scispace - formally typeset
Search or ask a question
Book

The theory of transformations in metals and alloys

TL;DR: In this paper, the authors present a general introduction to the theory of transformation kinetics of real metals, including the formation and evolution of martensitic transformations, as well as a theory of dislocations.
Abstract: Part I General introduction. Formal geometry of crystal lattices. The theory of reaction rates. The thermodynamics of irreversable processes. The structure of real metals. Solids solutions. The theory of dislocations. Polycrystalline aggregates. Diffusion in the solid state. The classical theory of nucleation. Theory of thermally activated growth. Formal theory of transformation kinetics. Part II Growth from the vapour phase. Solidification and melting. Polymorphic Changes. Precipitation from supersaturated solid solution. Eutectoidal transformations. Order-disorder transformations. Recovery recrystalisation and grain growth. Deformation twinning. Characteristics of martensic transformations. Crystallography of martensitic transformations. Kinetics of martensitic transformations. Rapid solidification. Bainite steels. Shape memory alloys.
Citations
More filters
Journal ArticleDOI
TL;DR: In this paper, an Aziz solute trapping model was used to obtain a more physically based unique solution to the growth velocity for a specified transformation temperature, and the new calculations on an Fe-C alloy indicate a smoothly increasing supersaturation during both nucleation and growth as the transformation temperature is reduced.
Abstract: An earlier theory for the nonequilibrium transformation of austenite in Fe-C alloys to partially supersaturated plates of ferrite is extended to include a recent solute trapping model by Aziz. The previous model yielded a relationship between interface velocity and supersaturation for a specified transformation temperature. However, a unique growth velocity was determined from a velocity maximization criterion that could not be justified. By including the Aziz solute trapping function as a third interface response function (in addition to functions describing the diffusion field velocity and interface mobility), it has been possible to obtain a more physically based unique solution to the growth velocity for a specified temperature. The new calculations on an Fe-C alloy indicate a smoothly increasing supersaturation during both nucleation and growth, as the transformation temperature is reduced. Both the nucleation and growth processes tend to become completely diffusionless only below the martensite start temperature.

39 citations

Journal ArticleDOI
TL;DR: In this article, the authors used the tetragonal-to-monoclinic transformation in zirconia (ΔV = 4.9% at room temperature) as a model system, the factors controlling the metastability of confined particles are discussed, i.e., matrix constraint, chemical composition position and nucleation barrier to the transformation.
Abstract: Current knowledge of displacive phase transformations in non-metals (in particular, in ceramics) is reviewed. Using the tetragonal-to-monoclinic transformation in zirconia (ΔV = 4.9% at room temperature) as a model system, the factors controlling the metastability of confined particles are discussed, i.e. matrix constraint, chemical composition position and nucleation barrier to the transformation. The model for martensitic nucleation in ceramics is based on a localized soft mode mechanism at strain singularities or concentrations in faceted particles. Other potential transformation togerther alternative to zirconia have been identified. For the first time, preliminary mechanical toughness data using the new tougheners is briefly presented. Composites of 20wt.% BTb2O3 in 80 vol.% MgO causes a thresfold increase at 1400°C. Monoclinic (β) dicalcium silicate dispersed in calcium zirconate exhibits a fivefold increase in toughness. Other new materials including refractory sulfides are examined from the point of view of transformation toughening. The application of high pressures during processing makes it feasible to alter thermodynamic phase fields and to develop yet other new transformation-toughened composites.

39 citations

Journal ArticleDOI
TL;DR: In this article, the authors examined rapid tempering data for a martensitic steel and separated the softening process into two stages: carbide nucleation and carbide coarsening or growth.
Abstract: The increased adoption of martensite-containing advanced high strength steels, such as martensitic and dual-phase steels, into automotive applications has led to concerns among practitioners with respect to softening during rapid tempering cycles such as those experienced during laser welding. Past studies on rapid tempering have successfully modeled the rapid tempering process; however, the activation energies and softening rates calculated did not match the classic literature values associated with martensite tempering. The present study examined rapid tempering data for a martensitic steel and separated the softening process into two stages: carbide nucleation and carbide coarsening or growth. The activation energies calculated for each process were found to be consistent with classic literature values for diffusion controlled nucleation and growth of carbides during martensite tempering.

39 citations

Journal ArticleDOI
TL;DR: In this paper, the morphology and growth kinetics of discontinuous precipitation and dissolution reactions in supersaturated Mg-Al solid solutions containing 7.3, 9.1 and 10.9 at % Al have been investigated by optical and scanning electron microscopy and X-ray measurements.
Abstract: The morphology and growth kinetics of the discontinuous precipitation and dissolution reactions in supersaturated Mg-Al solid solutions containing 7.3, 9.1 and 10.9 at % Al have been investigated by optical and scanning electron microscopy and X-ray measurements. The volume fraction of regions transformed by the discontinuous precipitation reaction, the reaction front velocity, the interlamellar spacing and the average composition of the solute-depleted lamellae were determined as a function of the temperature. For the first time, the kinetics of the discontinuous dissolution reaction has been studied in the Mg-Al system. It has been shown that the transport of the solute atoms during both reactions is governed by grain boundary diffusion.

39 citations

Journal ArticleDOI
TL;DR: Using in situ transmission electron microscopy heating methods with the Johnson-Mehl-Avrami-Kolmogorov (JMEK) theory, a correlation between the average grain size and temperature was found in this article.
Abstract: Sputtered NiTi thin films are commonly deposited in an amorphous state and require a high-temperature annealing step to crystallize them. Their crystallization process is driven by the kinetic interplay of both nucleation and growth, and their resulting microstructure dictates the martensitic transformation behavior and actuation properties. In this paper, we present the full description of the individual contributions of nucleation and growth. Using in situ transmission electron microscopy heating methods with the Johnson–Mehl–Avrami–Kolmogorov, theory, we are able to determine these key parameters. During heating, we observed and analyzed the microstructural development and found a correlation between the average grain size and temperature. With cooling, we observed directly the conversion of the high temperature phase (austenite) to its low temperature phases (R-phase and martensite). We also examined the effect of composition on the martensitic transformation and found the crystallization behavior was markedly different for small variations. Such insights provide details that enable the continued development of thin film materials with optimal properties.

39 citations