Visible Microstructure Research Articles

An Approach to Reduce Thermal Damages on Grinding of Bearing Steel by Controlling Cutting Fluid Temperature

The use of cutting fluid is crucial in the grinding process due to the elevated heat generated during the process which typically flows to the workpiece and can adversely affect its integrity. Considering the conventional technique for cutting fluid application in grinding (flood), its efficiency is related to certain factors such as the type of fluid, nozzle geometry/positioning, flow rate and coolant concentration. Another parameter, one which is usually neglected, is the cutting fluid temperature. Since the heat exchange between the cutting fluid and workpiece increases with the temperature difference, controlling the cutting fluid temperature before its application could improve its cooling capability. In this context, this work aimed to analyze the surface integrity of bearing steel (hardened SAE 52100 steel) after grinding with an Al2O3 grinding wheel with the cutting fluid delivered via flood technique at different temperatures: 5 °C, 10 °C, 15 °C as well as room temperature (28 ± 1 °C). The surface integrity of the workpiece was analyzed in terms of surface roughness (Ra parameter), images of the ground surface, and the microhardness and microstructure beneath the machined surface. The results show that the surface roughness values reduced with the cutting fluid temperature. Furthermore, the application of a cutting fluid at low temperatures enabled the minimization of thermal damages regarding visible grinding burns, hardness variation, and microstructure changes.

Influence of Steel Structure on Machinability by Abrasive Water Jet.

Although the abrasive waterjet (AWJ) has been widely used for steel cutting for decades and there are hundreds of research papers or even books dealing with this technology, relatively little is known about the relation between the steel microstructure and the AWJ cutting efficiency. The steel microstructure can be significantly affected by heat treatment. Three different steel grades, carbon steel C45, micro-alloyed steel 37MnSi5 and low-alloy steel 30CrV9, were subjected to four different types of heat treatment: normalization annealing, soft annealing, quenching and quenching followed by tempering. Then, they were cut by an abrasive water jet, while identical cutting parameters were applied. The relations between the mechanical characteristics of heat-treated steels and the surface roughness parameters Ra, Rz and RSm were studied. A comparison of changes in the surface roughness parameters and Young modulus variation led to the conclusion that the modulus was not significantly responsible for the surface roughness. The changes of RSm did not prove any correlation to either the mechanical characteristics or the visible microstructure dimensions. The homogeneity of the steel microstructure appeared to be the most important factor for the cutting quality; the higher the difference in the hardness of the structural components in the inhomogeneous microstructure was, the higher were the roughness values. A more complex measurement and critical evaluation of the declination angle measurement compared to the surface roughness measurement are planned in future research.

Fabrication and operating characteristics of a flat tubular segmented-in-series solid oxide fuel cell unit bundle

A unit bundle of a flat tubular segmented-in-series (SIS)-solid oxide fuel cell (SOFC) for intermediate temperature (650–800 °C) operation was fabricated and operated in this study. We fabricated flat tubular ceramic supports through an extrusion process and analyzed the basic properties of the flat tubular ceramic support: the visible microstructure, porosity, mechanical strength, and pore size distribution. After that, we manufactured a flat tubular SIS-SOFC single cell using screen printing and a vacuum slurry dip-coating method for the electrode/interconnect and electrolyte. In addition, to make a unit bundle for a flat tubular SIS-SOFC, five SIS-SOFC single cells with an effective electrode area of 0.8 cm2 were coated onto the surface of the prepared ceramic support and were connected in series using an Ag + glass interconnect between each single SIS-SOFC cell. The performance of the 5-cell unit bundle for a flat tubular SIS-SOFC in 3% humidified H2 and air at 800 °C had a maximum power of 2.5 W.

Interface Reaction between Ceramic Moulds and High Nb-TiAl Alloys

Abstract The interface reaction between Ti-44Al-8Nb-0.2W-0.1B-0.1Y (at%) alloy and Al 2 O 3 /ZrO 2 /Y 2 O 3 crucibles was investigated. The thicknesses of the interface reaction layers are about 40, 170 and 20 μm. The most interesting is the microstructure transformation of Ti-44Al-8Nb-0.2W-0.1B-0.1Y solidifying in different crucibles. After solidifying in Al 2 O 3 /ZrO 2 /Y 2 O 3 crucibles, the oxygen contents in Ti-44Al-8Nb-0.2W-0.1B-0.1Y alloy are measured to be 0.35, 0.41 and 0.11 (at%). During melting and solidification, oxygen in crucibles will diffuse into the alloy matrix. High oxygen content causes microstructure transformation. Peritectic reaction occurs in the alloys solidifying in Al 2 O 3 and ZrO 2 crucibles. For contrast, Ti-49.5Al-2Cr-2Nb alloy was chosen to make investigation. No visible microstructure difference is found in alloys solidified in various crucibles though the oxygen contents are determined as 0.40, 0.63 and 0.25 (at%).

Near-infrared femtosecond laser machining initiated by ultraviolet multiphoton ionization

We report on the experimental study of microstructures fabricated on the surface of fused silica by two femtosecond laser pulses, a tightly focused 266 nm beam followed by a loosely focused 800 nm beam. By setting the fluence of each pulse below the damage threshold, visible microstructures are fabricated using the combined beams. Our results suggest that the ultraviolet pulse generates seed electrons through multiphoton absorption, and the near-infrared pulse utilizes these electrons to cause damage by avalanche ionization.

Soft sheets of fibrillar bone from a fossil of the supraorbital horn of the dinosaur Triceratops horridus

Soft fibrillar bone tissues were obtained from a supraorbital horn of Triceratops horridus collected at the Hell Creek Formation in Montana, USA. Soft material was present in pre and post-decalcified bone. Horn material yielded numerous small sheets of lamellar bone matrix. This matrix possessed visible microstructures consistent with lamellar bone osteocytes. Some sheets of soft tissue had multiple layers of intact tissues with osteocyte-like structures featuring filipodial-like interconnections and secondary branching. Both oblate and stellate types of osteocyte-like cells were present in sheets of soft tissues and exhibited organelle-like microstructures. SEM analysis yielded osteocyte-like cells featuring filipodial extensions of 18–20μm in length. Filipodial extensions were delicate and showed no evidence of any permineralization or crystallization artifact and therefore were interpreted to be soft. This is the first report of sheets of soft tissues from Triceratops horn bearing layers of osteocytes, and extends the range and type of dinosaur specimens known to contain non-fossilized material in bone matrix.

Fabrication and Operation of Tubular Segmented‐In‐Series (SIS) Solid Oxide Fuel Cells (SOFC)

AbstractA tubular segmented‐in‐series (SIS) solid oxide fuel cell (SOFC) sub module for intermediate temperature (700–800 °C) operation was fabricated and operated in this study. For this purpose, we fabricated porous ceramic supports of 3 YSZ through an extrusion process and analyzed the basic properties of the ceramic support, such as visible microstructure, porosity, and mechanical strength, respectively. After that, we fabricated a tubular SIS SOFC single cell by using dip coating and vacuum slurry coating method in the case of electrode and electrolyte, and obtained at 800 °C a performance of about 400 mW cm–2. To make a sub module for tubular SIS SOFC, ten tubular SIS SOFC single cells with an effective electrode area of 1.1 cm2 were coated onto the surface of the prepared ceramic support and were connected in series by using Ag + glass interconnect between each single cell. The ten‐cell sub module of tubular SIS SOFC showed in 3% humidified H2 and air at 800 °C a maximum power of ca. 390 mW cm–2.

Influence of Mo in the structure of rapidly solidified Fe–Mo–Cr–Mn–Si–C alloy

An Fe–Mo–Cr–Mn–Si–C alloy was prepared in an induction furnace and was cast into cylindrical rod in a copper mould in castmatic equipment (low pressure casting). A single phase non-equilibrium featureless (no visible microstructures after deep etching) phase was observed over a certain range of thickness of the rod. In this present work, the extent of the featureless phase was studied with different concentrations of Mo (5–25 wt-%) for 5·5 mm diameter of cylindrical rod at a cooling rate of 1100 K s–1. Light optical microscopy, scanning electron Microscopy and Vickers hardness tests were used to analyse the samples. The amount of the featureless area varies as the Mo content changes and the maximum featureless area was obtained for 7 wt-% of Mo. This single phase featureless structure exhibits very high hardness (>1350 HV) which can be used in many interesting applications with or without suitable heat treatments.

Microstructures and OH-bearing nano-inclusions in "wet" olivine xenocrysts from the Udachnaya kimberlite

Mantle olivine xenocrysts from the Udachnaya kimberlite pipe (Yakutiya, Siberia) were investigated by optical microscopic and TEM methods. From optical observations two types of olivine xenocrysts are discriminated. Crystals exhibiting an optically visible cross-hatched microstructure, caused by linear features oriented parallel to [100], [001], [101] and [−101] directions in the olivine host are assigned to type 1, and the optically clear ones are assigned to type 2. TEM investigation showed that both type 1 and type 2 samples contain OH-bearing nano-inclusions with a grain size between several tens and several hundreds of nanometres, composed of hydrous magnesium silicates such as “hydrous olivine” (occasionally), the 10-A phase, serpentine and talc. In the investigated samples, the 10-A phase is to a large extent replaced by the low-pressure assemblage serpentine + talc. On TEM scale, the difference between type 1 and type 2 olivine samples is that the inclusions in type 1 are grouped in arrays (high density of precipitation), while in type 2 they are randomly arranged (low density of precipitation). The cross-hatched linear features in type 1 correspond to arrays of the OH-bearing nano-inclusions precipitated in (001), (100), (101) and (−101) planes of olivine. The presented data confirm that nano-inclusions filled by hydrous magnesium silicates, both high-pressure (“hydrous olivine” and 10-A phase) and low-pressure ones (serpentine and talc), are much more frequent and typical for olivine nodules in kimberlites than it would have been expected earlier. The amount of water in the investigated olivine samples ranges from 37 to 300 ppm (Koch-Muller et al. , 2006) and does not vary significantly depending on whether the samples exhibit an optically visible microstructure or not. We conclude that the xenocrysts crystallized as “wet” olivine in a mantle environment, whereas the OH-bearing nano-inclusions formed later during eruption and transport of olivine fragments from depths to the surface. The origin of nano-inclusions is discussed in terms of subsolidus aggregation of intrinsic OH-bearing point defects in olivine; this event has been initiated by deformation processes in the kimberlite pipe during eruption.

Multiphase visualisation of fat containing β-lactoglobulin–κ-carrageenan gels by confocal scanning laser microscopy, using a novel dye, V03-01136, for fat staining

Abstract In this study, the gel strength and visible microstructure of fat containing β-lactoglobulin–κ-carrageenan gels were investigated using puncture testing and confocal scanning laser microscopy, respectively. The gel strength was closely linked to the visible microstructure of the whey protein network as stained with Rhodamine B. Covalent labelling of κ-carrageenan with FITC prior to gel formation enabled localisation of the hydrocolloid phase, but caused a significant drop in the gel strength. This effect coincided with the observed reduction of the κ-carrageenan intrinsic viscosity, which was found to be a result of the labelling process. The use of a novel dye, V03-01136, for the staining of fat allowed for the specific and concurrent visualisation of the protein, hydrocolloid and fat phases under the conditions applied in the study.

Microstructure analysis of aluminum extrusion: grain size distribution in AA6060, AA6082 and AA7075 alloys

Microstructure and material flow of aluminum alloys have a significant influence on the mechanical properties and surface quality. In extrusion of aluminum billets at high temperatures the microstructure is dependent on the alloy and the forming and temperature history. A prediction of grain size and precipitation is of increasing importance in order to design the process by adjustment of parameters such as punch speed, temperatures, and quenching. To give references for microstructure prediction based on material flow, and with it strain and strain rate history, this paper deals with the microstructure during the extrusion process of AA6060, AA6082, and AA7075 alloys. Billets have been partly extruded to axisymmetric round profiles and the microstructure of the press rests consisting of the billet rests in container and die has been considered. Furthermore, these rests have been analyzed to show the material flow, dynamic and static recrystallization based on macro etchings and visible microstructure under different conditions, e.g. as in the area of high strain rate near the container wall, or in dead zones [1]. To allow an accurate simulation of the extrusion process, punch force and temperature conditions during the tests have been measured and are presented in this paper, too.

Microstructural origins of radiation-induced changes in mechanical properties of 316 L and 304 L austenitic stainless steels irradiated with mixed spectra of high-energy protons and spallation neutrons

A number of candidate alloys were exposed to a particle flux and spectrum at Los Alamos Neutron Science Center (LANSCE) that closely match the mixed high-energy proton/neutron spectra expected in accelerator production of tritium (APT) window and blanket applications. Austenitic stainless steels 316 L and 304 L are two of these candidate alloys possessing attractive strength and corrosion resistance for APT applications. This paper describes the dose dependence of the irradiation-induced microstructural evolution of SS 316 L and 304 L in the temperature range 30–60°C and consequent changes in mechanical properties. It was observed that the microstructural evolution during irradiation was essentially identical in the two alloys, a behavior mirrored in their changes in mechanical properties. With one expection, it was possible to correlate all changes in mechanical properties with visible microstructural features. A late-term second abrupt decrease in uniform elongation was not associated with visible microstructure, but is postulated to be a consequence of large levels of retained hydrogen measured in the specimens. In spite of large amounts of both helium and hydrogen retained, approaching 1 at.% at the highest exposures, no visible cavities were formed, indicating that the gas atoms were either in solution or in subresolvable clusters.

Visible microstructures in cryosectioned versus high resolution T1 MR images

Visible microstructures in cryosectioned versus high resolution T1 MR images

Experimental constraints on shock-induced microstructures in naturally deformed silicates

Planar deformation features (PDFs) in various minerals have long been accepted as evidence of impact-induced deformation. The uniqueness of this association was challenged in the context of the K/T Boundary extinction debate, after mosaicism and microstructures similar to PDFs were reported from the products of explosive volcanism. As a result of this debate, a significant volume of new experimental and observational data on the development of shock-induced microstructures has become available over the last ten years. The results reveal that factors such as pre-shock temperature, pulse duration, and crystallographic orientation of target minerals to the shock wave have a primary influence on how these microstructures develop. Data from diamond anvil cell and high-pressure friction experiments reveal that the same solid-state amorphization process that produces shock-induced PDFs at low temperatures also occurs at much lower strain rates in static experiments.The experimental data indicate that the amorphization process is thermally activated and that the character of the resulting PDFs is a function of the applied strain rate. Shock-induced amorphization occurs along those crystallographic planes that are most readily transformed to the high-pressure phase during very short pulse durations and produces PDFs that are visible at the optical scale. Lower strain rate deformation produces TEM scale amorphization with orientations that are more homogeneously distributed throughout the target mineral and produces no optically visible PDFs. The data confirm the uniqueness of multiple intersecting sets of optically visible PDFs as a diagnostic indicator of hypervelocity impact. The data also support the hypothesis that the amorphization process can occur at a wide range of strain rates, and that the limiting pressure for the process is controlled by the phase stability of the target mineral under the applied loading conditions, not by the HEL. The data also suggest that the onset pressure, the maximum pressure, and the pressure range for producing optically visible PDFs decrease with increasing temperature and decreasing strain rate. As the pressure range for optically visible PDF formation decreases, it is replaced by homogeneous amorphization as observed in the anvil cell experiments. Thus, the uniqueness of multiple intersecting sets of optically visible PDFs to hypervelocity impact is not due to a unique process, but rather to a specific set of loading conditions that produce an optically visible microstructure. Likewise, single sets of microdeformations observed in volcanic rocks are produced by the same process, but at different loading conditions that preclude the development of multiple intersecting sets of PDFs. The data also indicate that shock mosaicism, which occurs above the HEL, represents a plastic response of the target mineral to loading rates that are too large to be accommodated by crystal plastic mechanisms.Observational data for some naturally deformed samples from the K/T Boundary, the Vredefort Dome, and volcanic rocks, along with the experimental observations, are used to constrain the range of conditions under which the natural microstructures form, and to understand the differences between microstructures produced by impact, volcanic, and other natural processes. Finally, some possible mechanisms for producing the microstructures observed in volcanic rocks are proposed.

Visible Photoluminescence and Microstructure of Annealed and Chemically Etched Amorphous Si

ABSTRACTWe have studied the visible photoluminescence (PL) and microstructure of porous Si layers (PSLs) fabricated by the chemical etching of annealed amorphous Si (a-Si). The a-Si layers were partially crystallized by annealing between 550°C-1150°C in N2 and the PSL formed by etching in a HF-HNO3-based solution. No visible PL was observed after etching of unannealed a-Si. Visible PL was detected after etching a-Si layers first annealed at temperatures ≥725°C, coinciding with the observation of Si microcrystallites in the annealed layer prior to etching. The results suggest that an initial crystalline structure is important for fabricating luminescent PSLs.

Magnetic petrology of eastern North America diabases, I. Olivine-normative dikes from western South Carolina

The oxide mineralogy and magnetic properties were examined in a suite of fifteen olivine-normative diabase dike samples from western South Carolina in an attempt to elucidate their magnetic petrology. Titanomagnetite (1–2 vol.%) is the dominant Fe-Ti oxide mineral. Ilmenite and secondary magnetite are generally present in very minor amounts. Chromite constitutes up to 0.5 vol.%; its abundance and composition correlate with bulk rock Cr. Various types of fine-scale microstructure are evident in titanomagnetite crystals. The most important are patterned anisotropism and the development of trellis-type ilmenite lamellae. Microprobe analyses indicate: (1) titanomagnetite compositions, x, are mostly between 0.4 and 0.55, and (2) low analytical totals are characteristic of most titanomagnetites. Curie temperatures of the diabases are 500–540°C, which are several hundred degrees higher than predicted from the observed titanomagnetite x's (150–300°C). We attribute these higher Curie temperatures to oxidation of the titanomagnetites, which has produced “titanomaghemites” having visible microstructure and yielding low analyses (because they are cation deficient). Natural remanence magnetization and REM (ratio of natural remanence to saturation remanence) vary between 4 and 100 × 10 −4 A m 2 kg −1 and 0.0019 and 0.032, respectively. These properties inversely correlate with Cr content and demonstrably contrast Cr-rich and Cr-poor samples. Initial susceptibility, saturation magnetization and coercivity values show a two- to three-fold range. Variations in initial susceptibility and coercivities appear to be largely related to the type and extent of oxidation-induced microstructure in the titanomagnetites.

Collective effects in the a-Si:H growth process

We regard the growth of a-Si:H as a thermodynamically open system in non-equilibrium. The formation of dissipative structures must appear and may occur as the creation of visible microstructure. The question of metastability is regarded in terms of self-organization. A mathematical model of the a-Si:H growth process is suggested.