In an earlier report we have shown that the infrared photoluminescence (PL) from nanocrystalline Si films shifts to lower energies with increasing deposition temperature (in the range of 180-340 °C) and with thermal annealing. These films were deposited on Corning 1737 glass substrates using a Plasma-Therm SLR 770 ECR-PECVD system to a thickness of 4500 Å. The redshift of PL correlates well with the narrowing of (111) XRD peak, the redshift of the optical absoiption profile, the increasing conductivity and the decreasing activation energy for conductivity. Therefore, the energy shift of the PL has been considered as the result of variations in bandgap due to variations in crystallite size; i.e., variations in the quantum confinement. For the samples investigated, the PL band peak was found within the extrema of 0.99 to 0.81 eV (at 77 K). These extreme values correspond to the film deposited at 180 °C (0.99 eV PL) and the same film annealed at 600 °C for 72 hours (0.81 eV PL).

Al thin films, used as interconnects in integrated circuit devices, are subject to voiding failures due to electromigration and stress. Electromigration is a diffusion process and voids are known to form at points of flux divergence such as triple junctions. Void formation in Al-Cu films has also been associated with 9θ-phase (Al2 Cu) precipitates [1], which form preferentially at grain boundaries and triple junctions. Some triple junctions are favored as nucleation sites [2], presumably due to energetic differences arising from the crystallographic nature of the junctions. Their character can be calculated from the crystallographic orientations of the surrounding grains and the associated grain boundary dislocation networks [3]. Bollmann's method of analysis results in two categories of triple lines: I-lines - the special case where the grain boundary dislocations balance; and U-lines - the general case where the dislocation arrays do not balance. U-lines should have higher energies than I-lines and should therefore behave differently [3, 4]. This paper investigates the relationship between triple-line character and the location of Al2 Cu precipitates at certain triple junctions in Al-lCu thin films.

Stainless steel-zirconium (SS-Zr) alloys have been developed as waste forms to immobilize and retain fission products generated during the electrometallurgical treatment of spent nuclear fuel. The baseline waste form is a stainless steel-15 wt.% zirconium (SS-15Zr) alloy, which is prepared by melting appropriate amount of Type 316 stainless steel (SS316) and high purity zirconium. As zirconium has very low solubility in iron, the addition of zirconium to SS316 results in the formation of ZrFe2 -type Laves intermetallic phases. The corrosion behavior of stainless steel has been widely studied; however, the corrosion behavior of the Zr-based-intermetallic has not been previously investigated. In this paper, we present a microstructural characterization of the corrosion layer formed on the Zr-intermetallic phase using energy-filtering transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS).

Specimens of SS-15Zr alloy, crushed to 75 to 150 μm sizes, were immersed in 90°C deionized water for a period of two years.

In the processing of sheet steel, slabs are normally heated in a reheat furnace in the temperature range of 1200° -1300° C, extracted, hot rolled on a hot strip mill (HSM) and further processed. Because of the high operating temperature and the availability of oxygen, the steel surface is usually severely oxidized. The furnace scale could be a few millimeters thick. Abnormally thick scale may not be easily removed by high-pressure water sprays at the HSM. Rolled-in scale can contribute to underpickling and potentially result in the generation of steel surface defects.

Furnace scale typically consists of three oxide layers, Fe2O3 (hematite) on the outside surface, Fe3O4 (magnetite) in the middle and FeO1+x (wustite) next to the steel substrate. An example is shown in Figure 1. The three oxide layers are identified by H (hematite), M (magnetite) and W (wustite). Furnace scale samples of low carbon steel have been analyzed via x-ray diffraction (XRD) and optical metallography in order to characterize the scale.

Laves phase (Cr2X) strengthened Cr solid solution [Cr(X)]-based alloys are under development for a variety of high-temperature structural applications. Among the most promising alloys are castings based on the Cr(Ta)-Cr2Ta eutectic, which exhibit room-temperature fracture toughness in the 10-12 MPa√m range and creep rupture lives in excess of 1000 h at 1000° (138 MPa) in air. These alloys exhibit superior high-temperature oxidation resistance to previously developed Cr(Nb)-Cr2 Nb based alloys despite the general similarities of Ta and Nb. In order to optimize high-temperature oxidation resistance an understanding of why the Cr(Ta)-Cr2Ta alloys are more oxidation resistant is needed. Detailed EPMA characterization of the oxidized scaleswas initiated as a first steptowards gaining this understanding.

Fig. 1 shows a backscattered electron image of cast and heat treated and heat treated Cr-10Nb at.% after a 6 cycle, 120 h exposure at 1100°C in humid air. Most of the coupon was converted to a complex mixture of Cr-, Nb-, and Cr+ Nb- oxides.

Thermal barrier coatings (TBCs) insulate gas turbine hot section components from the hot (∽1200 - 1450°C) combustion gas exhaust stream. An airline company can save millions of dollars per year by using TBCs to protect vital engine components and to improve fuel efficiency. TBCs typically consist of an 8 wt.% yttria-partially-stabilized zirconia (YPSZ) ceramic topcoat deposited on a platinum-nickel-aluminide (Pt-Ni-Al) bondcoat covering a nickel-based superalloy substrate. Thermal exposure during YPSZ electron beam-physical vapor deposition (EB-PVD) and engine operation promotes the formation of a thermally grown oxide (TGO) between the Pt-Ni-Al and the YPSZ layers. Stresses can develop at the Pt-Ni-Al/TGO and TGO/YPSZ interfaces due to TGO growth and thermal expansion coefficient mismatch. These stresses eventually cause spallation of the YPSZ, leaving the metallic substrate vulnerable to high temperature degradation since exhaust temperatures are often higher than the melting temperature of most nickel-based superalloys (∽1200 - 1450°C).

Deformation substructures, especially dislocations, play an important role in the fabrication of the Caribbean steel drum and experimental evidence also suggests dislocations play a crucial role in the harmonic tuning and related musical qualities as well. In this study, we have examined and compared the dislocation substructures in high-quality, low-carbon (0.04-0.06 weight percent carbon) steel drum heads as manufactured, and sections cut from variously deformed (10% to 50% reduction) drum head sections, including those patterned with musical notes and heat treated; utilizing TEM.

We have recently shown that the requisite heating of a steel drum over a narrow temperature range (200 to 500°C) prior to tuning actually involves strain aging. Fundamentally, strain aging in steels has been explained by dislocation theory, but as far as we know, no experimental proof exists. This study also attempts to examine the more fundamental issues in strain aging, especially as it applies in the development of a high-quality, musical steel drum instrument.

Long term aging of martensitic Fe-12Cr steels at elevated temperatures can result in a significant decrease in toughness. The mechanism responsible for this has been generally attributed to either impurity segregation and/or precipitation of second phases. The aging embrittlement of higher Cr-containing ferritic steels has long been attributed to the precipitation of bcc Cr-rich alpha prime phase[l]. Alpha prime has also been shown to embrittle certain Ni base alloys [2]. The current work has shown that alpha prime forms in Fe-12Cr steels which have been aged at 450°C for up to 32khrs. Coincident with the precipitation of alpha prime is a marked decrease in toughness.

Historically, extraction replicas and to a limited extent thin-foil TEM microscopy have been used to identify alpha prime. However, both are not without problems in these magnetic, corrosion-resistant steels, due to the fact that the alpha prime is small (<20nm) and coherent with the matrix. Volume fraction studies have been essentially impossible.

Much work has been devoted to TEM studies of nanoscale precipitates consisting of non-soluble elements in Al, as the Al matrix acts as a unique crucible enabling the study of melting/ solidification and crystal phase transformations at a nanometer scale. Recently, this work has been extended to include the ternary system of Al-Pb-Cd. This system is of particular interest, as both Pb and Cd display a large liquid miscibility gap with Al, but together they form a eutectic system. Bimetallic inclusions consist of an fcc Pb and an hcp Cd segment, joined along an internal interface parallel to the {111}Al planes. In this work, the microstructure and composition of off-eutectic Pb-Cd inclusions are studied. Polycrystalline Al samples were implanted with 1 x 1020 ions/m2 (∼3 at.%) with a Cd:Pb ratio of either 8:2 or 2:8, at temperatures to form inclusions in the 10 nm size range.

Ni-Cr-Fe alloys such as Alloy 600 and Alloy 690 are single phase fee alloys with excellent resistance to corrosion. Alloy 600 is generally used in a thermally-treated condition which is characterized by the intergranular precipitation of Cr-rich M7C3 and, depending upon the aging temperature, Cr-rich M23C6. These alloys are usually cast and processed by rolling or forging. These alloys can exhibit microstructures in which there are nonuniform distributions of intragranular carbides that appear as bands aligned parallel to the working direction (i.e. longitudinal) of the material. It is also possible for these materials to exhibit duplex grain sizes which can be associated with the banded carbide structure. Banded microstructures can become more prominent after further anneals. The resistance of the carbide bands to dissolution during solution annealing at temperatures up to 1150°C has prompted the further evaluation of banding in Alloy 600, specifically in terms of identifying those elements associated with the carbide bands.

In a study of the precipitation and aging of Invar particles in Cu, we observed that the particles evolved from spherical to cuboidal as they grew in size. This behavior has been observed in other systems, and predicted by Voorhees et al. ; they showed that the precise shape of the particle is a balance between elastic anisotropy and surface energy. The correlation between our results and their predictions are very good. It is the purpose of this note to point out that simultaneous measurements of size, shape, and mismatch of a coherent particle can be used to estimate the interfacial energy under favorable conditions.

Ternary alloys consisting of Cu - 12.8 wt% Ni -7.2 wt% Fe were arc-melted, held at 1030°C to develop extended regions of the Cu-rich solid solution, quenched, then aged at various times and temperatures to develop FCC precipitates near the Invar composition in the FCC Cu matrix.

Studies aimed at improvements in the properties of titanium aluminides continue and efforts on optimizing the microstuctural parameters and a variety of processing techniques have attracted significant attention. In particular alloy compositions containing Ti-44to48at%Al and Nb as the major ternary addition (often with other minor alloying element additions) have been found quite promising. A fine fully lamellar structure in these TiAl-based intermetallic alloys has been reported to possess a combination of improved room temperature ductility, excellent fracture toughness, good oxidation resistance and creep properties. One of the serious problems associated with the TiAl-based alloys is the large grain size that develops in these alloys especially upon casting. A recent approach is to use directional solidification techniques in producing the TiAlbased alloys and it has been shown that desired orientations can indeed be produced by choice of suitable processing parameters.

In this study, we have examined the microstructural features associated with chill-cast as well as directionally solidified Ti-44at%Al-l lat%Nb alloy.

The copper alloys commonly referred to as nickel aluminum bronzes (NAB) are widely used in marine applications due to their excellent seawater corrosion resistance and good mechanical properties. Unfortunately, these alloys are susceptible to a variety of surface sensitive degradation processes such as cavitation and wear which significantly reduce service life. Laser surface melting and cladding techniques have recently demonstrated a potential to substantially enhance the performance of NAB components. This is associated with the occurrence of a martensitic or Widmanstätten transformation from the high temperature bcc β phase accompanied by precipitation of ordered intermetallic particles collectively referred to as κ. Optimization of these techniques requires an improved understanding of the evolution of microstructure in the NAB system under conditions of rapid solidification, however little data is currently available. In this paper, transmission electron microscopy is used to examine the microstructures of a series of laser surface melted NAB alloys containing from 8 to 12 wt. % Al, 3.8 to 6.5 wt. % Ni, 3.8 to 6.5 wt. % Fe, ∽1 wt. % Mn and, in some cases, lesser amounts of Ti or Zr.

In electronic packaging, it is very important to understand and control the interfacial microstructure formed due to the reaction between the metallization scheme and solders. Often, the interfacial reaction is exploited/controlled to obtain an optimum properties of the joints. The strength and interfacial properties of the solder joints are determined by the interfacial microstructure. The evolution of interfacial microstructure in solder joints is governed by the diffusion path during processing and in service. Even though the semiconductor industry uses a wide variety of complex metallization schemes, recently the Pd-Ni metallization scheme on Cu has gained a lot of interest. Furthermore, the design of new metallization scheme(s) to control the interfacial microstructure and to improve the quality of solder joints is the cornerstone of advanced electronic packaging. We have carried out a systematic study of diffusion and interfacial reaction, both in the liquid and solid states, between Pb-Sn eutectic solder and the Pd-Ni metallization scheme on Cu.

For over two decades considerable effort has been directed towards the development of Al-Li base alloys with the objective of replacing conventional high aluminum alloys, due to the fact that lithium additions cause substantial reduction in density accompanied by significant increase in the elastic modulus, implying, therefore, in appreciable improvement in the specific properties of the resulting alloys. These properties depend on the miscrostucture evolution during heat treatment or welding cycle. The microstructure of the commercial Al-Li systems is complex due to the addition of alloying elements, which increases the number of the allowed stable and metastable phases. During the thermo-mechanical processing of the 2091 alloy, the probable metastable are δ’, GPB zones and S’, the stable phases are S, T2 and the high temperature R (1-3). Further, the Zr precipitates the Al3Zr. The present study deals with the microstructure evolution of welded joints of the 2091 alloy studied by transmission electron microscopy, TEM.

A Ti50Ni48Fe2 alloy, which is famous as a typical shape memory alloy, exhibits the cubic (parent phase) to trigonal (R-phase) martensitic transformation upon cooling. It is well known that this structural transformation is accompanied by some precursor phenomena, such as appearance of weak diffuse scattering in electron diffraction patterns of the parent phase. Since the diffuse scattering is visible at around 1/31/3 0 and its equivalent positions in diffraction patterns, as similar to the superlattice reflections in the R-phase, it is believed to be closely related with the formation of the R-phase. However, neither structural nor morphological aspect of this pre-martensitic state is clear, since a precise analysis of the weak diffuse scattering is quite difficult along with a conventional electron microscopy, because of the presence of strong background arising from inelastic scattering. The purpose of the present work is to precisely observe the weak diffuse scattering and to reveal the structural and morphological features of the pre-martensitic state by electron microscopy with the aid of a recently developed omega-type magnet.

Power electronic circuits are used in electric vehicle or hybrid electric vehicle to drive the main electric motor. All the transistors and diodes in a sealed power electronic package will experience repeated high current cycling during their service life. The aluminum bonding wires which connect these devices to the rest of the circuit will experience repeated thermal strain cycling. When design a power electronic package, the thermal fatigue durability of these bonding wires would be a concern. A power electronic module with pure aluminum bonding wires of 0.5mm in diameter from a vendor was power cycled with the following schedule. Each transistor in the circuit was on for 10 seconds with the current at 400 Amperes followed by the transistor being off for 30 seconds. The wires from the diodes to the copper trace lines are about twice as long as those from the transistors to the copper trace lines.

Among those intermetallic phases in Zn-Fe system formed in the hot-dip galvanized coating and/or galvanneal coating, the microstructure of Γ phase was the least mentioned. The Γ phase form in the coating layer is usually too thin to observe by a microscope. However, it has been reported that the performance of coating is closely related to the microstructure of Γ phase. Tokunaga et al. has reported that the cracks were generated from the Γ layer or Γ+δ layer. Y.Lin et al. demonstrates that coherent interface forms between Γ and steel interface on annealed electrogalvanized steel sheets indicating that failure would not occur at this interface.

Samples used in this study were lab-made hot-dip galvanized steel sheets. To investigate the microstructure of coating, especially the Γ phase layer, specimens were heated to create the designed layer interface. It was found that the heat-treated conditions ranged from 700°C to 750°C for one hour was appropriate to observe the nucleation and growth of Γ phase layer.

X-ray diffraction (XRD) techniques can readily be utilized for the characterization of textures in crystalline materials. The advantages of XRD techniques are: 1) the test is nondestructive, 2) samples can easily be prepared, and 3) data can be collected and analyzed quickly.

Three low-C steel tin mill coils were manufactured during a mill trial which was conducted to optimize the processing parameters necessary for the production of material with low cup earing behavior. The processing parameters evaluated included hot mill conditions (roughing, finishing and coiling temperatures), cold rolling conditions (during first and second cold reduction), and continuous annealing conditions (line speed and strip temperature). Samples A, B, and C were secured from the coil center-width position of each coil, respectively, and were analyzed via XRD.

Properties such as normal anisotropy (r bar) and planar anisotropy (Δ r), have been correlated with an X-ray Intensity Ratio (XIR) at the Technical Center of National Steel.

Electron channeling contrast imaging (ECCI), performed using a scanning electron microscope, has been used to observe dislocations in bulk TiAl with a duplex microstructure. The ECCI technique is based on the dependence of the back-scattered electron (BSE) yield (of the incident beam orientation) on the crystal lattice and defect orientation near the specimen surface. This allows nearsurface defects to be imaged in bulk specimens [1, 2]. ECCI was carried out in a Camscan 44FE FEG-SEM operated at 25 kV using a beam divergence of ∽8 mrad and a beam current of ∽ 2nA. Specimens were observed at a working distance of approximately 11 mm. To record the BSE signal, the microscope was fitted with an annular (four quadrant) silicon diode detector array attached to the final lens pole-piece, resulting in a solid angle collection of approximately ∽0.6 π str. Images were recorded as 32 frame averages using ∽1.1 frames/sec.