Cu atoms are diffused into Si single-crystal samples containing bulk-type stacking faults (SFs), and whole images of the SFs are observed with a transmission electron microscope.
In the samples without Cu diffusion, hexagonal SFs with hexagonal Si oxide precipitates are observed. In the case of the samples with Cu diffusion, SFs having branches and CuSi precipitates on the edges or inside of the branches are observed.
CuSi precipitates grow on the Frank dislocation loop, and interstitial Si atoms are released. Such interstitial Si atoms condense around the CuSi precipitates, and branches grow in the ⟨110⟩ direction from the SFs.

View full abstract

Phase equilibria between γ and γ′ in Ni-base Ni–Al–Ta alloys have been investigated by analytical electron microscopy (AEM). The chemical compositions of the γ and γ′ phases in the two-phase alloys were determined by an energy dispersive X-ray spectrometer (EDS) and then tie lines in the γ+γ′ two-phase region and the partitioning of Ta in the γ and γ′ phases were evaluated. The ALCHEMI (atom location by channeling enhanced microanalysis) technique revealed that Ta occupies most favorably the Al sites in the γ′ phases irrespective of stoichiometry. The lattice constants of the γ and γ′ phases were determined by convergent beam electron diffraction (CBED). The lattice misfits between the γ and γ′ phases were then calculated from the lattice constants and were compared with those determined from the analysis of the misfit dislocations.

View full abstract

An investigation was made on the effect of rotational stirring on the microstructures, distribution of solute elements, carbide formation, phosphorus segregation, and distribution coefficients between solid and liquid phases in the Ni-base superalloy TMP-3 (Ni-11.15%Cr-6.74%Co-3.12%Mo-3.98%Al-2.74%Ti-3.93%Nb-3.25%W) by rheocasting with the rotation of a stirrer in the range of 20 to 70 rev/s. The main results obtained are summarized as follows:
(1) When the TMP-3 superalloy was sufficiently agitated at 70 s⁻¹ from the start of solidification, the dendrite structure was broken up and an equiaxed grain structure with the average primary solid particle size of 65±15 μm was formed.
(2) The distributions of Ni, Cr, Co, Al, Ti, Mo, Nb, W, P and C in the superalloy TMP-3 ingots rheocast at 70 s⁻¹ and stationary cast were measured by using a computer-aided microanalyzer (CMA). The concentrations of main eight metallic elements in the center of equiaxed grains in the rheocast alloy were almost equal to those in the center of dendrites in the stationary cast alloy.
(3) It was observed from the measurement on the distribution of Ti and Al that the size of γ′ phases in the rheocast alloy tend to decrease as compared with that in the stationary cast one.
(4) It was observed that granular MC carbides containing mainly Nb, Ti and Mo precipitate uniformly along the grain boundary in the rheocast alloy, although the plate-like MC carbides precipitate in the grain boundary of the stationary cast alloy.
(5) The distribution of P measured by CMA showed that P segregates considerably in the grain boundary, but the degree of phosphorous segregation in the rheocast alloy tend to decrease as compared with that in the stationary cast one.
(6) The solid-liquid distribution coefficients estimated from the concentration of main eight elements in the center of primary crystals were almost consistent with the equilibrium distribution coefficients obtained by thermodynamic calculation including an additional consideration on solute interactions.

View full abstract

The lattice invariant shear in the β₁→γ₁′ martensitic transformation in a Cu–Al–Ni alloy is confirmed to be ⟨111⟩_γ1′ Type II twinning by X-ray diffraction and two-surface analysis using single crystals. However, Type II twins have not been observed by electron microscopy in the past. To resolve this conflict, the twins in the martensite were reinvestigated by electron microscopy. Since unambiguous twin diffraction patterns for Type II twins are available only for specific orientations, well-prepared single crystals with the {101}_β1 surface were used. As a result, the presence of Type II twins were unambiguously proved by the twinned diffraction patterns from the unique η₁ direction and by those, in which η₁ is normal to the electron beam. The reason for non-observation of Type II twins in the past were also discussed. The widths of Type II twins were found to be one order of magnitude larger than those of Type I twins. Thus, the boundary energy of Type II twin is suggested to be larger than that of Type I twin in the present martensite.

View full abstract

An experimentnal study has been made on the effect of heat-treating temperature (800, 850, 900, 950, 1000 and 1050°C) and time (2, 4, 6, 8, & 10 h) on the transformation behaviour of a 7.5Mn–5Cr–3.0Cu white cast iron developed to resist aqueous corrosion in different environments. Structural changes on heat-treating were monitored using hardness measurements.
It was observed that on heat-treating from 800°C the hardness increased marginally with the soaking period. Hardness was independent of the soaking period on heat-treating at 850, 900 and 950°C. On heat-treating from 1000 and 1050°C, the hardness decreased with time markedly. These changes are consistent with the resultant microstructural changes.
The hardness (H) vs time (t) plots at any temperature are linear and can be represented by
H=C₁+C₂t(T°C)
The hardness vs temperature plots as influenced by time, which, in effect represented how effectively the alloy sustained hardness, are most appropriately represented by a 3rd order polynomial
H=C₁+C₂T+C₃T²+C₄T³(t·S)
leading to a horizontal ‘S’ shape.
Based on fundamental considerations, the final model interrelating hardness with temperature and time is
H=65.7e^2337.4⁄T+(0.0217−1.9×10⁻⁵·T)t
where T=temperature in K, t=time in seconds and H=Vickers hardness number, 294 N (VHN₃₀).
The overall validity and the usefulness of the model have been discussed.

View full abstract

The deformation behavior of a 10 mass%Cr-30 mass%Mn-0.1 mass%C austenitic steel was investigated over the temperature range from room temperature to 873 K after neutron irradiation in JMTR at 573 K to a fast neutron fluence of 8.5×10²² n/m² (E>1 MeV). A high density of irradiation-produced dislocation loops with the size of about 5 nm and 10–30 nm was observed. Irradiation caused an increase in yield stress with a prominent yield point and a decrease in total elongation near room temperature. These behaviors became diminished with increasing test temperature. The deformation of the irradiated specimens was localized in bands of dislocation channeling. Most of the irradiation-produced dislocation loops were disappeared in the bands. At high temperatures above 673 K, the deformation dislocation structure was homogenous, being similar to that observed in the unirradiated specimens. The appearance of yield point was discussed by taking into account of the pinning of mobile dislocations and subsequent dislocation multiplication. The decrease in total elongation was shown to be due to a decrease in work hardening rate.

View full abstract

The elastic energy, displacement field, and Peierls stress of a+c dislocations have been calculated on the basis of anisotropic elasticity theory for several h.c.p. metals. The preferences of glide planes predicted from the self-energy of an edge dislocation and the profile of nonuniform displacement distribution around a screw dislocation agree with the experimental observations for the strongly anisotropic metals, Zn and Cd, but not for the others. The Peierls stress of an a+c edge dislocation exhibits little correlation with experiments; the plane of the lowest Peierls stress is not always the observed glide plane. The calculated Peierls stress is primarily governed by the geometry of the slip system, i.e. the magnitude of the Burgers vector and the interplanar spacing, rather than the elastic anisotropy.

View full abstract

Two kinds of hydrogenation reaction of SiCl₄(g), i.e.:
SiCl₄(g)+H₂(g)=SiHCl₃(g)+HCl(g),
and
Si(s)+3SiCl₄(g)+H₂(g)=4SiHCl₃(g)
have been studied under various inlet gas compositions and temperatures in a fixed bed reactor at an atmospheric pressure and without any catalyst addition in order to elucidate their intrinsic reaction kinetics in this investigation. A higher conversion rate has been obtained in the latter gas-solid reaction scheme. A segment compartment model has been used to analyse the reactor performance of a plug flow type for these conversion reactions. A second order, reversible rate equation for the former gas-gas reaction has been assumed and adapted in the rate expression, which has been then used in the reactor performance model calculation. For the latter gas-solid reaction, the two step-wise reaction mechanism; i.e. the first gas-gas reaction step to produce HCl(g) and the second gas-solid reaction step of this HCl(g) with Si(s) with a topo-chemical rate model, has been adapted in the rate expression, which was then used in the reactor performance calculation. There have been shown good correspondence between the experimental results and the reactor performance calculation using these postulated reaction rate equations.

View full abstract

Electrocrystallization of atomically controlled metallic multilayers has been discussed on the basis of a nucleation-growth mechanism and experimental observations. Monatomic steps on Pt single crystal surfaces have been directly imaged using a conventional transmission electron microscope in the reflection mode. With this reflection electron microscopy (REM) technique, the initial stages of Co electrocrystallization on Pt(111) surfaces have been studied under potential control. The REM images have revealed a layer by layer growth, strictly speaking, a simultaneous multinuclear multilayer growth of Co deposition in the range from submonolayer coverage up to some ten monolayers. Based on the observations of the surface morphology and the reflection electron diffraction from an REM study, the feasibility of electrocrystallization to produce Co/Pt multilayers with a comparable structure to those prepared by vapor-phase deposition techniques is discussed.

View full abstract

Oxidation of dense plates of Cu₅Fe_1−xS_4−y in which the (1−x)-value varied from 1.01 to 0.13 was carried out at 973, 1023 and 1073 K in the O₂–N₂ gas flow. The mass change of the samples and the concentration of evolved SO₂ gas were continuously measured during the oxidation.
The mass change of the sample Cu₅Fe_1.01S_3.77 exhibited that the reaction proceeded by the following 3 steps. In the early stage of the oxidation, the sample mass increased without the evolution of SO₂ gas; a dense layer composed of Fe₂O₃ and Fe₃O₄ was formed on the sample surface. The oxidation rates at the first and second stages of oxidation were thought to be controlled by the diffusion of Fe in the sulfide and in the oxide, with activation energies of 145 and 160 kJ/mol, respectively. In the third stage, SO₂ gas evolved and the sample mass decreased to form a porous oxide composed of Fe₂O₃, Cu₂O and CuO. Estimation of the sulfide composition at the time when the sample gained the maximum mass revealed that the composition of each sample was located on the tie line between Cu₂S and Cu₅FeS₄.

View full abstract

In order to clarify the rate and mechanism of the formation of Sm–Fe intermetallic compounds by the reduction-diffusion (R-D) process, three kinds of experiments were carried out: (1) the reduction of pellets of Sm₂O₃ powder mixed with CaH₂, (2) the R-D reaction for the pellets which were composed of Sm₂O₃, CaH₂ and Fe (powder or wire) at 1300, 1400 and 1500 K, and (3) diffusion experiment by using Sm–Fe diffusion couples with Mo wire as a marker at 963 K.
The reduction of Sm₂O₃ uniformly proceeded in the pellets; more than 90% of Sm₂O₃ was reduced at 1400 and 1500 K in a reaction time less than 1 ks, though about 80% at 1300 K at a reaction time of 1 ks. During the R-D reaction, a Sm₂Fe₁₇ layer was formed on the Fe surface. The thickness of the Sm₂Fe₁₇ layer grew according to a parabolic rate law at 1300 K. At 1400 and 1500 K, however, the Fe dissolved in a liquid Sm or Sm–Ca melt, since the reduction rate of Sm₂O₃ was high. The experiment with the diffusion couple revealed that Fe diffused faster than Sm in the SmFe₂ layer.

View full abstract

(Fe, Cr)₇C₃ carbide bulk alloys with different chromium contents were prepared by melting pure materials. Abrasion wear resistance of the carbide alloys was examined using a pin-on-disk type wear tester in relation to microstructure and hardness. Hardness and wear resistance of the carbide alloys were raised with increasing the chromium content and the dependence of wear resistance on hardness was seen remarkably under a low applied load. For the alloys with microstructures consisting of (Cr, Fe)₇C₃ carbide and retained austenite, a linear relationship was seen between wear resistance and the volume fraction of carbide up to the fraction of unity, but not between wear resistance and hardness. It was also found that the carbide alloys have a relatively large coefficient of thermal expansion comparable to steels and thus a strong bonding with substrate metals can be expected for an application of carbide alloys as a hardfacing material.

View full abstract

A new process for the preparation of ultrafine particles (UFP) of metals was developed by means of a rapid vapor condensation technique. In this method, the evaporated metal vapor was rapidly condensed by a cold fluid (such as liquid N₂ or liquid CO₂) and then deposited into a trap or a cyclone before being coalesced. The size of particles obtained by this method (Ag, Cu, Au, Fe–Ni, Pd–Si) was very fine (about 10–50 nm in diameter) and the size distribution was quite sharp. In this paper, silver particles prepared by this method were investigated by electron microscopy and X-ray diffraction analysis. Most of the silver particles were spherical and single crystals.

View full abstract

Three regions in the power-law creep regime have been recognized on the creep features of polycrystalline single-phase TiAl intermetallics at 1100 K under 63∼400 MPa. In each region, creep curves show a distinctive type. The parameters which indicate the effects of composition, grain size, stress and temperature on the minimum creep rate also have characteristic values in each stress range. The deformation process in the high stress range is necklace-type dynamic recrystallization. Deformation processes operating in the intermediate- and low-stress ranges remain to be specified.

View full abstract