Transmission Electron Microscopy Of Foils Research Articles

Kinetics of sensitization and de-sensitization of duplex 308 stainless steel

The kinetics of, and the factors responsible for, sensitization and de-sensitization were determined for duplex 308 stainless steel. Samples consisting of 10 vol.% of ferrite, balance austenite were heat treated at 600 and 550°C for times of 15 min-300h. The chromium contents of the α−γ boundaries and γ−γ grain boundaries of heat treated samples were measured by a potentiostatic electrochemical technique. Transmission electron microscopy of foils and surface replicas of heat treated samples was used to observe carbide precipitation on the boundaries and decomposition of the ferrite. Carbide precipitation occurred exclusively along the α−γ boundaries. Most of the chromium in the carbide came from the ferrite phase. However, intergranular corrosion susceptibility resulted from a narrow chromium depleted zone that was formed on the austenite side of the interface and a chromium depleted zone that formed along the γ−γ grain boundaries. The latter developed in spite of the absence of carbides along the γ−γ grain boundaries. It resulted from grain boundary diffusion of chromium to the carbides growing along the α−γ boundaries. There was a maximum in the degree of sensitization with time of heat treatment. At aging times < t max , the degree of sensitization was limited by the achievement of a chromium depleted zone of a critical minimum width. An upper bound estimate of the latter was ~ 25 Å. At aging times > t max , de-sensitization occurred. This was controlled by the chromium content in the matrix at the carbide-matrix interface. Initially, the rate of de-sensitization was rapid and was produced by chromium diffusing from the ferrite phase and into the chromium depleted zone in the austenite. When the ferrite phase started to decompose the rate of de-sensitization decreased dramatically and was produced by volume diffusion of chromium in the austenite phase.

High-resolution and in situ tem studies of annealing of Ti-Si multilayers

The solid state amorphization reaction in sputtered amorphous-siliconpolycrystalline-titanium multilayers has been studied in cross-section by high-resolution transmission electron microscopy (TEM). Heat treatments included rapid thermal annealing and in situ heating in the microscope. The bilayer spacing of the sample is 25.0 nm and the composition is 50at.%Ti-50at.%Si. Growth of the alloy is strictly planar. The amorphization does not occur preferentially along titanium grain boundaries. The reaction is diffusion controlled with an activation energy of about 2.0 eV atom −1. When the layers are partially reacted, the amorphous alloy composition is silicon rich, with an estimated Ti:Si atomic ratio of 1:2. Ónce all of the elemental silicon is consumed the alloy incorporates more titanium, reaching a composition of about Ti 45Si 55. In situ studies reveal that Kirkendall voids form at this point in place of the silicon layers. In situ annealing studies duplicate the microstructure observed in the bulk-annealed samples; from this we conclude that bulk diffusion dominated in the thin TEM foil.

Transformation of Mg 2Si during TEM foil preparation

Decomposition of Mg 2Si particles was observed as foils of aluminum alloys were jet polished for transmission electron microscopy (TEM). Mg 2Si in contact with a HNO 3-methanol solution is converted to an amorphous SiO(H) phase. The amorphous phase remains as an artifact in the foil because the volume change associated with the transformation is small. Primary silicon particles were not altered during jet thinning.

Radiation damage effects in GaAs transmission electron microscopy specimens prepared by ion milling

Radiation damage effects produced during ion milling of GaAs specimens were investigated by transmission electron microscopy (TEM). The characteristics of the damage were (1) a surface amorphous layer, (2) a subsurface damage region and (3) second-phase particles at the TEM foil edge. A simple model involving damage production by energetic singly and doubly charged ions was developed to explain these observations. The particles were introduced by sputtering from the specimen holder in the ion mill.

Mechanical damage introduced into aluminum monocrystals during TEM thin-foil preparation

The mechanical damage that is introduced into annealed aluminum by the various steps used in the preparation of thin foils for transmission electron microscopy (TEM) is discussed. These steps are: (1) preparation of 3-mm discs by mechanical punching; (2) preparation of 3-mm discs by spark-cutting; and (3) intermediate thinning by hand-grinding discs to thicknesses of 500, 375, 300, or 200 ..mu..m. Often these steps precede the final electrochemical jet-thinning used to obtain perforated TEM foils. The mechanical damage produced by these steps was evaluated by comparing, in the TEM, thin foils utilizing one of these steps with other thin foils of annealed (undamaged) aluminum. Damage was manifested by an increased dislocation density. The mechanical punching was performed on a device machined at the Lawrence Livermore National Laboratory that was very similar to smaller, commercially available punches. The spark-cutting was performed on a Metal Research LTD Servomet at a setting of 6 using a tubular brass cutting tool. Jet-thinning was done on a Struers Tenupol 2 using an electrolyte of 469 mL methyl alcohol, 25 mL H/sub 2/SO/sub 4/ and 6 mL HF at 265 K. Thinning was performed at 25 V. The aluminum (99.999% pure) was provided by Highways Internationalmore » as plate (1 x 100 x 100 mm). The plate was annealed at 723 K for 20 min in vacuum. The resulting average grain size was about 4 mm. Therefore, the discs that were punched, spark-cut, and ground were smaller than the typical grain or monocrystal.« less

Effect of stress on hydrogen solubility and the low temperature deformation characteristics in vanadium containing hydrogen

The effect of applied stress near the yield stress on the dissolution temperature of hydrides in vanadium has been investigated by transmission electron microscopy (TEM) and by resistivity measurements. 1. (1) The dissolution temperature of hydrides in thin foil TEM specimens increases by 5 (0.036at.%) to 16 K (0.5 at.%) by the external tensile stress. 2. (2) In wire specimens, the change in the dissolution temperature by the external stress is within the accuracy of experiments (~ 1 K). Although the estimate by the conventional theory is in apparent agreement with the resistivity result on wire specimens, it is suggested that the TEM result on thin foil specimens should be regarded as better representing the effect of the external stress. In order to clarify the role of hydrides in the mechanical strength at low-temperatures, the elastic limit and the resistivity of wire specimens have been measured simultaneously. It is concluded that the hardening is due to hydrogen clustering along moving dislocations.

Electronmicroscopic Examination of Corroded Aluminum‐Copper Alloy Foils

The formation of particles of copper through selective dissolution of dilute Al‐Cu solid solutions in sulfuric acid was studied by transmission electron microscopy of foils prethinned before corrosion. A technique was employed for prethinning without surface enrichment. At −500 mV vs. SCE, a significant fraction of the copper made available by selective dissolution appeared as particles, but not at −100 mV vs. SCE. The results are discussed with reference to concurrent AES observations on the Cu‐enriched solid solution beneath the anodic film over the main body of the electrode.

Microstructures and Precipitation in a Rapidly Solidified Copper-Beryllium Alloy

A study of direct strip cast copper-beryllium alloys is of interest to determine if enhanced properties could be obtained from rapidly solidified material compared to those of conventionally processed material. The present investigation was undertaken to characterize the as-cast microstructure of this material and to study the metastable phases which formed in this alloy as a result of precipitation from the rapidly quenched condition.The melt spinning technique was used to produce ribbons of a copper-beryllium alloy of nominal composition Cu-1.90wt% Be containing 0.25 wt% cobalt. The as-cast ribbon was approximately 0.1 mm thick and 12 mm wide. The Metglas Products Division of Allied Corporation provided the material. As-cast specimens were salt bath aged at 370 C for 5 min or 3 hours. Thin foils for transmission electron microscopy (TEM) were prepared from the melt spun ribbons by electrolytically thinning in a twin-jet electropolisher using a solution of 30% nitric acid in methanol at -30 C and 25 volts. The specimens were examined in a Siemens 102 transmission electron microscope operating at 125 kV.

An Analytical Electron Microscopy Characterization of Melt-Spun Iron/Rare-Earth/Boron Magnetic Materials

Iron/rare-earth/boron permanent magnet materials have recently been delveloped to reduce the need for the strategic element cobalt, which was previously the primary canponent of high-energy magnets. These materials are generally produced by annealing rapidly solidified ribbons or by conventional powder metallurgy techniques. This paper will report results from an analytical electron microscopy characterization undertaken to establish the relationship between the magnetic properties and the microstructure of two iron/rare-earth/boron (Fe/RE/B) alloys. Ribbons of Fe75Pr15B10 and Fe77Tb15B8 were produced by melt-spinning. To obtain optimum magnetic properties, both alloys were then annealed at 700°C, the FePrB ribbons for 6 minutes and the FeTbB ribbons for 90 minutes. Foils for transmission electron microscopy were prepared by ion-milling the ribbons on a cold stage and examined using a Philips 400T TEM/STEM equipped with an energy dispersive x-ray unit.

Structure of molybdenum bombarded with low-energy hydrogen and helium ions during creep tests

To find the causes of the increase in the creep resistance as a result of ion bombardment, methods of high-voltage and analytic transmission electronmicroscopy were used to make a detailed study of the three-dimensional structure of specimens of single-crystal molybdenum, deformed without irradiation and under bombardment with low-energy ions from a glow discharge. Foils for transmission electron microscopy (TEM) were prepared from the axial testsections of the molybdenum specimens, which had been earlier subjected to creep tests [2]. Since bombardment with ions from a glow discharge causes bulk changes in the structure of the metal by acting on its surface, it seemed natural to expect the most significant and informative (in relation to an understanding of the phenomenon as a whole) structural changes near the surface. Accordingly, we first made a detailed study of the defect structure of the surface layers in the specimens subjected to bombardment without a mechanical load. For this purpose a series of disk-shaped (diameter 3 mm) single-crystal specimens of molybdenum were prepared [3] and were bombarded with helium and hydrogen ions from a glow discharge (T = 1500~ T = 1 h), after which the well-known methods of [4, 5] were used to prepare foils for TEM and their surface structure was studied with the aid of tomography. Most of the foils were examined in JEM-1000 and EM-301 G microscopes at an accelerating voltage of 1 }fV and i00 kV, respectively. The three-dimensional dislocation structures of the specimens bombarded in a.discharge of H2 or a mixture of He + H2 under strain differ considerably from the structures Of specimens tested in a vacuum. Figure 1 presents photomicrographs of low-angle boundaries in molybdenum specimens after creep testing without (a, b) and with (c, d) irradiation from a mediumof pure hydrogen. Even though the average size (~i00 ~m) and shape of the blocks in both specimens are roughly the same, the dislocation structures of the interblock boundaries and the form of the dislocations themselves differ markedly, as can be seen well from the photomicrographs. In the specimen tested under bombardment the dislocations are highly curved, while in block boundaries they are intertwined, often forming pileups that cannot be resolved by TEM. Near block boundaries are dislocation loops of a size of 30-80 n m, whose density varies within wide limits. Extremely diverse dislocation configurations are formed in specimens that have been bombarded under strain with ions from a glow discharge in an He + H~ mixture (Fig. 2). The photomicrographs in Fig. 2a, b show a large-cell hexagonal dislocation wall and a wall with elements of tetragonal cells formed in the bombarded specimen under strain. In practically all of the dislocation lines of such walls, including purely screw dislocation lines, a fine serrated structure was detected at higher magnifications. Even larger-celled dislocation walls with a less regular structure are encountered (Fig. 2c) and so are individual phase precipitates of

Elastic distortion of α-Fe particles in a Cu matrix caused by orowan loops

We attempted direct detection of elastic distortion in α-Fe particles embedded in a Cu matrix and surrounded by Orowan loops, by utilizing moiré fringes which were formed by nearly parallel matrix {111} Cu and particle {110} Fe planes. Foils for transmission electron microscopy were made out of a work hardened Cu-Fe sample. Rotation angles of the moiré fringes, which gave the inclination angles of the particle {110} Fe planes to the matrix {111} Cu planes, were examined before and after foil annealing. The annealing rotated the panicle {110} Fe planes in the same direction for almost all the panicles examined, indicating the decrease in the elastic distortion of the panicles due to the disappearance of the Orowan loops. The measured rotation angles on the annealing were in the correct order of magnitude predicted by an elasticity calculation, although the absolute magnitude was smaller in the measurement.

Characterization of precipitate s in a Fe-10Cr-6Mo-0.5 Nb ferritic steel

In the course of studying radiation damage in ferritic steels, there was a need for information on the nature of precipitate phases in one of the steels, an alloy of composition Fe-10Cr-6Mo-0.54Nb-0.33V-0.45Mn-0.3Si-0.05C (wt%). Since suitable data were not available in the literature an analysis was performed. The experiments were done with 3-mm diam disks punched from 0.5-mm thick rolled strips. The disks were annealed in evacuated quartz capsules for 1h at 1150/sup 0/C, followed by cooling to room temperature in an unheated part of the furnace, then reheated to 730/sup 0/ for 1h and cooled again in the cold zone. The microstructure consisted of equiaxed ferrite grains containing several apparently different precipitates. A morphological distinction between the various precipitates was made by optical metallography and transmission electron microscopy (TEM). The precipitates were analyzed in the TEM foils and in extracted form on carbon films by electron diffraction and energy dispersive x-ray spectroscopy (EDS), and in extracted form on single-crystal silicon substrates using conventional x-ray diffraction. 9 references 3 figures.

Transmission Electron Microscopy of Fine Powder Samples

There is increasing interest in the possible use of parts fabricated from fine powders of metallic alloys for structural purposes because of possible improvements in strength both at low and high temperatures. Since powders can experience very high solidification rates, alloys prepared in powder form by rapid quenching may achieve a degree of homogeneity not obtainable by any other means. Also, these high solidification rates might make it possible to produce amorphous powders.Determination of the microstructures of such powders may require transmission electron microscopy of either replicas or thin foils. This report describes a relatively simple method of preparing thin foils of powders, and illustrates the microstructures of fine powders of a nickel-base superalloy and of an amorphous alloy. The method involves incorporating the powders into a metal matrix, and thinning matrix and powder by ion-milling or by electropolishing.

Transmission electron microscopy foil preparation and results for incoloy 901

A two-step single-electrolyte technique for preparing foils from the iron-nickel superalloy, Incoloy 901, for examination in an electron transmission microscope is described. Some typical transmission electron micrographs are presented.

The mechanical behaviour of cuprous oxide

The stress-strain behaviour under compresion at constant strain rate of single crystals (〈051〉 and 〈122〉) compression axis) and polycrystalline samples of cuprous oxide have been examined at room temperature and hydrostatic pressure up to 12 kb and at atmospheric pressure and high temperature up to 600° C. At high environmental pressure, plastic flow occurs at 6 kb. At high temperatures and one atmosphere, extensive plastic deformation was observed after 500° C. The resultant slip planes were of the {110} and {100} types. Transmission electron microscopy of thin foils prepared from deformed specimens shows that the Burgers' vectors of the glide dislocations are of the 〈111〉, 〈110〉 and 〈100〉 types.

Electropolishing of T-111 foils for transmission electron microscopy

Electropolishing of T-111 foils for transmission electron microscopy

A simple technique for the preparation of silicon thin foils for transmission electron microscopy

A simple technique has been developed for the preparation of silicom thin foils. X-ray topography examination has indicated that the finished foils are free from any defects introduced during the preparation process.

Note on the electropolishing of iridium foils for transmission electron microscopy—some additional techniques

Note on the electropolishing of iridium foils for transmission electron microscopy—some additional techniques

On preparation of oriented foils from ferromagnetic materials for tem

A method of preparation of oriented foils for transmission electron microscopy from ferromagnetic material by jet electropolishing and chemical dissolution of thick edge of perforated disc is described. The minimization of the mass of a ferromagnetic foil in the microscope results in an important reduction of additional astigmatism. An image of better quality is easily obtained. The case of preparation of foils from Fe-3% Si alloy by this method is treated in detail. The principle of the suggested method is applicable to other ferromagnetic materials.

Study of the origin of coercivity in the semihard permanent magnet alloy, 82Co-12Fe-6Ti

The dependence of coercivity, resistivity and mechanical hardness on aging time and temperature was studied in solution treated and quenched 5 mil thick 82Co-12Fe-6Ti tape and related to changes in microstructure observed using transmission electron microscopy of thin foils. The results indicate that a fine scale periodic array of coherent precipitates is responsible for the increase in coercivity in this alloy in the solution treated, quenched, and aged state. This periodic coherent phase mixture must coarsen appreciably in order to produce a significant increase in coercivity, whereas mechanical hardness is significantly increased by the development of the modulated structure from the onset of precipitation.