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Microstructural Investigation (microstructural + investigation)
Selected AbstractsMicrostructural Investigation of Walking Parts of Military Tanks Coated with Arc SprayingADVANCED ENGINEERING MATERIALS, Issue 7 2008U. Ozsarac The walking parts are the most important mechanical components in military tanks and other vehicles having palettes. The matrix phase of carrying wheels is Cu-based aluminum alloy. In this study, the microstructure of walking parts of military tanks was investigated deeply by optically and scanning electron microscopy. [source] Microstructural investigation of low-dose neutron irradiation effects in martensitic steels for nuclear application by means of small-angle neutron scatteringJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007Rainer Lindau The microstructural effect of low-dose neutron irradiation and subsequent high-temperature tempering in the reduced activation ferritic/martensitic steel F82H-mod. (7.73 Cr, 0.09 C, 0.08 Mn, 0.19 V, 2.06 W, 0.02 Ta, wt%, bal. Fe) has been studied using small-angle neutron scattering (SANS). The investigated samples were irradiated with thermal neutrons at 523,K, to dose levels of 2.4 displacements per atom then tempered for 2,h at 1043,K. The SANS measurements were carried out at the D22 instrument of the High Flux Reactor at the Institut Max von Laue,Paul Langevin, Grenoble, France. The differences observed in nuclear and magnetic small-angle neutron scattering cross-sections after subtraction of the reference sample from the irradiated one suggest that the irradiation and the subsequent post-irradiation tempering produce the growth of non-magnetic precipitates; the results are also compared with those obtained on other ferritic/martensitic steels, with different chemical composition, irradiated under the same conditions. [source] Microstructural Characteristics of an AZ91 Matrix-Glassy Carbon Particle Composite,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Anita Olszówka-Myalska This paper presents the results of a microstructural investigation of a new type of ultralight glassy carbon particles (Cp)-AZ91 magnesium alloy matrix composite manufactured by the powder metallurgy method. Glassy Cp with unmodified surfaces and surfaces modified with SiO2 amorphous nanocoating were used in the experiment. The composite microstructure, with an emphasis given on the interface, was characterized by scanning electron microscope (SEM), TEM, and HRTEM microscopy. Uniform distribution of the particles in the matrix and their good bonding with the metal matrix were observed. A continuous very thin MgO oxide layer containing needle-like Al2MgO4 phase was detected at the glassy carbon,AZ91 interface. An increase of aluminum concentration at the interface as a result of Mg and Al diffusion into the SiO2 nanolayer was observed in the case of particles modified with SiO2. Crystalline phases containing carbon were not detected at the interface. [source] Scanning electron microscopy and transmission electron microscopy microstructural investigation of high-speed tool steel after Nd:YAG pulsed laser meltingJOURNAL OF MICROSCOPY, Issue 1 2006S. KAC Summary This article presents the microstructure of a pulsed Nd:YAG laser-melted high-speed steel, namely HS6-5-2. The high chemical homogeneity and fine structure of the melted zone was attributed to high cooling rates due to the short duration of interaction with the Nd:YAG pulsed laser radiation and the relatively small volume of the melted material. The structure obtained in the surface layer after laser melting has a high level of hardness and shows improved wear resistance. [source] Formation of Ceramics from Metakaolin-Based Geopolymers: Part I,Cs-Based GeopolymerJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009Jonathan L. Bell The structural evolution and crystallization of a cesium-based geopolymer (Cs2O·Al2O3·4SiO2·11H2O) on heating was studied by a variety of techniques including X-ray diffraction, thermal analysis, dilatometry, pycnometry, specific surface area, and microstructural investigation. The Cs geopolymer gradually crystallized into pollucite (Cs2O·Al2O3·4SiO2) on heating above 900°C. Its low crystallization temperature is believed to be due to the presence of nuclei in the geopolymer precursor, which are formed after curing at 50°C for 24 h. The Cs-based geopolymer was found to be more refractory compared with K- and Na-based geopolymers. Significant shrinkage, due primarily to viscous sintering, did not occur until the samples were heated to above 1200°C. The microstructure of unheated geopolymer had ,20,30 nm-sized precipitates that coarsened on heating above 1000°C. By 1350°C, the geopolymer surface had a smooth, glassy texture, although large macropores and closed pores remained. After heating to 1600°C, the closed pores were removed, and the geopolymer reached ,98% of the theoretical density of pollucite. Higher than expected levels of Cs were found near large voids, as seen by scanning electron microscopy and transmission electron microscopy analysis. The presence of this extra Cs was due to Cs left behind in pore water, which was not bound within the geopolymer structure. [source] FIB-Nanotomography of Particulate Systems,Part II: Particle Recognition and Effect of Boundary TruncationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Beat Münch The focused ion beam-nanotomography (FIB-nt) technique presented in Part I of this article is a novel high-resolution three-dimensional (3D) microscopy method that opens new possibilities for the microstructural investigation of fine-grained granular materials. Specifically, FIB-nt data volumes allow particle size distributions (PSD) to be determined, and the current paper discusses all the processing steps required to obtain the PSD from 3D data. This includes particle recognition and the subsequent PSD estimation. A refined watershed approach for 3D particle recognition that tolerates concavities on the particle surfaces is presented. Particles at the edge of the 3D data volume are invariably clipped, and because the data volume is of a very limited size, this effect of boundary truncation seriously affects the PSD and needs to be corrected. Therefore, two basic approaches for the stereological correction of the truncation effects are proposed and validated on artificially modeled particle data. Finally, the suggested techniques are applied to real 3D-particle data from ordinary portland cement and the resulting PSDs compared with data from laser granulometry. [source] In Situ Characterization of a Nb and Mo Containing , -TiAl Based Alloy Using Neutron Diffraction and High-Temperature Microscopy,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Ian J. Watson Abstract In recent times, novel titanium aluminides containing the bcc , -phase at high temperatures are being developed for improved hot-working capabilities, however, predictions of the phase diagrams are merely uncertain. Here we present in-situ neutron studies, which are particularly sensitive to the atomic disorder in the ordered phases. Complementary laser scanning confocal microscopy is employed for in-situ microstructural investigations. [source] Cleavage fracture of RPV steel following warm pre-stressing: micromechanical analysis and interpretation through a new modelFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9-10 2006S. R. BORDET ABSTRACT In this paper, the warm pre-stress (WPS) effect on the cleavage fracture of an 18MND5 (A533B) RPV steel is investigated. This effect, which describes the effective enhancement of the cleavage fracture toughness at low temperature following a prior loading at high temperature, has received great interest in light of its significance in the integrity assessment of structures, such as nuclear pressure vessels, subjected to thermal transients. Several loading cycles between room temperature (RT) and ,150 °C are considered: Load-Unload-Cool-Fracture (LUCF), Load-Cool-Fracture (LCF) and Load-Cool with Increasing K-Fracture (LCIKF). All experiments complied with the conservative principle, which states that no fracture will occur if the applied stress intensity factor (SIF) decreases (or is held constant) while the temperature at the crack-tip decreases, even if the fracture toughness of the virgin material is exceeded. The experimental results indicate that an effective WPS effect is present even at small pre-load (Kwps= 40 MPa,m), and that a minimum critical slope (,,K/,T) in the LCIKF cycle has to be exceeded to induce cleavage fracture between RT and ,150 °C. Numerical modelling was performed using mixed isotropic and kinematic hardening laws identified on notched tensile (NT) specimens, tested in tension to large strains (up to 40%), followed by large compressive strains. Detailed microstructural investigations on compact tensile (CT) and NT fracture test specimens were performed so as to determine the nature of the cleavage initiation sites, as well as the local mechanical conditions at fracture. Based on this local information, a new cleavage model was calibrated and applied to predict the probability of cleavage fracture after WPS: it is shown that the predictions are in good agreement with the experimental results. [source] Mechanical and microstructural investigations into the crack arrest behaviour of a modern 2¼Cr-1 Mo pressure vessel steelFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2001E. Bouyne Tests were performed on a 2¼ Cr,1 Mo steel to measure the fracture toughness at initiation, KIc and at arrest, KIa,. The results were compared with those obtained on another pressure vessel steel (A508) of similar strength. Two techniques were used to measure KIa,: (i) isothermal compact crack arrest (CCA) tests, and (ii) specially designed thermal shock experiments using an externally notched ring. These specimens were cooled to ,196 °C and then heated by induction in the centre of the ring to produce very steep thermal gradients. This caused crack initiation from the notch. The crack propagates very rapidly (,500 m s,1,) and stopped when it reached the warmer region of the specimen. The specimens were analysed using an elastic,plastic finite element method to determine KIa values. These tests reveal a greater temperature shift (,100 °C) between KIc and KIa in 2¼ Cr,1 Mo steel than in A508 steel. Detailed metallographical examinations of the micromechanisms of crack propagation and arrest in the 2¼ Cr,1 Mo steel showed that this involves the nucleation of a three-dimensional network of cleavage microcracks which change their direction at bainitic packet boundaries. The remaining uncracked ligaments between the cleavage microcracks break by ductile rupture mechanism [source] Investigation of mechanism of Al(OH)3 crystal growthTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009I. Nikoli Abstract Crystallization of Al(OH)3 that occurs during the decomposition of caustic soda solutions is an important part of Bayer process for alumina production. Several phenomena, which influence the physicochemical characteristics of precipitated Al(OH)3, occur simultaneously during this process. They are nucleation, agglomeration, and crystal growth of Al(OH)3. In this article, we have investigated the mechanism of Al(OH)3 crystal growth from pure caustic soda solutions and in the presence of oxalic acid. The results have shown that the growth of Al(OH)3 crystals from caustic soda solutions follow the B,+,S model (birth and spread). New Al(OH)3 particles, formed during the decomposition process of pure caustic soda solutions, are characterized by regular hexagonal shape. The nuclei have the same geometry as the contact face. However, microstructural investigations of Al(OH)3 samples, obtained by crystallization from caustic soda solutions in the presence of oxalic acid, have shown the presence of nuclei of irregular shape in addition to regular ones. So, the presence of oxalic acid in the caustic soda solutions leads to a change in crystal habit. Besides, the results obtained by kinetic investigation confirmed the mentioned mechanism of Al(OH)3 crystal growth. La cristallisation de l'Al(OH)3 qui accompagne la décomposition de solutions de soude caustique est une caractéristique importante du procédé Bayer de production d'alumine. Plusieurs phénomènes influant sur les caractéristiques physicochimiques de l'Al(OH)3 précipité, se produisent simultanément lors de ce procédé. Ce sont la nucléation, l'agglomération et la croissance des cristaux de l'Al(OH)3. Dans cet article, nous avons étudié le mécanisme de croissance des cristaux de l'Al(OH)3 à partir de solutions de soude caustique pures et en présence d'acide oxalique. Les résultats montrent que la croissance des cristaux d'Al(OH)3 à partir des solutions de soude caustique suit le modèle B,+,S (naissance (birth),+,dispersion (spread)). Les nouvelles particules d'Al(OH)3, formées lors du procédé de décomposition des solutions de soude caustique, se caractérisent par une forme hexagonale régulière. Les nuclei ont la même géométrie que la face de contact. Cependant, des recherches sur la microstructure des échantillons d'Al(OH)3 obtenus par cristallisation à partir des solutions de soude caustique en présence d'acide oxalique, montrent la présence de nuclei de forme irrégulière en plus de ceux de forme régulière. Ainsi, la présence d'acide oxalique dans les solutions de soude caustique mène à un changement dans le comportement des cristaux. En outre, les résultats obtenus dans l'étude cinétique confirment ce mécanisme de croissance des cristaux d'Al(OH)3. [source] | |||||||||||||