The heat affected zone (HAZ) of friction stir welded Al 7075 T7 shows diminished corrosion resistance properties when compared with the parent material. Corrosion attack in this region of the weld is primarily intergranular and is associated with the presence of precipitate free zones. Current TEM research conducted at Brigham Young University by Dr. Bin Cai finds a correlation between precipitate free zone (PFZ) width and grain boundary geometry. As both grain boundary geometry and the PFZ are associated with modes of failure in 7XXX aluminum, this paper makes a comparison of grain boundary character distributions (GBCD) in the HAZ and the parent metal via multi-section plane five-parameter stereology. The stereology is conducted in a convenient macroscopic coordinate frame, associated with the HAZ. This is the first investigation to determine the GBCD in the HAZ of friction-stirred weld material and requires multiple section plane sampling. It is discovered that aluminum here exhibits the property of non-sidedness, a long assumed but unproven characteristic. Further comparisons between the two microstructures are conducted relative to (2-dimensional) grain boundary network connectivity, recovered from EBSD data in each section plane. It is shown that the relative fraction of grain boundaries of misorientation character associated with smaller PFZ size is larger in the HAZ as compared to the parent material. A commensurate decrease in the connectivity (radius of gyration) of grain boundaries of character conducive to larger PFZ size is also found in the HAZ, relative to the parent material. Distribution of inclinations changes as a function of grain boundary geometry. Surface area per unit volume of CSL and low angle random (LAR) misorientations increases in the HAZ, while high angle random (HAR) boundaries decrease. In the case of LAR and some CSL boundaries, a reorientation occurs in which macroscopic normals of these interfaces rotate. It is anticipated that these significant changes in the GBCD within the HAZ could be important in terms of understanding the post-weld mechanical and physical properties in friction-stirred materials.

<p>The municipality of Västervik, with support from Envipro Miljöteknik AB, is carrying out a main study of the minefields at Gladhammar. Mining of iron, copper and cobalt under different periods from the 16th century until the end of the 19th century has led to discharges of metals to the lakes situated downstream. The aim of the main study is to investigate the possibilities to reduce the environmental load on the surrounding ground and water caused by heavy metals from the mine. </p><p>The present report is a part of the main study. The aim of the work is to investigate the geochemistry of the groundwater. As a starting point, questions concerning affected areas, occurring metals and possible processes for propagation and limitation of the pollutants, have been posed. </p><p>The work is based on data from a pre-study and of the main study. In total, there are 25 groundwater pipes in the area. A subset of these pipes has been chosen in order to delimit the task at hand. The number of analysed measurements for each groundwater pipe range from five to 15. The data material has been compiled and subsequently evaluated with respect to natural background, variation in time, correlation with precipitation, depth and other measured parameters. Geochemical modelling using the computer code PHREEQC has also been conducted. </p><p>The waste of the minefields at Gladhammar is constituted of waste rock, slag and tailings. Arsenic, cobalt, copper, lead and zinc are the prevailing metals in the area. Iron, manganese and sulphur control the behaviour of heavy metals in water to a great extent and they have, as well as the prevailing metals, therefore been in focus for the study. </p><p>The data compilation shows that pipes in the proximity of slag and waste rock have the highest content of cobalt and copper. </p><p>The groundwater is affected, with respect to guideline-values, by, above all, cobalt and copper, but also to a certain extent by lead. The content of arsenic and zinc is classified as low to moderate. The groundwater is most affected in the areas of Holländarefältet and Torsfall. </p><p>The data analysis shows that out flush of secondarily retained metals is a likely pollutant process. Primarily, this is valid for cobalt and copper. The pollution propagation is likely limited by precipitation of secondarily minerals as well as adsorption to iron, manganese and aluminium particles. </p><p>The groundwater in the pipes close to waste rock and slag most certainly consists of surface water that runs off from the heaps on top of the hill. This is demonstrated by the high metal content of the surface run off. According to calculations on mixing, the groundwater at the shore is made up by a mixture of lake water and mine entrance water.</p>

Many technologically important alloys such as Ni base superalloys and Ti-Al base alloys benefit from the precipitation of an ordered β phase from a disordered α matrix. When the crystallographic symmetry of the β phase is a subgroup of that of the disordered α phase, the microstructure may contain multiple orientational variants of the β phase, each with its own (anisotropic, crystallographically equivalent) misfit (lattice parameter mismatch) with the matrix phase. Examples include orthorhombic precipitates in a hexagonal matrix in Ti-Al-Nb alloys, and tetragonal precipitates in a cubic matrix in ZrO2-Y2O3. We have studied two-phase microstructures containing multiple variants of the precipitate phase. In particular, we have used phase field simulations to study the effect of elastic stresses in a two dimensional system containing a disordered matrix and three different orientational variants of the precipitate phase, with a view to elucidate the effect of different levels of anisotropy in misfit. We consider a two dimensional, elastically homogeneous and isotropic model system in which the matrix (α) and precipitate (β) phases have hexagonal and rectangular symmetries, respectively, giving rise to three orientational variants of the β phase. Therefore, our phase field model has composition (c) and three order parameters (η1, η2, η3) as the field variables.Due to the difference in crystallographic symmetry, the precipitate-matrix misfit strain tensor, ε*, can be anisotropic. ε*maybe represented in its principal form as ε *= (ε xx 0 ) 0 εyy where ε xx and ε yy are the principal components of the misfit tensor. We define t= εyy/εxx as the parameter representing anisotropy in the misfit. In this thesis, we report the results of our systematic study of microstructural evolution in systems with different values of t, representing different levels of anisotropy in misfit: •Case A: t=1 (dilatational or isotropic misfit) • Case B: 0 <t<1 (principal misfit components are unequal but have the same sign) • Case C: t=0 (the principal misfit along the y direction is zero) • Case D: -1 <t<0 (principal misfit components have opposite signs and unequal magnitudes) • Case E: t= -1 (principal misfit components are equal, but with opposite signs; pure shear) In Cases D and E, there is an invariant line along which the normal misfit is zero. In Case D, this invariant line is at ±54.72◦, and in Case E, it is at ±45◦, with respect to the x-axis. Our simulations of microstructural evolution in this system are based on numerical integration of the Cahn-Hilliard and Cahn-Allen equations which govern the evolution of composition and order parameter fields, respectively. In each case, we have studied two different situations: isolated particle (single variant) and many interacting particles (multivariant). Dynamical growth shape of an isolated precipitate In systems with an isotropic misfit (Case A), the precipitate shape remains circular at all sizes. In Cases B and C, the precipitate shape is elongated along the y-axis, which is also the direction in which the magnitude of the misfit strain is lower. In all these cases, the symmetry of the particle shape remains unaltered at all sizes. In contrast, in Cases D and E, the particle shape exhibits a symmetry-breaking transition. In Case D, the precipitate elongates initially along the y direction (i.e. the direction of lower absolute misfit), before undergoing a transition in which the mirror symmetry normal to x and yaxes is lost. In Case E, the particle has an initial square-like shape (with its sides normal to the 11directions) before losing its four-fold rotation axis to become rectangle-like with its long axis along one of the the 11directions. The critical precipitate size at which the symmetry-breaking shape transition occurs is obtained using bifurcation diagrams. In both Cases D and E, the critical size for the dynamical growth shapes is larger than those for equilibrium shapes[1].This critical size is larger when the matrix supersaturation is higher or shear modulus is lower. Microstructural Evolution In all the five cases, the elastic stresses have a common effect: they lead to microstructures in which the precipitate volume fraction is lower than that in a system with no misfit. This observation is consistent with the results from the thermodynamics of stressed solids that show that a precipitate-matrix misfit increases the interfacial composition in both the matrix and the precipitate phase. In systems with isotropic misfit (Case A), the microstructure consists of isolated circular domains of the precipitate phase that retain their circular shape during growth and subsequent coarsening. In Cases B and C with anisotropic misfit with t≥0, the three orientational variants of the precipitate phase are elongated along the directions of lower misfit (y-axis and ±120◦to y-axis). At a given size, particles in Case C (in which one of the principal misfits is zero) are more elongated than those in Case B. Systems with a higher shear modulus enhance the effect of misfit stresses, and therefore, lead to thinner and longer precipitates. When the precipitate volume fraction is increased, these elongated precipitates interact with (and impinge against) one another to a greater extent, and acquire a more jagged appearance. For Cases D and E, each orientation domain is associated with an invariant line along which the normal misfit is zero. Thus, in Case D, early stage microstructures show particles elongated along directions of lower absolute misfit (y-axis and ±120°to y-axis). At the later stages, the domains of the precipitate phase tend to orient along the invariant lines; this leads some of the particles to acquire a ‘Z’ shape before they completely re-orient themselves along the invariant line. In Case E, each variant grows as a thin plate elongating along the invariant line. The growth and impingement of these thin plates leads to a microstructure exhibiting complex multi-domain patterns such as stars, wedges, triangles, and checkerboard. These patterns have been compared (and are in good agreement) with experimental observations in Ti-Al-Nb alloys containing the precipitate (O) and matrix (α2)phases[2]. Since in Case E the sum of misfit strains of the three variants is zero, elastic energy considerations point to the possibility of compact, self-accommodating clusters of the three variants, sharing antiphase boundaries (APBs). Thus, if the APB energy is sufficiently low, the microstructure may consist of such compact clusters. Our simulations with such low APB energy do show triangle shaped clusters with six separate particles (two of each variant)in a self-accommodating pattern. (Refer PDF file)

Among the potential high temperature shape memory alloys, due to its low cost, medium ductility and high work output NiTiHf seems to be the most promising HTSMA for a wide range of applications in the 100-250ºC. A detailed investigation into the shape memory properties and transformation behavior for the Ni-rich HTSMA with the compositions of Ni45.3Cu5Ti29.7Hf20, Ni50.3Ti29.7Hf20 and Ni45.3Pd5Ti29.7Hf20 was carried out. It is possible to form Ni-rich precipitates in Ni-rich NiTiHf alloys and tailor the TTs by heat treatments that results in increased strength and stable response at high temperatures. The coherent Ni-rich precipitates deplete the Ni content from the matrix increasing the transformation temperatures and strengthen the material by hindering the dislocation motion. The effect of aging on the microstructure, shape memory and mechanical properties are revealed. Optimum aging conditions have been found determined to get the most favorable combination of high transformation temperatures with stable and good shape memory properties. The Ni50.3Ti29.7Hf20 and Ni45.3Pd5Ti29.7Hf20 aged at 500ºC-600 ºC were found to be formidable candidates for high temperature applications.

Quando combinados no interior do canal, hipoclorito de sódio e clorexidina formam um produto insolúvel em água. Esse trabalho teve como objetivo avaliar as conseqüências da utilização do hipoclorito de sódio 1% pH 9 (NaOCl) como substância durante o preparo e do gel de clorexidina a 2% (CLX) como medicação intracanal em diferentes condições, sob a luz do microscópio eletrônico de varredura ambiental (MEVA). Cinqüenta pré-molares humanos inferiores foram preparados com ProTaper Universal®, sendo quarenta com auxílio de NaOCl e Endo-PTC Leve®. Outros dez dentes foram preparados apenas com CLX (Grupo 2). Os espécimes foram submetidos à irrigação final com ácido cítrico (Grupos 1 e 2) e com tiosulfato de sódio 10% e ácido cítrico (Grupo 3). Todos os grupos experimentais foram medicados por 7 dias com clorexidina. Após esse período, a medicação foi removida e foram contados os túbulos visíveis e os túbulos patentes da superfície dentinária, nas imagens obtidas através do MEVA. Houve diferença estatística entre os grupos experimentais e o Grupo controle negativo, exceto no Grupo 3, em que foi utilizado o tiosulfato. Portanto, apenas quando o NaOCl foi inativado, pode-se observar quantidades desejáveis de túbulos visíveis e patentes. / When combined in the interior of the canal, sodium hypochlorite and chlorhexidine form an insoluble product. The aim of this study was to evaluate the consequences of the use of the hipoclorito of sodium 1% pH 9 (NaOCl) as substance during prepare and gel of clorexidina 2% (CHX) as intracanal medication in different conditions, using environmental scanning electron microscope (ESEM). Fifty extracted mandibular premolars had been prepared with ProTaper Universal®. In forty, was used NaOCl and EndoPTC Leve (Tween 80, Urea peroxide and Carbowax associated) during the prepare. Ten teeth had been prepared using CHX only (Group 2). These had been submitted to the final irrigation with citric acid (Groups 1 and 2) and with sodium thiosulfate 10% and citric acid (Group 3). All the experimental groups received 7 days of intracanal medication with CHX. After this period, the medication was determined the numbers of visible and patent tubules on the root dentin surface, using the images captured on ESEM. There were significant differences between the control group and the experimental groups, except in the case where the tiosulfato was used. Therefore, only when NaOCl is inactivated, desirable amount of visible and patent tubules can be observed.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第16510号 / 工博第3503号 / 新制||工||1530(附属図書館) / 29167 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 落合 庄治郎, 教授 田中 功 / 学位規則第4条第1項該当

The defect structure, atomic structure, and energy of the interphase boundaries between an fcc matrix and a lath-shaped bcc precipitate in Ni-45 wt% Cr were investigated. The interfacial structure on the side facet of the precipitate consists of regular structural ledges and misfit dislocations. No regular defect structure can be found on the habit plane, or broad face, of the lath except for atomic-scale structural ledges. High resolution electron microscopy (HREM) observations show the (12¯1)_f habit plane is coherent and is a good matching interface. Based upon conventional transmission electron microscopy (TEM) observations, the orientation of the habit plane results from advancing growth ledges on the conjugate plane of the Kurdjumov-Sachs orientation relationship. Using embedded atom method (EAM) simulations, the interfacial energy of the (12¯1)_f habit plane is calculated and the simulated interphase structure is compared with the HREM observations. The simulated interface represents a major portion of the observed interface. The calculated interfacial energy of the (12¯1)_f habit plane is 210 mJ/m², lower than typical grain boundary energies indicating this habit plane is a low-energy interphase boundary. A non-Bain lattice correspondence is identified and employed to predict the (12¯1)_f habit plane successfully, although a Bain correspondence is more successful at predicting the elongation direction for the precipitate. Geometric matching is proposed to be responsible for determining the orientation of the precipitate habit plane and the growth direction. Lattice correspondence-based approaches such as the invariant line model and the phenomenological theory of martensitic crystallography can mimic aspects of geometric matching, but they do not accurately reflect the transformation mechanism during precipitation of bcc laths from an fcc parent. / Ph. D.

We investigated the structure and defects associated with interphase boundaries between a γ (fcc) matrix and plate-shaped precipitates of the δ (orthorhombic) phase in Inconel 718. Based upon transmission electron microscopy (TEM) observations, the average habit plane was confirmed to be (111)_γ which is consistent with previous reports. A parallel array of misfit dislocations with Burgers vector b=1/6[112̅]_γ, (designated M1) are always observed lying along the [11̅0] direction. Another array of misfit dislocations appears in some regions of the interface with Burgers vector b=1/6[21̅1̅]_γ (designated M2). These dislocations also lie along the [11̅0] direction. Irregular ledges were identified on the interface and are believed to contribute to the thickening of δ plates. Dislocations in the matrix were also characterized. Most matrix dislocations have a 1/2[1̅01]_γ Burgers vector. The growth ledges in the habit plane of a single δ plate have a variety of effective Burgers vectors. A geometric matching approach based upon near-coincident sites was employed to explain the interfaces structure of interphase boundaries in Inconel 718, as well as fdc/bcc in Ni-45wt% Cr. In both cases, the conjugate plane is the plane with the highest areal density of near-coincident sites over a small region while the average habit plane is determined by the continuity of near-coincidence sites over a large area. The M1 interfacial dislocations in the γ/δ interface accommodate misfit in the habit plane whereas M2 dislocations do not and are probably a by-product of the dissociation of matrix dislocations. In the fcc/bcc system, the habit plane is not parallel to the conjugate plane and the partial dislocations associated with matrix stacking faults improve matching in the habit plane even though their Burgers vector lies out of this plane. / Ph. D.

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