Topology-driven dimensional stability of micro-milled structures on Laser Directed Energy Deposition (L-DED) Inconel 718 after precipitation hardening

Laser Directed Energy Deposition (L-DED) of Inconel 718 (IN718) is typically followed by precipitation hardening to achieve the required mechanical properties, yet the response of micro-milled surface structures to this thermal exposure remains insufficiently understood. This study investigates the dimensional and morphological stability of deterministic micro-structures produced on L-DED IN718 before and after a Solubilization + Direct Aging (SDA) treatment, focusing on three representative geometries: micro-channels, micro-cubic pillars, and semipyramidal pillars. Structures were fabricated under identical micro-milling conditions and characterized by confocal microscopy with statistical replication. All geometries preserved their global architecture after SDA, with no loss of periodicity or macroscopic distortion. However, measurable dimensional variations were found to be strongly dependent on feature topology. Continuous channel structures retained width and spacing, exhibiting only a minor reduction in height (1.6%), whereas discrete pillar-based geometries showed lateral drift, with width increases up to 3% and corresponding spacing reduction, while height remained largely unchanged. The combined analysis of geometrical descriptors and profile parameters indicates that dimensional evolution is not governed by bulk volumetric shrinkage associated with phase transformation, but predominantly by edge-condition evolution in high-curvature regions. These findings establish a topology-driven mechanism controlling dimensional stability and provide a physically grounded basis for the design of micro-structured IN718 surfaces compatible with post-machining precipitation hardening.