研究目的
Investigating the microstructure evolution of Ti–6Al–4V during laser powder bed fusion using a Multi-Phase Field model and an Orientation Field.
研究成果
The MPF approach provides a thermodynamically motivated description of the phase transformations during melting and re-solidification, which captures the effect of supercooling. The OF allows investigating the evolution of individual grains, and therefore, the texture evolution phase primarily precipitated from the melt within the LBPF processed parts. The orientation relationship between the β and α phases can be used to model the solid-state phase transformation and final texture.
研究不足
The proposed approach does not fully account for all relevant effects. For the solid-state transformation, there is no preference for any of the 12 variants resulting from the orientation relationship between β- and α-phase.
1：Experimental Design and Method Selection
A Multi-Phase Field (MPF) model in combination with an Orientation Field (OF) is proposed to describe the microstructure evolution of an individual grain induced by laser–material interaction. Relevant phase transformations are taken into account by nucleation and growth processes using the free enthalpy as driving force.
2：Sample Selection and Data Sources
The study focuses on the LPBF processing of the titanium alloy Ti–6Al–4V.
3：List of Experimental Equipment and Materials
The computational domain is a cuboid with an edge length of 5 mm in x1- and x2-direction and 1 mm x3-direction. The initial edge length of the cubic cells was 0.1 mm and 3 μm after mesh refinement in the region of interest.
4：Experimental Procedures and Operational Workflow
The simulation model takes into account the fluid dynamics of multiple fluid phases (molten titanium, shielding gas, and metal vapor) including free convection of shielding gas and thermo-capillary convection, heat transport including thermal radiation of the free surface, laser–material interaction excluding the reflectivity of the material, the kinetics of phase transformations by a nucleation and growth process driven by the free enthalpy, and the evolution of individual grains.
5：Data Analysis Methods
The texture evolution over several layers was computed. The scan pattern is chosen in such a manner that is no heat accumulation within the computational domain.
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