Solution heat treatment of support-free IN625 overhang sections fabricated via laser powder bed fusion (LPBF)
摘要
This study reports the change in microstructure and microhardness occurring during solution heat treatment of a support-free zero-degree IN625 overhang processed using laser powder bed fusion. In as-built condition, the bulk section consisted of fine cellular structure (0.7 ± 0.2 µm) with Nb segregation and a dislocation density of 1.34 × 1014 m−2. In contrast, the downskin displayed a coarser solidification structure of 4.7 ± 2.1 µm and a lower dislocation density of 0.74 × 1014 m−2. This structural variation resulted hardness gradient ranging from 322 ± 17 HV in the bulk to 278 ± 18 HV in the downskin. After solution treatment (ST), the bulk region exhibited recrystallization and grain growth, while the downskin experienced limited grain growth, which is explained by the smaller stored strained energy in the latter. The microhardness gradient was reversed, where the bulk has a lower hardness than the downskin (252 ± 15 vs 271 ± 10 HV). The lower hardness for the bulk is associated with recrystallization, while the similar value in hardness for the downskin was ascribed to an equivalent change in the strengthening contribution from cell-boundary strengthening to Orowan dispersion strengthening.