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order-disorder transformation
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Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 March 2012
DOI: 10.31399/asm.tb.pdub.t53420171
EISBN: 978-1-62708-310-2
... decomposition intermediate phases order-disorder transformation spinodal transformation structures superlattice structures PHASE DIAGRAMS are often quite complex, with a number of different reactions occurring at different compositions and temperatures. In most cases, the appearance of several...
Abstract
This chapter explains how the presence of intermediate phases affects the melting behavior of binary alloys and the transformations that occur under different rates of cooling. It begins by examining the phase diagrams of magnesium-lead and copper-zinc, noting some of the complexities associated with intermediate phases. It then discusses the difference between ordered and disordered phases and how they are accounted for on phase diagrams. It describes how the atoms in a disordered solution may arrange themselves into an ordered array, forming a superlattice in the process of cooling, and goes on to identify the most common superlattice structures and their corresponding alloy phases. It also discusses the factors that limit the formation of superlattices along with the kinetics of spinodal decomposition and its effect on microstructure development.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2008
DOI: 10.31399/asm.tb.tm.t52320197
EISBN: 978-1-62708-357-7
... mentioned below occurs in accordance with heating or cooling. This is called an order-disorder transformation or an order-disorder transition. (Low temperature) ordered state ⇄ Disordered state (high temperature) This ordering phenomenon was confirmed by x-ray diffraction in 1923...
Abstract
This chapter covers the analytical methods developed to characterize ordering phenomena in crystal structures. The chapter gives examples of ordering phenomena and discusses models for long-range ordering, such as the Bragg-Williams-Gorsky (B-W-G) model, and for short-range ordering. Examples of ordering and phase separation due to ordering by the B-W-G model are described. The chapter includes an appendix covering the effect of phase separation inversion type.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 June 2008
DOI: 10.31399/asm.tb.emea.t52240041
EISBN: 978-1-62708-251-8
... that it is stable up to the melting point. Fig. 3.6 Solid-solution structures An order-disorder transformation typically occurs on cooling from a disordered solid solution to an ordered phase. During this phase transformation, there is a rearrangement of atoms from random site locations...
Abstract
When a metal is alloyed with another metal, either substitutional or interstitial solid solutions are usually formed. This chapter discusses the general characteristics of these solutions and the effects of several alloying elements on the yield strength of pure metals. It presents four rules that give a qualitative estimate of the ability of two metals to form substitutional solid solutions: relative size factor, chemical affinity factor, relative valency factor, and lattice type factor. The chapter provides information on alloys that form an ordered structure during heating. It describes the intermediate phases that are formed during solidification between the two extremes of substitutional solid solution on the one hand and intermetallic compound on the other. The chapter concludes with a section on strain aging in low-carbon steels that allows the interstitial atoms to diffuse to the dislocations and again form atmospheres that pin dislocation movement.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2008
DOI: 10.31399/asm.tb.tm.t52320013
EISBN: 978-1-62708-357-7
... and NaCl as shown in Fig. 2.5(b) . Perhaps it is supposed that the change of order is almost equal when a liquid is transformed into a gas because a liquid itself has no structure. 2.2 Entropy and Free Energy <xref ref-type="bibr" rid="t52320013-ref3">(Ref 3...
Abstract
This chapter describes the basics of energy and entropy and “free energy.” Fundamentals of internal energy U , the enthalpy H , entropy S , free energies G , and F of a substance are presented. The chapter also presents the thermal vibration model to promote a better understanding of the U , S , and F of the crystal. It covers basic concepts of thermodynamics of magnetic transition and discusses the role and the meaning of magnetic transition in iron and steel. The chapter concludes with a general discussion on an amorphous phase from a thermodynamic viewpoint.
Series: ASM Technical Books
Publisher: ASM International
Published: 01 July 2009
DOI: 10.31399/asm.tb.bcp.t52230179
EISBN: 978-1-62708-298-3
... at.% or 3 wt%. There are two congruent melting phases: The beta phase, with a cesium chloride-ordered cubic structure, melts at 1420 °C (2590 °F), and the gamma phase melts at 1400 °C (2550 °F). Gamma and gamma prime are closely related, with gamma being a disordered version of gamma prime. There are two...
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 March 2012
DOI: 10.31399/asm.tb.pdub.t53420263
EISBN: 978-1-62708-310-2
... relationships that reflect structure with respect to different crystal types, but such conditions must be externally formulated and imposed on the model. Equally, special relationships apply if the model is to be used to simulate order-disorder transformations. Fig. 13.2 Simple body-centered cubic...
Abstract
This chapter provides an overview of a computational method, called CALPHAD, used for the study of phase equilibria in multicomponent systems. It describes the thermodynamic models and calculation techniques employed in the software and explains how it applies to complex alloys used in industry. It also provides examples showing how CALPHAD has been used to determine the formability of metallic glass, calculate the dilation of stainless steel during phase transformation, and predict the beta transus and approach curves of commercial titanium alloys.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2008
DOI: 10.31399/asm.tb.tm.t52320259
EISBN: 978-1-62708-357-7
... by a sigmoidal curve ( Fig. 9.1a ). Fig. 9.1 The structure change of the nucleation type (sigmoidal curve) and the non-nucleation type (asymptotic curve) On the other hand, in order-disorder transition, A and B atoms in an ordered solid solution (α) that have been arranged in a perfect order...
Abstract
This chapter provides a classification of the types of microstructural changes and transformations and then reviews each type. It presents the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation and explains the thermodynamics of eutectic solidification and eutectoid transformation. An appendix covers growth of eutectoid structure in carburized pearlite.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 January 2015
DOI: 10.31399/asm.tb.spsp2.t54410039
EISBN: 978-1-62708-265-5
..., then either a phase transformation (for example, the austenite-to-pearlite transformation under consideration here) or microstructural rearrangement without a phase change (for example, grain growth or particle coarsening) would occur in order to lower free energy to the minimum possible value. The free...
Abstract
The microstructure of carbon steel is largely determined by the transformation of austenite to ferrite, cementite, and pearlite. This chapter focuses on the microstructures produced by diffusion-controlled transformations that occur at relatively low cooling rates. It describes the conditions that promote such transformations and, in turn, how they affect the structure of various phases and the rate at which they form. The chapter also discusses the concepts of transformation kinetics, minimum free energy, and nucleation and growth, and provides information on alloying, interphase precipitation, and various types of transformations.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 January 2015
DOI: 10.31399/asm.tb.spsp2.t54410113
EISBN: 978-1-62708-265-5
..., in contrast to acicular ferrite, the dispersed particles have a granular or equiaxed morphology. The ferrite crystals of the matrix, as shown by TEM ( Ref 7.10 , 7.11 , 7.30 ), are quite fine, on the order of a few micrometers in size; are equiaxed in shape; contain a high density of dislocations...
Abstract
This chapter describes the ferritic microstructures that form in carbon steels under continuous cooling conditions. It begins with a review of the Dubé classification system for crystal morphologies. It then explains how cooling-rate-induced changes involving carbon atom diffusion and the associated rearrangement of iron atoms produce the wide variety of morphologies and microstructures observed in ferrite. The chapter also describes a classification system developed specifically for ferritic microstructures and uses it to compare common forms of ferrite, including polygonal or equiaxed ferrite, Widmanstatten ferrite, quasi-polygonal or massive ferrite, acicular ferrite, and granular ferrite.
Series: ASM Technical Books
Publisher: ASM International
Published: 01 March 2012
DOI: 10.31399/asm.tb.pdub.t53420303
EISBN: 978-1-62708-310-2
... alloys such as nickel-aluminum and nickel-titanium (~50 to 50 ratio) are also part of this alloy group, with a bcc parent phase. Because the transformations are diffusionless and lattice correspondence is maintained, order or disorder present in the parent phase is transferred to the martensite phase...
Abstract
This chapter examines two important strengthening mechanisms, martensitic and bainitic transformations, both of which occur under nonequilibrium cooling conditions. It explains how time-temperature-transformation diagrams are constructed and how they are used to understand and control the formation of martensite and bainite in steel and other alloys. It describes the morphology of both types of structures, the factors that influence their formation, how they respond to tempering processes, and their effect on mechanical properties and behaviors. It also discusses the role of transformation hysteresis in shape memory alloys.
Series: ASM Technical Books
Publisher: ASM International
Published: 01 June 1983
DOI: 10.31399/asm.tb.mlt.t62860163
EISBN: 978-1-62708-348-5
...) . Localized enhancement effects in Pd-Ag alloys. Phys. Rev. Lett . 33 , 91 – 94 . 10.1103/PhysRevLett.33.91 Nabarro F. R. N. (1967) . Theory of Crystal Dislocations . Clarendon Press , Oxford . Nix F. C. and Shockley W. (1938) . Order-disorder transformations in alloys...
Abstract
This chapter presents topics pertaining to resistance at cryogenic temperatures: measurement, the resistive mechanisms, and available data. The chapter also presents brief descriptions of the various mechanisms that are operative in producing resistance at low temperatures. The alloys discussed are the nondilute mixtures of metals. An introduction to low-temperature electrical properties of specific metals and alloys is included.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 October 2012
DOI: 10.31399/asm.tb.lmub.t53550299
EISBN: 978-1-62708-307-2
... ordering temperature ( T c ). These ordered intermetallics usually exist in relatively narrow compositional ranges around simple stoichiometric ratios. Fig. 6.1 Atomic arrangements of conventional alloys and ordered intermetallic compounds. (a) Disordered crystal structure of a conventional alloy...
Abstract
Titanium aluminides are lightweight materials that have relatively high melting points and good high-temperature strength. They also tend to be stronger and lighter than conventional titanium alloys, but considerably less ductile. This chapter begins with a review of the titanium-aluminum phase diagram, focusing on the properties, compositions, and microstructures of alpha-2 Ti3Al alloys. It then describes the properties, microstructures, and compositions of orthorhombic, gamma, and near-gamma alloys as well as the processing methods and procedures normally used in their production.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 January 2015
DOI: 10.31399/asm.tb.tpmpa.t54480141
EISBN: 978-1-62708-318-8
... difference is that intermetallic phases generally melt at a constant temperature. An ordered structure, on heating to a critical temperature, becomes disordered and melts as an alloy over a range of temperatures. Alloys based on the α 2 (Ti 3 Al) and γ (TiAl) ordered structure are termed titanium...
Abstract
The practical application of metals and alloys is guided largely by information obtained through the study of their microstructure. This chapter examines a wide range of titanium microstructures, identifying characteristic features and explaining what they reveal about processing, properties, and performance. It includes images of elongated and equiaxed structures, primary alpha, transformed beta, and metastable phases as well as spheroidal and intergranular beta, alpha case, and intermetallic compounds. It also defines important terms and provides step-by-step procedures for preparing titanium for metallographic analysis.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 August 1999
DOI: 10.31399/asm.tb.lmcs.t66560427
EISBN: 978-1-62708-291-4
... sites. Contrast with ordered structure. drawing. (1) A term used for variety of forming operations, such as deep drawing a sheet metal blank; redrawing a tubular part; and drawing rod, wire, and tube. The usual drawing process with regard to sheet metal working in a press is a method for producing...
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 August 2013
DOI: 10.31399/asm.tb.ems.t53730011
EISBN: 978-1-62708-283-9
.... Liquids do not have the high degree of order of crystals or the complete disorder of gases. For most materials, freezing causes a volume decrease of 1 to 6%. However, there are a few materials (water, silicon, germanium, bismuth, gallium, etc.) that have packing in the solid state that is not dense...
Abstract
Phases are distinct states of aggregation of matter and one of the primary leverage points for understanding and applying materials. This chapter discusses the phase nature of metals and alloys, the concept of solid solutions, and the use of phase diagrams. It also describes some of the metallurgical effects of freezing or solidification, including the segregation of solutes and the formation of metal glasses.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 November 2010
DOI: 10.31399/asm.tb.sap.t53000017
EISBN: 978-1-62708-313-3
... Antiphase-boundary (APB) energy in the presence of an ordered precipitate (γ′, γ″). The APB represents the energy needed for the dislocation to cut through the ordered precipitate, because cutting could result in disordering between the matrix and precipitate. Volume fraction of the precipitate (γ′, γ...
Abstract
This chapter discusses the metallurgical changes that occur and the improvements that can be achieved in superalloys through solid-solution hardening, precipitation hardening, and dispersion strengthening. It also explains how further improvements can be achieved through the control of grain structure, as in columnar-grained alloys, or by the elimination of grain boundaries as with single-crystal superalloys.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 October 2011
DOI: 10.31399/asm.tb.mnm2.t53060333
EISBN: 978-1-62708-261-7
... bronze, spinodal-hardening alloys, and order-hardening alloys) Quench-hardened (martensitic) copper alloys (such as aluminum bronze, nickel-aluminum bronzes, and some copper-zinc alloys) Solution-treated and aged magnesium alloys Solution-treated and aged nickel alloys Solution-treated...
Abstract
Nonferrous alloys are heat treated for a variety of reasons. Heat treating can reduce internal stresses, redistribute alloying elements, promote grain formation and growth, produce new phases, and alter surface chemistry. This chapter describes heat treatment processes and how nonferrous alloys respond to them. It provides information on aluminum, cobalt, copper, magnesium, nickel, and titanium alloys and their composition, microstructure, properties, and processing characteristics.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 31 December 2020
DOI: 10.31399/asm.tb.phtbp.t59310029
EISBN: 978-1-62708-326-3
... ferrite is approximately 2.87 Å at 20 °C (70 °F) and increases to approximately 2.9 Å at 910 °C (1670 °F). In contrast, the lattice parameter of the austenitic unit cell is on the order of approximately 3.57 Å at the transformation temperature of 912 °C (1674 °F). This provides greater interatomic space...
Abstract
The existence of austenite and ferrite, along with carbon alloying, is fundamental in the heat treatment of steel. In view of the importance of structure and its formation to heat treatment, this chapter describes the various microstructures that form in steels, the various factors that determine the formation of microstructures during heat treatment processing of steel, and some of the characteristic properties of each of the microstructures. The discussion also covers the constitution of iron during heat treatment and the phases of heat-treated steel with elaborated information on iron phase transformation, hysteresis in heating and cooling, ferrite and austenite as two crystal structures of solid iron, and the diffusion coefficient of carbon.
Book Chapter
Series: ASM Technical Books
Publisher: ASM International
Published: 01 March 2002
DOI: 10.31399/asm.tb.stg2.t61280025
EISBN: 978-1-62708-267-9
.... The ordered precipitates possess an energy (antiphase domain boundary or APB) representing the extra energy associated with ordered atom positions versus normal disordered or random positions. Higher APB energies require correspondingly more force for deformation to occur. Precipitate size. When the size...
Abstract
This chapter describes the metallurgy of superalloys and the extent to which it can be controlled. It discusses the alloying elements, crystal structures, and processing sequences associated with more than a dozen phases that largely determine the characteristics of superalloys, including their properties, behaviors, and microstructure. It examines the role of more than 20 alloying elements, including phosphorus (promotes carbide precipitation), boron (improves creep properties), lanthanum (increases hot corrosion resistance), and carbon and tungsten which serve as matrix stabilizers. It explains how precipitates provide strength by impeding deformation under load. It also discusses the factors that influence grain size, shape, and orientation and how they can be controlled to optimize mechanical and physical properties.
Series: ASM Technical Books
Publisher: ASM International
Published: 01 December 2018
DOI: 10.31399/asm.tb.fibtca.t52430027
EISBN: 978-1-62708-253-2
... in a liquid state, metals have a highly disordered noncrystalline structure. However, when a molten metal or alloy cools and solidifies to form a bulk solid, it develops a crystalline structure with an ordered arrangement of atoms. In a crystalline solid there is a repetitive or periodic arrangement of atoms...
Abstract
This chapter describes the metallurgy, composition, and properties of steels and other alloys. It provides information on the atomic structure of metals, the nature of alloy phases, and the mechanisms involved in phase transformations, including time-temperature effects and the role of diffusion, nucleation, and growth. It also discusses alloying, heat treating, and defect formation and briefly covers condenser tube materials.