ISSN:0267-0836    

DOI:10.1179/mst.1992.8.2.101

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThis paper describes an approach to the modelling of the processing and engineering properties of materials. A flowchart for model development is described and problems associated with the coupling between parts of the model are discussed. Modelling techniques are reviewed, with particular emphasis on the internal state variable approach and the construction of mechanism maps.MST/1574

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.2.102

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.2.112

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractComputer based numerical modelling of solidification is being increasingly used in an effort to develop and improve casting processes, a long term goal of this work being the prediction of microstructural features such as grain shape, size, and dendrite arm spacings throughout a casting. In a numerical heat flow model this can be achieved only through the inclusion of the kinetics of nucleation and dendrite growth. In the present paper strategies for including columnar and equiaxed solidification kinetics into a finite element model are reviewed. A detailed model for columnar solidification is then presented together with results obtained from calculations on an Al–5 wt-%Cu alloy and a multicomponent nickel based superalloy. It is shown that the inclusion of a dendrite tip undercooling is important, particularly in systems having a low Stefan number. Furthermore, the thermal histories in the superalloy can only be accurately calculated if an experimentally determined solid fraction versus temperature relationship is employed. A model for equiaxed solidification is also discussed and results obtained for an Al–5 wt-%Cu alloy outlined. In particular, the effects of heat transfer coefficient, heterogeneous nucleation site density, and nucleation undercooling on the grain size variation along a one dimensional casting have been examined. Finally, it is shown that grain sizes predicted by the present finite element model agree reasonably well with those of a previous numerical model for an Al–7 wt-%Si alloy.MST/1468

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.2.114

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractPhysical models for the development of microstructure have the potential of revealing new phenomena and properties. They can also help identify the controlling variables. The ability to estimate quantitatively the weld metal microstructure relies on a thorough understanding of the phase transformation theory governing the changes that occur as the weld solidifies and cools to ambient temperature. Considerable progress has been made with the help of thermodynamic and kinetic theory, which accounts for the variety of alloying additions, non-equilibrium cooling conditions, and other variables necessary to specify fully the welded component. These aspects are illustrated with the aim of presenting a brief account of the methodology and of those problems which have yet to be solved.MST/1499

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.2.123

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.2.134

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThis paper briefly reviews the various approaches, both analytical and numerical, that have been used to model the microstructural changes that occur during primary recrystallisation. For prediction of the kinetics of recrystallisation and the resulting grain structure, analytical methods based on the Avrami equation are still limited because of the complexity of the parameters in the equation. Numerical simulations based on a similar model show great promise, but are still not sufficiently sophisticated to accurately reproduce the grain size distributions found in practice. Monte Carlo simulations, which can successfully model grain growth after recrystallisation, have been used to model recrystallisation but cannot as yet be performed on a large enough scale to take into account the complexity of the deformed structure. A preliminary account is given of a new network model which aims to model recrystallisation mechanisms by simulating subgrain boundary migration.MST/1597

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.2.135

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractAlthough wide use has been made of numerical techniques to analyse material behaviour, it is only recently, as a result of the increasing availability of cheap computing capacity, that such techniques have been applied to manufacturing processes. In this paper forging, casting, and quenching operations are used to illustrate the application of modelling to various manufacturing processes. The modelling technique is outlined and a brief review of the current state of development given for each operation.MST/1469

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.2.145

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.2.151

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe mechanisms of dynamic recrystallisation of nickel have been analysed by carrying out compression tests over a wide range of temperatures and strain rates and by examining the microstructures using optical and transmission electron microscopy. Under all deformation conditions, the true stress–true strain (σ–ɛ) curves display a typical maximum corresponding to dynamic recrystallisation, followed by a steady state flow. A correlation is shown to exist between the global strain hardening rate during high temperature straining (region of dynamic recrystallisation) and the microstructural features. Before the flow stress peak, commonly assumed to be the result of dynamic recrystallisation, two stages of strain hardening are observed, corresponding to a homogeneous (the higher hardening rate) and a heterogeneous mode of deformation, respectively. It is demonstrated that observable strain localisation takes place through the conversion of deformation bands from micro- to macrodimensions, a process which results in the global softening of nickel at high temperatures. This process leads to the formation and migration of recrystallisation fronts within periodically passive bands of localised deformation.MST/1494

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.2.153

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor