Etch Pit Technique Research Articles

Closure and growth behavior of short fatigue cracks at notches in 3% silicon iron.

Sharply notched specimens of 3 % silicon iron were fatigued under several stress ranges, either above or below the notched fatigue limit for complete fracture. The growth behavior of short fatigue cracks near the notch root was analyzed based on the crack closure. A computer-aided high-resolution unloading elastic compliance method was employed to measure the closure of short fatigue cracks. The etching susceptibility of 3 % silicon iron was used to observe the plastic zones around notches and cracks. The growth rate of short fatigue cracks first decelerated with increasing crack length, and then accelerated or became non-propagating, depending on the applied stress range. Similar deceleration was observed when the growth rate was correlated with the stress intensity range. The effective stress intensity range was a unique parameter in correlating the growth rate of short fatigue cracks, and the relation was identical to that obtained for long cracks. Notch plasticity was not a direct cause for the deceleration. The highly strained zone size, measured by the etch pit technique, was useful for estimating the effective stress intensity range for short cracks.

銅単結晶の変形段階IIにおける2次すべりの発生

Corroborative evidence for the origin of generation of secondary slip at stage II in the stress-strain curve has been obtained by detailed analyses with the etch-pit technique in copper crystals. It is shown that a sudden occurrence of secondary slip at stage II is directly related to the formation of deformation bands, particularly to the building-up of kink-band walls that is, as reported previously, the trigger for the transition from stage I to II. Among secondary slip systems actually observed in the kink-band wall region, the operation of the cross slip system (S42) is of particular interest because of its Schmid factor being zero. This strongly suggests that the sudden generation of secondary slip is caused by the internal stress induced by primary main slip (S11) dislocations piled-up against the kink-band wall. From the calculation based on a pile-up model, it is understood that primary coplanar slip S13 and secondary systems such as critical main slip S31, conjugate main slip S21, critical coplanar slip S23 and cross slip S42 are subject to fairly large internal stresses due to the pile-up of S11 dislocations. Especially, the operation of S21 and S33 is important because of their interaction with S11 which leads to the formation of Lomer sessiles.

Dynamic recovery during compression testing of monocrystalline NaCl at elevated temperatures

Single crystals of NaCl in a 〈100〉 orientation were tested under compression in the constant-strain-rate mode at 873 and 973 K. The evolution of the dislocation microstructure was studied at both temperatures over the entire range of strains (up to 0.2) using standard etch-pitting techniques. At 873 K the flow stress σ slowly increases monotonically with strain even though the free dislocation density ϱ (the dislocations within subgrains) passes through a maximum at a plastic strain of about 0.02. At 973 K, ϱ behaves similarly, although nearly steady state flow is eventually observed; in this stage the substructure as well as the flow stress remain invariant with further straining. It is argued that the initial increase in ϱ is comparable with that which occurs on the loading of a sample during a creep test. However, since the loading rate during a constant-strain-rate test is typically much slower than it is during a creep test, the increase in ϱ at small strains is easier to follow. On establishment of the maximum dislocation density compatible with the (approximate) steady state flow stress at elevated temperatures, recovery produces coarsening of the dislocation network. The attendant reduction in ϱ at nearly constant σ is then entirely analogous to the decrease in ϱ that occurs during primary creep in conventional creep tests.

Dislocation structures in deformed CoO and MnO

Transmission electron microscopy (TEM) and etch-pitting techniques have been used to examine dislocation structures of CoO and MnO single crystals deformed into steady state from 1000 to 1400° C. In this temperature range, studies have shown that there are low- and high-temperature activation energies (Q) and stress exponents (n). No change was observed in the structures of samples deformed within this temperature range. It is concluded, therefore, that any change inQ andn values is due to a change in oxygen diffusion path from the bulk at higher temperatures to along dislocation cores at lower temperatures, rather than being due to a change in the rate-controlling mechanism of deformation

Etching studies on crystals of thallium arsenic selenide

Abstract An etchpit technique was developed and used to reveal the dislocations in crystals of thallium arsenic selenide (Tl3AsSe3). The etchpit density was higher near the surface of the cylindrical crystals than at the corresponding central region. Also the density was very high near the seed-bulk joint. Taken together these features suggest that the etchpits were related to stresses induced by the temperature distribution in the growing crystal. A calculation of the thermal stress distribution in the Bridgman-grown crystal by means of a finite element method supports the observations of the etchpit studies.

Surface damage of CdTe produced during sample preparation, and determination of dislocation types near microhardness indentations

Abstract The influence of cutting, grinding and polishing during sample preparation of CdTe Bridgman monocrystals has been investigated by an etch-pit technique. Dislocations, mainly produced by cutting the sample with a diamond wire saw, were found to move several hundreds of micrometres from the surface into the bulk of the samples. The structure of dislocation loops near microhardness indentations was analysed by the same etch-pit technique and by birefringence observations. The Burgers vectors of the dislocations were determined by X-ray topography. Long dislocation segments were found to be screw dislocations.

Transmission Kossel study of the formation of (110) [001] grains after an intermediate annealing in grain oriented silicon steel containing a small amount of Mo

The transmission Kossel (TK) technique was applied in an attempt to elucidate the formation of (110) [001] grains in the recrystallized texture of high induction and low core loss grain oriented silicon steel containing a small amount of Mo after an intermediate annealing. Prior to the detailed TK examination, the etch pit technique was also used for seeking the representative areas of (110) [001] grains. The average matrix grain size of an intermediate annealed steel containing a small amount of Mo is slightly smaller than that with no Mo. The formation of (110) [001] grains in the vicinity of the steel surface is also strengthened due to the addition of Mo. The diameters of single (110) [001] grains are comparable to or slightly larger than those of other matrix grains, but those of the colonized (110) [001] grains occupy extremely large areas (about 40 pet at the maximum area). The areal fraction of (110) [001] grains of the intermediate annealed sheets containing a small amount of Mo is approximately 1 to 5 times as large as that with the conventional inhibitors such as MnSe and Sb. The colonies of (110) [001] grains formed during an intermediate annealing are compatible with the volume fraction inherited from small and well-defined (110) [001] areas with the sharpened TK patterns in the hotrolled sheet containing a small amount of Mo. It is believed that the preferential formation of (110) [001] grains during an intermediate annealing is inherited by the structure memory from the original hot-rolled texture, and it is noticeably strengthened with the addition of Mo.

Growth of single crystals of potassium chloride from gels

AbstractThe growth of single crystals of potassium chloride (KCl) in silica gels upto 3 × 3 × 3 mm3 in size is described. To crystallize KCl incorporated in the gel, hydrochloric acid has been used to crystallize the KCl in the gel media. The crystalline perfection has been studied by the chemical etch pit technique.

Effects of crystallographic orientation on plastic deformation and SCC initiation of zirconium alloys

In order to investigate the effects of crystallographic orientation on deformation and crack initiation in iodine-induced SCC of zirconium alloys, uniaxial tensile tests of zirconium and Zircaloy-2 plates were conducted in an iodine atmosphere. The crystallographic orientation of individual grains was determined by an etch-pit technique prior to testing. After testing, the etch-pit technique showed that prismatic slip was predominant in the plastic deformation and that cleavage cracks extended along basal planes. The plastic deformation of individual grains was significantly influenced by their crystallographic orientations, which varied from one grain to another. Accordingly, inhomogeneous plastic deformation occurred between grains. The crack initiation took place preferentially at grain boundaries where differences of crystallographic orientations were large between adjacent grains. This indicated that crack initiations was caused by stress concentration due to strain incompatibility at those grain boundaries.

Chemical and electrolytic etch pits on the (111) surface of silver single crystals

The etch pit technique was utilized to reveal the dislocation structure on the (111) surface of silver single crystals. The study included the orientation of etch pits formed chemically and electrolytically on the (111) face. Changes in the crystallographic orientation of the etch pits were obtained by varying the current density and the concentration and composition of the etching solution. Grooved etch pits were obtained in a cyanide bath, whereas circular and triangular pits were obtained in an ammonium hydroxide bath. A one-to-one correspondence between the etch pits and the dislocation lines intersecting the surface was established.

The reduction of grown-in dislocation density in anthracene crystals due to heat treatment and growth conditions

Two kinds of experiments were carried out to improve the perfection of anthracene single crystals: (1) dependence of the grown-in dislocation density on crystal size and (2) heat treatment. Non-basal dislocation densities were measured by an etch-pit technique. The results are discussed in the light of the motion of non-basal dislocations.

Dislocation motion in MgO crystals under plate impact

Dislocation dynamics in MgO single crystals is studied by means of plate impact experiments in which specimens are subjected to stress pulses of 214 to 376 MPa resolved shear stress with duration in the range of 0.09 to 0.23μsec. Dislocation structures in the recovered crystals are observed by an etch pit technique and by transmission electron microscopy. Etch pit studies show that inclusions play a role in the generation of interior glide bands and that there is a 20 to 40-fold increase in dislocation densities outside the glide bands. Assuming the average dislocation velocity is approximately proportional to the applied stress the drag coefficient for MgO at dislocation velocities of 1 to 2 km sec−1 is observed to be 5×10−5 Nsec m−2. Transmission electron microscopy determines the spacing and curvature of dislocations in glide bands.

Recrystallization of Si films on thermal SiO2-coated Si substrates using a high-speed e-beam line source

Lateral zone melting from a fast-scanning (5-30-cm/s) e-beam line source has been used to grow single-crystal films with an area limited only by the e-beam scan field. Electron backscattering contrast and etch pit techniques have been used to study the crystallographic orientation and the extent of single-crystal silicon film growth on thermal SiO 2 -coated silicon (SOI) wafers.

Transmission Kossel study of the formation of Goss grains after an intermediate annealing in grain oriented silicon steel.

Transmission Kossel (TK) technique has been applied in an attempt to investigate the formation of (110)[001] grains in the recrystallized texture after an intermediate annealing in the high induction grain oriented silicon steel. Prior to the detailed TK examination, the etch pit technique was also used for seeking the representative areas of (110)[001] grains. The preferential formation of (110)[001] grains takes place within the definite elongated matrix zone along the rolling direction at about 1/10 depth under the steel surface, and most of (110)[001] grains form at the colonies. Within the matrix zones in which (110)[001] grains are preferentially formed, there are many recrystallized {hk0}(001) grains. The colonies of (110)[001] grains formed during an intermediate annealing are compatible with the volume fractions of (110)[001] areas inherited from the highly oriented one with the sharpened TK patterns in the hot-rolled sheet. They also correspond to the subsequent volume fraction of colonies of the large primary recrystallized (110)[001] grains, which are formed during the as-decarburized and primary recrystallized annealing, prior to the secondary recrystallization treatment. It is considered that the preferential formation of (110)[001] grains during an intermediate annealing has been inherited by the structure memory from the original hot-rolled texture and the nice memory of the structure is indispensable for the development of the celebrated (110)[001] secondary grains.

Dislocation mobility in LiF at low temperatures

AbstractThe mobility of dislocations in LiF has been measured at 4.2 and 10 K by means of an etch pit technique. The average velocity of screw dislocations is 2–5 times as large as edge dislocations. The results of the stress and temperature dependence of the velocities correlate well with the data of the critical shear stress in the same temperature region, and are well described by the theory of Peierls mechanism with thd Peierls stress of about 20 MPa for edge dislocations on {110} slip plane.

Silicon film recrystallisation using e-beam line source

Lateral zone melting from a fast-scanning (50 to 30 cm/s) E-beam line source has been used to grow single-crystal films with an area limited only by the E-beam scan field. Electron backscattering contrast and etch pit techniques have been used to study the crystallographic orientation and extent of single crystal silicon film growth on SiO 2 -coated silicon wafers. (100) textured films have been grown on these (0.35 to 1.0 μm thick) SiO 2 layers containing periodic openings to permit seeding during recrystallisation. Recrystallisation of non-seeded polysilicon produced (111)-textured films. Enhancement mode n-channel MOSFETs have been made in both types of films. Channel mobility as high as 600 cm 2 /V-sec has been measured in the (100) textured films.

Etch pits on single crystals and bicrystals of niobium

Three types of etch pit were observed on single crystals and bicrystals of niobium. The relationship between the shape of the pits and the orientation of the etching surface was established and discussed on the basis of the surface energy concept. It was demonstrated that misorientations of tilt boundaries can be determined in bicrystals using the etch pit technique.

亜鉛における{11\bar22}⟨\bar1\bar123⟩すべりの温度依存性

The tensile deformation behavior of zinc thin sheet crystals was investigated at the temperature range from 207 to 333 K. The tensile axis of specimens is parallel to 〈11\bar20〉, and the surface is parallel to {0001} (A specimens) or {00\bar10} (B specimens). B specimens showed such anomalous dependence that the yield stress increased from 11 to 13 MPa with increasing temperature, in contrast with the yield stress of A specimens decreasing from 13 to 9 MPa. The length of slip bands which appeared just after yielding decreased from 3 to 0.3 mm, and the mean free path of edge dislocations evaluated by the etch pit technique decreased from 300 to 10 μm with increasing temperature. The stress-strain curves of both A and B specimens exhibited stage I having the small work hardening ratio and then stage II having the large ratio. Stage II began just after the bundle of slip bands widening with strain filled up the whole of specimen. With increasing temperature, the strain of stage I decreased and the work hardening ratio at stage II increased rapidly.From the standpoint of propagation of dislocation multiplication, the above results were explained by structural peculiarity of edge dislocation core, prismatic loops as barriers and dislocation reaction.

An investigation of the stress exponent and subgrain size in Al after stress reduction

Abstract Stress-change and uninterrupted tests were performed on Al over the high-temperature range 0·65–0·99T m, where T m is the melting point, and at stresses varying from 7 × 10−6 G to −2 × 10−4 G, where G is the shear modulus. In addition, dislocation substructure that developed during creep was examined by means of the etch-pit technique and transmission electron microscopy. By comparing the mechanical and substructural data of stress-reduction tests with those obtained in uninterrupted tests, two observations are made. First, the stress exponent inferred from stress-reduction tests is essentially equal to that obtained from uninter rupted tests. Second, as a result of stress reduction, the subgrain size coarsens and reaches the new steady-state value whicli would be attained in an uninterrupted test at the reduced stress. Evidence of subgrain coarsening is demonstrated not only by changes in size, but also by relevant substructural phenomena, such as subgrain-boundary dissolution, which are noted d...

Correlation between creep behavior and substructure in an Al-3at.%Mg solid solution alloy

The dislocation substructure formed during the creep of an Al-3at.%Mg alloy under steady state conditions was investigated. The stress dependence of the substructure was examined by an etch pit technique and transmission electron microscopy over a normalized stress range extending from τ/G = 10 −5 to τ/G = 10 −3 (where τ is the applied shear stress and G is the shear modulus). On the basis of this examination, the substructural behavior of the alloy is divided into three distinct regions, depending on the value of the normalized stress. In region I ( τ/G > 4 × 10 −4), the substructure consists of an essentially random distribution of long curved dislocations with no significant tendency to form subboundaries in the interiors of grains. In region III ( τ/G < 2 × 10 −5), well-developed subgrains are formed and dislocations sometimes form irregularly spaced networks inside subgrains. In region II (2 × 10 −5 < τ/G < 4 × 10 −4), which represents a transition region between region I and region III, the substructure consists of a large number of long curved dislocations and subboundaries in the process of development. It is demonstrated that the present substructural observations together with the mechanical evidence are in conformity with the prediction that the creep behavior of a solid solution alloy would change from control by viscous glide to control by dislocation climb with decreasing stress.