The microstructure selection at both high and low growth rates is studied. For the high rate extreme, melt spinning of a Fe-Si-B alloy is employed. The microstructural variations with changing wheel speed and factors affecting these variations are examined through various characterization techniques. Particular attention was given for the influence of melt pool behavior on the competition between nucleation of crystalline solidification products and glass formation. It is found that there exists a window of wheel speeds which give rise to a stable melt-pool and production of amorphous ribbons. The surface-controlled melt-pool oscillation is found as the dominant factor governing the onset of unsteady thermal conditions accompanied by varying amounts of crystalline nucleation observed near the lower wheel speed limit. For the upper wheel speed limit, a criterion based on mass-balance and momentum transfer is developed for predicting the window of wheel speeds for obtaining uniform and fully amorphous ribbons. For the low rate extreme, solidification and morphological selection of the faceted silicon phase is investigated in a near eutectic Al-Si system by utilizing a Bridgman type directional solidification unit. Particularly, the role of certain defect mechanisms, namely twinning, in the selection of microstructure and growth crystallography is investigated. At the imposed growth rates of 0.5 and 1 micron/s and temperature gradient of 7.5 K/mm, a unique silicon morphology consisting of 8-pointed stars is observed to grow with 001 texture within continuous domains across the sample. The growth crystallography of this unique silicon structure is characterized and it is found that substantial amount of [210] type twinning exists within the central core of this star-shaped morphology. It is found that the twinning phenomenon at the core is an essential feature for branching, morphological selection, and adjustment of spacing between the star-like silicon features. These mechanisms and the associated growth characteristics are examined in detail.

The microstructures formed upon solidification are strongly influenced by the imposed growth rates on an alloy system. Depending on the characteristics of the solidification process, a wide range of growth rates is accessible. The prevailing solidification mechanisms, and thus the final microstructure of the alloy, are governed by these imposed growth rates. At the high rate extreme, for instance, one can have access to novel microstructures that are unattainable at low growth rates. While the low growth rates can be utilized for the study of the intrinsic growth behavior of a certain phase growing from the melt. Although the length scales associated with certain processes, such as capillarity, and the diffusion of heat and solute, are different at low and high rate extremes, the phenomena that govern the selection of a certain microstructural length scale or a growth mode are the same. Consequently, one can analyze the solidification phenomena at both high and low rates by using the same governing principles. In this study, we examined the microstructural control at both low and high extremes. For the high rate extreme, the formation of crystalline products and factors that control the microstructure during rapid solidification by free-jet melt spinning are examined in Fe-Si-B system. Particular attention was given to the behavior of the melt pool at different quench-wheel speeds. Since the solidification process takes place within the melt-pool that forms on the rotating quench-wheel, we examined the influence of melt-pool dynamics on nucleation and growth of crystalline solidification products and glass formation. High-speed imaging of the melt-pool, analysis of ribbon microstructure, and measurement of ribbon geometry and surface character all indicate upper and lower limits for melt-spinning rates for which nucleation can be avoided, and fully amorphous ribbons can be achieved. Comparison of the relevant time scales reveals that surface-controlled melt-pool oscillation may be the dominant factor governing the onset of unsteady thermal conditions accompanied by varying amounts of crystalline nucleation observed near the lower limit. At high quench-wheel velocities, the influence of these oscillations is minimal due to very short melt-pool residence times. However, microstructural evidence suggests that the entrapment of gas pockets at the wheel-metal interface plays a critical role in establishing the upper rate limit. An observed transition in wheel-side surface character with increasing melt-spinning rate supports this conclusion.

Aluminium is an important metal in manufacturing, due to its versatile properties and the many applications of both the processed metal and its alloys in different industries. Fundamentals of aluminium metallurgy provides a comprehensive overview of the production, properties and processing of aluminium, and its applications in manufacturing industries.Part one discusses different methods of producing and casting aluminium, covering areas such as casting of alloys, quality issues and specific production methods such as high-pressure diecasting. The metallurgical properties of aluminium and its alloys are reviewed in Part two, with chapters on such topics as hardening, precipitation processes and solute partitioning and clustering, as well as properties such as fracture resistance. Finally, Part three includes chapters on joining, laser sintering and other methods of processing aluminium, and its applications in particular areas of industry such as aerospace.With its distinguished editor and team of expert contributors, Fundamentals of aluminium metallurgy is a standard reference for researchers in metallurgy, as well as all those involved in the manufacture and use of aluminium products. - Provides a comprehensive overview of the production, properties and processing of aluminium, and its applications in manufacturing industries - Considers many issues of central importance in aluminium production and utilization considering quality issues and design for fatigue growth resistance - Metallurgical properties of aluminium and its alloys are further explored with particular reference to work hardening and applications of industrial alloys

The concept of reinforcing a material by the use of a fiber is not a new one. The Egyptian brick layer employed the same principle more than three thousand years ago when straw was incorporated into the bricks. More recent examples of fiber reinforced composites are steel-reinforced concrete, nylon and rayon cord reinforced tires, and fiberglass reinforced plastics. In the last several years considerable progress has been made on new composite structures particularly utilizing boron (on tungsten substrate) fibers in various matrices. Many of these advances have been reviewed recently by P. M. Sinclair1 and by Alexander, Shaver, and Withers.2 An excellent earlier survey is available by Rauch Sutton, and McCreight.3 Boron-reinforced epoxy composites are being fabricated and tested as jet engine components, fuselage components, and even as a complete aircraft wing because of the tremendous gain in experimentally demonstrated properties such as modulus, strength, and fatigue resistance, particularly on a weight normalized (e.g., strength/density) basis. Other than glass/epoxy and boron/ epoxy composites and perhaps boron/aluminum, the systems now under study are in the early stages of research and development. These include other boron/metal composites, graphite/polymer, graphite/metal, graphite/graphite, alumina/metal, and aligned eutectic (directionally, solidified) combinations. As Sinclair points out, designers are wary about filamentary composites becausethere is little background information and scant experience.

Solidification is one of the oldest processes for producing complex shapes for applications ranging from art to industry, and remains as one of the most important commercial processes for many materials. Since the 1980s, numerous fundamental developments in the understanding of solidification processes and microstructure formation have come from both analytical theories and the application of computational techniques using commonly available powerful computers. This book integrates these developments in a comprehensive volume that also presents and places them in the context of more classical theories. This second edition highlights the key concepts within each chapter to help guide the reader through the most important aspects of the topics. The figures are now in color, in order to improve the visualization of phenomena and concepts. Recent important developments in the field since the first edition was published have also been added. The three-part text is aimed at graduate and professional engineers. The first part, Fundamentals and Macroscale Phenomena, presents the thermodynamics of solutions and then builds on that subject to motivate and describe equilibrium phase diagrams. Transport phenomena are discussed next, focusing on the issues of most importance to liquid-solid phase transformations, then moving on to describing in detail both analytical and numerical approaches to solving such problems. The second part, Microstructure, employs these fundamental concepts for the treatment of nucleation, dendritic growth, microsegregation, eutectic and peritectic solidification, and microstructure competition. This part concludes with a chapter describing the coupling of macro- and microscopic phenomena in microstructure development. The third and final part describes various types of Defects that may occur, with emphasis on porosity, hot tearing and macrosegregation, presented using the modeling tools and microstructure descriptions developed earlier.