Si Alloy Single Crystals Research Articles

Special misorientations in localized deformation regions in Fe-3%Si alloy single crystals

Extended regions located at an angle of 20° to the rolling plane are observed inside deformation bands in a (110)[001] Fe-3%Si alloy single crystal at a high strain (∼60%). These regions were interpreted earlier as shear bands. The lattice orientation in these bands is close to (110)[001], and their habit plane is parallel to the {112} planes of the deformed {111}〈112〉 matrix. The misorientations between the bands and the matrix group around special misorientations Σ9, Σ19a, Σ27a, and Σ33a, which are characterized by close angles of rotation about axis 〈110〉. During primary recrystallization, the (110)[001] grains growing from the bands retain segments of the corresponding special boundaries with the deformed matrix.

Effects of Temperature and Strain Rate on Stress-Strain Relationship and Deformation Twinning in Fe-5%Si Alloy

The effects of temperature and strain rate on the stress–strain relationship and deformation twinning, during tensile tests, in polycrystalline Fe–5%Si alloy were studied. We performed tensile tests over a wide range of temperatures from 173 to 273 K, and strain rates ranging from 0.0001 to 0.1 /s, to clarify the relationship between total elongation and ratio of deformation twins, and the dependence of deformation twinning on grain orientation. All tensile specimens were fractured in a completely brittle manner. The total elongation decreased as the temperature decreased and the strain rate increased. The presence of deformation twins, in all fractured specimens, was confirmed by scanning electron microscope–electron backscattering diffraction analyses. The area fraction of the deformation twins increased as the total elongation decreased. However, a strong influence from the grain orientation on twinning activity was not observed for all temperatures and strain rates. A previous study on Fe–Si alloy single crystals showed that deformation twins form easily in <001>-oriented single crystals, but not in <111>-oriented single crystals. Our observations, on the dependence of deformation twinning on grain orientation in polycrystalline Fe–5%Si alloy, did not agree with those from single crystals. The present findings suggest that grain orientation does not play an important role in determining the occurrence of deformation twinning; not even in polycrystals. It is believed that the stress concentration, due to piled-up dislocations, during tensile deformation, cannot be relieved by the slip at low temperatures or high strain rates, and thus significantly affects deformation twinning.

Influence of copper on the deformation and primary recrystallization of Fe-3% Si alloy single crystals

Influence of copper on the deformation and primary recrystallization of Fe-3% Si alloy single crystals

Crystallographic study of fatigue crack growth in Fe–Si alloy single crystals

Abstract Crystallographic fatigue crack growth has been studied using iron–silicon single crystals having a notch plane of (1 1 0) or (1 1 2). In crystals containing a notch direction within an angle of ∼35° to [0 0 1] on a notch plane of (1 1 0), a crack grows by the separation of slip planes on the basis of evenly operated alternating shear on the intersecting slip systems at the crack tip. These crystals exhibit considerably high resistances to fatigue crack growth. In a crystal with a notch direction rotated at an angle of ∼55° to [0 0 1] on (1 1 0), two competing mechanisms, i.e. cleavage-like cracking related to the generation of sessile dislocations and saw-toothed feature formation due to the activation of multiple slip systems, appeared instead of an alternating shear mechanism. When alternating shear occurs unevenly on asymmetrically arranged slip planes, the fatigue crack growth resistance is low as compared to that in the case in which it occurs evenly.

Differential method of analysis of luminescence spectra of semiconductors

A method for analyzing the luminescence spectra of semiconductors is suggested. The method is based on differentiation of the spectra. The potentialities of the method are demonstrated for luminescence in the region of the fundamental absorption edge of Si and SiGe alloy single crystals. The method is superior in accuracy to previously known luminescence methods of determining the band gap of indirect-gap semiconductors and practically insensitive to different conditions of outputting radiation from the sample.

Cyclic Softening of Cu-Ni-Si Alloy Single Crystals under Low-Cycle Fatigue

Cu-2.2wt%Ni-0.5wt%Si alloy single crystals were grown by the Bridgman method and aged at 723 K for 10 h to form Ni2Si precipitates. Fully reversed tension-compression fatigue tests were conducted on the aged single crystals with a single slip orientation under constant plastic-strain amplitudes at room temperature. Cyclic softening occurred at plastic-strain amplitudes between 2.5x10-4 and 2.5x10-2. Using the maximum stress amplitude in each cyclic hardening/softening curve, a pseudo cyclic stress-strain curve (CSSC) was obtained. The CSSC was found to exhibit a plateau region with a stress level of about 167 MPa. Transmission electron microscopic observation revealed the formation of persistent slip bands (PSBs) in the plateau regime. It was found that the Ni2Si precipitate particles were intensively sheared by glide dislocations within the PSBs and were eventually re-dissolved into the Cu matrix. The macroscopic cyclic softening can be attributed to the local softening induced by the re-dissolution of the Ni2Si particles in the PSBs.

Fe-3 mass%Si 合金単結晶の微小試験片における破壊挙動とその試験片寸法効果

Fracture tests have been performed for both macro- and micro-sized specimens prepared from an Fe-3%Si alloy single crystal, and the size effects on fracture behavior have been considered. Micro-sized cantilever beam specimens with dimensions of 10 μm×10 μm×50 μm were prepared by focused ion beam machining. Notches with a depth of 5 μm were introduced into the micro-sized specimens and fatigue pre-crack was also introduced ahead of the notch. Macro-sized three-point bending specimens with dimensions of 2 mm×2 mm×10 mm were also cut from same Fe-3%Si alloy single crystal. Notches with a depth of 1 mm were introduced into the macro-sized specimens, and fatigue pre-crack was also introduced. Notch plane was set to be (100), which is a cleavage plane of this material, and notch direction was set to be [010] for both type of specimens. For macro-sized specimens, cleavage fracture occurred during introducing fatigue pre-crack. In constant, the micro-sized specimens were fractured by ductile manner. A plastic zone was clearly observed on the specimen surface near the crack tip and dimples were found on the fracture surface. The plastic zone size of this material is calculated to be 90 μm. This size is small enough to satisfy small scale yielding for macro-sized specimens, although this size corresponds to large scale yielding in micro-sized specimens. This may cause the size effect on the fracture behavior of this material. The results obtained in this investigation provide important information for designing actual MEMS devices.

Fracture Behavior of Micro-Sized Fe-3%Si Alloy Single Crystals

Fracture tests have been performed for both millimeter-sized and micro-sized specimens prepared from a Fe-3 mass%Si alloy single crystal, and the size effects on fracture behavior have been considered. Notch plane was set to be (100), which is a cleavage plane of this material, and notch direction was set to be [010] for both type of specimens. For millimeter-sized specimens, cleavage fracture occurred during introducing a fatigue pre-crack. In contrast, the micro-sized specimens were fractured by ductile manner. This phenomenon is discussed based on the plastic zone at crack tip and the ligament size. The results obtained in this investigation provide important information for designing actual MEMS devices.

Effects of Sample Size on the Fracture Behavior in Fe-3%Si Alloy Single Crystals

AbstractFracture tests have been performed for both macro- and micro-sized specimens prepared from an Fe-3%Si alloy single crystal, and the effects of length scale on fracture behavior have been investigated. Micro-sized cantilever beam specimens with dimensions of 10 × 10 × 50 μm3 were prepared by focused ion beam machining. Notches with a depth of 5 μm were introduced into the micro-sized specimens and fatigue pre-crack was also introduced ahead of the notch. Macro-sized three-point bending specimens with dimensions of 2 × 2 × 10 mm3 were also cut from the same Fe-3%Si alloy single crystal. Notches with a depth of 1mm were introduced into the macro-sized specimens, and fatigue pre-crack was also introduced. Notch plane was set to be (100), which is a cleavage plane of this material, and notch direction was set to be [010] for both size of specimens. For macro-sized specimens, cleavage fracture occurred during introducing fatigue pre-crack. In contrast, the micro-sized specimens were fractured by ductile manner. A plastic zone was clearly observed on the specimen surface near the crack tip and dimples were found on the fracture surface. The plastic zone size of this material is calculated to be 90 μm. This size is small enough to satisfy small scale yielding for macro-sized specimens, although this size corresponds to large scale yielding in micro-sized specimens. This may cause the size effect on the fracture behavior of this material.

Deformation and Recrystallization of Tensile-deformed or Rolled Fe-3%Si Alloy Single Crystals

Fe-3%Si alloy single crystal samples with various tensile directions were deformed to strains of 0.25 to 0.65 and subsequently annealed. Necking occurred and work-hardening was very small in all tensile-deformed samples. After annealing, no recrystallized grain was formed. Fe-3%Si alloy single crystal sample of {111}‹112› orientation was lightly rolled to 25% and subsequently annealed. Many recrystallized grains were formed in the rolled sample. The orientation of recrystallized grains formed at the rolled surface was totally different from the orientation of those formed in the interior of the sample. These results are discussed based on the tendency for cross-slip and the dislocation network model for nucleus of recrystallized grain.

Relationship between Deformation and Recrystallization Structures in Fe-Si Single Crystal and Bicrystal Containing {111}‹112› Grain

To study the relationship between slip morphology and recrystallization of body centered cubic metals, an Fe-3%Si alloy single crystal sample of {111} orientation and a bicrystal sample having {111}(112) and {001} component grains were deformed in tension and subsequently annealed. Both samples exhibited necking at the beginning of plastic deformation. The appearance of slip bands was totally different in the component grains of the bicrystal sample. Straight slip bands aligned along the traces of two {110} slip planes were observed in the {111}(112) grain. On the other hand, wavy slip bands accompanied by high-step cross-slip were observed in the {001}(110) grain. After annealing, the tensile-deformed single crystal sample did not recrystallize. In the bicrystal sample, recrystallized grains were formed only in the {111}(112) grain. The difficulty in recrystallization of tensile-deformed samples is discussed in relation to the tendency to cross-slip.

Influence of a magnetic field on the magnetoelasticity of commensurate spin-density-wave Cr–Ru and Cr–Si alloy single crystals

Previously reported attempts to produce a single-Q commensurate (C) spin-density-wave (SDW) state in a dilute Cr alloy by magnetic field cooling through the Néel temperature (TN), were unsuccessful. In the present study the influence of a cooling field of 4.5 T on the magnetoelasticity of Cr+0.3 at.% Ru and Cr+1.6 at.% Si alloy single crystals, both having CSDW phases below TN, are reported. The results show that cooling the Cr+0.3 at.% Ru crystal through TN in a field of 4.5 T has no influence on the first-order commensurate–incommensurate SDW magnetic phase transition. On the other hand, cooling the Cr+1.6 at.% Si crystal in a field of 4.5 T through TN noticeably affects the elasticity in the CSDW state, suggesting a condensation of part of this crystal into a single-Q CSDW phase.

BOB Acoustic-mode vibrational anharmonicity in Cr-Si alloy single crystals

Measurements are reported of the hydrostatic-pressure dependences of the elastic constants of $\mathrm{C}\mathrm{r}+0.5\mathrm{}\mathrm{at}.\mathrm{}%$ Si and $\mathrm{C}\mathrm{r}+1.6\mathrm{}\mathrm{at}.\mathrm{}%$ Si alloy single crystals through the N\'eel transition. In the former crystal the N\'eel transition is a second-order incommensurate (I) spin-density-wave (SDW)-to-paramagnetic (P) transition, while it is a first-order commensurate (C) SDW-to-P transition in the latter crystal. The pressure derivatives of the elastic constants at different constant temperatures are used to calculate the acoustic-mode Gr\"uneisen parameters, which quantify the vibrational anharmonicity, as a function of temperature through the N\'eel transition of each crystal. For the $\mathrm{C}\mathrm{r}+0.5\mathrm{}\mathrm{at}.\mathrm{}%$ Si crystal the mean long-wavelength acoustic mode Gr\"uneisen parameter, ${\overline{\ensuremath{\gamma}}}^{\mathrm{el}}\ensuremath{\approx}\ensuremath{-}5,$ jumps by $\ensuremath{\Delta}{\overline{\ensuremath{\gamma}}}^{\mathrm{el}}=30,$ from ${\overline{\ensuremath{\gamma}}}^{\mathrm{el}}\ensuremath{\approx}\ensuremath{-}5$ to ${\overline{\ensuremath{\gamma}}}^{\mathrm{el}}=+25,$ in going through the second-order ISDW-P N\'eel transition, and then decreases to a value of ${\overline{\ensuremath{\gamma}}}^{\mathrm{el}}\ensuremath{\approx}+5$ at temperatures well into the paramagnetic phase. This jump is much larger, $\ensuremath{\Delta}{\overline{\ensuremath{\gamma}}}^{\mathrm{el}}=170,$ from ${\overline{\ensuremath{\gamma}}}^{\mathrm{el}}=\ensuremath{-}50$ to ${\overline{\ensuremath{\gamma}}}^{\mathrm{el}}=+150,$ in going through the first-order CSDW-P N\'eel transition of $\mathrm{C}\mathrm{r}+1.6\mathrm{}\mathrm{at}.\mathrm{}%$ Si, after which ${\overline{\ensuremath{\gamma}}}^{\mathrm{el}}$ decreases to ${\overline{\ensuremath{\gamma}}}^{\mathrm{el}}\ensuremath{\approx}0$ at temperatures deep into the paramagnetic phase. The results show very strong coupling of the SDW to the long-wavelength longitudinal-acoustic phonons in both crystals. Coupling to the long-wavelength shear acoustic phonons is relatively weak. In both crystals there is also strong coupling of the longitudinal phonons with the spin fluctuations above ${T}_{N}.$ The present measurements are compared with anharmonic effects observed through the second-order CSDW-P N\'eel transitions of $\mathrm{C}\mathrm{r}+0.3\mathrm{}\mathrm{at}.\mathrm{}%$ Ru and $\mathrm{C}\mathrm{r}+3.5\mathrm{}\mathrm{at}.\mathrm{}%$ Al alloy single crystals.

X-ray scattering topography involving local spectroscopy

X-ray scattering topography using multichannel detectors as a position sensitive detector and an energy dispersive solid state detector is described. The system involves measuring the X-ray spectrum at each local place. The new topography system adds another dimension to X-ray scattering topography proposed by the present authors over the past ten years. It produces topographs, constructed with certain physical quantities, such as crystal orientation, as well as an ordinary integrated intensity map. Included in the paper is the orientation topography for an Fe-3%Si alloy single crystal, structural observation of an Al-4%Cu alloy polycrystal having a welded region, and the nondestructive testing of an amorphous rubber tyre. Emphasis is placed on the first proposal of X-ray spectroscopy topography.

A Method for Measuring Strain by Analyzing Sharpness of ECP WithImage Analysis

A method for measuring strain by analyzing sharpness of Electron Channeling Pattern (ECP) with Image analysis has been newly developed. The relative value of sharpness of first‐order pseudo‐Kikuchi line in ECP is used as a parameter of strain. Strain change of Fe‐3.25%Si alloy single crystal and polycrystal during deformation and recrystallization was analyzed by this method. This method was compared with the conventional methods; hardness and line broadening of X‐ray. This method can be used for measuring strain in material with any crystal orientation.

The short-range order structure of a water-quenched Ni-12.5 at. pct Si alloy—a synchrotron x-ray diffuse scattering study

A wide-angle X-ray diffuse scattering measurement of a water-quenched Ni-12.5 at. pct Si alloy single crystal was performed using synchrotron radiation. The Cowley-Warren short-range order (SRO) parameters and static displacement terms between atom pairs were obtained. The first seven SRO parameters were fitted in an 8000-atom model, from which it was deduced that no orderedγ′ domains existed in the water-quenched structure, but an enhancement of the C16 and C17 nearest-neighbor configurations did occur as compared to a completely random model. The C16 configuration is the basic structural unit of the L12 ordered structure, and the C17 may be thought of as a faulted variant thereof. These results were confirmed by performing equivalent SRO modeling in a 140,608-atom model. Silicon-silicon nearest neighbors show a repulsive strain of approximately 12 pct, while Ni-Ni pairs contract by less than 1 pct.

Positron annihilation lifetime measurement of cyclically deformed Fe-0.5wt%Si alloy single crystals

Positron annihilation lifetime measurement of cyclically deformed Fe-0.5wt%Si alloy single crystals

ＥＣＰにおける１次の擬菊池線の鮮明度解析による格子不規則性の評価方法

A method for measuring strain by analyzing the sharpness of first-order pseudo-Kikuchi line in Electron Channelling Pattern (ECP) was newly developed. The relative value of sharpness of first-order pseudo-Kikuchi line, which is the ratio of sharp ones in the first-order pseudo-Kikuchi lines, was used as a parameter of strain. Fe-3.25% Si alloy single crystal and polycrystal were used as the test specimens. Strain changes during their deformation and recrystallization were analyzed by this method. The main results obtained are as follows.(1) This method is useful for measuring strain in material with any crystal orientation.(2) The relative value of sharpness of first-order pseudo-Kikuchi line decreased as strain was increased. This method is useful for measuring strain less than 15% cold reduction.(3) The relative value of sharpness of first-order pseudo-Kikuchi lines was influenced by the initial crystal orientation before deformation. This phenomenon, recognized specially in the case of smaller strain, shows that accumulated strain is mainly influenced by the initial crystal orientation before deformation.(4) It is thought that this method is useful for analyzing crystal orientation dependence of accumulated strain and release of strain during recovery and recrystallization, as well as inhomogeneity of strain in the grain interior and near the grain boundary.

A small-angle neutron scattering study of the kinetics of phase separation in a supersaturated Ni-12.5 at. pct Si alloy

The kinetic behavior of precipitation in a supersaturated Ni-12.5 at. pct Si alloy single crystal has been studied by the small-angle neutron scattering (SANS) technique to supplement earlier transmission electron microscopy (TEM) and wide-angle X-ray diffraction (XRD) work. The SANS measurements performed at room temperature on quenched specimens subjected to isothermal anneals at 400, 450, 505, and 550 °C for various amounts of time have revealed the presence of an interference peak in the scattering function. The particle size, determined according to the Guinier approximation, is found to grow in accordance with the diffusion controlled model put forth by Lifshitz and Slyozov, and independently by Wagner. The activation energy for solute diffusion is determined using the rate constants governing the growth of particle size and the variation of the mean interparticle distance. Results are in agreement with the values given in the literature. Transition from an earlier growth stage has been observed, and enhanced diffusion is noted at temperatures below 505 °C; both observations are consistent with the previous X-ray results. The dynamical scaling law appears to be followed by the data obtained in the coarsening stage. A disruption of scaling occurs at the point when the particle growth changes from a parabolic rate behavior to a cubic coarsening rate. Dynamical scaling offers the potential for projecting the service lifetimes for components from experimental measurements carried out over a much shorter time interval. Discrepancies in the size parameters determined by different techniques are discussed.

Carbon segregation to the low-index surfaces of an Fe–10 at. % Si single crystal

Several mechanisms for carbon segregation to iron and iron alloy surfaces, specifically Fe–Si alloy single crystals, have been reported. This paper reports on measurements of carbon segregation to the (111) surface of an Fe–10 at. % Si crystal as measured with Auger electron spectroscopy in the temperature range 573–690 K. Three distinct consecutive processes have been identified in support of reported results on the (100) and (110) surfaces. The first is bulk to surface diffusion until the surface coverage reaches a value of 12–14 at. %. The activation energy for this process is 41±5 kJ/mol. The second process is associated with the growth of two-dimensional graphite islands on the surface until a surface coverage of about 45% is reached. This coverage is described as a ‘‘stable monolayer.’’ Further increase in the carbon concentration is associated with a further two-dimensional growth. The rate constants for the last two processes were determined by a fit of the Avrami equation to the data. The activation energies, determined from the Arrhenius plots, are, respectively, 115±10 and 147±10 kJ/mol. The results also indicate that the segregated graphite layer has some epitaxial relation to the substrate.