Identification of texture characteristics for improved creep behavior of a L-PBF fabricated IN738 alloy through micromechanical simulations

Abstract

Additive manufacturing (AM) of nickel-based superalloys, due to high temperature gradients during the building process, typically promotes epitaxial growth of columnar grains with strong crystallographic texture in form of a 〈001〉 fibre or a cube texture. Understanding the mutual dependency between AM process parameters, the resulting microstructure and the effective mechanical properties of the material is of great importance to accelerate the development of the manufacturing process. In this work, a multi-scale micromechanical model is employed to gain deeper insight into the influence of various texture characteristics on the creep behavior of an IN738 superalloy. The creep response is characterized using a phenomenological crystal plasticity creep model that considers the characteristic γ–γ′ microstructure and all active deformation mechanisms. The results reveal that the creep strength increases with decreasing texture intensities and reaches its maximum when the 〈001〉 fibre and cube textures are misaligned to the specimen building direction by 45°. The simulations also predict that the uncommon 〈111〉 and 〈110〉 fibres offer significantly higher creep resistance than the typically observed 〈001〉 fibre, which provides a further incentive to investigate AM processing conditions that can produce these unique textures in the material. As the intensities and the alignment of 〈001〉 fibre and cube textures can be attributed to the laser energy density and the scan strategy employed and as the formation of distinct fibre textures depends on the geometry of the resulting melt pool, the laser powder bed fusion process parameters can be optimized to obtain microstructures with features that improve the creep properties.