Electroprobe Microanalysis Research Articles

Mineralogical characterisation to improve understanding of oral bioaccessibility of Cr and Ni in basaltic soils in Northern Ireland

Underlying bedrock is often the source of elevated levels of potentially toxic elements (PTEs) (including Ni and Cr) in soils, which can be at concentrations exceeding regulatory guidelines for the protection of human health. However geogenic contaminants are often not significantly bioavailable to humans as they are bound tightly within the soil matrix. Therefore oral bioaccessibility testing can be used to refine human health risk assessment by quantifying bioaccessible PTEs in soils, but should be augmented with soil mineralogy data to support its use in risk assessment. Elemental mapping using Electro Probe Microanalysis (EPMA) and mineralogical mapping using QEMSCAN®, an automated mineral/phase analysis system based on a scanning electron microscope, were combined with quantitative X-ray Diffraction (XRD) and previous oral bioaccessibility and non-specific sequential extraction (CISED) results for 3 soil samples overlying Palaeogene basalt lavas in Northern Ireland, to determine the effect of soil mineralogy on oral bioaccessibility of Ni and Cr. Results indicate that Cr concentrations are principally related to recalcitrant chrome spinel and primary iron oxides, which explains the relatively low bioaccessibility of Cr. In contrast, Ni is more widely dispersed within the soils, with a proportion of total Ni found in carbonates and weathering products, including secondary iron oxides and precursor clay minerals, leading to the higher oral bioaccessibility measurements recorded for Ni than Cr.

Bismuth core fibers

Elemental bismuth (Bi) exhibits a high magnetoresistance as a typical example of semimetal, which has significant application in information technologies. Silicate glass-clad Bi core fibers were fabricated by a molten core method and maintained core diameter of 100–150µm and overall diameter of 300–450µm. X-ray diffraction (XRD) and micro-Raman spectra showed the core to be highly crystalline with no observed secondary phases. Electro-probe micro-analyzer (EPMA) measurements confirmed a very well-defined core-clad interface. Demonstration of fibers with high magnetoresistance core materials and the potential integration with current state of the art technologies represents the first step in providing the building blocks for all-fiber sensors.

Microstructure and partitioning behavior characteristics in low carbon steels treated by hot-rolling direct quenching and dynamical partitioning processes

In this work, a new process and composition design are proposed for “quenching and partitioning” or Q&P treatment. Three low carbon steels were treated by hot-rolling direct quenching and dynamical partitioning processes (DQ&P). The effects of proeutectoid ferrite and carbon concentration on microstructure evolution and mechanical properties were investigated. The present work obtained DQ&P prototype steels with good mechanical properties and established a new notion on compositions for Q&P processing. Microstructures were characterized by means of electro probe microanalyzer (EPMA), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and X-ray diffraction (XRD), especially the morphology and size of retained austenite. Mechanical properties were measured by uniaxial tensile tests. The results indicated that introducing proeutectoid ferrite can increase the volume fraction of retained austenite and thus improve mechanical properties. TEM observation showed that retained austenite included the film-like inter-lath austenite and blocky austenite located in martensite/ferrite interfaces or surrounded by ferrites. It was interesting that when the carbon concentration is as low as ~0.078%, the film-like inter-lath untransformed austenite cannot be stabilized to room temperature and almost all of them transformed into twin martensite. The blocky retained austenite strengthened the interfaces and transformed into twin martensite during the tensile deformation process. The PSEs of specimens all exceeded 20GPa.%.

Microstructures and properties of rapidly solidified Cu90Zr10-x Al x alloys

Cu90Zr10-xAlx (x=1, 3, 5, 7, 9; at.%) alloy rods were synthesized based on rapid solidification method. The structure, distribution of elements, mechanical properties and electrical conductivity of the Cu-based alloy samples were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), electro-probe micro-analyzer (EPMA), uniaxial compression test and four-probe technique. The as-cast Cu90Zr10-xAlx (x=1, 3, 5; at.%) alloy rods with a diameter of 2 mm exhibit good mechanical properties and electrical conductivity, i.e., high compressive yield strength of 812-1513 MPa, Young’s modulus of 52-85 GPa, Vickers hardness of 250-420 and electrical conductivity of 11.1%-12.6% IACS (International Annealed Copper Standard). The composite microstructure composed of high density fibrous duplex structure (Cu5Zr and α-Cu phases) is thought to be the origin of the high strength.

Effects of heating rate on the hardness and microstructure of Al-Cu and Al-Cu-Zr-Ti-V alloys

Effects of heating rate on hardness and microstructure of Al-Cu and Al-Cu-Zr-Ti-V alloys were investigated by means of scanning electron microscope (SEM), electro-probe microanalyzer (EPMA) and transmission electron microscopy (TEM). The cast alloys were heat treated with a heating rate of 50 °C/h and 300 °C/h, respectively. The results show that the hardness and microstructure of both alloys can be controlled by changing heating rate. As compared with the lower heating rate, both the two alloys heated with higher heating rate exhibit a significant improvement in hardness and a decrease in the holding time for obtaining peak hardness. The heating rate is also closely relative to the size and distribution of Al3Zr precipitates. TEM statistic size of the precipitates shows the higher heating rate not only gives a larger mean size of precipitates, but also significantly activates the nucleation sites on the dendrite edge. The influences of heating rate in hardness and microstructure are attributed to the higher heating rate causing more defects and stronger mobility of solute or vacancies in the matrix.

Dynamic recrystallization behavior of 7085 aluminum alloy during hot deformation

The dynamic recrystallization behavior of 7085 aluminum alloy during hot compression at various temperatures (573–723 K) and strain rates (0.01–10 s−1) was studied by electron back scattered diffraction (EBSD), electro-probe microanalyzer (EPMA) and transmission electron microscopy (TEM). It is shown that dynamic recovery is the dominant softening mechanism at high Zener–Hollomon (Z) values, and dynamic recrystallization tends to appear at low Z values. Hot compression with ln Z=24.01 (723 K, 0.01 s−1) gives rise to the highest fraction of recrystallization of 10.2%. EBSD results show that the recrystallized grains are present near the original grain boundaries and exhibit similar orientation to the deformed grain. Strain-induced boundary migration is likely the mechanism for dynamic recrystallization. The low density of Al3Zr dispersoids near grain boundaries can make contribution to strain-induced boundary migration.

Effect of Trace Strontium Addition on Microstructure and Room Temperature Fracture Toughness of Nb-12Si-22Ti Alloys

The effect of strontium (Sr) addition (0.2 at.%) on the microstructure and mechanical properties of Nb-12Si-22Ti alloys were studied. Microstructure of the alloys was observed by scanning electron microscope, and their phase compositions were analyzed with X-ray diffraction and Electro-Probe Microanalyzer. The room temperature fracture toughness was measured. The results indicated that the phases of Nbss and Nb3Si were presented in Nb-12Si-22Ti alloys. However, with the Al and Sr addition, the alloys were composed of Nbss and β-Nb5Si3. Compared with the Nb-12Si-22Ti alloys, the value of room temperature fracture toughness increased about 46% and 73% with the addition of Al and Sr alloy, respectively. The relationship between the microstructure and the mechanical properties was discussed.

Bismuth‐Doped Multicomponent Optical Fiber Fabricated by Melt‐in‐Tube Method

Bismuth‐doped multicomponent optical fiber was fabricated by a melt‐in‐tube method. The fiber was prepared at drawing temperature where the clad was softened, while the fiber core glass was melted. The obtained fiber was characterized by electroprobe microanalyzer and X‐ray diffraction. No obvious precipitation of crystals or bismuth metals was observed in the fiber. Excited by 808‐nm laser, intense broadband near‐infrared emission with full width at half maximum of about 325 nm was observed from the fiber. Consequently, this fiber is promising for broadband fiber amplification. The melt‐in‐tube method is generally applicable for fabricating bismuth‐doped multicomponent optical fiber.

Broadband 27 μm amplified spontaneous emission of Er^3+ doped tellurite fibers for mid-infrared laser applications

Er3+ doped tellurite fibers have been fabricated using a convenient suction technique. Different scanning calorimetry (DSC), Electro-probe micro-analyzer (EPMA), Raman, steady and dynamic luminescence spectra were performed to investigate their thermal, structure, and luminescent properties. Broadband 2.7 μm amplified spontaneous emission (ASE) emission with concurrent 1.5 μm and visible up-conversion emissions have been achieved in fibers with various lengths upon the excitation of 980 nm laser diode (LD). A quantitative study of the spectroscopic properties has been further analyzed in detail according to the Jude-Ofelt model, rate equation, and Dexter’s theory to evaluate the competitive relationship among them. The desirable spectroscopic characteristics associated with excellent thermal stability and mechanical properties indicate that the Er3+ doped tellurite fibers are excellent host matrices for 2.7 μm lasing and may provide applications in mid-infrared fiber lasers and amplifiers.

B23-P-14Composition and microstructure study by using additive manufacturing process for implant application

Nitinol alloy is a well-known materials due to the unique shape memory property and thus extensive used as medical device. However, nitinol alloy is also hard to cast, forge, and machine, and thus the device design is limited. Additive manufacturing process is a potential method to direct fabricate the nitinol medical device. Composition and microstructure are the key points to affect the shape memory property of additive manufactured nitinol alloys. In this research, the composition and microstructure evolution of nitinol alloy from powder to additive manufactured specimen has been investigated. The material nature and microstructure are examined by X-ray diffraction (XRD), and scanning electron microscopy (SEM). In addition, chemical composition of these specimens are examined by electro-probe microanalyzer (EPMA). All of the results will be discussed in details. B23-P-13 doi:10.1093/jmicro/dfv287

Structure, Microsegregation, and Precipitates of an Alloy 690 ESR Ingot in Industrial Scale

The structure, interdendritic, and intergranular segregation, and precipitates of an Alloy 690 electro-slag remelting (ESR) ingot in commercial scale (3t) were investigated by the optical microscopy, electroprobe microanalysis, scanning electron microscopy, and transmission electron microscopy (TEM) techniques. The results indicate that the central longitudinal section of the ESR ingot comprised the ramp-up, steady-state, and hot-top regions, which could be easily distinguished from each other through the macrostructures of them. In the interdendritic area, Cr and Ti were enriched, while Ni and Fe were depleted, and the nominal segregation indexes (ζ i = C 0 i /C interdendritic i ) of Ti, Cr, and Ni were 0.40, 0.91, and 1.04, respectively, in the hot-top region where suffered the severest segregation. Nitrides, principally precipitated between dendrites, were identified as TiN by TEM and EDS. The morphology, size distribution, and volume fraction of them were determined as well. In terms of the intergranular area, Cr and C coexisted, while Ni and Fe were depleted. And the dendrite-like carbides continuously distributed on the interface between grains, which were identified as M23C6 by the selected area diffraction pattern.

Struvite Precipitation Induced by a Novel Sulfate-Reducing Bacterium Acinetobacter calcoaceticus SRB4 Isolated from River Sediment

This article presents a study of struvite formation in liquid medium induced by the sulfate-reducing bacterium Acinetobacter calcoaceticus SRB4, a strain isolated from river sediment. We identified the bacterial strain A. calcoaceticus SRB4 and analyzed its micromorphology. The minerals formed were studied with an electroprobe microanalyzer, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray diffraction, thermogravimetry, differential thermogravimetry, and differential scanning calorimetry. Acinetobacter calcoaceticus SRB4 was found to induce struvite precipitation, whereas sterile control cultures did not. Many transparent stick-shaped struvite precipitates were distributed at the bottom of the conical flasks in the experimental group. Most bacteria were spherical and a large quantity of spherical struvite particles (less than 200 nm in diameter) adhered to the bacterial surface. An electron probe microanalysis showed that the precipitates contained C, O, P, Mg, and other elements. Fourier transformation infrared spectra showed that the precipitates contained crystalline water, NH4+, and PO43− groups. X-ray diffraction spectra showed that the precipitates were struvite crystals, with preferential orientation and lattice distortion. Thermogravimetry showed that the weight loss was caused by the evaporation of crystalline water at temperatures lower than 136°C and the release of ammonia from struvite at temperatures of 136–228.5°C. In this article, we discuss the possible mechanism of struvite formation and the possible role played by A. calcoaceticus SRB4. Our study extends our understanding of the phosphate biomineralization mechanism and should prove useful in recycling phosphorus in wastewater.

Effect of thermal cycling on microstructure evolution and elements diffusion behavior near the interface of Ni/NiAl diffusion couple

The interdiffusion behavior of pure Ni vs. NiAl alloy was investigated via diffusion couple after diffusion annealing treatment under two different thermal cycling (20 and 60 cycles) conditions and isothermal condition. A combination of scanning electron microscope, transmission electron microscope and electroprobe microanalysis was used to characterize the microstructures and measure the concentration profiles across diffusion zones in the Ni/NiAl couples. A thick Ni-rich NiAl layer and a thin γ′-Ni3Al layer were formed near the interface in each couple. The martensite layer with Ni concentration of 63–67at.% was formed in the Ni-rich β-NiAl layer near the Ni/NiAl interface upon cooling. Meanwhile, the Kirkendall plane was formed close to the initial Ni/NiAl interface due to the different diffusion rate of Ni and Al near the interface. Additionally, results indicated that thermal cycling influenced the microstructure evolution behavior of Ni/NiAl diffusion couple. The γ′-Ni3Al/γ-Ni and γ′-Ni3Al/β′-martensite interfaces were rumpled after the diffusion annealing treatment under thermal cycling conditions and the rumpling became more severe under thermal cycling condition with 60 cycles. Furthermore, the slope of interdiffusion coefficients vs. Al concentration curve under thermal cycling condition with 60 cycles was higher than that under cycling condition with 20 cycles and isothermal condition, suggesting that thermal cycling might have influence on the interdiffusion behavior near the Ni/NiAl interface.

Characterization of diffusion-bonded joint between Al and Mg using a Ni interlayer

Aluminum and magnesium were joined through diffusion bonding using Ni interlayer. The microstructure and mechanical performance of the Al/Ni/Mg joints at different temperatures was investigated by means of scanning electron microscope (SEM), electro-probe microanalyzer (EPMA), X-ray diffraction (XRD), Vickers hardness testing, and shear testing. The results show that the addition of Ni interlayer eliminates the formation of Mg–Al intermetallic compounds and improves the bonding strength of the Al/Mg joints. The Al/Ni/Mg joints are formed by the diffusion of Al, Ni and Mg, Ni. The microstructure at the joint interface from Al side to Mg side is Al substrate/Al–Ni reaction layer/Ni interlayer/Mg–Ni reaction layer/Mg substrate multilayer structure. The microhardness of the Mg–Ni reaction layer has the largest value of HV 255.0 owing to the existence of Mg2Ni phase. With the increase of bonding temperature, the shear strength of the joints increases firstly and then decreases. The Al/Ni/Mg joint bonds at 713 K for 90 min, exhibiting the maximum shear strength of 20.5 MPa, which is greater than that of bonding joint bonded directly or with Ag interlayer. The fracture of the joints takes place at the Mg–Ni interface rather than the Al–Ni interface, and the fracture way of the joints is brittle fracture.

Femtosecond laser induced migration of alkali ions in calcium silicate glasses

We report on an abnormal migration phenomenon of alkali ions in calcium silicate glasses, induced by 250kHz, 800nm femtosecond laser irradiation. The diameter of the laser-affected zone is not dependent on the glass-transition temperature of glass samples. Elemental analysis by Electro-Probe Microanalyzer demonstrates that K ions migrate to the periphery of the laser-affected zone, while Cs ions show an opposite tendency in the two alkali ions coexisting glass. The possible mechanism on the observed abnormal phenomenon is discussed.

Control of the IN100 Superalloy Ingot Solidification Structure with Linear Electromagnetic Stirring

In order to achieve high quality superalloy ingots, an investigation of applying linear electromagnetic stirring to the superalloy vacuum casting solidifying process has been put into effect with electroprobe microanalysis and optical microscope. The results indicate that an one sided, upward linear electromagnetic stirring with 50Hz frequency and 140A current can effectively refine the isometric crystals and shorten the ratio of central shrinkage cavity in superalloy ingots.

The characteristics of intermetallic compounds and hardness of Ni-Cr/AC8A composites under different infiltration temperatures

With the rapid development of aerospace and automobile industries, there is an increasing need for structural materials with excellent mechanical properties such as can be used at high temperatures. Aluminum matrix composite have attracted much attention because of its excellent performance, particularly the existence of the high temperature resistance inter-metallic compounds. Aluminum-based compos- ites with inter-metallic compounds have been studied recently. In this study, Ni-Cr porous preform is reinforcement when Al-alloy (AC8A) is base metal and Ni-Cr/AC8A composites were manufactured under low pressure infiltration limited to the maximum of 0.5 Mpa at 700 o C, 750 o C, 800 o C and 850 o C, respectively. The microstructure and phase composition of the composites were evaluated by optical microscope, X-ray diffraction (XRD) and electro-probe micro analyzer (EPMA), intermetallic compounds Al3Ni and CrSi were found as newly formed phases in the composites. In addition, Vickers hardness of Ni-Cr composites was also tested.

Solidification structure analysis of cold crucible directionally solidified Nb-Si based alloy

The water cooled copper crucible directional solidification was used to prepare Nb-12Si-24Ti-4Cr-4Al-2Hf(at.%) alloy in this paper. An obvious growth trend of directional solidification in the stably solidified area of the sample was observed by scanning electron microscopy(SEM). Microstructure analysis and phases identification of the alloy were examined by X-ray diffraction (XRD), Electro Probe Micro Analyzer (EPMA). The results showed that the phases were composed of Nb solid solution(Nbss), β-Nb5Si3 andγ-Nb5Si3 intermetallic phase, and a small amount of HfO2. The volume fractions of β-Nb5Si3 and γ-Nb5Si3 were different among the initially solidified area(ISA), the stably solidified area(SSA) and the finally solidified area(FSA). Energy Disperse Spectroscopy(EDS) analysis showed that there was a certain deviation of chemical composition of the initially solidified area, the stably solidified area and the finally solidified area. This may be atributed to that the large thermal conductivity of Nb and the strong lateral heat lead to the low superheat of liquid alloy and the reduction of solute homogenized diffusion process. The technology trend of using water cooled copper crucible directional solidification technology to prepare high-temperature Nb-Si based alloy is to further improve the thermal efficiency of the cold crucible and the temperature gradient of the solid-liquid interface.

Effect of rotation mode on microstructure and mechanical properties of directionally solidified Nb-Silicon based alloys

Nb-xSi(x=3,9)-22Ti-3Cr-3Al-2Hf (at.%) have been successfully prepared by directional solidification(DS) in an optical floating zone furnace with different rotation mode. Microstructure analysis and phases identification of the alloys were examined by X-ray diffraction (XRD), Electro Probe Micro Analyzer (EPMA) and Energy Disperse Spectroscopy (EDS). Fracture toughness specimens without pre-crack were prepared and room temperature fracture toughness of alloys was tested by three-point bending method. The results showed the microstructure and fracture toughness of directionally solidified Nb-silicon based alloys were seriously affected by the rotation mode in the processing of directional solidification. The influence of rotate mode on microstructure and fracture toughness had been discussed in this paper.

Microstructure and Hardness of Ni-Cr Porous Preform Reinforced Al-Based Composites by Low Infiltration Method

With the rapid development of aerospace and automobile industries, metal matrix composites (MMCs) have attracted much attention because of its excellent performance. In this paper, Ni-Cr/AC8A composites reinforced with porous Ni-Cr preform were manufactured by low pressure infiltration process, infiltration temperatures are 700oC~850oC. The microstructure and phase composition of composites were evaluated using optical microscope, X-ray diffraction (XRD) and electro-probe microanalysis (EPMA), It's found that they're intermetallic compounds generated in the composites. Recently, intermetallic compounds have attracted much attention as high-temperature material. We study the hardness of Ni-Cr/AC8A composites, the results show the Ni-Cr/AC8A composite has high hardness due to the intermetallic compounds exist.