3D laser ultramicroscopy: A method for nondestructive characterization of micro- and nanoinclusions in high-purity materials for fiber and power optics

This paper describes a 3D laser ultramicroscopy technique and apparatus for the nondestructive characterization of heterophase inclusions in bulk high-purity materials for fiber and power optics. In this technique, the concentration and size of inclusions undetectable by optical microscopy are determined using CCD detection of the light scattered by them in a direction normal to the incident laser beam at wavelengths from 0.63 to 0.98 μm. The detection limit of the technique in terms of inclusion size is n × (10–100) nm, the range of detectable number concentrations is 1–10¹¹ cm^?3, and the scan depth in the sample is ～1 cm. Its performance has been evaluated using test systems. The potential of the technique is illustrated by the dispersion analysis of promising materials for IR fiber-optic applications.     

Characterization of heterophase inclusions in glasses opaque in the visible range

We have designed an apparatus and developed a nondestructive laser ultramicroscopy technique involving digital detection of the 0.98-μm radiation scattered by individual inclusions for determining the concentration and size of submicron heterophase inclusions in high-purity glasses opaque in the visible range. The capabilities of the technique have been illustrated by analyzing several test systems. The detection limit for the inclusion size is shown to be n × (10–100) nm, depending on the refractive indices n of the inclusions and glass. The working range of inclusion concentrations is 10² to 10⁹ cm^?3, and the maximum scan depth is ～1 cm. The technique has been used to assess the microinhomogeneity of selenium and As-S-Se glass samples.     

A numerical study of inclusion-matrix debonding in the presence of a nearby crack

Debonding of an inclusion from the surrounding matrix in the presence of a nearby crack tip is studied numerically. Finite element models of symmetric three-point bend configurations are implemented in conjunction with a stiffness degradation method and the maximum tensile stress criteria to investigate the influence of debonding on crack tip parameters. The geometry considered is a single edge cracked beam having a symmetrically positioned stiff or soft cylindrical inclusion ahead of the crack tip. The numerical model is first validated by interferometric measurements on an edge cracked epoxy specimen with a glass inclusion. The measured quantities namely, the crack mouth opening displacement, crack mouth compliance, energy release rate, dominant strain, are all successfully captured by the adopted numerical methodology, before and after the inclusion debonds from the matrix. Subsequently, the effects of parameters such as the distance between the crack tip and inclusion center (L), the inclusion diameter (d), and the Young’s modulus ratio between the inclusion and the matrix, are studied using the model. A stiff inclusion of constant (d/L) ratio debonds from the matrix at higher load levels when the inclusion interface is farther away from the crack tip. The increase in the crack driving force due to debonding is the highest when the inclusion proximity parameter ρ is approximately 0.4 and it decreases when ρ is increased or decreased relative to this value. However, when d/L ratio is varied, higher crack driving forces due to debonding are observed for larger size inclusions due to a greater loss of crack tip shielding and reinforcement. The influence of the modulus ratio (E_i/E_m) due to debonding is most prominent in the range 0-1 for fixed d/L and ρ values. Additionally, a stiffer inclusion tends to debond from the matrix at lower loads for a constant interfacial strength.     

Experimental investigation on statistics of extremes for three-dimensional distribution of non-metallic inclusions

Abstract

A wide range of studies have shown that the lower bound of fatigue properties of high strength steels is determined by the maximum size of non-metallic inclusions that are present in a component. The maximum size of inclusions in a given component or material volume can be reasonably estimated using the statistics of extremes. However, as long as the estimation is based on microscope inspections of two-dimensional (2D) surfaces, there will be errors and uncertainties in estimating the maximum particle in a three-dimensional (3D) volume. In addition it has been recently found that in some steels the distribution of extreme defects is composed of a mixture of different particle types. The scope of this paper is to clarify the validity of 2D inspections on the basis of 3D distribution of inclusions in a modern super clean steel. The 3D distribution was obtained with a combination of inclusions detected with a repeated slicing procedure and of particles at fatigue fracture origin. The 3D distribution of inclusions is composed of a mixture of two types of particles having similar chemical compositions and different 3D morphological structures: one with a large population and another with few rare particles. The 3D large population can be accurately estimated from maximum inclusions on small polished sections, while in order to estimate the characteristic size of inclusions at fatigue fracture origin by 2D inspections it is necessary to adopt a minimum inspection area S _crit. In the case of the material examined in this study (SCM435 steel) this minimum inspection area is ~ 10 000 mm².     

Photoluminescence properties of emission-tunable Ca9Y(PO4)7: Tm,Dy phosphor for white light emitting diodes

A white-emitting Ca₉Y(PO₄)₇: Tm³⁺, Dy³⁺ phosphor has been successfully prepared by conventional high-temperature solid-state reaction. X-ray diffraction (XRD) and fluorescence spectrophotometer were used to characterize the as-synthesized phosphors. The excitation and emission spectra show that all the Tm³⁺ and Dy³⁺ co-doped Ca₉Y(PO₄)₇ samples can be effectively excited by UV light and then emit blue and yellow light simultaneously. Furthermore, the emission and color coordinate of as-obtained samples pumped by 365 nm are able to be adjusted around white light by varying the doping concentrations of Tm³⁺ and Dy³⁺. So, the as-fabricated single-composition Ca₉Y(PO₄)₇: Tm³⁺, Dy³⁺ phosphor will have a promising application in the area of white light emitting diodes.     

Gigacycle fatigue properties of 1800 MPa class spring steels

Fatigue tests up to 10⁸ cycles were carried out for two spring steels (Heats A and D1) and one valve spring steel (Heat F) with tensile strength, σ _B, of 1720, 1725 and 1764 MPa, respectively. The size and composition of inclusions in Heats Dl and F were controlled. The surface‐type fracture occurred at shorter lives below 10⁶ cycles, while the fish‐eye‐type fracture occurred at longer lives. The fatigue limit, σ _W, at 10⁸ cycles was 640 MPa for Heats A and D1 and 700 MPa for Heat F. Al₂O₃ inclusions for Heat A and both TiN inclusions and matrix cracks, i.e. internal facets, for Heat F were observed at the fish‐eye‐type fracture sites, while only matrix cracks were observed for Heat Dl. ODA, i.e. optically dark area, which is considered to be related to hydrogen effects, were formed around Al₂O₃ and TiN inclusions. Fatigue tests were also conducted after specimens were heated up to 573 K in high vacuum of 2 × 10^–6 Pa. The heat treatment eliminated matrix cracks for Heat D1 and the fatigue limit at 10⁸ cycles recovered to the estimated value of 920 MPa from the equation σ _w= 0.53 σ _B for the surface fracture. These results suggest that inclusions control and hydrogen influence the gigacycle fatigue properties for these high strength steels. In addition, it is expected that the creation of a martensite structure with a high resistance to hydrogen effects in the inclusion‐controlled steel could achieve the higher fatigue limit estimated for the surface‐type fracture.     

Antiquenching effect of modifying cations on samarium clustering: Physical,structural and luminescent behavior of heavy metal borate glass systems

In this paper an attempt has been made to correlate the structural modifications and luminescence efficiencies by changing the environment of the glass network by modifying oxides. Sm³⁺ doped lead borate (SPB) and lead cadmium alumino borate (SCPB) glasses have been fabricated by melt quench technique at high temperature. The glass samples are characterized by XRD, FTIR, optical absorptions, fluorescence and density measurements. The effect of Sm³⁺ ion and glass host interaction on the emission spectra has been discussed in the view of the ionicity and covalency of hosts. The ratio of the intensities of electric to magnetic dipole emissions are calculated by varying both the concentration of the Sm³⁺ ion and the composition of the glass matrix. The XRD profile of all the glasses confirms their amorphous nature and FTIR spectrum shows the presence of BO₃ and BO₄ groups. These glasses have shown strong absorption bands in the visible (VIS and NIR) region and emit strong orange red wavelengths when excited by ultraviolet light. The concentration quenching has been noticed and ascribed to energy transfer through cross-relaxation between Sm³⁺ ions. Shifting of UV absorption edge towards longer wavelength with addition of Sm₂O₃ concentration has been observed. Incorporation of Al₂O₃ and CdO in 2nd glass system is responsible for strong effect on luminescence of the present glass system. Based on these results, an attempt has been made to throw some light on the relationship between the structural modifications and luminescence efficiencies in two different glass hosts as a laser active medium in the visible region. Moreover the optical basicity values were theoretically determined along with covalent behavior of two glass systems.     

Cluster adsorption on oxide inclusions in liquid steel

We refine the determination of forms of the existence of disperse oxide inclusions in liquid steel by taking into account the phenomenon of cluster adsorption near interfaces in structurally microinhomogeneous liquids. We show that every nonmetallic inclusion in steel is surrounded by a shell consisting of many layers of adsorbed metal clusters with thicknesses of a few tens of micrometers. From new positions, we quantitatively evaluate certain specific features of the behavior of oxide inclusions in liquid steel, namely, the effect on its viscosity, the buoyancy of inclusions, and their ability to float up depending on their nature (MgO, ZrO₂, Al₂O₃, and SiO₃) and size. Odessa State Polytechnic University, Odessa. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 5, pp. 53–58, September–October, 1999.     

Optical characterization of thin chalcogenide films by multiple-angle-of-incidence ellipsometry

Optical properties of thin chalcogenide films from the systems As-S(Se) and As-S-Se were investigated as a function of the film composition, film thickness and conditions of illumination by light using multiple-angle-of-incidence ellipsometry. Thin films were deposited by thermal evaporation and exposed to white light (halogen lamp) and to monochromatic light from Ar⁺ — (λ = 488, 514 nm) and He-Ne- (λ = 632.8 nm) lasers. The ellipsometric measurements were carried out at three different angles of light incidence in the interval 45-55°, at λ = 632.8 nm. An isotropic absorbing layer model was applied for calculation of the optical constants (refractive index, n and extinction coefficient, k) and film thickness, d. The homogeneity of the films was checked and verified by applying single-angle calculations at different angles. It was shown that the refractive index, n of As-S-Se films is independent of film thickness in the range of 50 to 1000 nm and its values varied from 2.45 to 3.05 for thin layers with composition As₂S₃ and As₂Se₃, respectively. The effect of increasing in the refractive index was observed after exposure to light which is related to the process of photodarkening in arsenic containing layers. The viability of the method for determining the optical constants of very thin chalcogenide films with a high accuracy was confirmed.     

Microanalytical characterization of microscopic defects in NiCr-based alloys of low impurity content

The quality of thin foil components made from NiCr-based alloys can be reduced by three-dimensional defects formed during alloy preparation and roMng cycles of foil manufacturing. In particular, the appearance of microscopic holes, i.e. defects transparent to light, air or other matter, can completely prevent special applications. Thus for the optimization of foil manufacturing procedure microanalytical investigations were needed to support the decision for either a model of solely vacancy coalescence or a combined model of vacancy coalescence in the presence of second-phase inclusions and direct interaction of inclusion and roll surface. The identification of corundum particles as a major inclusion of almost all investigated transparent defects confirms that thodefects are formed due to both different mechanical behaviour (of-Al₂O₃ inclusions and NiCr-alloy) and vacancy coalescence at the appropriate phase boundary during rolling deformation.     

On the effect of non-metallic inclusions on hydrogen damage in aluminium-killed steel

The effect of non-metallic inclusions on corrosion and on hydrogen damage in an aluminium-killed steel was studied by considering the size, shape, composition and number of inclusions. Accurate determinations of the compositions of the different inclusion compounds were performed by energy-dispersive analysis of replica-extracted particles. Clusters of alumina inclusions appear to be preferred sites for the occurrence of blisters. Complex inclusions with the phases 3Al₂O₃ · 2SiO₂, MnO, MnS and Al₂O₃ frequently presented blisters. Blisters appeared to be nucleated in voids produced during working of the steel. Blisters were never found in MnS inclusions.     

Calculated elastic constants of alumina-mullite ceramic particles

Using two theoretical models, we estimated the isotropic elastic constants of an alumina-mullite ceramic composite. The alumina phase, 20% by volume, consisted of brickshaped particles with a 4:1 aspect ratio embedded in a mullite matrix (mullite = 3Al₂O₃·2SiO₂). We took alumina elastic-constant values from the literature, and we measured mullite's elastic constants using a megahertz-frequency pulse-echo method. The two theoretical models, Datta-Ledbetter and Mori-Tanaka, proceed from very different viewpoints. The Datta-Ledbetter model uses the long-wavelength limit of a scattered plane wave ensemble-average approach. The model estimates the speed of a plane harmonic wave, averages the scattered field by the Waterman-Truell procedure and uses Lax's quasicrystalline approximation to sum over pairs. The Mori-Tanaka method proceeds by estimating the average matrix stress in a material containing ellipsoidal inclusions. For randomly oriented ellipsoids, it extends Eshelby's solution for a single ellipsoidal inclusion. Both models lack adjustable parameters. Surprisingly, the two models with different physical approaches give practically identical results. A rough check on our estimates is that they lead to correct predictions of the elastic constants of an alumina-mullite-particle aluminium-matrix composite.     

Investigation on the effect of Tb(dbm)3phen on the luminescent properties of Eu(dbm)3phen-containing mesoporous silica nanoparticles

Eu(dbm)₃phen and Tb(dbm)₃phen complexes (tris(dibenzoylmethane) mono(1,10-phenantroline) Ln(III)) were impregnated in ordered mesoporous silica nanoparticles (MSNs) with an average size of 50–70 nm and a pore diameter centred at 2.8 nm, with the aim of increasing the luminescence by avoiding concentration quenching and having mainly in mind the application as down-shifter for multi-crystalline solar cells. The morphological, structural, textural and luminescent properties of the synthesized samples were characterized by N₂ adsorption–desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–visible spectroscopy and photoluminescence measurements. It is demonstrated that inclusion in the MSNs allows one to use much higher loadings (23 wt%) of the Eu-complex than in other matrices, and that co-doping with Tb(dbm)₃phen improves luminescence for samples with Eu(dbm)₃phen content lower than about 10 wt%. Results are interpreted by using a simple sphere of action model adapted to the case of a pore-limited system.     

In situ studies of the agglomeration phenomena for calcium–alumina inclusions at liquid steel–liquid slag interface and in the slag

Studies of inclusion behavior at the metal–slag interface are of great importance for the steel industry in order to obtain better control of the size and of inclusions as well as improving the steel quality and casting process. In this work the agglomeration of liquid Al₂O₃–CaO particles at the liquid steel–liquid slag interfaces are studied with a confocal scanning laser microscope. In addition, the agglomeration of liquid Al₂O₃–CaO inclusions already transferred to the slag is investigated. It is found that agglomeration of the liquid inclusions at the steel–slag interface could only take place when the inclusions were forced towards each other, while the agglomeration of liquid particles was seen to be noticeably enhanced when the particles were already in the slag.     

Microstructure and inclusion of Ti–6Al–4V fabricated by selective laser melting

Selective laser melting (SLM) was used in fabricating the dense part from pre-alloyed Ti-6Al-4V powder. The microstructural evolution and inclusion formation of as-fabricated part were characterized in depth. The microstructure was characterized by features of columnar prior β grains and acicular martensite α'. High density defects such as dislocations and twins can be produced in SLM process. Investigations on the inclusions find out that hard alpha inclusion, amorphous CaO and microcrystalline Al₂O₃ are three main inclusions formed in SLM. The inclusions formed at some specific sites on melt pool surface. The microstructural evolution and inclusion formation of as-fabricated material are closely related to the SLM process.     

Effect of inclusion size on mechanical properties of alumina toughened cubic zirconia

The relationship between alumina inclusion size and mechanical properties of particulate cubic zirconia-alumina composites was studied. The composites of the diverse size and content of alumina inclusions and of the nearly constant size of zirconia grains were used. Physical mixtures of the 8 mol% Y₂O₃-ZrO₂ nano-powder and the γ-Al₂O₃ or α -Al₂O₃ micro-powder were cold isostatically pressed and then pressurelessly sintered for 2 h at 1300^∘C in air. The γ -Al₂O₃ and α -Al₂O₃ powder was composed of the particles of 0.17 and 0.36 μ m in size, respectively. Crystallites of the zirconia powder had the size of 6 nm. Microstructural features of the composites have been characterised quantitatively. Hardness, critical stress intensity factor and bending strength of the composites was measured and correlated with the microstructural features. Depending on the size and content, the alumina inclusions influenced strength of the composites by influencing their fracture toughness and the presence of flaws of critical size. An increase in size of the alumina inclusions was accompanied by the increase of fracture toughness due to the additional contribution of large alumina inclusions to the crack deflection mechanism. It was found that decreasing the alumina inclusion size significantly below the cubic zirconia matrix grain size (more than 3 times) did not lead to the increased values of fracture toughness of the composites. The highest increase in fracture toughness (up to 3.9 MPa⋅ m^0.5) has been found when the inclusion size was comparable to the matrix grain size.     

含Ce2O3氧化物对改善双相不锈钢亚稳态点蚀的机理研究

利用扫描电镜、原子力显微镜、恒电位脉冲等研究了2205双相不锈钢在中性含Cl-环境下氧化物引起点蚀萌生的机理。实验发现MgO-Al_2O_3系夹杂物中MgO偏聚处以及MgO-Al_2O_3-CaO系夹杂物中CaO富集处会引起夹杂物处基体同周围基体接触电势差增加。此外,CaO富集处易使夹杂物表面出现显微缝隙并使基体裸露,产生亚稳态蚀坑。经Ce处理后发现夹杂物成分变为含Ce_2O_3·11Al_2O_3或Ce_2O_3·Al_2O_3为主的复合夹杂,夹杂物与基体接触电势差减小并且在含Ce_2O_3复合夹杂物处未发现点蚀萌生现象,最后阐述了非金属氧化物引起点蚀的机理以及Ce与氧化物反应的机制。     

Nature of inclusions in steel weld metals and their influence on formation of acicular ferrite

Abstract

The chemistry and structure of weld metal inclusions has been studied. Four submerged arc welds which utilized plate and consumables to cover a range of oxygen and deoxidant contents were examined. Analysis of the inclusions was carried out on carbon extraction replicas in a Philips 400T scanning transmission electron microscope, fitted with an energy dispersive analyser. Two major types of inclusion were found. With weld metal aluminium approaching the stoichiometric ratio with oxygen, the inclusions were crystalline and had a spinel structure at the centre with a discontinuous, polycrystalline, titanium-rich phase on the surface. With weld metal oxygen high compared with the stoichiometric ratio with aluminium, inclusions were glassy and essentially manganese silicate in composition, again with areas of a polycrystalline, titanium-rich phase on the surface. The interinclusion spacing varied little with weld metal oxygen content in the range 0·0268–0·0858 wt-%. The spacing was found to be of a similar order to the acicular ferrite grain size. The titanium-rich surface phase in all the welds was of fcc structure with a lattice parameter of 0·42 nm, which suggests a mixture of TiO and TiN, possibly rich in TiO. The spinel phase was also fcc and had a composition between galaxite (Al₂O₃MnO) and γ-alumina. Both these phases have a low lattice misfit with ferrite. A low lattice misfit of the inclusion surface layers with ferrite coupled with closely spaced inclusions would seem to be key factors in the development of an acicular ferrite weld metal microstructure.

MST/543     

Separation of electrically neutral non-metallic inclusions from molten steel by pulsed electric current

ABSTRACT

Effect of a pulsed electric current on the distribution of Al₂O₃ inclusions in liquid steel is explored; these inclusions ranged in size from micrometres to nanometres. When no electric current was applied, the inclusions were randomly distributed in the steel. However, when an electric current was applied, the inclusions were found in highly populated regions near the various interfaces. Moreover, this process applies to a wide range of inclusion diameters, in contrast to conventional inclusion removal methods which tend to apply to larger (>20?μm) particles only. Consequently, the application of pulsed electric current provides a method of removing inclusions from the steel and thereby improving the mechanical, physical and corrosion resistance properties of the steel.

This paper is part of a themed issue on Materials in External Fields.     

Enhancing the magnetic characteristics of BiFeO3 nanoparticles by Ca,Ba co-doping

Multiferroic nanoparticles (NPs) of pristine and Ca, Ba co-doped BiFeO₃ were synthesized by a facile sol–gel route. Co-doping was done by fixing the total dopant concentration at 5 mol% and then the relative concentrations of Ca and Ba was varied. Structural, optical and magnetic properties of the NPs were investigated using different techniques. UV–Vis absorption spectra of BiFeO₃ NPs showed a substantial blue shift of ∼100 nm (530 nm → 430 nm) on Ca, Ba co-doping which corresponds to increase in band gap by 0.5 eV. ⁵⁷Fe Mössbauer spectroscopy confirmed that iron is present only in 3⁺ valence state in all co-doped samples. The coercive field increased by 18 times for Bi_0.95Ca_0.01Ba_0.04FeO₃ samples, which is the maximum enhancement, observed amongst all the 5 mol% doped samples. At the equimolar (2.5 mol% each) concentration of co-dopants, the coercive field shows a significant enhancement of about 9 times (220 Oe → 2014 Oe) with concomitant increase in saturation magnetization by 7 times. Thus, equimolar co-doping causes simultaneous enhancement of the twin aspects of magnetic properties thereby making them better suited for device applications.