Electron beam side-surface remelting of porous Inconel 625 alloy: periodic liquid film micro melt pools and effects on microstructure and mechanical properties

By simulating the complete process of selective electron beam melting (SEBM), remelting tests were carried out on the side surface of porous Inconel 625 alloy prepared by powder metallurgy. The results show that the periodically occurring liquid film micro melt pools (LFMPs) dominated the formation of surface precipitates. Periodic 100 μm-thick LFMPs formed at the top due to edge thermal effects. The α-(Cr) phase on the upper surface of the melt pool encapsulated NbNi₃ and MoNb₃, and generated a Cr + NbCr₂ eutectic with the fine γ-(Ni) dendrites. The ~2 μm LFMP in the layer-by-layer melted region facilitates surface grain refinement, twinning, and dislocation pile-ups, resulting in an increase in average microhardness from 1.93 GPa to 3.04 GPa. After solidification, the surface formed α-(Cr, Fe) phase, influenced by Cr enrichment and Fe introduced by the scraper. Meanwhile, periodic electron beam scanning caused the base material (BM) near the remelted side surface (RSS) to remain within the intermediate temperature range for an extended period, promoting the precipitation of large, continuous grain boundary Laves and μ phases (TCP phases), along with the formation of hole defects. Combined with the limited load-bearing area of the porous material, these factors contribute to brittle fracture, reducing the bonding strength between the RSS and the BM to 37 MPa, compared to 51 MPa for the BM. To prevent the RSS from becoming a mechanically weak region, it is essential to control the overall heating temperature to avoid the intermediate temperature range. Alternatively, introducing new alloying elements to enhance grain boundary performance can also mitigate this issue.