reduction ratio increased with temperature up to 225 °C. The H₂ molecule was activated by anthraquinone. This activated hydrogen acts as a reduction reagent from Ni²⁺ to Ni⁰. The process may proceed by heterogeneous reaction of Ni²⁺ ion and solid anthraquinon as follows: (1) anthraquinon is hydrated, (2) Ni²⁺ ion is absorbed on anthraquinon hydride, and (3) this complex decomposes to Ni⁰ powder, anthraquinon, and H₂O. The particle size of nickel powder obtained increased with increasing temperature and with decreasing pH. The average particle size was about 350 nm. The reduction kinetics were in good agreement with a core model equation with surface reaction, that is, 1 − (1 −x)^1/3 =kt, wherex is a reaction ratio andt is reaction time. Arrhenius plots showed two slopes with activation energies 65.9 kJ/mol at higher temperature and 377.2 kJ/mol at lower one. This result shows that the hydration of anthraquinon and adsorption of Ni²⁺ ion onto anthraquinon hydride and decomposition to Ni metal and anthraquinone proceed by consecutive reactions and rate determining steps change in each temperature range.     

Role of Tungsten in the Tempered Martensite Embrittlement of a Modified 9 Pct Cr Steel

The effect of tempering on the mechanical properties and fracture behavior of two 3 pct Co-modified 9 pct Cr steels with 2 and 3 wt pct W was examined. Both steels were ductile in tension tests and tough under impact tests in high-temperature tempered conditions. At T ≤ 923 K (650 °C), the addition of 1 wt pct W led to low toughness and pronounced embrittlement. The 9Cr2W steel was tough after low-temperature tempering up to 723 K (450 °C). At 798 K (525 °C), the decomposition of retained austenite induced the formation of discontinuous and continuous films of M₂₃C₆ carbides along boundaries in the 9Cr2W and the 9Cr3W steels, respectively, which led to tempered martensite embrittlement (TME). In the 9Cr2W steel, the discontinuous boundary films played a role of crack initiation sites, and the absorption energy was 24 J cm^?2. In the 9Cr3W steel, continuous films provided a fracture path along the boundaries of prior austenite grains (PAG) and interlath boundaries in addition that caused the drop of impact energy to 6 J cm^?2. Tempering at 1023 K (750 °C) completely eliminated TME by spheroidization and the growth of M₂₃C₆ carbides, and both steels exhibited high values of adsorbed energy of ≥230 J cm^?2. The addition of 1 wt pct W extended the temperature domain of TME up to 923 K (650 °C) through the formation of W segregations at boundaries that hindered the spheroidization of M₂₃C₆ carbides.     

Interaction of Sodium Ions with Feldspar Surfaces and Its Effect on the Selective Separation of Na- and K-Feldspars

K-feldspar and Na-feldspar exhibit similar mineralogical, chemical and surface properties. Froth flotation is known to be the only technique to enable their separation. Our earlier studies revealed a good selectivity in the presence of K⁺ and to a larger extent with Na⁺ ions. In this context, in order to further identify the role of Na⁺ ions in the selective separation of these minerals, ion selective electrodes were employed to determine the released Na and K ions released from albite and microcline into the solution and those adsorbed ions onto the mineral surfaces. Adsorption isotherms in feldspars/inorganic systems were constructed and the regions representing ion exchange and ion adsorption isotherms delineated. The mechanism of selective separation was elaborated on the basis of micro-flotation, solubility, adsorption and zeta potential measurements.     

Thermodynamic properties and diffusion thermodynamic factors in B2-NiAl

The vaporization of Ni-Al alloys has been investigated in the temperature range 1178 to 1574 K by Knudsen effusion mass spectrometry (KEMS). Thirteen different compositions have been examined in the composition range 38 to 57 at. pct Al. The partial pressures and thermodynamic activities of both Ni and Al have been evaluated both directly from the measured ion intensities for a component in both the alloy and the pure element, I _M ⁺ /I _M ⁺ °, and also from the ion intensity ratios of the alloy components, I _Al ⁺ /I _Ni ⁺ , by means of a Gibbs-Duhem integration. Reliable partial molar enthalpies and entropies for both components have been obtained by mass spectrometry for this system for the first time. Both properties are found to be nearly temperature independent over the wide temperature range investigated. Two separate component diffusion thermodynamic factors have also been evaluated for the first time by taking into account the large vacancy concentrations in these alloys. The enthalpy and Gibbs energy of mixing of stoichiometric Ni_0.5Al_0.5 at 1400 K, evaluated using the Gibbs-Duhem ion intensity ratio (GD-IIR) method, are −78.4±1.2 and −49.0 kJ/mol, respectively, with Al(liquid) and completely paramagnetic Ni(fcc, cpm) as reference states.     

Silver ion catalysis in nitric acid dissolution of Ni3S2

The dissolution of Ni₃S₂ in nitric acid solutions in the presence of silver ions was investigated. The effect of stirring, particle size, temperature and silver ion concentration were examined. In addition, the reaction residues at various levels of nickel extraction were examined by SEM, X-ray diffraction, electron microprobe and chemical analysis. These observations indicated that the dissolution reaction is topochemical and fits a surface reaction control model. The activation energy was calculated to be 52.6 ± 3.6 kJ/mol, which is reasonable for a rate-limiting surface reaction. The order of the reaction was 0.2 with respect to Ag⁺ concentration. An electrochemical reaction between nitric acid and the intermediate product Ag₂S occurring on the surface of Ni₃S₂ appears to be the rate-determining step.