Powder reuse effects on refreshed Invar 36 batches and selected PBF-LB/M part properties

Invar 36 is used in aerospace and dimensionally stable assemblies because of its exceptionally low coefficient of thermal expansion (CTE). Laser beam powder bed fusion of metals (PBF-LB/M) enables the fabrication of complex Invar components, making powder reuse relevant to process efficiency and part consistency. This study evaluates a route in which gas-atomized powder was recovered, sieved at 63 µm, and refreshed with 10 wt% virgin powder after each build. Virgin batch (N1) and refreshed batches sampled after 10 (N2) and 20 (N3) build–recovery–sieving–refresh cycles were characterized by bulk chemistry, O/N/C/S analysis, scanning electron microscopy/energy-dispersive spectroscopy, laser diffraction, and Hall flow. Corresponding specimens were assessed for roughness, density, optical porosity, microstructure, microhardness, and heat-treated thermal expansion. An ideal-mixing mass balance predicted mean build-exposure ages of 5.86 and 7.91 builds for N2 and N3, confirming mixed particle histories. Across N1–N3, Ni was 36.2–36.7 wt%, oxygen varied non-monotonically, and D50 was 34.4–36.7 µm; N2 and N3 flowed at 13–14 s/50 g. Relative density was 99.38–99.88%, optical porosity 0.04–0.21%, microhardness 141–145 HV0.3, and incremental CTE at 100 °C was 1.04–1.06 × 10⁻⁶ K⁻1. The results support condition-based monitoring of refreshed powder batches.