H13 tool steel-copper composite fabricated by laser powder bed fusion and melt infiltration for high thermal conductivity tooling applications

A two-step fabrication process was successfully developed to produce a tool steel/copper (H13/Cu) interpenetrating phase composite (IPC) intended for improving heat management in mold and die applications. H13 functionally graded lattice structures (FGLS) were first fabricated via laser powder bed fusion (LPBF) additive manufacturing (AM). X-ray diffraction (XRD) analysis of the as-built H13 FGLS revealed a predominantly lath martensite microstructure with 16% retained austenite (RA). The microstructure transformed into a fully tempered martensitic phase through a heat treatment, which involved air quenching at 1020 ºC and tempering at 500 ºC for 2 h (QT500). The subsequent infiltration of the H13 lattice with Cu, followed by the QT500 heat treatment, yielded a H13/Cu IPC with a relative density of 99.8%. The H13/Cu interface analysis indicated complete wettability, minimal α(Fe,Cr) precipitates in the Cu matrix (< 2%), and Cu penetration into H13 struts to a depth of 47 ± 7 μm. The microstructure and microhardness of the H13 after Cu infiltration followed by QT500 remained similar to the QT500 reference sample. The effective thermal conductivity ( k e ) of the composite was highly tailorable by adjusting the H13 lattice density, with measured k e values ranging from 145.2 ± 0.7 Wm -1 K -1 to 34 .1 ± 0.1 Wm -1 K -1 for H13 volume fractions of 40% to 90%, respectively. These measurements aligned well with predictions from the Torquato approximation and finite element modeling, confirming the potential to customize thermal properties for specific tooling applications.