Thixoforming : Semi-solid Metal Processing

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5 Thermochemical Simulation of Phase Formation Bengt Hallstedt and Jochen M. Schneider 5.1 Methods and Objectives 5.1.1 General In this chapter, we will explore the use of thermochemical simulation methods to support alloy selection and processing in the semi-solid state. Alloy selection is discussed more in detail in Chapters 2–4. Processing-related issues are discussed in detail in Chapters 9 and 11. The use of thermochemical simulation for alloy selection has also been treated in, for example, [1–4]. The focus at RWTH over the last few years has been on semi-solid processing of steels and, therefore, only steels will be discussed here. The steels of main interest here are the relatively high-carbon steels X210CrW12 and 100Cr6. Their compositions are given in Table 5.1. A key property for semi-solid processing is the fraction of the liquid phase as a function of temperature (and possibly time), and this will be dealt with in some detail. It is necessary to know the fraction of liquid phase in order to be able to control the process and in order to simulate the viscous flow during various forming operations (Chapters 6 and 7). It is possible to determine the fraction of liquid phase experimentally using, for example, differential thermal analysis (DTA) or metallography (more details are given in Chapter 3), but this is far from trivial [5]. The approach used here is to calculate the fraction of liquid phase from thermodynamic (and sometimes diffusion) data. If the thermodynamic properties of a system are known, then any phase diagram can be calculated. This is illustrated in Figure 5.1, which also shows that the thermodynamic description actually contains much more information than the phase diagram alone, since the thermodynamic properties of the included phases are defined for the complete composition range, and not only for the range where they are stable. Not only the stable phase diagram, as shown in Figure 5.1, and any thermodynamic property of the stable state, but also any metastable state can be A List of Abbreviations and Symbols can be found at the end of this chapter. j147
148j 5 Thermochemical Simulation of Phase Formation Table 5.1 Standard chemical composition (mass%) of the steels, used for the calculations in the present chapter. Alloy C Mn Si Cr Mo V W 100Cr6 1.00 0.30 0.30 1.50 — — — X210CrW12 2.15 0.30 0.30 12.0 — — 0.7 HS6-5-2 0.84 0.30 0.30 4.15 4.95 1.9 6.30 calculated. This can be used, as just one example, for calculating the driving force for the precipitation of the stable phase from a metastable state. The coupling of thermodynamics and phase diagrams has been realized within the Calphad method [6–8], which was essentially developed in the 1970s and is now used to deal with a wide variety of alloy systems, oxide systems, salt systems and so on. In the Calphad method, the Gibbs energy of each phase is parameterized in terms of temperature and composition and, in principle pressure, but this is rarely used, based on crystallographic and compositional data. The Gibbs energy functions contain variable coefficients, which are optimized to experimental phase diagrams and thermodynamic data. Crystallographic and thermodynamic data from ab initio calculations are increasingly being used to support and extend the experimental data. In this chapter, we use the Thermo-Calc software [9] for thermodynamic calculations with the TC-Fe 2000 [10] and TCFE4 [11] steel databases. The more recent TCFE4 database essentially gives the same results as TC-Fe 2000 for the steels treated here, but additionally contains molar volume data. In the general case, the coverage and quality of the database(s) used are a concern, but for the steels dealt with Figure 5.1 The relation between Gibbs energies of the individual phases and the resulting phase diagram. The dashed line shows the temperature at which the Gibbs energy curves are drawn.
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Thixoforming Semi-solid Metal Proce
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Further Reading Herlach, D. M. (ed.
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The Editors Prof. Dr. G. Hirt Insti
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VI Contents 1.3.5.2 Other Aluminium
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VIII Contents 4.6.1 Thixocasting 13
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X Contents 7.4.2 Isothermal Non-ste
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XII Contents 9.4.1.3 Simulation Res
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Preface Semi-solid forming of metal
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XVIII List of Contributors Andreas
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XX List of Contributors Alexander S
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2j 1 Semi-solid Forming of Aluminiu
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10j 1 Semi-solid Forming of Alumini
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Table 1.1 Overview of semi-solid pr
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Part One Material Fundamentals of M
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32j 2 Metallurgical Aspects of SSM
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44j 3 Material Aspects of Steel Thi
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Temperature (ºC) 1550 1500 1450 14
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Page 174 and 175: Figure 5.2 Calculated temperature v
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Page 180 and 181: Figure 5.7 The density of X210CrW12
Page 182 and 183: 5.3 Calculations for the Bearing St
Page 184 and 185: Figure 5.11 Composition profiles of
Page 186 and 187: Figure 5.14 The density of 100Cr6.
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196j 6 Modelling the Flow Behaviour
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7 A Physical and Micromechanical Mo
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3. Macroscopic averages or homogeni
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displacement boundary conditions or
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and liquid are both assumed to be i
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are the strain rate concentration t
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Semi-solid viscosity (Pa s) into cl
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Load (kN) strain to rupture, leadin
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Load (kN) 7 6 5 4 3 2 1 0 0 7.5 Con
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adius R radius of the spherical inc
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Part Three Tool Technologies for Fo
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242j 8 Tool Technologies for Formin
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9 Rheocasting of Aluminium Alloys a
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Figure 9.2 Processes for the semi-s
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Two Italian companies gained the fi
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9.2 SSM Casting Processesj317 For t
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Figure 9.7 Oil pump cover for Honda
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Figure 9.9 Middle temperature cours
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Figure 9.12 Components of cartridge
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Figure 9.15 Process adapted multipa
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step-shot experiments. It is also s
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Figure 9.18 (a) Meander tool for fl
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Figure 9.19 (a, b) Wear appears in
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Table 9.2 Temperature determination
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and are plausible on the left. Furt
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Figure 9.27 Development of the micr
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some places can be observed as smal
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Figure 9.31 Simulation of the metal
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Figure 9.33 So-called Constant Temp
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Figure 9.35 Comparison of the micro
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9.4 Rheoroutej347 If rounding of th
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9.4.1.2 Parameters: Cooling to the
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Figure 9.36 Results of the 2D-MICRE
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homogeneous microstructure and no d
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grain fragment density [mm -1 ] 200
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can be considered for rheocasting o
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Figure 9.44 Microstructure of Zr/Sc
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Figure 9.45 MAGMAsoft simulation: c
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The cooling to the process temperat
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D grain diameter of a circle DGM De
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27 Doppelbauer, M. (2003) Wirtschaf
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10 Thixoforging and Rheoforging of
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1970s [7]. Also, the quality of the
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10.3 Heating and Forming Operations
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With the solution of the Equations
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10.3.1.2 Modelling of Inductive Hea
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material properties have to be cons
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10.3 Heating and Forming Operations
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Figure 10.9 Experimental results, d
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Figure 10.12 Segregation in compone
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10.3.4 Thixoforging of Steel In thi
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10.3.5 Thixojoining of Steel In the
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einforcing element. The possibiliti
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Figure 10.20 The robot controller a
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Figure 10.21 Experimental results w
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Figure 10.24 Design and working pri
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The investigations show that the rh
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Figure 10.31 Scheme of the heat tra
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Table 10.2 Definition of boundary c
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Figure 10.35 Experimental and simul
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References 1 Koesling, D., Tinius,
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steel billets into the semi-solid s
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412j 11 Thixoextrusion The followin
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414j 11 Thixoextrusion channel with
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416j 11 Thixoextrusion parameter co
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418j 11 Thixoextrusion Both concept
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420j 11 Thixoextrusion should be ju
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422j 11 Thixoextrusion Figure 11.8
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424j 11 Thixoextrusion Table 11.4 C
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426j 11 Thixoextrusion Temperature
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428j 11 Thixoextrusion impacts. Ext
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432j 11 Thixoextrusion shell format
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436j 11 Thixoextrusion Table 11.6 P
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440j 11 Thixoextrusion solidificati
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442j 11 Thixoextrusion GPa pressure
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444j Index arbitrary volume element
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446j Index equilibrium tests 141 eq
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448j Index - importance 273 ion flu
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450j Index oxygen-sensitive element
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452j Index - thixoforming 241 semi-
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454j Index - high pressure 131 - sc
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Thixoforming : Semi-solid Metal Processing

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