Etch Pit Technique Research Articles

Stress Corrosion Cracking of a SUS304 Stainless Steel in MgCl2 Solution

Stress corrosion cracking of a SUS304 stainless steel in boiling MgCl2 solution was studied fractographically with the aid of etch-pitting technique. An examination was also made on the applicability of linear fracture mechanics to SCC crack propagation. Fracture mode changed from transgranular to mixed intergranular-transgranular and again back to transgranular with an increase of stress intensity. The orientation of the transgranular fracture was predominantly {100} in fracture surface and <110> in propagating direction in the low stress region and changed to {110} surface and <110> direction in the high stress region. These fractures are likely to be caused by the complex effects of a number of mechanisms such as interaction of sessile dislocations or slip lines with chemical environment and decrease of surface energy in chemical environment. The linear fracture mechanics failed to valid in the high stress region where significant creep deformation was observed.

Yield Strength and Dislocation Mobility of KCl–KBr Solid Solution Single Crystals

The concentration and strain rate dependence of the critical shear stress in KCl–KBr solid solutions was measured by compression tests. These data were compared with the stress dependence of the dislocation velocity measured by an etch pit technique. Edge dislocation moved slower than screw dislocation at the same stress level. The critical stress was determined by the edge dislocation mobility, and the mobile dislocation density at yielding was about 1.2×1011 m-2 for the three kinds of composition tested. An analytical model of the hardening mechanism is proposed on the basis of the elastic interaction (size misfit) between an edge dislocation and solute atoms. When compared with experimental results, this model gives satisfactory results not only for KCl–KBr but also for NaCl–NaBr, and NaBr–KBr solid solutions.

&amp;lang;001&amp;rang;軸方位Cu-15 at%Al合金単結晶の高温定常変形

Copper-15 at% Al alloy single crystals with the 〈001〉 axis were deformed in tension at 873 and 973 K. The stress-strain curve exhibits a rapid work hardening initially and then levels off after several percent strain. In this stage, the condition of steady state deformation was satisfied. In the steady-state stage, the internal and effective stress levels were determined by the stress dip test using an extrapolation technique. Dislocation substructures formed in this stage were observed by the etch pit technique. The results obtained are as follows:(1) The axial orientation is stable during the entire period of deformation and the slip occurs on the four {111} planes at the same time.(2) In the steady-state stage, a cellular dislocation structure was built up. The dislocation density was proportional to the square of the applied stress. The cell size was inversely proportional to the square root of the dislocation density and to the applied stress.(3) The strain rate was proportional to the nth power of the applied stress, n being 3.8 at 873 K, or 3.6 at 973 K. These values are small in comparison with the Cu-Al alloy single crystals oriented for a single slip system. The difference in n arises from the difference of the dislocation structure between these alloys formed in the steady-state stages.(4) The ratio of the internal stress to the applied stress was 0.65∼0.8, depending on the applied stress monotonously.(5) The parameter m*, the effective stress sensitivity of dislocation glide velocity, was found to be nearly unity. This result indicates that high-temperature deformation of Cu-Al alloys is controlled by the viscous motion of dislocation in spite of the high n value.

Cu-2.5 at%Al合金単結晶の高温定常変形

Copper-2.5 at%Al alloy single crystals oriented for a single slip system were deformed in tension at 600 and 700°C. In the later stage of deformation, the condition of steady state deformation was satisfied; namely the specimens have been deformed at a constant stress, independent of strain. In this steady state deformation stage, the internal stress and the effective stress were determined by the stress dip test. The dislocation substructure formed in this stage were observed by the etch pit technique. The results obtained are as follows:(1) The tensile axis rotated into the direction predicted by the single glide on the (111)[\bar101] slip system. When the tensile axis approached the [001]-[\bar111] symmetry line, the steady state deformation was observed.(2) The strain rate is proportional to the nth power of the steady state stress and the n value is about 5.(3) The ratio of the internal stress to the applied stress is 0.6∼0.9 and depends on the applied stress. The effective stress increases with the applied stress.(4) The parameter m* describing the effective stress sensitivity of dislocation glide velocity was estimated assuming the mobile dislocation density to be proportional to the square of the applied stress and the m* value was found to be 1.1.(5) The subgrains elongating in the [1\bar21] direction are found on the (111) plane. On the (1\bar11) plane the rows of dislocations are found along the direction roughly parallel to the trace of the primary slip plane, and the high dislocation density regions, approximately perpendicular to the slip trace, are observed.

ステンレス鋼および炭素鋼の疲労き裂伝ぱと結晶方位

The effect of crystallographic orientation on fatigue crack propagation was studied with an 18-8 stainless steel and a carbon steel by applying the etch pit technique to observe their fracture surfaces. There was no marked preferential orientation on the fracture surfaces of both materials in contrast with the aluminum alloy previously studied. This seems to suggest that complex slip systems are operating around the tip of fatigue crack of these materials. In the case of the stainless steel, the combination of {100} fracture surface and <110> crack propagation direction was somewhat preferred, and a few cleavage-like facets associated with brittle striation-like patterns were observed on fracture surfaces, the orientation of the facets being {111} which is said to be a cleavage plane or twinning plane of face centered cubic metals.

Effect of electrolytic colouration on dislocation density in KBr and KCl

Average dislocation density in a number of electrolytically coloured and uncoloured crystals of KBr and KCl has been measured using the etch-pit technique. A decrease in density of dislocation after electrolytic colouration has been observed. This is attributed to the change in the dislocation pattern inside the crystals during colouration to produce more number of vacancies under the typical conditions of large electric field gradient at high temperature.

The growth of low dislocation density Sr1−x, Bax Nb2O6 crystals

The dislocation structures of both pure and Nd doped strontium barium niobate crystals, grown by the Czochralski method, were studied using an etch pit technique. It was determined that dislocations in the boule were being propagated from the seed and were confined to the center of the crystal. Typical dislocation density was 5x104 cm−2. Through the careful control of growth parameters and use of seed material cut from the dislocation free outer portion of a crystal, it was possible to grow crystals with very low dislocation densities, 1x102 cm−2, and on occasion dislocation free crystals.

Dislocation etch pits in gold

Newly developed etch-pitting technique for gold is reported. A one-to-one correspondence is obtained between etch pits and dislocations, with etchants of 1∶3 aqua regia and aqua regia plus suitable modifiers. The usefulness of these etchants has been established by several experimental results, such as the appearance of etch pit rosette patterns produced by indentation, correspondence between slip line and pit arrays in deformed crystals and climb polygonization arrays after annealing. It is also confirmed that the etchants are capable of differentiating positive and negative edge dislocations.

亜鉛単結晶の底面辷りの初期段階

An experimental study has been carried out to investigate the contribution of basal and nonbasal dislocations (forest dislocations) to the early stage of basal glide in 99.999% pure zinc single crystals compressed at room temperature. The relation between the basal shear stress and the shear strain was plotted and the increase of dislocation density during deformation was observed by means of the etch pit technique. The initial dislocation etch pit densities of the specimens used were 2.9×104∼3.7×104/cm2 on (0001) surface and 6.1×104∼5.2×105/cm2 on (11\bar20) surface. From these data, the length of basal and nonbasal dislocations per unit volume was calculated using equations developed by G. Schoeck. It was assumed that the density of forest dislocations did not change during the deformation since the critical resolved shear stresses for nonbasal slip systems are considerably higher than the stress employed in the experiments. The results obtained were as follows.(1) The multiplication stresses were approximately equal to the stresses required to break up the attractive junctions between basal and forest dislocations. (2) The yield stresses were represented by the sum of the stress necessary for the forest cutting and the internal stress due to the basal dislocations. From this result, it was concluded that the yield stress, was controlled by the forest cutting under the internal stress field of the basal dislocations.

Revealing Dislocations in m- Toluenediamine Single Crystals by a Selective Etch-Pit Technique

Abstract The etchant (benzene + 10% aniline) has been found for revealing dislocations in a new nonlinear single crystal of m-toluenediamine. The etchant reveals “as-grown” dislocations on the (010) and (001) planes as well as “fresh” ones (on the (010) plane). Kinetic observations on the (010) plane have been carried out using the selective etch-pit technique. Microhardness of the crystals and mean free path of dislocations as functions of the force acting on the indentor have also been determined.

Dislocation structures in copper matrix after constant stres cycling of copper/tungsten composites

Abstract Composites consisting of single crystal copper matrix containing 10 per cent volume fraction of uniaxially aligned tungsten fibres were subjected to constant stress cycling and the dislocation structures produced were studied by the etch-pitting technique. It was found that plastic deformation started in the soft region of the copper matrix away from the fibre. Dislocations piled up against the pre-existing sub-boundaries and cell walls. On cycling, progressively less permanent plastic strain was obtained. The cell structure seemed to be better defined. At stabilisation ( i.e. closed loop) the cell structure was fairly well developed thoughout the matrix although not of a uniform size. Cycling beyond stabilisation led to a greater rearrangement of dislocations into a metastable cellular structure. The stress cycling thus tended to make the copper matrix of a uniformly high dislocation density distributed in a more or less uniform cellular structure.

Perfection of copper-aluminum dilute alloy single crystals grown by the Bridgman method

The distribution and density of dislocations in 99.998% pure Cu, 0.05 and 0.10 at% Al-Cu crystals grown from the melt without cellular segregation were studied by an etch pit technique. The results obtained are as follows: (1) In pure Cu crystals, randomly distributed dislocations and subboundaries were formed. (2) In 0.05 at% Al-Cu crystals, no subboundaries were formed but many rosette patterns were observed. (3) In 0.10 at% Al-Cu crystals, some dislocation clusters were produced in addition to random dislocations, rosette patterns and subboundaries. (4) The rosette patterns and the dislocation clusters inherent in as-grown alloy crystals disappeared after thermal cyclic annealing. It is shown that these results are consistent with the concept of dislocation nucleation by impurity particles.

Production of highly perfect copper crystals with thermal cyclic annealing

Dislocation behavior in copper crystals in the course of annealing was studied, using an etch pit technique. Two annealing methods used were as follows: (1) isothermal annealing and (2) thermal cyclic annealing in which the temperature was changed between 1050° and 850°C with a period of 30 min. In the isothermal annealing, some of the isolated dislocations formed new sub-boundaries, without much reduction in the total number of dislocations. On the other hand, the thermal cyclic annealing was recognized to be conspicuously effective not only in the reduction of dislocations without forming new sub-boundaries but also in breaking-up of old sub-boundaries. With this thermal cyclic annealing highly perfect copper crystals were produced from crystals with initial dislocation densities as much as 1 × 10 6/cm 2.

The effects of crystallite orientation and size on the strength of polycrystals

The effect of crystallite orientation and crystallite size on polycrystalline strength has been investigated for Ferrovac E alpha-iron. Individual crystalline orientations, measured by etch pit techniques, have been used in determining weighted Taylor strength factors for different uniform grain sizes obtained by recrystallizing iron rods. Uniaxial tension tests and axisymmetric drawing tests were performed on specimens of each grain size. For the processing conditions and grain sizes obtained, no marked preferred orientation was present, and as a result only minor deviations from the theoretically predicted average random Taylor factors existed. Good agreement of orientation-corrected yield strength in uniaxial tension as a function of grain size was obtained using a Hall- Petch analysis. The present results on polycrystalline specimens have been used in conjunction with a previous analysis on single crystals of the same materials to determine the validity of the Taylor analysis, which predicts that strength is dependent on an orientation factor, M, and an orientation independent shear stress for slip, τ. It would appear that the Taylor analysis does not hold for polycrystalline specimens of various grain sizes.

The effects of pressurization on the microstructure and mechanical properties of magnesium oxide

Changes in microstructure in single crystals of MgO, containing elastic discontinuities, which result from pressurization treatments in the range 0.2 to 2 GN m−2 have been studied using an etch-pitting technique. Complex dislocation arrays have been observed around cubical and spherical cavities and precipitates. The observations are discussed in terms of stress and strain criteria. Production of {100} and {110} cracks at high pressure is also described. Following a 1 GN m−2 pressurization the flow stress was observed to decrease by < 10% and this has been related to the induced dislocation density. In polycrystalline MgO the fracture strength was unaltered by pressurization but the critical temperature difference of thermal shock,ΔTC, was increased by 55K. This has similarly been attributed to the movement of pressurization-induced dislocations.

Growth and Properties of Manganese Zinc Ferrite Single Crystals by the Flame Fusion Method

Homogeneous and fairly largesized manganese-zinc ferrite single crystals, which are applicable to ferrite head in VTR, has been grown by the flame fusion method. The operation conditions of the flame fusion apparatus and the preparation of suitable powder by calcination of the manganese-zinc-iron oxalate are described. The flame fusion technique is feasible for the single crystal growth of ferrite by the use of particular raw powder, when the conditions for the growth are controlled properly.X-ray microanalyser revealed that the distributions of manganese and zinc were homogeneous in the single crystal boule except the surface layer with the thickness of 0.5mm.The dislocation density was determined by an etch-pit technique. The pit-density of annealed sample was about 4.5×104 per cm and about one-tenth times smaller than that of the as-grown sample. The magnetic and the electric properties of the single crystals are also described.The output and the mechanical wear resistances of the ferrite head manufactured from the single crystal under investigation are dependent on the orientation of crystal axes in head construction.

Effect of Impurity Concentration and Plastic Deformation on Dislocation Density of KCl Crystals

AbstractUsing the etch pit technique both the distribution and density of dislocations in undeformed and dynamically deformed nominally pure and Sr2+ or Pb2+ doped KCl crystals are examined. Additionally, the role of specimen geometry in the plastic deformation within the I deformation stage is determined. For all the crystals examined the relationship between screw dislocation density and plastic flow stress obeys the formula τ ⋍ ϱsc.1/2.

Progress Report on Recent Advances in Physical Metallurgy: (B) Dislocation Morphology

The atomic structures of individual dislocations, the shapes adopted by isolated dislocation lines and loops, and the arrangement of groups of dislocations in networks, pile-ups, or multipoles may all be regarded as different aspects of dislocation morphology. Experimental information on these topics is largely obtained from transmission electron microscopy, supplemented by field-ion microscopy when the atomic configuration is being considered and by X-ray microscopy and etch-pitting techniques when dislocation arrangements are being investigated. Theoretical calculations are also important, and attention has recently been concentrated on problems in which either the elastic anisotropy or the core energy is significant.

Direct Observation of the Dislocation Motion in Ferromagnetic Crystals under Alternating Magnetic Fields

Motion of dislocations in Ni and Ni-50%Co single crystals by the application of alternating magnetic fields has been observed using the etch-pitting technique. Additional distances of motion of dislocations caused by the fields after the application of an external stress are distributed randomly in the range between several microns and about 80 µm at the yield point of each crystal, and their distances are almost independent of the field frequency. Experimental results are discussed on the basis of the interaction between individual dislocations and oscillating domain walls in ferromagnetic crystals.

Dislocation studies in bismuth-antimony alloy single crystals by etch pit technique

Dislocation studies in Bi-Sb crystals were made by etch pit techniques on the cleavage plane. A new reagent capable of revealing dislocations inclined to the cleavage plane is reported. Dislocation spirals and loops on the quenched specimens have been observed.