The high temperature equilibrium β phase in Cu-based alloys has a disordexed bcc structure. Its stability at high temperatures is due to the large amplitude ﹛0 ζ ζ)﹜ <0 ζ ζ> soft mode which provides a large vibrational entropy. This stability decreases with temperature as the entropy term in the Gibbs free energy becomes smaller. However, by quenching it is possible to retain the β phase avoiding decomposition by diffusion controlled transformations. in ternary β phase Cu-Zn- Al alloys, ion irradiation at room temperature has been reported to induce a phase transformation to a close packed structure or to produce γ phase precipitates. in order to further study the tendency of the β phase to decompose into other phases at room temperature, ion irradiation experiments in binary Cu-Zn single crystals were carried out using a beam of 30 keV Ar ions. The changes in the microstructure were examined using transmission electron microscopy.

Previous studies on aluminum-potassium-silicon (AKS) doped tungsten wire have shown that the dispersion which provides the interlocking grain structure in recrystallized tungsten wire is bubbles of elemental potassium. However, there is little previous work on the K-containing dispersion in doped Mo. This paper will describe analyses of doped Mo.

The creation of dopant inclusions in Mo powder and generation of K bubbles in doped Mo wire both prior to and following various heat treatments has been studied. The effect of doping Mo with K, Al and Si is to increase the recrystallization temperature of the Mo and to produce a microstructure of coarse, interlocking grains after recrystallization.

Mo wire is produced in a similar manner to AKS doped tungsten, however lower processing temperatures are typically used in the production of Mo wire. The dopants are added to Mo oxide powder as potassium silicate and aluminum chloride.

It is well known that rare-gas Xe atoms embedded in a crystalline Al matrix form precipitates having cuboctahedral shapes bounded by ﹛100﹜ and ﹛111﹜ surfaces1. Below a certain critical size, Xe precipitates are observed to be solid, even at room temperature. This is a result of the Laplace pressure, which is inversely proportional to the radius of the precipitate. Donnelly et al. reported that the critical size of Xe solidification was expected at 4nm in radius at room temperature.

Using high-resolution transmission electron microscopy, it is possible to observe these particles directly. It has been demonstrated that under off-Bragg conditions, the Al lattice fringes are minimized whereas the Xe lattice fringes are maximized. From such observations, it was confirmed experimentally that the average critical size of Xe precipitates is around 4 to 5nm in radius. However, much larger Xe precipitates are sometime observed to remain solid.

Atomic structure on the 1-2 nm scale, often referred to as “medium-range order” (MRO), is of great importance for understanding the properties of disordered materials. It is, however, difficult to adequately characterize medium-range order. Fluctuation microscopy is a newly developed TEM technique that has successfully been employed to characterize MRO in amorphous semiconductors. The predominance of highly directional covalent bonds leads naturally to the presence of MRO in amorphous semiconductors. For metallic glasses, however, the bonding is primarily metallic and nondirectional. Thus, it is not readily apparent whether MRO would exist, or whether fluctuation microscopy is a useful tool for studying the structure of metallic glasses. in this work we report the use of fluctuation microscopy to identify differing degrees of MRO in Zr-based bulk metallic glasses; the MRO depends on the alloy content and the method of TEM specimen preparation.

In recent years there has been a significant increase in magnesium use as a structural material. Applications include aerospace and automotive industries as well as appliances and sporting goods. The most attractive feature about magnesium alloys is related to their low density. However, their mechanical properties require improvement to surpass the specific strength of the high strength aluminum alloys. The purpose of the present paper is to report the crystal structure determination of the precipitates found in the alloy Mg- 1.5%wtCa-6%wtZn produced by melt spinning.

The as solidified alloy was analyzed by means of Transmission Electron Microscopy(TEM), Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive X-ray Spectroscopy (EDS). The crystal structure of the new precipitate observed was determined by means of comparison of experimental and simulated selected area electron diffraction patterns (SADP) and High Resolution Electron Microscopy (HREM) images. The simulations were obtained using the software EMS.

Much attention has been devoted to develop the new generation of microalloyed steels in recent years to meet the needs of high performance and low cost for the 21st century. The new type of steels is characterized by reduced carbon content, improved cleanness and refined grain size through the phase transformations.11'21 Precipitation of the carbonitrides in the steels is also one of the keypoints for controlling mechanical properties of the steels.

In the present work ultra-low carbon clean microalloyed steels, which contain 0.029∽0.047(wt)%C, 1.48∽1.54(wt)% Mn, 0.044∽0.052(wt)%Nb, 0.025∽0.044Ti(wt)%, 0.0015∽0.0020(wt)%B and 0.0045∽0.0070(wt)%N, were prepared in a vacuum induction furnace in laboratory. The contents of S and P of the steels are 0.0005(wt)% and 0.0010∽0.0024(wt)% respectively. Total amount of the impurity elements O, S, P and H in the steels is 0.0061∽0.0077%. Dominant component of the structure in both casting and as-forged samples is acicular ferrite or bainite.

Boundary properties between two adjacent grains with different crystallographic orientation relation are important factors in deciding the mechanical properties of materials. in our previous reports, we introduced the geometric compatibility equation as a factor determining the brittle crack propagation condition into the adjacent grain in banitic low alloy steel as follows:

M = cos α · cos θ

where α is the angle between crack normal in the cracked grain-I and normal to (001) plane in the adjacent grain-II and θ is the angle between normal to (001) plane in the grain II and loading axis.(see FIG. 1) Higher M gives greater possibility to the crack propagation. The geometric compatibility factor (M) could be easily calculated from the crystallographic data obtained from Electron Backscatter Diffraction (EBSD) analysis, and successfully predicted actual crack propagation plane. We also found that there was a critical M value to arrest the brittle crack propagation at the boundaries.

The insertion of hydrogen in metals promotes severe modifications of physical and mechanical properties. in the case of nickel, hydrogen induces intergranular cracking [1] and decrease of ferromagnetism [2]. Hydrogen occupies the octahedral interstices of the fee structure promoting cell expansion. Large amounts of the fcc (β hydride may be produced by high pressure hydrogenation [3] or electrolytic charging [4]. The H/Ni relation (x) in the P hydride range from 0.6 to 1.0, depending on the method and conditions of hydrogenation. The β hydride is known to be metaestable at room temperature and normal pressure [5].

In this work, a thin foil (0.02mm thick) of high purity nickel was hydrogenated by electrolytic charging in a 1N H2SO4 solution with 20 mA/cm2 by 24 hours. AS2O3 was used as catalyst in a concentration of 5xl0−5mol/l. The hydrogenated samples were analysed by X-ray diffraction and SEM immediately after and 4 hours after the charging (room temperature aging).

The mechanical alloying (MA) process has been probed to be an effective method to conveniently develop materials with novel structures. The products of MA can be processed by conventional powder metallurgy routes for further consolidation. However, the novel features conferred to the powders, such as fine crystal size and chemical homogeneity can be lost during sintering operations, due to the high chemical activity of some of the synthesized phases. The Spark Plasma Sintering (SPS) process is an alternative route to obtain highly dense MA′ed products while retaining these novel microstructures, including a metastable state. Advantages of the SPS process over conventional sintering processes are the fast heating and cooling rates, and the high pressure applied. Combining these two material processing techniques (MA and SPS) it is possible to obtain materials with interesting (far from equilibrium) microstructures. Co-Ti alloys were obtained by MA and SPS, as described in related publications.

Although amorphous phases produced by mechanical alloying (MA) in the Ni-Mo system have been reported before. It has not been presented the influence of using different milling devices and atmospheres. This work is focused to the characterization of amorphous structures thus obtained in a Mo-47 at. % Ni alloy. Selected composition corresponds to the equiatomic NiMo intermetallic. The characterization was carried-out by XRD, SEM-EDS, DSC and TEM. High resolution XRD reveals that the MA′ed products undergo partial amorphization, as shows Figure 1. The main difference in the patterns is a region that corresponds to typical Nickel reflections. Nickel preferential amorphization after milling was evident. Apparently, a major grade of amorphization was attained when using the Simoloyer mill. A rough crystallite size was calculated using Scherrer equation, which reveals that this parameter reached its minimum value with the Simoloyer mill. During DTA analysis, it was observed the presence of an exothermic peak in all samples.

In the study of metal oxidation, there is a wide gap between information provided by surface science methods and that provided by bulk oxidation studies. The former have mostly examined the adsorption of up to ∽1 monolayer (ML) of oxygen on the metal surface, where as both low and high temperature bulk oxidation studies have mainly focused on the growth of an oxide layer at the later stages of oxidation. Hence, we are visualizing the initial oxidation stages of a model metal system by in situ ultra-high vacuum (UHV) transmission electron microscopy (TEM), where the surfaces are atomically clean, in order to gain new understanding of these ambiguous stages of oxidation. We have previously studied the growth of Cu2O islands during initial oxidation of Cu(100) film. We are presently investigating the initial stages of Cu(110) oxidation, from 10−4 Torr O2 to atmospheric pressures and temperature range from room temperature to 700 °C.

Deposition of highly textured ReBa2Cu3O7−δ (RBCO) films on metallic substrates requires a buffer layer to prevent chemical reactions, reduce lattice mismatch between metallic substrate and superconducting film layer, and to prevent diffusion of metal atoms into the superconductor film. Nickel tapes are bi-axially textured by cold rolling and annealing at appropriate temperature (RABiTS) for epitaxial growth of YBa2Cu3O7−δ (YBCO) films. As buffer layers, several oxide thin films and then YBCO were coated on bi-axially textured nickel tapes by dip coating sol-gel process. Biaxially oriented NiO on the cube-textured nickel tape by a process named Surface-Oxidation- Epitaxy (SEO) has been introduced as an alternative buffer layer. in this work we have studied in situ growth of nickel oxide by ESEM and hot stage.

Representative cold rolled nickel tape (99.999%) was annealed in an electric furnace under 4% hydrogen-96% argon gas mixture at 1050°C to get bi-axially textured nickel tape.

This research program is intended to develop new insight into the mechanisms of localized corrosion initiation in passive metals through unique approaches based on examining corrosion initiation on needle-shaped samples similar to field emitter tips. Samples with this geometry allow localization of corrosion initiation to the tip itself and therefore pit initiation can be confined to a small lateral area. Local electric fields can also be controlled, thus permitting damage to be confined in the passive over layer, and characterized before pit initiation.

High purity Al wire was used for the initial studies. Wire shaped specimens were electropolished in a 20 % perchloric in methyl alcohol solution at -30°C to obtain the fine needle geometry. The resultant tip radii ranged from 40 to 150 nm with no further sample prep needed and without the presence of artifacts.A custom-designed TEM holder for a Philips CM30 was fabricated, which allowed the needles to be characterized by TEM both prior to and after experiments.

The corrosion of copper is an important area in materials science because of the widespread use of copper in structural devices and electronics. These widespread uses in conjunction with its thermodynamic instability in most atmospheric conditions have prompted numerous atmospheric copper corrosion studies. The goal of these investigations has been to identify the underlying mechanisms by which corrosion proceeds in order to prevent any detrimental corrosion effects. Despite these studies, the microstructure of copper and its oxides remains poorly understood. Therefore, our investigation is concentrated on determining this microstructure.

In our investigation, copper films are electron-beam evaporated onto SiO2 coated Si wafers and then exposed to an electron-cyclotron-resonance (ECR) O2 plasma, which simulates an aggressive oxidizing environment. The ECR-grown oxide is fully oxidized to CuO at the surface and changes to CU2O further into the sample. The thickness of the oxide layer is controlled by the sample exposure time to the ECR plasma.