Architectured Metamaterial Structural Lattices by Laser Powder-Bed Fusion of 17-4PH Steel

Additive manufacturing build parameters are used to engineer architectured metamaterial structural lattices with controllable mechanical performance, achieved through microstructural grading of 17-4PH steel without compositional or geometric modification. The high solidification rates of laser powder-bed fusion suppress the thermal martensitic transformation and lead to elevated levels of retained austenite. Diamond cubic lattices built at low energy density (low thermal strain) retain a low martensite phase fraction (3 vol%) and exhibit a bend-dominated compression response. Lattices built at high energy density experience increased thermal strain which causes in-situ deformation-driven transformation, yielding >40 vol% martensite; these exhibit a stretch-dominated compression response. Metamaterial lattices, with high and low energy density parameters as a superimposed composite-style arrangement, exhibit intermediate compression responses. Controllable mechanical response was achieved through control of microstructure, using build parameters to adjust thermal strain and selectively suppress or trigger the martensitic phase transformation in-situ.