Technology & Engineering
Solidification
Solidification is the process by which a substance changes from a liquid or gaseous state to a solid state. In the context of technology and engineering, solidification is a crucial process in the manufacturing of various materials, such as metals and plastics. It involves controlling the cooling and crystallization of the material to achieve desired properties and structures.
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10 Key excerpts on "Solidification"
eBook - ePub- R. E. Smallman, A.H.W. Ngan(Authors)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
Chapter 3 Solidification Casting is a common way for fabricating engineering metals and alloys; and in this chapter, the mechanisms and products of the Solidification process are discussed. Solidification involves a nucleation and growth process. The advancement of the solidified front in the melt often leads to solute segregation, which can deteriorate properties but at the same time lead to purification of the solidified cast. Techniques to cast batch products continuously and materials with special microstructures are also discussed. Keywords Crystallization; nucleation; growth; dendrites; porosity; segregation; directional Solidification; zone refining 3.1 Crystallization from the melt 3.1.1 Freezing of a pure metal At some stage of production the majority of metals and alloys are melted and then allowed to solidify as a casting. The latter may be an intermediate product, such as a large steel ingot suitable for hot working, or a complex final shape, such as an engine cylinder block of cast iron or a single-crystal gas-turbine blade of superalloy. Solidification conditions determine the structure, homogeneity and soundness of cast products, and the governing scientific principles find application over a wide range of fields. For instance, knowledge of the Solidification process derived from the study of conventional metal casting is directly relevant to many fusion welding processes, which may be regarded as ‘casting in miniature’, and to the fusioncasting of oxide refractories. The liquid/solid transition is obviously of great scientific and technological importance. First, in order to illustrate some basic principles, we will consider the freezing behaviour of a melt of like metal atoms. The thermal history of a slowly cooling metal is depicted in Figure 3.1 ; the plateau on the curve indicates the melting point (m.p.), which is pressure dependent and specific to the metal. Its value relates to the bond strength of the metal
- Esther Belin-ferre(Author)
- 2008(Publication Date)
- World Scientific(Publisher)
73 CHAPTER 4 Solidification Peter Gille Crystallography Section, Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, Theresienstrasse 41, D-80333 München, Germany E-mail: [email protected] Solidification of a metallic melt is basic to various technological processes like ingot casting, directional freezing of composite alloys, single-crystal growth and rapid Solidification of metallic glasses. Apart from varying scientific or industrial goals and significant technical differences in these areas of application, most of the fundamental problems are common to these fields. Starting from slight deviations from equilibrium thermodynamics, various aspects of the transforma-tion process of a melt to the solid state are treated in this tutorial chapter: homogeneous and heterogeneous nucleation, kinetic aspects of crystal growth, segregation phenomena, and interface instability caused by constitutional supercooling. An understanding of the mechanisms of Solidification and how they influence practical processes and alloy properties are the main objectives rather than a complete treatment of all Solidification techniques. A short overview of the most important methods of bulk crystal growth from the melt is given. 1. Introduction Solidification means any process transferring a fluid phase into the solid state. In a narrower sense it is understood as crystallizing a liquid caused by lowering its temperature below the melting point or its liquidus temperature. In this chapter, basic principles of Solidification are treated that should be considered when crystallizing a binary or higher-component melt. Solidification of well-defined samples or even single crystals may be regarded as the goal of these processes. The same 74 Peter Gille principles, problems and equations are also fundamental to several other technical disciplines of Solidification, like casting or welding.
eBook - PDF- M Ferry(Author)
- 2006(Publication Date)
- Woodhead Publishing(Publisher)
Chapter 2 Overview of Solidification Processing 2.1 Introduction Solidification is the transformation of liquid into the solid crystalline state via the nucleation of the solid phase and its subsequent growth to consume the liquid. The Solidification reaction is fundamental to many technological processes such as ingot and foundry casting, continuous slab casting, net-shape die casting, welding and joining and single crystal growth for the production of semiconductor devices and turbine blades. The production of strip products by direct strip casting (DSC) is particularly reliant on a sound fundamental understanding of the atomic processes that govern both the nucleation and growth stages of Solidification. The control of these stages dictates the microstructure and many important properties of the as-cast strip. This chapter provides an overview of some of the more important theoretical and practical aspects of Solidification phenomena applicable to casting of metals and alloys. 2.2 Development of Solidification microstructure 2.2.1 Nucleation from the melt When a liquid is cooled below its equilibrium melting temperature (Tm), there is a thermodynamic driving force for Solidification ( !1G ). Figure 2.1 shows the free energy as a function of temperature for a solid and liquid phase which indicates how the change in free energy (£1G) varies with respect to T m· 25 26 Direct strip casting of metals and alloys .. .. .. ··~ .. T '• L.G •• •••• .. .. .. .. .. .. .. .. .. :······················G I S I I I i GL I I I I ~T--+: Tm Temperature Figure 2.1. Free energy as a function of temperature for a solid and liquid. The free energies of both the liquid and solid at a temperature, T, are given by GL =HL -TSL and G 5 =H 5 -TS 5 , respectively,where HL and H 5 are enthalpy terms and SL and 5 5 entropy terms.
eBook - ePub- David A. Porter, Kenneth E. Easterling, Mohamed Y. Sherif(Authors)
- 2021(Publication Date)
- CRC Press(Publisher)
4 SolidificationDOI: 10.1201/9781003011804-4Solidification and melting are transformations between crystallographic and noncrystallographic states of a metal or alloy. These transformations are of course basic to such technological applications as ingot casting, foundry casting, continuous casting, single-crystal growth for semiconductors, directionally solidified composite alloys, and rapidly solidified alloys and glasses. Another important and complex Solidification and melting process, often neglected in textbooks on Solidification, concerns the process of fusion welding. An understanding of the mechanism of Solidification and how it is affected by such parameters as temperature distribution, cooling rate and alloying, is important in the control of mechanical properties of cast metals and fusion welds. It is the objective of this chapter to develop some of the basic concepts of Solidification and apply these to some of the more important practical processes such as ingot casting, continuous casting and fusion welding. We then consider a few practical examples illustrating the casting or welding of engineering alloys in the light of the theoretical introduction.4.1 NUCLEATION IN PURE METALS
If a liquid is cooled below its equilibrium melting temperature (T m ) there is a driving force for Solidification(and it might be expected that the liquid phase would spontaneously solidify. However, this is not always the case. For example, under suitable conditions liquid nickel can be undercooled (or supercooled ) to 250 K below T m (1453°C) and held there indefinitely without any transformation occurring. The reason for this behavior is that the transformation begins by the formation of very small solid particles or nuclei. Normally undercoolings as large as 250 K are not observed, since in practice the walls of the liquid container and solid impurity particles in the liquid catalyze the nucleation of solid at undercoolings of only ~1 K. This is known as heterogeneous nucleation. The large undercoolings mentioned above are only obtained when no heterogeneous nucleation sites are available, i.e., when solid nuclei must form homogeneously from the liquid. Experimentally this can be achieved by dividing the liquid into tiny droplets, many of which remain impurity-free and do not solidify until very large undercoolings are reached.1− Δ G =)G L−G S
eBook - PDF- Mikell P. Groover(Author)
- 2012(Publication Date)
- Wiley(Publisher)
Part II Solidification Processes 5 FUNDAMENTALS OF METAL CASTING Chapter Contents 5.1 Overview of Casting Technology 5.1.1 Casting Processes 5.1.2 Sand-Casting Molds 5.2 Heating and Pouring 5.2.1 Heating the Metal 5.2.2 Pouring the Molten Metal 5.2.3 Engineering Analysis of Pouring 5.3 Solidification and Cooling 5.3.1 Solidification of Metals 5.3.2 Solidification Time 5.3.3 Shrinkage 5.3.4 Directional Solidification 5.3.5 Riser Design In this part of the book, we consider those manufacturing pro- cesses in which the starting work material is either a liquid or is in a highly plastic condition, and a part is created through Solidification of the material. Casting and molding processes dominate this category of shaping operations. The solidifica- tion processes can be classified according to the engineering material that is processed: (1) metals, (2) ceramics, specifically glasses, 1 and (3) polymers and polymer-matrix composites (PMCs). Casting of metals is covered in this and the follow- ing chapter. Glassworking is covered in Chapter 7, and poly- mer and PMC processing are treated in Chapters 8 and 9. Casting is a process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity. The term casting is also applied to the part that is made by this process. It is one of the oldest shaping processes, dating back 6,000 years. The principle of casting seems simple: Melt the metal, pour it into a mold, and let it cool and solidify; yet there are many factors and variables that must be considered in order to accomplish a successful casting operation. Casting includes both the casting of ingots and the casting of shapes. The term ingot is usually associated with the primary metals industries; it describes a large casting that is simple in shape and intended for subsequent reshap- ing by processes such as rolling or forging.
- Leo Alting(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
10 Liquid Materials: Casting Processes 10.1 INTRODUCTION In previous chapters the shaping or forming of materials in the solid or granular state was discussed. Shaping can also take place in the liquid material state; this is known as casting and is described in this chapter. In casting, the liquid material is poured into a cavity (die or mold) corresponding to the desired geometry. The shape obtained in the liquid material is now stabilized, usually by Solidification, and can be removed from the cavity as a solid component. Casting is the oldest known process to produce metallic components. The main stages, which are not confined to metallic materials alone but are also applicable to some plastics, porcelain, and so on, are: production of a suitable mold cavity; the melting of the material; pouring the liquid material into the cavity; stabilization of the shape by Solidification, chemical hardening, evaporation, and so on; removal or extraction of the solid component from the mold; and cleaning the component. In principle, no limits exist regarding the size or geometry of the parts that can be produced by casting. The limitations are set primarily by the material properties, the melting temperatures, the properties of the mold material (mechanical, chemical, thermal), and the material’s production characteristics (i.e., whether it is used only once or many times). Normally, the term casting is applied to metals, but in general, the principal stages and many of the characteristic problems are the same for most materials which can be shaped from the liquid state. The term casting should be treated more broadly, allowing the carryover of new ideas from one field to another (foundry industry, glass industry, plastic industry, etc.)
eBook - PDFFundamentals of Modern Manufacturing
Materials, Processes, and Systems
- Mikell P. Groover(Author)
- 2019(Publication Date)
- Wiley(Publisher)
184 P A R T III 10 Solidification PROCESSES This part of the book covers those manufacturing processes in which the starting work material is either a liquid or in a highly plastic condition, and a part is created through Solidification of the material. Casting and molding processes dominate this category of shaping operations. With reference to Figure 10.1, the Solidification processes can be classified according to the engineering material that is processed: (1) metals, (2) ceram- ics, specifically glasses 1 , and (3) polymers and polymer matrix composites (PMCs). Casting of metals is covered in this and the following chapter. Glassworking is the subject of Chapter 12, and the processing of polymers and PMCs is treated in Chapters 13 and 14. Casting is a process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity. The term casting is also applied to the part that is made by this process. It is one of the oldest shaping processes, dating back 6000 years (see Historical Note 10.1). The principle of casting seems simple: Melt the metal, pour it into a mold, and let it cool and solidify; yet, there are many factors and variables that must be considered in order to accomplish a successful casting operation. Casting includes both the casting of ingots and the casting of shapes. The term ingot is usually associated with the primary metals industries; it describes a large casting that is simple in shape and intended for subsequent reshaping by processes such as rolling or forging. Ingot casting is discussed in Chapter 6. Shape casting involves the production of more complex geometries that are much closer to the final desired shape of the part or product. It is with the casting of shapes rather than ingots that this chapter and the next are concerned. A variety of shape casting methods are available, thus making it one of the most versatile of all manufacturing processes.
eBook - PDFFundamentals of Modern Manufacturing
Materials, Processes, and Systems
- Mikell P. Groover(Author)
- 2016(Publication Date)
- Wiley(Publisher)
10 III P A R T Solidification PROCESSES 181 Fundamentals of Metal Casting This part of the book covers those manufacturing processes in which the starting work material is either a liquid or in a highly plastic condition, and a part is created through Solidification of the material. Casting and molding processes dominate this category of shaping operations. With reference to Figure 10.1, the Solidification processes can be classified according to the engineering material that is processed: (1) metals; (2) ceramics, specifically glasses; 1 and (3) polymers and polymer matrix com- posites (PMCs). Casting of metals is covered in this and the fol- lowing chapter. Glassworking is the subject of Chapter 12, and the processing of polymers and PMCs is treated in Chapters 13 and 14. Casting is a process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity. The term casting is also applied to the part that is made by this process. It is one of the oldest shaping processes, dating back 6000 years (see Historical Note 10.1 at www.wiley.com/college/groover). The principle of cast- ing seems simple: Melt the metal, pour it into a mold, and let it cool and solidify; yet there are many factors and variables that must be considered in order to accomplish a successful casting operation. Casting includes both the casting of ingots and the casting of shapes. The term ingot is usually associated with the primary metals industries; it describes a large casting that is simple in shape and intended for subsequent reshaping by processes such as rolling or forging. Ingot casting is discussed in Chapter 6. Shape casting involves the production of more complex geometries that are much closer to the final desired shape of the part or product. It is with the casting of shapes rather than ingots that this chapter and the next are concerned.
- Donald Askeland, Wendelin Wright(Authors)
- 2018(Publication Date)
- Cengage Learning EMEA(Publisher)
In many situations though, as discussed in Section 9-1, metals and alloys are first cast into ingots, and the ingots are subsequently subjected to thermomechanical processing (e.g., rolling, forging, etc.). During these steps, the cast macrostructure is broken down and a new microstructure will emerge, depending upon the thermomechanical process used (Chapter 8). 9-8 Solidification Defects Although there are many defects that potentially can be introduced during Solidification, shrinkage and porosity deserve special mention. If a casting contains pores (small holes), the cast component can fail catastrophically when used for load-bearing applications (e.g., turbine blades). Shrinkage Almost all materials are more dense in the solid state than in the liquid state. During Solidification, the material contracts, or shrinks, as much as 7% (Table 9-2). Often, the bulk of the shrinkage occurs as cavities if Solidification begins at all surfaces of the casting, or pipes , if one surface solidifies more slowly than the others (Figure 9-11). The presence of such pipes can pose problems. For example, if in the production of zinc ingots a shrinkage pipe remains, water vapor can condense in it. This water can lead to an explosion if the ingot gets introduced in a furnace in which zinc is being remelted for such applications as hot-dip galvanizing. A common technique for controlling cavity and pipe shrinkage is to place a riser , or an extra reservoir of metal, adjacent and connected to the casting. As the casting solidi-fies and shrinks, liquid metal flows from the riser into the casting to fill the shrinkage void. We need only to ensure that the riser solidifies after the casting and that there is an internal liquid channel that connects the liquid in the riser to the last liquid to solidify in the casting. Chvorinov’s rule can be used to help design the size of the riser. The following example illustrates how risers can be designed to compensate for shrinkage.
eBook - PDFThe Fabrication of Materials
Materials Technology
- J. G. Tweeddale(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
In general, however the presence of hydrogen gas, even in this last way, is not liked and every effort is made to get rid of it. Various methods of removal can be used, such as reaction with a suitable flux, or by purging, in which an insoluble carrier-gas is bubbled through the liquid to create large surface areas at which the hydrogen can gather and be carried away. Presolidifying followed by quick remelting is also used, to reduce the amount of dissolved hydrogen. Because gases such as nitrogen, carbon dioxide and carbon monoxide, that may be present during a melting operation, are not so generally harmful as oxygen and hydrogen their presence can usually be ignored. 2.9 CHEMICAL Solidification CASTING There are four mechanisms by which a controlled chemical Solidification reaction may take place. (a) A liquid chemical solvent or inhibitor may be used to keep apart particles of a substance that will bond spontaneously together when the solvent is evaporated away. Alternatively, a similar liquid 'binder' may be used to hold particles of a similar type lightly together without bonding until evapor-ation can cause direct bonding. (b) Two potentially reactive substances may be mixed together, possibly with a liquid inhibitor or binder, and subsequently 25 caused to react by raising the temperature, or by other changes in the environment, or both. (c) A suitable substance, or substances may be mixed with a liquid or powder 'hardener' that will itself react at a controll-able rate, in an ordered manner, to cause intermolecular bonds to form in sufficient numbers to give consolidation. Alternatively the hardener will act as a catalyst to induce similar formation of normal intermolecular bonds, previously not easily or rapidly formed.
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