Grain Morphology and Texture Development in a Co-Cr-Mo Alloy Fabricated by Powder Bed Fusion with an Electron Beam

Abstract

Grain morphology, size, and growth direction are crucial in determining the performances of metallic implant components. Understanding the effects of the manufacturing characteristics of powder bed fusion with an electron beam (PBF-EB), an additive manufacturing process, on microstructure formation and anisotropy development during solidification is essential to achieve flexible microstructure control. In this study, PBF-EB was employed to fabricate a Co-Cr-Mo alloy and the grain morphology and texture formation with different process parameters were analyzed by experimental characterization with the aid of computational thermal-fluid dynamics simulations. It was found that the epitaxial growth with resulting columnar grain and near-cubic texture tended to be dominant in the solidification process, due to competitive grain growth and the heat flow characteristics in the snake-scanning strategy. However, the molten pool connection between adjacent melt tracks resulted in the random orientation of <001> in the horizontal plane, producing a fiber-like texture. In addition, nucleation and new grain growth rather than extensive epitaxial growth could be achieved by manipulating the molten pool geometry and overlap between adjacent melt tracks. Increasing the slope of the solid/liquid interface of the molten pool and decreasing the remelting fraction of adjacent melt tracks favored the formation of new grains with random orientations to restrict the extensive epitaxial growth of the columnar grains and attenuate the microstructural anisotropy.