Evolution of solidification texture during additive manufacturing

Abstract

Striking differences in the solidification textures of a nickel based alloy owing to changes in laser scanning pattern during additive manufacturing are examined based on theory and experimental data. Understanding and controlling texture are important because it affects mechanical and chemical properties. Solidification texture depends on the local heat flow directions and competitive grain growth in one of the six <100> preferred growth directions in face centered cubic alloys. Therefore, the heat flow directions are examined for various laser beam scanning patterns based on numerical modeling of heat transfer and fluid flow in three dimensions. Here we show that numerical modeling can not only provide a deeper understanding of the solidification growth patterns during the additive manufacturing, it also serves as a basis for customizing solidification textures which are important for properties and performance of components.

Microstructure, Solidification Texture, and Thermal Stability of 316 L Stainless Steel Manufactured by Laser Powder Bed Fusion

“…Therefore, each next layer inherits the texture repeatedly, layer after layer, forming a three-dimensional solidification texture in the final 3D object. Formation of solidification <100> texture has been reported for cubic materials like austenitic stainless steel [5,46,47], Ni-base superalloys [9,34], Al alloys [48], tantalum [49], and others. Strongly textured as-built LPBF 316 L samples with a high fraction of <100> oriented grains have been investigated by [18,46], while in [47], relatively low fraction of <100> textured grains were reported.…”

“…The formation of the final 3D texture is dependent on the laser scanning directions, and therefore, it could be predicted and controlled if the manufacturing strategy is known. Experimentally, the possibility to control microstructure through adjustments of the scanning strategy and process parameters has been presented for DED Ni-base alloys [34,50] and LPBF Ni- [51,52], and Al-alloys [48]. In the present investigation, to visualize microstructure and texture in the LPBF 316 L steel, the specimen was cross-sectioned so that the surface of interest was coplanar to the X 1 and Y 1 directions.…”

“…Equation (2) shows a strong correlation between λ 1 , and thermal gradient G and solidification rate R. The solidification rate is not a constant within the moving molten pool. At a selected point at the solid-liquid interface, it is coupled with the energy source movement velocity by an expression that includes a misorientation factor [19,27,34,35]:…”

Modeling of Ti-W Solidification Microstructures Under Additive Manufacturing Conditions

“…Later models expanded on this work to include material addition, with the corresponding forces on the molten pool arising from powder injection. [23][24][25] More recently, Wei et al [26] modeled a beam-based melting and solidification problem with fluid flow, heat transport, and solidification in order to study the effects of epitaxy on the grain growth and texture of multiple deposited layers. Acharya et al [27] modeled a similar problem for scanning laser epitaxy use in part repair, investigating the role of process parameters and fluid transport on solidification conditions.…”

“…Specifically, the effects of epitaxial growth [26] as well as the movement of the laser beam [9,13,72] can have a significant effect on the dendrite orientations. Epitaxial growth leads to preferred initial growth in prescribed directions, which may not align with the large thermal gradients.…”