Comprehensive investigation of single track characteristics in laser powder bed fusion of IN625 via absorptivity-calibrated normalized enthalpy

This work introduces and validates an absorptivity-calibrated normalized enthalpy N E η , a single thermophysical metric that predicts track geometry and defect formation in laser powder bed fusion (LPBF) of IN625 and enables direct process window selection and optimization. Absorptivity η ∈ [ 0 . 33 , 0 . 88 ] is calibrated in situ from the dimensionless penetration depth δ ∗ = D / ( 2 ω ) , allowing consistent N E η assignment across 23 power–speed ( P – v ) pairs (150 W to 350 W; 288 mm s -1 to 4356 mm s -1 ) after 75 preconditioning layers. Single-track responses are comprehensively characterized and mapped to N E η : surface profilometry quantifies roughness R a ; X-ray computed tomography (XCT) resolves pore size, morphology, and spatial distribution; and electron backscatter diffraction (EBSD) maps microstructural features. Clear mode thresholds are established: balling ( N E η < 5 ) , conduction ( 5 ≤ N E η < 10 ) , stable keyhole ( 10 ≤ N E η ≤ 13 ) , and the onset of instability ( N E η ≳ 13 ) . Within the conduction–stable-keyhole range, R a decreases monotonically. In contrast, beyond the instability threshold, XCT reveals a transition from sparse, near-circular pores to larger, irregular defects (areas up to 1860 µm 2 ) concentrated near the keyhole root. Rank correlations (Kendall τ ) confirm trends with N E η : depth 0.83, width 0.59, and roughness R a − 0 . 45 . By collapsing melt pool responses across disparate P – v pairs, the validated N E η framework reproduces track cross-sections under iso- N E η conditions and enables parameter selection to meet geometry and porosity targets. The reported Surface Profilometry/XCT metrics and calibrated thresholds provide immediately actionable guidance for process mapping and qualification of IN625, and the methodology is transferable to other LPBF alloys. • Absorptivity-calibrated normalized enthalpy N E η predicts LPBF track geometry. • η calibrated in situ from penetration depth ∗ ; 0.33–0.88 across 23 P – v pairs. • Actionable N E η thresholds: balling < 5; conduction 5 ≤ N E η < 10; stable keyhole 10 ≤ N E η ≤ 13 . • Iso-NE design: distinct P – v pairs reproduce geometry and roughness. • Multi-modal validation (profilometry, XCT, EBSD); pores up to 1860 μ m 2 at high N E η .