Microstructural and geometric characteristics of interfaces in functionally graded 17-4PH stainless steel fabricated by laser powder bed fusion

Abstract Laser powder bed fusion (PBF-LB/M) of nitrogen atomized 17-4PH stainless steel enables the fabrication of functionally graded components with spatially varying fractions of ferromagnetic martensite ( α ′ ) and paramagnetic austenite ( γ ), achieved through strategic modulation of energy density and the resulting thermal gradients. Commercial PBF-LB/M systems, however, restrict in-situ parameter variations, with prior studies reporting cracks at interfaces between regions of differing γ – α ′ phase fractions. A volumetric slicing method was developed to dynamically modulate energy density via localized adjustment of laser power, scan speed, and duty cycle within individual scan lines, producing sharply defined transitions between γ - and α ′ -promoted regions on an open-architecture PBF-LB/M system. Cross-sectional microscopy revealed that such transitional interfaces exhibit both lower overall porosity and sharper transitions compared to graded samples that were printed conventionally. The varied energy density input yielded distinct microstructure and porosity outcomes across the sample width, with each modulated parameter displaying different results for microstructure and porosities, paving the way for tailored mechanical and magnetic properties through process–microstructure linkage.