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About this book

This book demonstrates the potential of novel in-situ experiments, performed on microscopic and macroscopic length scales, for investigating localized deformation processes in metallic materials, particularly their kinetics and the associated evolution of local strain fields. It features a broad methodological portfolio, spanning optical and electron microscopy, digital image correlation, infrared theromgraphy and acoustic emission testing, and particularly focuses on identifying the localized microscopic deformation processes in high-strength/high-ductility CrMnNi TRIP/TWIP (TRansformation Induced Plasticity/TWinning Induced Plasticity) steels. Presenting state-of-the art methodology applied to topical and pertinent problems in materials engineering, this book is a valuable resource for researchers and graduate students working in the field of plasticity and deformation of structural materials.

Table of Contents

Frontmatter

1. Motivation

Abstract
This chapter is an introduction to the topic of this book dealing with in situ characterization techniques applied on high-alloy austenitic TRIP/TWIP steels for improving knowledge on deformation processes and related complex microstructures. The chapter provides a motivation for the application of complementary in situ characterization techniques such as in situ deformation in scanning electron microscope, digital image correlation, acoustic emission measurements and infrared thermography. An overview on the outline of the book is presented and a short summary of the main content of each chapter is provided.
Anja Weidner

2. Plastic Deformation and Strain Localizations

Abstract
This chapter gives an overview of basic knowledge on plastic deformation and strain localizations. The chapter starts with general remarks on plastic deformation continuing with details on deformation mechanisms such as dislocation glide and twinning were shortly summarized focusing for most common crystal lattices in metallic materials: (i) face-centred cubic lattice, (ii) body-centred cubic lattice and (iii) closed-packed hexagonal crystal lattice. In addition, the critical resolved shear stress is introduced and the mechanisms of strain hardening are described. Finally, different phenomena of strain localization are described distinguishing between strain localizations on microscopic scale (slip bands, deformation bands, persistent slip band and shear bands) and macroscopic strain localizations (Lüders effect, Portevin–Le Chatelier effect).
Anja Weidner

3. Martensitic Phase Transformation

Abstract
This chapter provides a summary of basic knowledge on martensitic phase transformation in general and in steels, in particular. Besides the thermodynamic aspects of martensitic phase transformation, the different transformation path’s (direct γ to α’, direct γ to ε, direct ε to α’ and indirect γ to ε to α’) occurring in steels are described in detail in combination with the relevant orientation relationships. In addition, the influence of stacking-fault energy is discussed. Finally, the kinetics of the martensite transformation process is described according to the well-known Olson–Cohen model.
Anja Weidner

4. Advanced High-Strength Steels

Abstract
This chapter is concerned with the advanced high-strength steels (AHSS). The focus is on AHSS of second generation—the high-alloy austenitic steels with twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP). For both groups, the state-of-the-art knowledge regarding the thermodynamic aspects, the deformation behaviour and the modelling of the deformation and strain-hardening behaviour is provided. The deformation behaviour is discussed with respect to the influence of different parameters such as temperature, strain rate and grain size as well as the appearance of strain localizations.
Anja Weidner

5. In Situ Techniques for Characterization of Strain Localizations and Time Sequence of Deformation Processes

Abstract
This chapter gives a comprehensive overview on in situ characterization techniques, which are useful for the characterization of strain localizations and the temporal evolution of deformation processes. The chapter is divided into four parts regarding (i) general remarks, (ii) in situ imaging techniques, (iii) in situ acoustic emission measurements and (iv) in situ full-field measurement techniques. The part of in situ imaging techniques is divided into (i) optical microscopy and scanning electron microscopy, whereas the part of full-field measurement techniques is separated into digital image correlation (measurement of displacement and/or strain fields) and infrared thermography (measurement of thermal fields). For all in situ techniques, a short historical overview is given together with a summary of the basic knowledge and a review of state-of-the-art research (starting from the year 2000 provided in the appendix).
Anja Weidner

6. Object of Investigations—High-Alloy Fe–16Cr–6Mn–xNi–0.05C Cast Steels with TRIP/TWIP Effect

Abstract
This chapter concerns with the material used for the characterization of strain localizations and the temporal evolution of deformation processes—the group of low-carbon, high-alloy austenitic CrMnNi TRIP/TWIP steels. This chapter focuses on a comprehensive description of both the mechanical behaviour and the microstructural evolution of these steels. The results on mechanical behaviour are divided into (i) uniaxial monotonic loading, (ii) uniaxial cyclic loading and (iii) planar-biaxial loading. The description of the microstructural evolution is separated according to the different austenite stabilities of these steels resulting from varying nickel contents. The used methods for mechanical testing and microstructure characterization are shortly summarized. Detailed descriptions are provided by references.
Anja Weidner

7. Case Studies on Localized Deformation Processes in High-Alloy Fe–16Cr–6Mn–xNi–0.05C Cast Steels

Abstract
This chapter is together with Chap. 6 the principal part of this book. This chapter provides detailed results on the application of the in situ characterization techniques introduced in Chap. 5 in terms of three case studies: (i) the microscopic strain localizations during plastic deformation, (ii) the temporal evolution of deformation processes and (iii) the macroscopic strain localization during plastic deformation. The part on microscopic strain localizations provides high-resolution (sub-µm) results of strain field calculations obtained during both tensile deformation at different temperatures (RT, 100 and 200 °C) and cyclic deformation at room temperature. Furthermore, the magnitude of shear for individual microstructural constituents (austenite, ε-martensite and α′-martensite) was experimentally determined and shows a good agreement with theoretical calculated values. The part on temporal evolution of deformation processes shows that the acoustic emission is a powerful tool to study the kinetics of deformation processes since it allows to separate acoustic signals belonging to different sources such as dislocation movement, twinning, formation of stacking faults and martensitic phase transformation. The part on macroscopic strain localizations demonstrates well that the combination of different in situ characterization techniques such as digital image correlation, infrared thermography and acoustic emission applied to the Portevin–Le Chatelier effect can gain a deeper knowledge and understanding on ongoing processes and material behaviour.
Anja Weidner

8. Prospects of Complementary In Situ Techniques

Abstract
This chapter summarizes benefits of the application of complementary in situ characterization techniques. First of all, the advantages and disadvantages of each in situ characterization technique are summarized and discussed. Furthermore, the contribution of the results out of these complementary techniques to the modelling of materials behaviour is discussed. Furthermore, four examples are presented where the author sees a benefit from the application of these techniques: (i) modelling of the strain-hardening behaviour of TRIP/TWIP steels, (ii) damage behaviour of TRIP matrix composites, (iii) deformation and damage behaviour of laminated TRIP/TWIP steels and (iv) the application to shape memory alloys.
Anja Weidner

9. Concluding Remarks

Abstract
This chapter provides concluding remarks including on the main achievements obtained by the complementary in situ characterization techniques—(i) in situ SEM testing in combination with digital image correlation, (ii) in situ acoustic emission measurements, and (iii) fully-coupled full-field measurements using thermography and digital image correlation. It is shown that the application of these techniques facilitates the investigation of both the microscopic strain localization occurring in high-alloy CrMnNi cast TRIP/TWIP steels on a sub-micrometre resolution and the time sequence of activated deformation mechanisms. In addition, an outlook is provided on further developments and applications of these techniques.
Anja Weidner

10. Correction to: Deformation Processes in TRIP/TWIP Steels

Anja Weidner

Backmatter

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