Microstructural development in non-oriented lamination steels

The microstructures produced during continuous cooling of two particular non-oriented lamination steels have been examined using light microscopy, scanning electron microscopy and transmission electron microscopy. In addition to proeutectoid ferrite and pearlite, cementite was present on ferrite grain boundaries and on proeutectoid ferrite/ pearl ite interfaces. Mechanisms for the formation of these cementite films are presented. The microstructural results demonstrate that ferrite is the active nucleus for pearlite in these low-carbon steels. In addition, the data suggest that in addition to branching, the pearlite reaction can be initiated by the nucleation of a series of cementite precipitates on the proeutectoid ferrite/austenite interface.     

〈012〉-oriented growth of the films LaNiO3/SiO2/Si(111) by pulsed laser deposition

The highly 012-oriented LaNiO3 thin films were fabricated on SiO2coated Si(111) wafers by pulsed laser deposition at 690°C with a well prepared target. The stability of the interface and the smoothness of the surface were confirmed by scanning electron microscopy and atomic force microscopy. The electrical resistivity of the films at 300 K is 2.6 × 10–5m. The results of this work suggest that the films can be applied to the bottom electrode of ferroelectric memory devices.     

An investigation of the effects of thickness on mechanical properties of LIGA nickel MEMS structures

This paper examines the effects of thickness on the mechanical properties of LIGA Ni MEMS structures plated from sulfamate baths. The as-plated LIGA Ni specimens of different thickness (50 m, 100 m and 200 m) were utilized in the microtensile experiments. Optical microscopy, orientation imaging microscopy and scanning electron microscopy were used to characterize the microstructure of the LIGA Ni specimens. Fracture Modes obtained from specimens with different thickness were revealed by scanning electron microscopy. The effects of specimen thickness are then discussed within the context of strain gradient plasticity theories.     

Structural components in needle-cokes as studied by etching with chromic acid

Structures within commercial calcined needle-cokes are characterized by optical microscopy to reveal optical texture and by scanning electron microscopy before and after etching with chromic acid solution at 400 to 423 K. The needle-cokes exhibit an optical texture of medium and coarse-grained mosaics, acicular flow domains and flow domains. The etching studies indicate that the acicular flow domains are made up of rolled and convoluted lamellae which etch to form laths (needle-like) 3 m across. The mosaics appear when the rolled structures are viewed microscopically sectioned perpendicular to the lamellae. The acicular flow domains appear in longitudinal section. The etching of the flow domains shows that they have a sedimentary structure, 1 to 2 m layer thickness, suggesting that mesophase coalesces within a layer but not between layers. A model is proposed to explain the origin and separation of structures in needle-cokes as created in the delayed coker.     

Pre-induction and induction hydration of tricalcium silicate: an environmental scanning electron microscopy study

Environmental scanning electron microscopy (ESEM) has been used to study the very early pre-induction, and induction physical processes that occur in the hydration of tricalcium silicate. An in situ experimental technique is described which allows direct, real-time observation of the sub-micrometre morphological changes that take place during this reaction. The results of this investigation are correlated with kinetic data obtained by differential scanning calorimetry (DSC). In this way, microstructural evolution has been identified with the stages of very early hydration. Upon first contact with water, a gelatinous coating was seen to form at grain surfaces and a crystalline secondary product was observed at the end of an extensive dormant period. These findings are viewed in the light of previous wet and dry microscopy studies, and are discussed within the framework of ordinary Portland cement as a possible explanation of induction. Comment is made as to the suitability of environmental SEM for analysis of such materials.     

The implant material, Ti6Al7Nb: surface microstructure, composition and properties

The excellent biocompatibility of titanium and its alloys is intimately related with the properties of the surface in contact with the biological environment, and therefore it is closely connected with the stable, passivating oxide layer that forms on its surface. In the present paper, the oxide layer on the alloy Ti6Al7Nb has been characterized using X-ray photoelectron spectroscopy, scanning Auger microscopy and pH-dependent lateral force microscopy. The alloying elements Al and Nb are incorporated in the oxide layer and detected in their most stable oxidized form, as Al₂O₃ and Nb₂O₅. Their distribution in the oxide reflects the underlying - microstructure, with enrichment of Al in the - and of Nb in the -phase (determined by electron microprobe). Friction measurements (lateral force microscopy) indicate slightly different, pH-dependent, lateral forces above the - and -phase structures that point to small local variations in surface charges. © 1999 Kluwer Academic Publishers     

Optical properties and scanning probe microscopy study of some AgAsSSe amorphous films

Doping of AsSSe amorphous films by silver photo-dissolution leads to a decrease of the optical gap and to an increase of the refractive index in forming AgAsSSe films. The difference of the optical gap and refractive index between undoped and doped films has been found in case of Ag₁₅As₂₆S₂₉Se₃₀ film up to 0.37 eV and 0.26, respectively. Transreflectance in far infrared spectral region indicates formation of AgAsS₂ and AgAsSe₂ entities in Ag₁₅As₂₆S₂₉Se₃₀ film. Scanning probe microscopy, namely atomic force microscopy, atomic force acoustic microscopy (AFAM) and Kelvin probe force microscopy (KPFM) was used for studying AgAsSSe films. It was found that silver growth is rather three dimensional and it is reminiscent of the Stranski-Krastanov growth mode. Observed silver protuberances represent silver reservoirs responsible for a local increase of silver content. Hence, the silver growth mode enhances formation of nano/meso inhomogeneities of the surface and near surface density/stiffness, seen in AFAM, and in the surface electric potential, seen in KPFM.     

Study of the recrystallisation of aluminium/alumina (SAP) alloys

The influence of the introduction of aluminium nuclei on the recrystallisation behaviour of SAP (sintered aluminium powder) was studied by metallographic observations using a new etching reagent, and by transmission electron microscopy. It was observed that the artificial nuclei can grow in the SAP matrix only in the temperature range in which the alloy recrystallises spontaneously. It is concluded that the physical process inhibited by the dispersed particles is grain-boundary migration.These results and those previously reported confirm Cahn's theory (which regards the formation of new grains as due to recovery phenomena localised in the regions of highest lattice distortion) supplemented by the coalescence mechanism proposed by Hu and Li, Moreover, the basic concepts of nucleation and growth currently employed to describe recrystallisation phenomena are critically discussed: it is concluded that a reformulation of these concepts is necessary on the basis of the information obtained by means of the more recent experimental techniques, such as electron microscopy.     

Phase transformation ß→α in sintered SiC involving feathers formation

The phase transformation has been studied in SiC sintered with addition of boron and carbon by optical microscopy, and scanning and transmission electron microscopy. In the late stage of densification and during subsequent anneals, a feathers develop at the expense of the grains. They are constituted of two adjacent grains whose crystalline structures are related to one another by four symmetry operations. From the orientation relationship it is shown that the feathers can be describe as penetration twins.     

Microstructural characterization of rapidly solidified nickel-base superalloys

Several Ni-Al-Mo-based eutectic superalloys were rapidly solidified using a chilled block melt spinning process. The effects of rapid solidification on the microstructure were studied using optical microscopy, transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). Results showed, except for the alloy containing chromium, that the microstructure varied as a function of ribbon thickness from segregationless solidification at the wheel side of the ribbon to dendritic solidification at the free side. In addition, alloys with the same solidification rate showed a large variation in microstructure depending upon the solid state cooling rate. The rapidly solidified eutectic Ni-Al-Mo alloy with a small amount of rhenium and vanadium did not show any improvement on delaying or prohibiting the formation of the embrittling-NiMo phase on ageing at 1000 C. This was determined from microstructural as well as chemical analysis using STEM. Differential thermal analysis was used to obtain melting temperature,-Ni₃Al solvus, and heat of formation for the alloys.     

High-temperature OM investigation of the early stage of (TiC+TiB)/Ti oxidation

The initial oxidation behavior of titanium matrix composites (TMCs) was studied in a temperature range 550 to 650C in a flow of purified oxygen at atmospheric pressure using thermogravimetry. The oxidation kinetics very initially follows approximately a linear rate law and then a parabolic rate law. The oxidation rate decreases gradually as the oxidation proceeds. The initial in situ oxidation was investigated by high-temperature optical microscopy in air. The oxide layer was examined by X-ray diffraction and scanning electron microscopy combined with an energy dispersive X-ray spectroscopy unit. It was found that the reaction products are predominantly rutile. The reinforcements of TiB and TiC can result in a decrease in the overall oxidation rate at 550, 600, and 650C. This is attributed to the interface cohesion and the clean interfacial microstructure between reinforcements and the titanium matrix alloy, which is strong enough such that the reinforcements can act as barriers to solid-state diffusion.     

Synthesis and characterization of novel PtSe2/graphene nanocomposites and its visible light driven catalytic properties

In this study, we report a novel PtSe₂/graphene nanocomposite by facile ultrasonic-assisted techniques. The “as-prepared” nanocomposites were further characterized by various techniques such as X-ray diffraction, scanning electron microscopy with an energy dispersive X-ray analysis, transmission electron microscopy, UV–Vis absorbance spectra analysis, diffuse reflectance analysis, and Raman spectroscopic analysis. The photocatalytic activities of the composites were investigated by the degradation of rhudamine B and methylene blue as a standard dyes. The photodegradation rates of organic dyes by the nanocomposites are found to be markedly high. This study suggests that the as-prepared PtSe₂/graphene composite can be utilized as highly efficient photocatalyst materials that employed visible light as an energy source.     

Influence of TiN-nanolayered insertions on microstructure and mechanical properties of TiSiN nanocomposite film

TiN nanolayers with different thicknesses were inserted in TiSiN nanocomposite film by magnetron-sputtering technique. The influences of TiN insertion nanolayers with different thicknesses on microstructure and mechanical properties of TiSiN film were investigated X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, and nanoindentation techniques. When the TiN insertion layer thickness is <0.5 nm, TiN nanolayers can coordinate the misorientations between TiN nanocrystallites in adjacent TiSiN layers, leading to the transformation from the nanocomposite structure with TiN nanocrystallites encapsulated by SiN _x interfacial phase into columnar crystal structure, and disappearance of the strengthening effect from the nanocomposite structure. When the TiN insertion layer thickness increases to 1.0 nm, the film is strengthened with the epitaxial growth structures between TiSiN and TiN layers. As the TiN insertion layers further thicken, the hardness and elastic modulus evidently decrease, which can be attributed to the breakage of epitaxial growth structures between TiSiN and TiN layers.     

Dislocations and twins in Czochralski-grown gallium phosphide single crystals

An etching and electron microscopy study has been carried out on {111} oriented slices of gallium phosphide (GaP) taken from Czochralski-grown ingots. The correlation of the etched structure with substructural defects as revealed by transmission electron microscopy has been determined, It has been found that GaP grown by this technique has a high dislocation density and exhibits polygonisation and mechanical twinning. It is found that there is a one-to-one correspondence between surface etch pits and grown-in and mechanically induced dislocations. Stacking faults are also revealed in the etching studies and are shown to be twins in the matrix of the {111} 112 type. It is proposed that the twinning occurs due to the severe growth conditions and may arise by dissociation of dislocations in the sub-boundaries.     

Studies on phase transformations of Cu-phthalocyanine thin films

Copper phthalocyanine (CuPc) thin films were obtained by a sublimation technique on Si wafer substrates maintained at room temperature. As-deposited CuPc films with less than 0.1 m thickness crystallize primarily in the -form with a preferential orientation of the crystallites in the [2 0 0] direction. The effect of randomizing of the orientation of the CuPc crystallites is observed as the film thickness increases, whereas the preference in appearance of the -form remains. The changes in phase composition, structure, morphology and surface chemical composition of as-deposited CuPc thin films due to different heat treatment conditions were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).     

The effect of crystallization of the grain-boundary phase on ambient temperature fatigue short-crack growth behaviour in Y-α′-β′-Sialon

The cyclic fatigue short-crack growth behaviour of Y---Sialons with both crystallized and amorphous grain-boundary phases, were investigated to determine whether crystallization of grain boundaries affected crack-growth behaviour under cyclic and monotonic loads. Micromechanisms for fatigue-crack growth in Y---Sialon were examined by scanning electron microscopy and high-resolution electron microscopy. These results show that the wear debris on the fatigue fracture surfaces gave evidence of a frictional wear crack-growth mechanism. Comparison of fatigue short-crack growth rates for Sialon of crystallized grain-boundary phases with that for the amorphous grain-boundary phases indicated that crystallization of grain-boundary phases does not appear to affect cyclic fatigue growth behaviour, similar to long-crack growth behaviour. The similarity of fatigue short-crack growth behaviour in both the crystallized and amorphous grain boundaries sialons is rationalized in terms of the thin residual amorphous grain-boundary regions.     

Ageing characteristics of furnace cooled eutectoid Zn-Al based alloy

Phase transformations and microstructural changes of a furnace cooled eutectoid Zn-Al based alloy were studied during ageing at 100 and 170°C using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Three phase transformations occurred in the furnace cooled eutectoid Zn-Al alloy. The metastable _FC phase decomposed during isothermal ageing. The four-phase transformation, + T + followed the discontinuous decomposition of the _FC phase. Typical morphologies of the decomposition of the _FC and phases were observed in scanning electron microscopy. Decomposition of Al-rich phase was observed during the prolonged ageing by transmission electron microscopy. The different types of decomposition of the different metastable phases dominated at different stages of ageing.     

Microstructure of a plasma-sprayed superalloy coating/substrate

Five different specimen preparation techniques were employed to characterize the microstructure of a cross-section of plasma-sprayed Rene 125 coating on a Rene 125 turbine blade substrate. These methods included optical microscopy, and transmission electron microscopy on three types of replicas and on thin foils. Interface and matrix precipitates were indentified using electron diffraction and energy dispersive spectrometry, with HfO₂ and (Hf, Zr)O₂ the predominant phases at the coating/blade interface, and both (Ti, Ta)C and HfO₂ present in the coating. Those blade precipitates examined contained Hf and Ta, with some Ti and a little Co. A unique dendritic structure of was also found intermittently along the interface. The combination of the five techniques provides a wide variety of information, and is a strong tool for characterizing complex microstructures.     

The mechanism of simultaneous sintering and phase transformation in alumina

The sintering behaviour of boehmitic alumina gels during the transformation to the stable phase has been studied using dilatometry, transmission electron microscopy, X-ray analysis and differential thermal analysis. The specimens for transmission electron microscopy were prepared from gel specimens, sintered to various predetermined temperatures, using an ion-beam thinning technique. The transmission electron microscope study and X-ray analysis have revealed a characteristic sintering behaviour which is associated with the to phase transition. The transformation to the phase occurs by a nucleation and growth process. During the growth process considerable redistribution of the fine porosity existing within the transition alumina matrix occurs, in the form of large elongated interconnected pores trapped within the nucleating grains. These pores grow rapidly to a size approximately one hundred times that of the grains. This process results in a rapid fall-off in sintering rate at the end of the transformation. A study of the/ interphase interface by transmission electron microscopy has led to the development of a model that accounts satisfactorily for the redistribution of the porosity.