摘要
This work investigated the effects of CoAl 2 O 4 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 CoAl 2 O 4 particles. After the SLM process, the CoAl 2 O 4 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 CoAl 2 O 4 inoculants. Specimens containing inoculants were also found to possess improved tensile properties following heat-treatment at both room temperature and 650 °C. Furthermore, creep testing at 650 °C/650 MPa revealed that the steady strain rate of IN718 was lowered from 8.8×10 −9 s −1 to 4.9×10 −9 s −1 , and the creep rupture life was extended by 52 hours in samples that were fabricated with CoAl 2 O 4 . These results strongly suggest that the decomposition of CoAl 2 O 4 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.