The Alpha–Beta Phase Transformation Interface
The Alpha–Beta Phase Transformation interface () is found under the Heat Transfer > Metal Processing () branch when adding a physics interface. The physics interface is intended for studying metallurgical phase transformations in α–β titanium alloys. You can use this interface to study diffusional, displacive, and user-defined (solid-solid) phase transformations. Physical phenomena, such as latent heat of phase transformation and transformation strains can be computed and used in Heat Transfer in Solids and Solid Mechanics. With the Nonlinear Structural Materials Module or the Geomechanics Module, plastic strains and hardening behavior of each metallurgical phase can be used in Solid Mechanics.
This interface is based on the Metal Phase Transformation interface. This chapter will only describe the nodes and settings that set the Alpha–Beta Phase Transformation interface apart from the Metal Phase Transformation interface. With regard to other settings at the physics interface level and feature level, see The Metal Phase Transformation Interface.
When the Alpha–Beta Phase Transformation interface is added, several nodes are added to the Model Builder — three Metallurgical Phase nodes and seven Phase Transformation nodes. The interface is tailored specifically to the phase transformations that can take place in α–β titanium alloys like Ti–6Al–4V. The Alpha–Beta Phase Transformation interface defines three major phases, whose node names are:
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Beta
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Widmanstätten Alpha
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Martensitic Alpha
Phase transformation modeling of α–β titanium alloys sometimes includes an alpha phase that forms at the beta grain boundaries. This alpha phase is omitted here, as it often exists in small fractions. Should this level of modeling detail be warranted, additional metallurgical phase and phase transformation nodes can be added to the interface.
The Initial Phase Fraction is set to 0.11 in the Beta node, and 0.89 in the Widmanstätten Alpha node. These initial phase fractions are approximate values corresponding to an α–β titanium alloy like Ti–6Al–4V, at room temperature. Seven Phase Transformation nodes are also created to define the relevant phase transformations:
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Beta to Widmanstätten Alpha. This phase transformation is active under isothermal or cooling conditions, and it is active provided that the fraction of beta phase exceeds its equilibrium value.
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Beta to Martensitic Alpha (Fast). This phase transformation is active under cooling conditions, when the cooling rate exceeds a certain threshold rate, and below the Martensite start temperature.
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Beta to Martensitic Alpha (Slow). This phase transformation is active under cooling conditions, when the cooling rate is lower than the threshold rate mentioned above, and below the Martensite start temperature. Under these conditions, the maximum fraction of formed Martensitic alpha is limited by the equilibrium value of beta phase.
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Alpha to Beta. This phase transformation is used to model the dissolution of Widmanstätten and Martensitic alpha, into beta phase. It is active under heating conditions, and when the temperature exceeds the so-called beta start temperature.
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Martensitic Alpha to Beta. This phase transformation represents the dissolution of Martensitic alpha into beta phase. It is active at temperatures above the martensite dissolution temperature. In this phase transformation, the beta phase strives toward its equilibrium value.
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Martensitic Alpha to Widmanstätten Alpha. This phase transformation represents the dissolution of Martensitic alpha into Widmanstätten alpha phase. It is active at temperatures above the martensite dissolution temperature. In this phase transformation, the Widmanstätten alpha phase strives toward its equilibrium value.
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Beta Re-Formation. This phase transformation represents a simplified description of complete dissolution of alpha phase. It is active when the temperature exceeds the beta transus.
A Parameters node is automatically created under Global Definitions. This node contains parameters for certain user inputs of the physics interface nodes. Generated parameters include default values for characteristic transformation temperatures, for the Martensitic alpha rate threshold, and so on.
From the Physics toolbar, you can delete or disable metallurgical phases and phase transformations that are irrelevant in a given situation, and you can add additional metallurgical phases and phase transformations. You can also right-click Alpha–Beta Phase Transformation to select physics features from the context menu.
For an example how to model phase transformation that occur during welding of a titanium plate, see Welding of a Titanium Plate: Application Library path Metal_Processing_Module/Titanium_Phase_Transformations/welding_of_a_titanium_plate.
Settings
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is abp.