Thixoforming : Semi-solid Metal Processing

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8.5 Developing Al 2O 3 PECVD Coatings for Thixoforming Mouldsj273 Figure 8.28 Phase-formation diagram of alumina films deposited by PECVD [44]. structure [55]. Based on the results presented here, it is proposed that both ion flux and ion energy at the substrate surface play an important role in the formation of a-alumina. Thus, a significant reduction in the deposition temperature can be obtained by enhancing the surface mobility of the deposited atoms by increasing the electrical power density at the substrate, which leads to an increase in both ion flux and ion energy at the substrate surface [44]. Other process parameters than the peak voltage can be controlled in order to tune the ion bombardment, for example, by varying the precursor content, PC, as has been shown using the second set of experiments (see Table 8.9). In order to quantify the ion bombardment, we determined the normalized ions flux (NIF) according to a method suggested by Kester and Messier [56]. The NIF is a function of the ratio between the measured ion flux and measured deposition flux. The contribution of secondary electrons to the ion flux is assumed to be negligible and the sticking coefficient of the deposited flux is assumed to be 1. The modification of PC leads to significant modifications of the deposition rate (a) and, therefore, of the NIF. This is presented in Figure 8.29, where one can observe a significant increase in a as a function of PC. Conversely, the NIF decreases from 480 to 50, meaning a decrease in the energy supplied to the growing film by ion bombardment. As expected, the constitution of the deposited films has a strong dependence on NIF, as shown in Figure 8.29. As the NIF is increased from 50 to 100, phase pure g-alumina is formed, whereas at NIF 140, phase pure a-alumina is observed (Figure 8.30). Again,theimportanceoftheion bombardment onthe phaseconstitutionofalumina films is clearly demonstrated and is explained by considering the additional energy supplied to the growing films. For the discharge conditions employed within this set of experiments, we have estimated, based on a simple model put forward previously, that the number of collisions in the cathode sheath is approximately 16 [17], with an average
274j 8 Tool Technologies for Forming of Semi-solid Metals Figure 8.29 Deposition rate (0.1 nm s 1 ) and normalized ion flux as a function of the precursor concentration (AlCl 3 þ O 2) [57]. Figure 8.30 Evolution of the crystallographic structure of alumina films with increasing normalized ion flux values for films deposited at 600 C [57].
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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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100j 3 Material Aspects of Steel Th
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106j 4 Design of Al and Al-Li Alloy
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5 Thermochemical Simulation of Phas
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here it can be assumed that the dat
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Figure 5.2 Calculated temperature v
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Figure 5.4 Composition profiles of
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It is clear that C has by far the s
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Figure 5.7 The density of X210CrW12
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5.3 Calculations for the Bearing St
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Figure 5.11 Composition profiles of
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Figure 5.14 The density of 100Cr6.
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area which is available for heat tr
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Part Two Modelling the Flow Behavio
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170j 6 Modelling the Flow Behaviour
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7 A Physical and Micromechanical Mo
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Page 252 and 253: are the strain rate concentration t
Page 254 and 255: Semi-solid viscosity (Pa s) into cl
Page 256 and 257: Load (kN) strain to rupture, leadin
Page 258 and 259: Load (kN) 7 6 5 4 3 2 1 0 0 7.5 Con
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Page 262: Part Three Tool Technologies for Fo
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Page 334 and 335: 9 Rheocasting of Aluminium Alloys a
Page 336 and 337: Figure 9.2 Processes for the semi-s
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Page 340 and 341: 9.2 SSM Casting Processesj317 For t
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Page 344 and 345: 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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