Rapid solidification processing is widely used in industry, but the underlying mechanisms are not completely understood. In the present work, an effort is made to understand the effects of rapid heat extraction and large undercooling on the solidification sequence, in particular: (1) the transition from diffusion-limited growth to impingement-limited growth; and (2) crystal nucleation in deeply undercooled liquids. Rapid solidification can be achieved either by (1) rapid quenching, or (2) large undercooling. Accordingly, two different methods are used in the present work. They are, (a) nanosecond pulsed laser quenching, and (b) bulk undercooling in a liquid flux. Thin films prepared by d.c. magnetron getter sputtering have been used in pulsed laser quenching. Both pure metals (Fe, Zr, Ti, Co, Ge) and binary alloys (Nb-Ni, Ti-Co) prepared by this method are investigated. Alloys Fe<SUB>40</SUB>Ni<SUB>40</SUB>B<SUB>20</SUB>, Ni<SUB>75</SUB>Si<SUB>8</SUB>B<SUB>17</SUB> and elemental Ge have been used in bulk undercooling. The metastable structures obtained are analysed by optical microscopy, scanning electron microscopy, electron probe microanalysis, transmission electron microscopy and X-ray diffraction. The results obtained are discussed in terms of non-equilibrium crystal nucleation and growth processes.

Thesis (Ph. D.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xii, 145 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 143-145).

Thesis (M.S.)--University of Wisconsin--Madison, 1983. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 184-187).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 310-316).

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 147-149).

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xi, 71 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 53-56).

Mémoire (M.Eng.)--Université du Québec à Chicoutimi, 1999. / Document électronique également accessible en format PDF. CaQCU

A novel computer model of the evolution of columnar and equiaxed microstructure during alloy solidification has been developed. A control volume finite difference model of conduction heat transfer is applied to a two-dimensional domain bounded by a relatively cold mould. The initial condition is that of superheated liquid, and nucleation occurs either at the mould wall, leading to columnar dendritic growth, or within the bulk liquid, leading to the growth of equiaxed dendrites. The columnar front or the equiaxed grain boundaries are represented by computationally sharp interfaces, which separate liquid from partially solid alloy. Interpolation between discrete computational markers is employed to describe these interfaces, and a front-tracking technique is used to predict the evolution of the grain structure, via movement of the markers, across the fixed grid. The front velocity is determined via considerations of the kinetics of dendrite growth. The heat equation is fully coupled to the front-tracking algorithm by means of source terms which represent the evolution of latent heat due to the dendritic growth (advancing tips and thickening mushy zone). The model, applied to binary Al-Cu alloys, is computationally efficient. It predicts the variation of the extent of liquid undercooling ahead of the growing columnar front, and new metrics have been established to determine the likelihood of the formation of an equiaxed zone here. The employment of these metrics to establish the influence of heat extraction rate and alloy composition agrees with reports from the literature. The model does not distinguish between individual grains of the columnar zone, but it is shown that this is not an important limitation for most metal casting applications. Direct simulation of the nucleation and growth of multiple equiaxed crystals has been carried out, in which the nucleation and growth of individual grams can be observed via animation, and the influence of melt superheat and heat extraction rate on equiaxed solidification has been determined.

The main aim of this work is to investigate heterogeneous nucleation of solidification of metals and alloys by a combination of differential scanning calorimetry and transmission electron microscopy using a newly modified entrained particle technique. Attention is focused on investigating (a) heterogeneous nucleation of Cd, In and Pb particle solidification by Al in rapidly solidified Al-Cd, Al-In and Al-Pb binary alloys; (b) effects of various ternary additions such as Mg, Ge and Si on heterogenous nucleation of solidification of Cd and Pb solidification by Al; (c) heterogenous nucleation of solidification of Si by solid Al in hypoeutectic Al-Si alloys. In addition, the melting behaviour of Cd, In and Pb particles embedded in an Al matrix is investigated. The rapidly solidified microstructures of melt spun Al-Cd, Al-In and Al-Pb alloys consist of faceted 5-200nm diameter Cd, In and Pb particles homogeneously distributed throughout an Al matrix. Cd particles exhibit an orientation relationship with the Al matrix which can be described as {111}_Al//{0001}_Cd and andlt;110andgt;_Al//andlt;112and#773;0andgt;_Cd, and In and Pb particles exhibit a near cube-cube and cube-cube orientation relationship with the Al matrix respectively. Cd, In and Pb particles embedded in the Al matrix exhibit distorted truncated octahedral or truncated octahedral shapes surrounded by {111}_Al and {100}_Al facets. The solid Al-solid Cd, solid Al-solid In surface energy anisotropies are constant over the temperature range between room temperature and Cd and In melting points respectively. The solid Al-liquid Cd and solid Al-liquid In surface energy anisotropies decrease with increasing temperature above Cd and In melting points. Solidification of Cd, In, Pb particles embedded in an Al matrix is nucleated catalytically by the surrounding Al matrix on the {111}_Al faceted surfaces with an undercooling of 56, 13 and 22K and a contact angle of 42°, 27° and 21° for Cd, In and Pb particles respectively. Addition of Mg to Cd particles embedded in Al increases the lattice disregistry across the nucleating plane, but decreases the undercooling before the onset of Cd(Mg) particle solidification. Addition of Ge to Al decreases the lattice disregistry across the nucleating plane, but increases the undercooling before the onset of Pb particle solidification embedded in the Al(Ge) matrix. These results indicate that chemical interactions dominate over structural factors in determining the catalytic efficiency of nucleation solification in Al-Cd-Mg and Al-Pb-Ge alloys. Contact between Si precipitates and Pb particles embedded in an Al matrix decreases the undercooling before the onset of Pb particle solidification. The equilibrium melting point of Cd particle in the melt spun Al-Cd alloy is depressed because of capillarity, and the depression of equilibrium melting point increases with decreasing particle size. In the melt spun Al-In and Al-Pb alloys, however, most of the In and Pb particles embedded within the Al matrix grains are superheated, and the superheating increases with decreasing particle size. The heterogeneous nucleation temperature for Si solidification by Al depends sensitively on the purity of the Al. Na and Sr additions have different effects on the Si nucleation temperatures. With an Al purity of 99.995%, Na addition increases the Si nucleation temperature, while Sr addition does not affect or decreases the Si nucleation undercooling, depending on the amount of Sr addition. The solidified microstructure of liquid Al-Si eutectic droplets embedded in an Al matrix is affected by the Si nucleation undercooling. With low Si nucleation undercooling, each Al-Si eutectic liquid droplet solidifies to form one faceted Si particle, however, with high Si nucleation undercooling, each Al-Si eutectic liquid droplet solidifies to form a large number of non-faceted Si particles embedded in Al.

Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2008. / La p. de t. porte en outre: Mémoire présenté à l'Université du Québec à Chicoutimi comme exigence partielle de la maîtrise en ingénierie. CaQQUQ Bibliogr.: f. [147]-152. Document électronique également accessible en format PDF. CaQQUQ