Tailored grain morphology via a unique melting strategy in electron beam-powder bed fusion

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:824

Article

Karimi, Paria¹  Sadeghi, Esmaeil¹  Algardh, Joakim²  Olsson, Jonas¹  Colliander, Magnus Hornqvist³  Harlin, Peter⁴  Toyserkani, Ehsan⁵  Andersson, Joel¹ 

[1] Univ West, Dept Engn Sci, S-46186 Trollhattan, Sweden

[2] Arcam EBM, S-43533 Molnlycke, Sweden

[3] Chalmers Univ Technol, Dept Appl Phys, S-41296 Gothenburg, Sweden

[4] Sandvik Addit Mfg, S-81181 Sandviken, Sweden

[5] Waterloo Univ, Dept Mech & Mechatron Engn, Waterloo, ON, Canada

关键词: Additive manufacturing;    Electron beam-powder-bed fusion;    Melting strategy;    Grain structure;    Alloy 718;   

DOI  :  10.1016/j.msea.2021.141820

来源: Elsevier

【 摘 要 】

This study presents a unique melting strategy in electron beam-powder bed fusion of Alloy 718 to tailor the grain morphology from the typical columnar to equiaxed morphology. For this transition, a specific combination of certain process parameters, including low scanning speeds (400-800 mm/s), wide line offsets (300-500 mu m) and a high number of line order (#10) was selected to control local solidification conditions in each melt pool during the process. In addition, secondary melting of each layer with a 90 degrees rotation with respect to primary melting induced more vigorous motions within the melt pools and extensive changes in thermal gradient direction, facilitating grain morphology tailoring. Four different types of microstructures were classified according to the produced grain morphology depending on the overlap zone between two adjacent melt pools, i.e., fully-columnar (overlap above 40 %), fully-equiaxed (overlap below 15 %), mixed columnar-equiaxed grains, and hemispherical melt pools containing mixed columnar-equiaxed grains (overlap similar to 20-25 %). The typical texture was < 001 >; however, the texture was reduced significantly through the transition from the columnar to equiaxed grain morphology. Along with all four different microstructures, shrinkage defects and cracks were also identified which amount of them reduced by a reduction in areal energy input. The hardness was increased through the transition, which was linked to the growth of the gamma precipitates and high grain boundary density in the fully-equiaxed grain morphology.

【 授权许可】

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