The existence of phases exhibiting five-fold symmetry patterns has recently been reported for conventional heat treated alloys as well as rapidly solidified alloys. The present paper reports initial results on the analysis of a Mo-rich phase in 316L stainless steel which exhibits this symmetry. The formation and growth of this Mo-rich phase were investigated as a function of aging time. In addition, the effect of nitrogen content on the formation of this five-fold phase was also investigated.

The materials investigated were type 316L stainless steels with nitrogen contents of 0.024% and 0.150%. The materials were solution-annealed at 1100 °C for 30 minites followed by an aging treatment at 700 °C for 10–50 hours in a vacuum sealed quartz tube. TEM samples were prepared by conventional twin-jet polishing and carbon replications extracted by use of a bromine-etch.

Irrespective of nitrogen content, the grain boundary phases after 50 hours of aging were totally observed as five different types of precipitates; M23C6 and M6C carbides, intermetallic η and χ phases, and the five-fold symmetry phase.

Stainless steels have significant applications due to their good corrosion resistance. However, for applications in a marine environment, i.e. for certain types of large naval structures, in addition to the good corrosion resistance, other requirements are imposed on the candidate material such as high strength and toughness coupled with suitable magnetic characteristics.

It has been demonstrated in earlier publications that significant improvements in the coercivity, maximum induction and remanence values can be achieved, by using a 2205 type Duplex austenitic -ferritic stainless steel (DSS) instead of the low alloy medium carbon steels currently being used. These improvements are achieved in the as received 2205 material, and after small amounts of cold rolling have been applied, to increase the strength. However, the 2205 type DSS exhibits “ marginal” corrosion protection in a marine environment as well as exhibiting some measurable ferromagnetic response. Therefore, a study has been undertaken to examine the mechanical properties and microstructures obtained in a super austenitic stainless steel of the 254 SMO type.

The bainitic reaction in steels has been extensively studied, however it is still controversial whether it proceeds by a diffusional or a shear mechanism. In a previous investigation of the bainite reaction in a Fe-3.9Si-0.9C steel the transformation was considered to be the result of two competing elementary mechanisms, i.e., the shear transformation of the α-iron lattice and the diffusion of interstitial carbon away from the transformation interface.

In this paper, the microstructural and crystallographic characteristics of the bainite products obtained through the step quenching experiments are examined, using TEM and Electron diffraction. The results are compared to those obtained by the corresponding bainitic transformation in a single step. The results obtained here support the proposed model in and the shear character of the bainitic transformation.

The same steel as in, an alloy with 3.9 w.t.% silicon and 0.9 w.t.% carbon, was used. After austenitizing at 1130°C for 30 minutes a number of samples were transformed at 420°C for 30 minutes and subsequently quenched in a second bath where they were kept for times increasing from one to thirty days at temperatures of either 360,340 or 290°C.

There has been increasing interest from industry to characterize the different precipitate distributions in ferrous materials to account for different mechanical properties that are observed. For this study, two different heat treatments were chosen for the experimental S5 tool steel, modified to have 0.24 wt% C. Alloy S5-1 received 1 hour of austenitizing at 970°C, was quenched at rate of 140°C/s and tempered for 1 hour at 200°C. Alloy S5-2 received 40 minutes of austenitizing at 940°C, was quenched at rate of 16°C/s and tempered for 1 hour at 200 °C. In this relatively low hardenability steel, both S5-1 and S5-2 show mixed microstructures of tempered martensite and bainite (Fig. 1, 2). Not surprisingly, the slower cooling rate for S5-2 created an alloy with inferior microstructure and mechanical properties. Even though these differences in precipitate distributions, could not directly account for differences in mechanical properties, it is of interest to study how the different heat treatments affected the precipitate distributions in S5-1 and S5-2.

Although the thickness of splat quenched (SQ) foils is normally less then 100 μm the solidified microstructure is usually not homogenous, but rather is determined by a cooling rate dependent nucleation and growth behavior of the different phases. The cooling rate and thus the microstructure changes significantly with distance from the edge to the middle of the SQ foils. Rapidly quenched nickel-vanadium (Ni-V) foils consist of three phases formed during solidification, a Ni-fcc, a V-bcc and a intermetallic σ phase [1-3]. To interpret the microstructure evolution in detail, a special TEM cross section sample preparation was applied. The SQ foil was ground to 30 μm, glued on a copper grid and ion-milled parallel to the foils (Fig.1a). In Ni-49V SQ foils seven typical microstructure regions (see Fig. 1 b) could be identified and were analyzed in detail by TEM investigations in plan view and cross section geometries. Furthermore, three solidification pathways were identified.

Nickel-based superalloys used in jet engines consist of a face-centred cubic Ni matrix, γ, containing a high density of Ll2-ordered Ni3Al precipitates, γ´. At high temperatures the strength of the alloy depends primarily on the strength of the γ´ phase, which begins to decrease above approximately 750°C, limiting the maximum operating temperature of the superalloy. The possibility of strengthening the γ´ phase by solid-state precipitation within the γ´ phase has been investigated in model Ni-Al superalloys containing Be. Beryllium, a light element, is also expected to be a potent solid solution strengthener in the γ´ matrix.

Four alloys were manufactured with compositions Ni-18.8 at. % Al-1.6% Be, Ni-19.0 at. % Al-2.6% Be, Ni-17.9 at. % Al-5.4% Be and Ni-15.9 at. % Al-11.9% Be. These Al levels result in a volume fraction of γ´ phase similar to that present in a commercial superalloy, and the Be addition places the superalloys in the γ-γ´-NiBe region of the ternary phase diagram, Fig. 1.

Quenched-in vacancies, vacancy agglomeration and solute-vacancy association can play a significant role in affecting the mechanical behavior of an alloy. It is well known that B2- NiAl can retain a high supersaturation of thermal vacancies which has been shown to manifest itself as dislocation loops, voids, or spiral dislocations. Dislocation climb loops formed in NiAl have been observed to emanate from impurity particles as concentric {100} loops which are prismatic in nature1. Impurity particles have also been shown to be responsible for nucleating faceted voids. However, addition of alloying elements can alter this mode of vacancy condensation and depending upon the degree of interaction between alloying element and vacancies, a completely different defect structure can result. In a recent study, addition of Boron to Fe-35 mol. % Al has been shown to produce complex {100} planar faults having both APB and stacking fault character, whereas Cr, Pd and W produced APBs on {111} planes.

It is the accepted wisdom that off-stoichiometric TiAl alloys with slightly Aluminum rich compositions, e.g. Ti-52 at.% Al and Ti-54 at.% Al, exist as single phase materials. However, previous studies have reported that Ti3Al5 ordering occurs in Al rich γ-TiAl of compositions 54-63 at.% Al [1,2]. The Ti3Al5 ordering involves the substitution of excess Al into selected Ti sites on the pure Ti plane (001) [1]. In the current work such Ti3Al5 ordering has been observed in TiAl alloys of compositions ranging from Ti-52 at.% Al to Ti-56 at.% Al which have been produced as described in earlier reports [e.g. 3].

Experimental and simulated selected area diffraction patterns (SAD) for the [111] zone axis of TiAl are shown in figure 1. A row of extra reflections which appears between the reflections corresponding to the Ll0 structure are clearly visible in the diffraction patterns obtained from the Ti-54 and 56 at.% Al alloys (Fig. 1b,1c).

Two-phase α2+γ TiAl alloys with microalloying additions, Fig. 1, are of interest due to the high strength-to-weight ratio they can provide in automotive and aircraft applications. In boron-doped α2+γTiAl containing Cr, Nb, and W, the B levels were found to be significantly depleted below the nominal alloy content in both the α2 andγ phases. The boron solubilities in the γ and α2 phases were 0.011 ± 0.005 at. % B and 0.003 ± 0.005 at. % B, respectively in Ti-47% Al-2% Cr-1.8% Nb-0.2% W-0.15 % B that was aged for 2 h at 900°C (base alloy). The majority of the B was in a variety of borides including TiB, TiB2 and a Cr-enriched (Ti,Cr)2B precipitate. With the exception of the smaller (< 50 nm thick) Cr-enriched (Ti,Cr)2B precipitates, Fig. 2, most of the borides were larger than ∼100 nm. A significant proportion of the microalloying additions is in these borides, Table 1.

The Aluminium Bronzes are successfully used in heat exchanger tubes, particularly in chemical and oil industries, where they are subjected to sligthly acid conditions or higher temperatures and stresses than other copper alloys allow. For a maximun resistance to corrosion an understanding of the effects of composition and metallurgical structure is desirable. This work study the different precipitates appearing in ASTM B148-C95800 complex Al bronze alloy, due to the structural development in as cast,forged and heat treated conditions, the presence of Fe and Ni as additions enhance the presence of many different precipitates all over the structure, changing the corrosion resistance and mechanical properties.

In this type of alloy the non-stoichiometric β phase breaks down progresively during cooling from high temperatures: 750° - 950°C to give a finely divided iron - nickel - aluminium “kappa” (κ) phase in a copper rich (α) matrix. Such α + κ alloys generally can contains small quantity of β and none γ2 (deleterious to all properties), showing excellent corrosion resistance combined with high tensile strength.

Recent interest in the literature on ternary compounds of the AlCuFe type has been prompted by the discovery of stable quasicrystalline phases in these type of alloys (1) . Therefore, different investigationes have been carried out in the past, related with the structural characteristics and also the mechanical properties of these compounds (2) . It is interesting to point out that very few studies have been carried out on the structural characteristics of the phases which commonly coexist with the icosahedral phase in this ternary alloy (3) . In this investigation an assessment of the chemical and structural properties of the phases obtained in alloys of AlCuFe is carried out.

Ternary alloys with approximately 20 different compositions have been prepared. The compositional ranges were: Al(60-65%at), Cu(20-25%at) and Fe(10-15%at). The preparation of the alloys used two different casting process; a gravity chill casting technique and also the spin wheel casting method. These casting techniques were able to provide different cooling velocities in the final ingots or metallic strips.

Laves-phase intermetallics are of potential use as high-temperature structural materials. NbCr2-based C15-structured alloys are of particular interest for such applications. by themselves, Laves phases generally have poor ductility and fracture toughness at low temperatures. Two phase alloys (i.e., Laves phase and the ductile bcc phase) are considered more promising for structural applications. The orientation relationships between the two phases can contribute to the mechanical behavior of the material. In this study, observations of two different orientation relationships in a Nb-NbCr2 eutectic are discussed and compared with previous studies of the NbCr2 system, as well as the TiCr2 system.

A Nb-NbCr2 eutectic alloy was prepared by arc-melting high-purity alloys followed by annealing at 1400°C for 100 h and then cooling at l°C/min. The complete details of the materials preparation have been given elsewhere. Specimens were prepared for observation in the transmission electron microscope (TEM) by cutting 3 mm discs with a coring saw, followed by dimpling and ion milling. Microstructural characterization was performed with a Philips CM30 TEM operating at 300 kV.

Although the unusual microstructural and electronic properties of charge density wave (CDW) modulated compounds have been extensively investigated over the past two decades, many aspects of the complex behaviour of these systems remain unexplained. As a result, the characterization of a new family of CDW structures, in which the CDW properties can be widely varied in a predictable manner, is of experimental and theoretical interest.

The Nb3X4 (X = S, Se, Te) family of compounds is based on a hexagonal unit cell built up of edge and face sharing NbX6 octahedra (Figure 1). The structure is characterized by zigzag Nb-Nb chains and large hexagonal tunnels running parallel to the c-axis. One member of this family, Nb3Te4, is known to undergo a CDW phase transition at ∼100 K. A large number of metal atoms can be introduced into the tunnels to form a family of isostructural, intercalated compounds AyNb3X4. Electrical resistivity measurements on polycrystalline pellets of InyNb3X4 (X = Se, Te) have revealed temperature anomalies indicative of the formation of CDW in these materials.

A new class of shape memory alloys, based on near-equiatomic compositions of Ta-Ru and Nb-Ru, was recently discovered at the Naval Research Laboratory. These alloys exhibit transformation temperatures ranging up to 1400 °C for Ta-Ru and 1100 °C for Nb-Ru, making them the highest transition temperature shape memory alloys yet discovered. Other shape memory alloys typically have transition temperatures within a couple hundred degrees of room temperature. These two alloy systems are quite similar in their transformation behavior. Near the equiatomic composition, the high temperature β phase of both systems has a B2-ordered cubic crystal structure. During cooling, the cubic lattice of β undergoes a slight tetragonal distortion to form the β' phase. Continued cooling of the tetragonal β'(within specific composition ranges) causes a transformation to β'', which is reported to have an orthorhombic crystal structure. The effect of alloy composition on the temperatures, hysteresis, and strains of these transformations was determined by dilatometry.

Palladium is widely used for metallization of electronic circuits and in electronic packaging. During soldering palladium dissolves in the liquid solder and form various intermetallics both at the solder/substrate interface and in the solder. Diffusion of atomic species lead to the formation of intermetallics in the solid state as well. As the dissolution and interfacial reaction continue, the solder comes in contact with other metallization layer(s) and eventually with copper. This leads to a very complex microstructural evolution process which ultimately affects the interfacial mechanics and transport properties. In order to improve the reliability of electronic packaging, it is necessary to understand and control the dissolution and solid-state reaction mechanisms between the metallization layers and currently used lead-tin solders. As a first step towards modelling and understanding this complex microstructural evolution, here we have undertaken a systematic study of interfacial reaction between lead-tin solders and palladium.

Pure Sn, Sn-38 mass% Pb and Pb-5 mass% Sn were used in this study.

Due to the interfacial reaction between the solder and substrate, either during manufacturing or in service, the solder joints may contain one or more intermetallic layers at the interface. While such intermetallic layers may provide strong bonding, they may also be responsible for problems associated with solderability and reliability of joints. Certain physical and mechanical properties of the intermetallic may determine the integrity and reliability of solder assembly. So far detailed analysis, modelling, and testing of simulated and actual joints have been performed with Pb-Sn solders. However, in view of the increasing environmental and legislative concerns, lead-free solders are currently being developed and designed for microelectronics applications. As the solder joints in high-performance electronic circuits are expected to carry increasing mechanical, electrical and thermal burdens, it is essential to address the technological and reliability issues for lead-free solders. Among the lead-free solders, tin-zinc based alloys can be designed to achieve melting and solidification behavior similar to those of lead-tin eutectic or near eutectic alloys.

The two important constituents of metallic tool alloys are transition metal carbides and metals of the iron group, Fe, Ni, Co. Combining them, based on WC, it is obtained a hard and tough cutting tool material. Many attempts have been made to develop alternative cemented carbide systems by substituting a portion of WC by other hard phases. In this investigation, microstructure and phases composition of 90 mass% [ (1-y) WC - y VC ] - 10 mass% Co with y = 0, 0.2, 0.4, 0.6 and 1.0 sintered cemented carbides were studied by Backscattering electron (BSE) compositional images, elemental dot maps and X - ray microanalysis. These techniques have allowed to determine the different phases present, their morphology and composition.

Cylindrical samples of 10 mm. in diameter and height were manufactured by vacuum sintering at 1400°C of uniaxially pressed compacts at 350 MPa. Liquid phase sintering is the predominant consolidation mechanism present in this system.

A combination of Si and transition metal element like V, Ni and Au can form an amorphous phase over a wide composition range. Extensive studies have been reported in relation to a change in the electron transport properties across the metal-insulator transition. It has been reported that the metal-insulator transition in the amorphous Si100−xVx alloys accompanies a substantial change in both the electronic structure and atomic structure around x=18, as revealed by the photoemission spectroscopy and neutron diffraction experiments[1]. It is of great interest to examine the structural change associated with the metal-insulator transition at an atomic level by utilizing the HRTEM[2]. However, the correspondence between the image contrast and projection of atomic structures in amorphous materials is usually indirect due to the well-known phenomena of phase contrast in HRTEM. High-angle detection annular dark field scanning transmission electron microscopy (HAADF-STEM) as illustrated in Fig.1 is a solution of the problem without contrast reversal due to the lens-defocus and thickness-variation of samples.

The structure of the homologous compounds InMO3(ZnO)m (M=In, Fe, Ga, and Al, m=integer) is considered to be a layered structure, consisting of InO21− layer (In-O) ) interleaved with MZnmOm+11+ layers (M/Zn-O) along the c-axis. In the M/Zn-O layers, the distribution of two kinds of metal atoms is considered to be random fashion from X-ray diffraction analysis. However, in the previous HRTEM study of InFeO3(ZnO)m with m larger than 6, we found a modulated structure, where the image contrast showed a sinusoidal modulation curve present only in the Fe/Zn-O layers. Elemental analysis by EDS clarified that the modulated structure was caused by the ordering of Fe atoms within the Fe/Zn-O layers. In the present study, we try to observe In2O3(ZnO)m compounds, where Fe3+ atoms are replaced by In3+ atoms which have larger ionic radii. We are interested in whether the replacement of Fe3+ by In3+ atoms may cause any structural changes between In2O3(ZnO)m and InFeO3(ZnO)m.

The samples were prepared by heating powders of In2O3 and ZnO sealed in Pt tube at 1350 °C for about 3 days and then rapidly cooled down to room temperature. The electron microscope observation was performed by using JEM-2000EX, operated at an accelerating voltage of 200 kV.

Yttria is an electroceramic material that has a negative temperature coefficient of resistivity (i.e. it is an NTC type semiconductor). This property, along with its high melting point and good stability, makes yttria a potential sensor material (thermistor) for measuring temperature differences in demanding applications. Recently there has been increasing interesting in studying this ceramic material. How-ever, there is very limited published information on the microstructural characteristics of pure yttria processed under various conditions. Furthermore, reported evidence on the effect of processing conditions on the electrical response of the material is still lacking. Studies within our Center have revealed a correlation between aging time and electrical behaviour in pure yttria samples. The present study examines the evolution of the microstructure of sintered yttria powder during different annealing treatments.

Yttria pellets (6mm diameter, 2mm height) were cold pressed and then sintered at 1550°C for 24h in air. The sintered pellets were then annealed at 1100°C for different times. Specimens for SEM examination were prepared by grinding the surface of the pellets (using grit paper up to 400) and subsequently polishing them using l μm alumina powders.