注氢硅中微结构缺陷的TEM观察

通过透射电子显微镜观察到注氢硅片中存在损伤带，损伤带的位置和注人氢的分布几乎一致，推断损伤带是由于氢的注入引起的。损伤带内主要以平行于正表面的{111}面状缺陷为主，另外还有斜交于正表面的{111}面状缺陷以及{100}面状缺陷，这是由于氢朝能量低的位置的迁移聚集而形成的。在损伤带的中间还可见到晶格紊乱团块和空洞，这是由于损伤带中间存在高浓度的氢和高密度的面状缺陷面导致形成的。     

Impurity segregation to voids in doped tungsten ribbon filaments

Filaments of Al-, Si-, and K-doped tungsten foil, 0.00254 cm thick, were heated to 2300°C in vacuo until a hot spot developed. Within the hot spot were voids varying in size from about 50 to 6000Å. The larger voids were faceted with the major facets parallel to {110}. The relative surface tensions in the doped foil were in the order {110} < {112}< {111} < {100} as determined from a model of the voids. Selected area diffraction showed that the void surfaces were coated with a thin epitaxial layer of potassium with [311] W ‖[311] K in the majority of cases.     

Impurity segregation to voids in doped tungsten ribbon filaments

Filaments of Al-, Si-, and K-doped tungsten foil, 0.00254 cm thick, were heated to 2300°C in vacuo until a hot spot developed. Within the hot spot were voids varying in size from about 50 to 6000?. The larger voids were faceted with the major facets parallel to {110}. The relative surface tensions in the doped foil were in the order {110} < {112}< {111} < {100} as determined from a model of the voids. Selected area diffraction showed that the void surfaces were coated with a thin epitaxial layer of potassium with [311] W ‖[311] K in the majority of cases.     

Secondary defects in quenched and aged platinum

Some results of a study of secondary defects in quenched platinum are presented. Transmission electron microscopy (TEM), used with field-ion microscopy (FIM), yielded direct evidence for the existence of prismatic loops, Frank loops, and polyhedral voids. The Frank loops were observed as black spots in the electron microscope and were resolvable only via FIM. The loop density was estimated to be 10¹³ per cu cm from TEM with an average size of approximately 50Å. Resolvable loops were found among networks of heavily jogged dislocations. The void concentration reached a maximum of 7 × 10¹⁴ per cu cm after annealing at 400°C for 24 hr and fell sharply on either side of this temperature. In general the voids could be described as regular octahedra, some truncated by {100} and occasionally by {111} planes. Small voids appear spherical due to strain contrast but careful tilting experiments reveal hexagonal cross sections implying {100} truncated octahedra. Small tetrahedral clusters have been observed via FIM and these may be the nuclei for both voids and dislocation loops. Larger voids are shown to be extremely stable almost to the melting point.     

Sputter-induced pits on {100} nickel surfaces

Nickel (Ni⁺) ions of 180 keV energy impinging on {100} faces of nickel single crystals produce sputtered surfaces. Examination of these surfaces exposed to fluences up to 8 X 10¹⁷ ions/cm² and at temperatures between 25 °C and 750 °C reveals pits with facets parallel to the {111} and {100} crystallographic planes of the nickel. Subsurface voids also form and, when intersected by the sputtered surface, become small pits which grow with further sputtering. The pits exhibit facets that are direct extensions of facets present on the voids. The voids nucleate and grow during the initial stages of bombardment at temperatures above 600 °C but shrink beyond fluences of ~3.5 X 10¹⁷ ions/cm². Voids are not observed after bombardment at temperatures less than 600 °C. Sputtering at these lower temperatures produces no pits unless the nickel is bombarded first at higher temperatures to produce the requisite voids. Measuring the rate at which the {100} surface recedes due to sputtering provides the sputtering yield. This yield, near 3.8 atoms per Ni⁺ ion, is independent of temperature from 25 °C to 750 °C. The growth rate of the pits,i.e., the rate at which oppositely inclined {111} faces separate, is also measured. At temperatures below 350 °C, the measured growth rate matches that based on sputtering of these inclined surfaces. The rate increases with increasing temperature above 350 °C, reaching nearly tenfold its low-temperature value by 750 °C. The mechanisms causing this accelerated growth with increasing temperature are discussed and related to the migration of the point defects produced by the bombardment. Formerly Visiting Scientist, Metallurgy Department, University of Connecticut     

Atmosphere change of vacuum to hydrogen and sharpness of {110}〈001〉 texture in thin-gaged 3 Pct Si-Fe alloy strips

Heating in vacuum finally resulted in a main {100}〈uvw〉 texture and a trace of {111}〈uvw〉 texture. However, the texture was changed to the {110}〈001〉 texture when the strip was heated in hydrogen or when the vaccuum was changed to hydrogen at a temperature T_c. As T_c increased, the sharpness of the {110}〈001〉 texture increased, resulting in the high magnetic induction. This can be understood in the light of surface segregation kinetics of sulfur.     

The effect of hydrogen on the surface energy of nickel

The effect of hydrogen in solid solution in nickel on the surface and grain boundary free energies at 1573 K was determined using the zero creep technique. Effects of O and H adsorption on the surface free energies were considered and shown to have only small effects under the experimental conditions. The surface energy of pure nickel was determined to be about 2.34 J/m². H concentrations of 300 at. ppm were shown to have no significant effect on the surface energy. Hydrogen had a somewhat greater effect on the grain boundary energy with . The implications of these results for hydrogen embrittlement mechanisms in Ni are discussed.     

Fracture of single crystals of the nickel-base superalloy PWA 1480E in hydrogen at 22 °C

The hydrogen-induced fracture behavior of notched single crystals of the PWA 1480E nickel-based superalloy was studied. Notched single crystals with seven different crystal orientations near [100], [110], [111], [013], [112], [123], and [223] were tensile tested at 22 °C in an hydrogen atmosphere at 34 MPa. The notch tensile strength degradation in hydrogen was orientation dependent. The specimen with the [100] orientation had the greatest strength degradation, while the crystal with the [111] orientation had the least. A stereoscopic technique combined with the use of planar γ′ morphologies was applied to identify cleavage plane orientations. All specimens failed predominately by {100}-type cleavage within about 0.5 mm of the notch and {111}-type cleavage toward the center of the crystal. Cleavage on {111}-type planes in the center of the crystals was not related to testing in hydrogen. Microcracking along the {100} γ/γ′ interfaces was observed in the area near the fractured surface. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies indicated that {100}-type cleavage within the notch region controlled the hydrogen-induced cleavage fracture in notched single crystals. Formerly graduate Student, Auburn University     

Hydrogen embrittlement of L12-type Ni3 (Al,Ti) single crystals

The deformation and fracture behavior of the L1₂-type Ni₃ (Al,Ti) single crystals were investigated on the effect of testing atmosphere and strain rate. The elongation and the ultimate tensile stress decreased in the sequence, vacuum > air > hydrogen and also these values decreased as strain rate decreased. The cleavage fracturing with the river-like patterns was dominant in the single crystals which were tensile-tested in air and hydrogen. Whereas, the ductile fracturing with the ridge patterns was dominant in the single crystals which were tensile-tested in vacuum and at a high strain rate. Macroscopic fracture planes changed from non-crystallographic plane, through {001} plane, to {111} and {011} planes as used atmosphere changed from vacuum through air to hydrogen gas. As the micro-mechanism responsible for the observed embrittlement, the “decohesion” mechanism was likely. Hydrogen accumulates at the microdefect created by dislocation reaction (or at a resultant micro crack tip) and thereby lowers the cohesive strength of the lattice at which the bond rupture occurs.     

Kinetics and mechanism of the reduction of molten nickel sulfide by hydrogen

The kinetics and mechanism of the reduction of M₃S₂ by hydrogen have been investigated between 1133° and 1300°C. When high flow rates of hydrogen and argon or helium bubbling through the melt are maintained the rate-determining step is a chemical process which can be expressed by a rate law of the form $$\begin{gathered} r_{H_2 S} = k_{expt} (N_S - \alpha )^2 p_{H_2 }^{1/2} \hfill \\ p_{H_2 } \geqslant 0.88atm \hfill \\ \end{gathered} $$ where k_expt = 85.1 atm^-1/2 min^-1, α = 0.17 at 1250°C. The experimental activation energy for this process is 20.1 ±3.0 kcal per mole. These results are discussed in terms of possible catalysis by nickel.     

Sulfate Formation and Decomposition of Nickel Concentrates

Nickel sulfide concentrates from two Canadian nickel concentrators were investigated to improve the understanding of SO₂ formation and release during processing. The concentrates were heated in gases of various oxygen concentrations up to 1573 K (1300 °C) in a thermal gravimetric analysis unit to simulate what may take place during calcine collection and processing. The resulting SO₂ gases were also measured. It was determined that during oxidation, there are competing reactions, such as \( 3{\text{FeS}} + 5{\text{O}}_{2} = {\text{Fe}}_{3} {\text{O}}_{4} + 3{\text{SO}}_{2} \) leading to mass loss, or \( 2{\text{FeS}} + 5{\text{O}}_{2} + {\text{SO}}_{2} = {\text{Fe}}_{2} \left( {{\text{SO}}_{4} } \right)_{3} \) causing mass gain. At temperatures up to approximately 973 K (700 °C), sulfates were formed readily, whereas at higher temperatures, they would decompose, evolving SO₂. By lowering the oxygen content in the surrounding gas, the sulfates decomposed more readily. In an argon or hydrogen atmosphere or in vacuum, it is possible to enhance the sulfate decomposition greatly, possibly allowing for reduced SO₂ emissions from the electric furnaces.     

Microreaction mechanism in reduction of magnetite to wustite

In order to understand the microreaction mechanism of the reduction of magnetite to wustite, hydrogen ions were implanted into magnetite at room temperature by an ion accelerator. The crystalloid transformation during the reduction process was investigated by using selected-area electron diffraction patterns. The experimental results showed that {220} planes on the surface of magnetite were changed first because the concentration of oxygen ions on the {220} planes is higher than other planes to follow the reaction of oxygen ions with hydrogen ions, leaving the {220} planes and resulting in rearrangement of ions. On the other hand, oxygen ions migrate more difficulty than iron ions in magnetite; therefore, {220} planes in the bulk are more stable than other planes. Based on the experimental facts, two kinds of microreaction mechanisms in reduction of magnetite to wustite are suggested. It was found that (1) wustite with [001] direction was formed on the magnetite with [001] direction, (2) (220) and (200) planes of wustite were parallel with (220) and (400) planes of magnetite, respectively, in crystal structure between parent phase and new phase, (3) some {220} planes were formed earlier than other ones in wustite during the reduction process. These results can be considered as due to the similar geometric distribution of oxygen ions between magnetite and wustite.     

Microstructural evolution in iron aluminide Fe-28Al-2C after high-temperature hydrogen treatment

High-temperature hydrogen attack (HA) in a carbon-alloyed iron aluminide of composition Fe-28.1Al-2.1C (in at. pct) has been studied. Well-polished samples were exposed to hydrogen gas (1 atm) at 700 °C and 900 °C for different times. The characteristics of HA were evaluated by two-dimensional microstructural analysis, performed on the rolling plane of the as-received and hydrogen-treated samples. The carbon-alloyed iron aluminide contained carbides in two different morphologies: blocky and needle shaped. The compositions of these carbides have been determined. The blocky carbides were preferentially attacked along the {111} and {110} crystallographic planes. The interfaces between the blocky carbides and grains were mainly affected by the hydrogen treatment. The needle-shaped carbides dissolved in the matrix after relatively short times. The degree of attack generally increased with increases in treatment temperature and time of exposure, as long as the surface was not completely covered with a protective oxide layer.     

Workability of 1045 spheroidized steel under superimposed hydrostatic pressure

Workability tests were performed on spheroidized {dy1045} steel to investigate the variation of forming limits due to the suppression of void growth under superimposed hydrostatic pressure. Results showed that increasing pressure enhances formability, as expressed by the increasing intercept and decreasing slope of the forming-limit line. A continuum mechanical model based on the growth and coalescence of voids under externally applied pressure is proposed that ex-plains the experimental results.     

The nature of quasicleavage fracture in tempered 5.5Ni steel after hydrogen charging

Quenched and tempered 5.5Ni steel was embrittled by hydrogen charging and broken in air at room temperature. The primary fracture mode was transgranular quasicleavage. The quasicleavage facets were studied by scanning electron fractography and by transmission electron microscopy of profile fractographic specimens. The latter were prepared by plating the fracture surface with nickel and thinning so that the fracture surface was contained within the region of the specimen that was transparent to the electron beam. The fracture surface generally followed martensite lath boundaries. In addition, interlath microcracks were frequently found in the material immediately beneath the fracture surface. These results suggest that transgranular hydrogen embrittlement in this steel is primarily an interlath cracking phenomenon. Since the lath boundary planes tend to lie in {110}, the results also explain the prevalence of {110} quasicleavage in the embrittled specimens, which contrasts with the {100} cleavage found in uncharged specimens broken below the ductile-to-brittle transition temperature.     

Catalytic decomposition of hydrogen peroxide by ferric ion in dilute sulfuric acid solutions

Hydrogen peroxide decomposition in acidic solutions is catalyzed by the free ferric ion, Fe³⁺. The following rate law for this reaction is determined by the initial rate method in solutions similar to those used for acidicin situ uranium leaching: wherek = 4.3 × 10⁻³ s^°1 at 25 °C. From 25° to 50 °C, the activation energy is 85.6 kJ/mol. The decomposition of hydrogen peroxide proceeds by a particular redox reaction sequence that depends on the ratio of the concentrations of hydrogen peroxide to free ferric ion. The rate law determined here is consistent with the form derived from the redox sequence for the case where the ratio of hydrogen peroxide to free ferric ion concentration is greater than 1.0. The magnitude of the rate constant indicates that the decomposition of hydrogen peroxide may cause rapid loss of this oxidant in leaching solutions containing ferric ion. Formerly a Graduate Student with the Department of Geochemistry and Mineralogy, Pennsylvania State University,     

Removal of Boron from Silicon by Moist Hydrogen Gas

New and cheaper refining methods for production of metallurgical silicon are needed to meet the increasing demands for low-cost, high-quality silicon for the solar cell industry. One promising refining method for boron is moist hydrogen treatment. In this work, an evaporation unit has been used to produce wet hydrogen gas, which subsequently has been sparged on top of silicon melts. The effect of temperature and gas composition on boron removal has been studied. The main results show that boron is removed from liquid silicon and the removal rate is controlled by chemical reaction depending on $ p_{{{\text{H}}_{ 2} {\text{O}}}} $ and $ p_{{{\text{H}}_{ 2} }} $ . Water vapor treatment of molten silicon can alone remove boron. However, in combination with hydrogen gas, the removal rate is significantly increased. In addition, the rate of boron removal in silicon has been found to decease with increasing temperature.