Journal
ADDITIVE MANUFACTURING
Volume 35, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.addma.2020.101328
Keywords
Selective laser melting; Superalloys; Inoculant; Tensile properties; Creep properties
Funding
- National Science Foundation (NSF), U.S.A. [1663068]
- Ministry of Science and Technology (MOST), Taiwan [MOST108-2218-E007-009]
- Directorate For Engineering
- Div Of Civil, Mechanical, & Manufact Inn [1663068] Funding Source: National Science Foundation
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This work investigated the effects of CoAl2O4 inoculants on the microstructure and mechanical properties of a superalloy - Inconel 718 (IN718), processed by selective laser melting (SLM). IN718 powder was blended with 0.2 wt. % of CoAl2O4 particles. After the SLM process, the CoAl2O4 particles reacted with IN718 and formed a dispersion of Al-rich nano-oxide particles in the matrix. These inoculants were observed to facilitate the formation of fine, equiaxed grains and reduce the degree of crystallographic texture in the as-built microstructure. The presence of the nano-oxide particles in the microstructure served to restrict the mobility of grain boundaries during heat-treatment and promoted the formation of a bimodal grain structure with comparatively finer average size. Due to the reduction of crystallographic texture, the elastic anisotropy present in as-built specimens was greatly minimized with the addition of CoAl2O4 inoculants. Specimens containing inoculants were also found to possess improved tensile properties following heat-treatment at both room temperature and 650 degrees C. Furthermore, creep testing at 650 degrees C/650 MPa revealed that the steady strain rate of IN718 was lowered from 8.8 x 10(-9) s(-1) to 4.9 x 10(-9) s(-1), and the creep rupture life was extended by 52 hours in samples that were fabricated with CoAl2O4. These results strongly suggest that the decomposition of CoAl2O4 into Al-rich oxides during SLM processing not only contributes to grain refinement and a reduction in the degree of crystallographic texture but also forms an oxide dispersion that restricts the mobility of dislocations and grain boundaries in IN718.
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