Electron Probe Microscopy Analysis Research Articles

Phase diagram of the Al–Cu–Fe quasicrystal-forming alloy system

Abstract The microstructures of as-cast and slowly solidified Al–Cu–Fe ternary alloys in the vicinity of the icosahedral phase region have been investigated using light microscopy and scanning electron microscopy. The chemical composition of the different phases present has been determined by energy-dispersive X-ray spectroscopy with a correction of electron probe microscopy analysis. The solidification process was studied by means of the differential thermal analysis and magnetothermal analysis measurements. In contrast to the equilibrium phase diagram, fast cooling leads to the formation of a metastable β′ phase (an ordered cubic structure) rather than to the formation of the φ phase. The nucleation of ω phase is very sluggish during the solidification. The results are presented as solidification paths, superimposed onto the liquidus surface projection to demonstrate the solidification sequences.

Microstructural characteristics in plasma sprayed functionally graded ZrO 2/NiCrAl coatings

Different functionally graded 20 wt.% MgO-ZrO 2/NiCrAl thermal barrier coatings were obtained through the plasma spraying process. The microstructures, chemical compositions and fractured surface were examined by means of electron probe microscopic analysis (EPMA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM and EPMA results showed that: (1) microstructures and compositions varied gradually in the coatings; (2) the elements Cr and Al were enriched along the sprayed lamellae boundaries and leaded to the formation of oxides. TEM observation enabled finding the formation of dense dislocations and deformation twins, and also the formation of the oxides Al 2O 3 and Cr 2O 3 between grain boundaries. The SEM observations of the fractured surface revealed that the intermediate graded layer had the compositive mechanical properties in strength and toughness, due to the microstructure improvement and relaxation of residual stress concentration.

Mechanisms of Fatigue Failure in Thermal Spray Coatings

The aim of this experimental study was to ascertain the fatigue failure modes of thermal spray coatings in rolling/sliding contact. These failure modes outline the design requirements of thermal spray coatings for high-stress tribological applications including impact and point or line contact loading. Recently, a number of scientific studies have addressed the fatigue performance and durability of thermal spray coatings in rolling/sliding contact, but investigations on the mechanisms of these failures are seldom reported. The understanding of such failure mechanisms is, however, critical in optimizing the generic design of these overlay coatings. This study takes a holistic approach to summarize the results of ongoing research on various cermet (WC-Co) and ceramic (Al2O3) coatings deposited by detonation gun (D-Gun), high-velocity oxyfuel (HVOF), and high-velocity plasma spraying (HVPS) techniques, in a range of coating thickness (20–250 µm) on various steel substrates to deliver an overview of the various competing failure modes. Results indicate four distinct modes of fatigue failure in thermal spray cermet and ceramic coatings: abrasion, delamination, bulk failure, and spalling. The influences of coating process, thickness, materials, properties of substrate materials, and prespray conditions on these fatigue failure modes are also discussed. A modified four-ball machine was used to investigate these failure modes under various tribological conditions of contact stress and lubrication regimes in conventional steel and hybrid ceramic contact configurations. Results are discussed in terms of pre- and post-test surface examination of rolling elements using scanning electron microscopy (SEM), electron probe microscopy analysis (EPMA), and surface interferometry, as well as subsurface observations using x-ray diffraction (XRD), residual stress analysis, and dye-penetrant investigations.

Application of microscale plasma to material processing

We generated microscale plasmas using novel electrodes fabricated by lithography and confirmed that Paschen's law can be extended to gaps between electrodes as narrow as 5 μm. To develop the application of a microscale plasma to material processing, we performed plasma chemical vapor deposition (P-CVD) of carbon films with this microscale plasma using a CH 4–H 2 gas system, for the first time. We deposited carbon films using various gas ratios of H 2/CH 4. Deposits were characterized by scanning electron microscopy (SEM), electron probe microscopy analysis (EPMA), Auger electron spectroscopy (AES), and Raman spectroscopy. Using Raman spectroscopy, it was found that the bonding nature of these carbon films changed from sp 2 to sp 3 with increasing H 2/CH 4 ratio. Lastly, we proposed an integrated plasma processing apparatus on a substrate, namely a plasma chip.

Growth of LiNbo3 crystal with periodic ferroelectric domain structure by current-induction and its acoustic application

In this report, Y-doped lithium niobate (LN) crystal with periodic ferroelectric domain structure (PFDS) was grown by the current-induction technique. The distribution of dopant (Y) along the growth direction was measured by an electron-probe microscopic analyzer. The periodic variation of the dielectric constant in the crystal was revealed by the light diffraction. When a radio-frequency electric field was applied, a 340 MHz ultrasonic wave was excited in the sample by the crossed-field scheme, which implies that the LN with PFDS is suitable for constructing the high-frequency bulk-wave acoustic devices.

Studies on capacity fade of lithium-ion batteries

The capacity fade of Sony 18650S Li-ion cells has been analyzed using cyclic voltammetry, impedance spectroscopy and electron probe microscopic analysis (EPMA). The surface resistance at both the positive (LiCoO 2) and negative (carbon) electrodes were found to increase with cycling. This increase in resistance contributes to decreased capacity. Impedance data reveal that the interfacial resistance at LiCoO 2 electrode is larger than that at the carbon electrode. The impedance of the positive electrode (LiCoO 2) dominates the total cell resistance initially and also after 800 charge–discharge cycles. EPMA analysis on carbon electrodes taken from the fresh and cycled cell show the presence of oxidation products in the case of cycled cells. No change in the electrolyte resistance is seen with cycling.

The formation of an fcc/l1 2 lamella structure in Ni-12.6Al-20Ir-5Nb refractory superalloys

The phase constitution of Ir–Nb–Zr alloys with a composition below 25 at% (Nb+Zr) was investigated by microstructure observation using scanning electron microscopy (SEM), composition analysis using electron probe microscopy analysis (EPMA), and phase identification using X-ray diffraction analysis (XRD). Partial isothermal sections of the Ir–Nb–Zr ternary system were determined at 1773, 2073, and 2373 K. It was found that the f.c.c. and L12 two-phase regions, which are shown in the Ir–Nb and Ir–Zr binary systems, were connected from the Ir–Nb side to the Ir–Zr side in the Ir–Nb–Zr ternary system. The potential of Ir–Nb–Zr alloys as high-temperature materials is discussed in terms of the microstructure and the lattice misfit between the f.c.c. and L12 phases.

Tribological properties of Ni 3Al-Cr 7C 3 composite coating under water lubrication

The tribological properties of Ni 3Al-Cr 7C 3 composite coating under water lubrication were examined by using a ball-on-disc reciprocating tribotester. The effects of load and sliding speed on wear rate of the coating were investigated. The worn surface of the coating was analyzed using electron probe microscopy analysis (EPMA) and X-ray photoelectron spectroscopy (XPS). The results show the friction coefficient of the coating is decreased under water lubrication. The wear rate of the coating linearly increases with the load. At high sliding speed, the wear rate of the coating is dramatically increased and a large amount of the counterpart material is transferred to the coating worn surface. The low friction of the coating under water lubrication is due to the oxidizing of the worn surface in the wear. The wear mechanism of the coating is plastic deformation at low normal load and sliding speed. However, the wear mechanism transforms to microfracture and microploughing at high load with low sliding speed, and oxidation wear at high sliding speed. It is concluded that the contribution of the sliding speed to an increase in the coating wear is larger than that of the normal load.

Tribological properties of Ni 3Al–Cr 7C 3 composite coatings under liquid paraffin lubrication

Tribological properties of Ni 3Al–Cr 7C 3 composite coatings on carbon steel lubricated with liquid paraffin were measured by using a ball-on-disc reciprocating tribotester. Effects of load, sliding speed, sliding time to the coatings' tribological properties were investigated. The worn surface of Ni 3Al–Cr 7C 3 coatings was examined using scanning electron microscopy (SEM), electron probe microscopy analysis (EPMA) and X-ray photoelectron spectroscopy (XPS). It shows that the wear rate of Ni 3Al–Cr 7C 3 coatings is lower than the bearing steel and the Ni 3Al coating at the same test conditions. Wear rate and friction coefficient of Ni 3Al–Cr 7C 3 coatings varies with the load, sliding speed, sliding time and Cr 7C 3 phase content. The results of the experiments were well explained by analyzing wear and friction mechanism of Ni 3Al–Cr 7C 3 coatings under different tribological parameters.

Failure modes of plasma sprayed WC–15%Co coated rolling elements

This experimental study addresses the failure modes of plasma sprayed coatings in rolling contact. A high velocity plasma spraying system was used to deposit WC–15%Co coatings on the surface of 15 mm diameter 440-C bearing steel cones. These coatings were deposited in two different thickness. Rolling contact fatigue (RCF) tests were conducted using a modified four ball machine in conventional steel ball bearing and hybrid ceramic bearing configurations. These tests were conducted under various tribological conditions of contact stress and lubrication regimes at room temperature. Failure modes were investigated on the basis of surface and subsurface observations of failed coated rolling elements. Surface observations were made using conventional scanning electron microscopy (SEM) and light microscopy. Subsurface observations were made using fluorescent dye penetrant technique. Observations of debris generated during the RCF tests, changes in topography of lower planetary balls, electron probe microscope analysis (EPMA), microhardness/fracture toughness investigations and, coating microstructural studies are also included to aid the discussion. Two modes of failures, i.e., surface wear and coating delamination, were observed during this investigation. Coated rolling elements failed in either one or a combination of these two modes depending upon the tribological conditions during the RCF test. Surface wear was associated with asperity contact in the presence of microslip/sliding within the contact region. The process was accelerated in the later stages of RCF tests in the presence of wear debris due to additional mechanism of three body abrasion. Coating delamination was associated with the initiation/propagation of subsurface cracks, which resulted due to defects in the coating microstructure. These cracks propagated at the depths of orthogonal shear stress and maximum shear stress under the surface of wear track.

Crystal growth of Cu(In 1− XGa X) 3Se 5 by horizontal Bridgman method

Crystalline Cu(In 1− X Ga X ) 3Se 5 ingots were grown by horizontal Bridgman method. Closed quartz ampoules were used to avoid the loss of selenium. Ampoules partially coated with carbon were used to prevent sticking of the melt. The composition variations along as-grown ingots were studied as a function of starting Ga content by Electron Probe Microscope Analysis (EPMA). X-ray powder diffraction (XRD) measurements were carried out to examine the lattice structure and lattice constants. Hall effect measurements were also carried out to determine electrical properties.

Metallic phases of Dong Ujimqin mesosiderite: A field emission scanning electron microscope study

The microstructure of Fe-Ni metallic phases in Dong Ujimqin mesosiderite was studied using the field emission SEM. Taenite is characterized by a zoned structure, consisting of outer clear taenite and inner cloudy zone (CZ). CZ has a typical “island-honeycomb” microstructure. The average size of the island phase is about 358 nm, suggesting a cooling rate of ∼ 0.5°C/Ma at low temperature (< 400°C). The Ni concentration profiles across kamacite and zoned taenite were also measured by electron probe microscope analysis (EPMA). Formation of the Fe-Ni metallic phases, microstructure in Dong Ujimqin mesosiderite was discussed based on the new low-temperature Fe-Ni phase diagram.

Formation of a functionally gradient (Si 3N 4+SiC)/C layer for the oxidation protection of carbon–carbon composites

Silicon infiltration has been used to form a functionally gradient layer on two-dimensional carbon–carbon (2D-C/C) composites. 2D-C/C composites were infiltrated with silicon at temperatures above the melting point of silicon in a NH 3-containing atmosphere. Some of silicon-infiltrated C/C composites were then coated with a CVD–SiC coating. Electron probe microscopic analysis, X-ray diffraction and secondary ion mass spectroscopy were employed to characterize the surface layer derived by silicon infiltration. Isothermal and cyclic oxidation tests on the C/C composites were carried out at temperatures up to 1550°C in air. A functionally gradient (Si 3N 4+SiC)/C layer was formed in the surface region of the C/C composites. Combined with an outer CVD–SiC coating, this composition-graded layer could provide excellent oxidation resistance for C/C composites.

Oxidation Behavior of a Ni ‐ La2 O 3 Codeposited Film on Nickel

A composite film has been developed by coelectrodepostion of particles with Ni onto pure Ni surfaces. An investigation by a high‐resolution electron microscope (HREM) revealed a dispersion of nanocrystallites (below 5 nm) in the as‐codeposited film. Isothermal (at 900 and 1000 °C) and cyclic (at 1000 °C) oxidation in air showed a significantly slower growth rate and a noticeably higher cracking resistance for NiO scale on ‐coated Ni than on Ni, and Ni with an electrodeposited film of pure Ni. Moreover, the grain size of the nickel oxide on the composite film was a factor of 6 ∼ 15 smaller than that on the ‐free specimens. Electron probe microscope analysis indicated that dispersed in the outer part of the NiO scale after the codeposited film has been oxidized completely. An analytical transmission electron microscope revealed that La segregated to the grain boundaries of the ‐doped NiO scale. It is therefore proposed that the rapid outward diffusion of Ni along short‐circuit paths in the ‐modified NiO layer may be inhibited by second‐phase particles and also by segregated lanthanum ions from the dissolution of nanoparticles which originally existed in the codeposited film.

Interfacial structure and properties of polyurethane/poly(methylacrylate-co-styrene) coating to regenerated cellulose film

A semiinterpenetrating polymer network (IPN) containing 72 wt % polyurethane (PU) and 6 wt % poly(methylacrylate-co-styrene) [P(MA-St)] was coated onto surfaces of regenerated cellulose (RC) film, which was prepared by coagulating a cellulose cuoxam from bagasse pulp. The interfacial structures, bonding manner, and the strength of the coated film were studied by infrared (IR),13C nuclear magnetic resonance (NMR), differential thermal analysis (DTA), transmission electron microscopy (TEM), and electron probe microscopy analysis (EPMA). It was shown that the RC film coated with PU/P(MA-St) has strong interfacial interactions, where covalent and hydrogen bonds are formed across the interface between cellulose and the PU/P(MA-St) coating. The interfacial structure of the coated film is regarded as a shared PU network crosslinked simultaneously with P(MA-St) and cellulose film. The tensile strength, water resistivity, and optical transmission of the coated films were considerably higher than that of the uncoated films. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2495–2501, 1997

Interfacial reactions in molten Sn/Cu and molten In/Cu couples

The interfacial reactions of molten Sn and molten In with solid Cu substrate were determined by studying their reaction couples. The annealing temperature was 300 °C. The phases formed at the interface were examined by optical microscopy, scanning electron microscopy, and electron probe microscopy analysis (EPMA). The thickness of the reaction layers was measured using an image analyzer. For Cu/Sn couples, two phases, e and η, were found. Only the Cu11In9 phase was observed at the interface of the Cu/In couples. In comparison with the results of couples of solid Sn and solid In with solid Cu substrate, their phase formation sequences were similar; however, the interfacial morphology and the reaction rates were different. For the liquid/solid couples, the reaction rate was much faster and the interface was nonplanar. A mathematic model was also proposed to describe the dissolution of the Cu substrate and the growth of the intermetallic compounds. Fast dissolution of the substrate was observed in the beginning of the reaction and was followed by a relatively slow growth of the intermetallic compounds at the interface.

Tribological properties of metal-plastic multilayer composites under oil lubricated conditions

Three kinds of metal-plastic multilayer composites, which were composed of a steel backing, a middle layer of sintered porous bronze and a surface layer of polytetrafluoroethylene (PTFE) filled by Pb or Cu 2O powders, were prepared. The friction and wear properties as well as the limiting pressure times velocity (PV) values of these metal-plastic multilayer composites sliding against 45 carbon steel under both dry and oil lubricated conditions were evaluated on a MPV-1500 friction tester with a steel axis rotating on a journal bearing. The worn surfaces of these metal-plastic multilayer composites and the transfer films formed on the surface of steel axis were examined by electron probe microscopy analysis (EPMA). Experimental results show that filling of Pb to PTFE reduces the friction coefficient and wear of the composite, while filling of Cu 2O to PTFE increases the friction coefficient but decreases the wear of the composite. The friction and wear properties as well as the limiting PV values of these metal-plastic multilayer composites can be greatly improved with the oil lubrication. EPMA investigations show that Pb and Cu 2O fillers preferentially transfer onto the surfaces of steel axis, which may enhance or deteriorate the adhesion between transfer films and steel surfaces. Meanwhile the transfer of these metal-plastic multilayer composites onto the steel surface can be greatly reduced with oil lubrication, which results in the remarkable decrease of the wear of these metal-plastic multilayer composites.

Optoelectronic Properties of CuInSe&lt;SUB&gt;2&lt;/SUB&gt; Grown by Traveling Heater Method Using Cu&amp;ndash;In Alloy Solvent

The CuInSe 2 (CIS) crystals were grown by traveling heater method(THM) using Cu-40 at%In alloy as the solvent metal. The composition mapping by electron probe microscopic analysis was stoichiometric and homogeneous throughout the crystal. The conduction was p-type with the carrier concentration and hole mobility in the order of magnitude of 10 20 -10 22 m 3 and 10 -3 m 2 Vs -1 at 300 K, respectively The emission peaks in the photoluminescence spectra were identified as the free exciton and the defects of Se vacancy(V Se ) and Cu antisite(Cu on In site, Cu In ). From the emission intensity measurement, it was found that the nonradiative recombination centers decreased in the direction from the bottom to the top end of the crystal, while the defects of V Se and Cu In remained almost uniform. The results indicate that the quality of the CIS crystal enhanced by the THM growth in comparison to that of the crystal by the Bridgman method in which non-radiative recombination centers were predominant..

Electron probe analysis of calcium distribution during active transport in chick chorioallantoic membrane

The embryonic chick chorioallantoic membrane actively transports calcium and the transported calcium is compartmentalized or sequestered, since it does not mix completely with calcium already contained within the membrane. Correlated electron probe and electron microscope analysis shows that only certain ectodermal cells of the membrane contain concentrations of calcium. We suggest that these are specialized cells which are specifically involved in trans-epithelial transport of calcium and represent the “compartments” containing the sequestered calcium.