Multi-material additive manufacturing enables the fabrication of functionally graded components that combine distinct material properties within a single part. However, achieving robust co-sintering of multi-material structures remains a critical challenge due to mismatched densification kinetics and shrinkage behaviors. In this study, successful co-sintering and process optimization were achieved by systematically investigating the sintering temperature (1260–1380 °C) dependent behavior of 316L/17-4PH multi-material structures fabricated via material extrusion (MEX). The multi-material structure exhibited non-monotonic densification behavior, reaching a maximum relative density of 95.84% at 1340 °C, followed by a decrease due to pore reconnection caused by oversintering of the 17-4PH region. Despite the linear shrinkage mismatch between the two materials, robust bonding was achieved without interfacial delamination. At all sintering temperatures, γ-austenite (face-centered cubic) and α-martensite (body-centered cubic) phases coexisted without the formation of intermetallic compounds, and energy-dispersive X-ray spectroscopy (EDS) analysis confirmed a limited elemental diffusion mechanism. Hardness displayed non-monotonic behavior with a peak value of 197.71 HV at 1340 °C, whereas ultimate tensile strength, yield strength, and elongation monotonically increased, reaching 649.97 MPa, 419.78 MPa, and 18.28% at 1380 °C, respectively. Fracture surface analysis revealed that interfacial integrity reached an optimal level at 1340 °C, characterized by dominant continuous fracture across the interface; however, interfacial delamination reoccurred above 1340 °C. Based on comprehensive characterization, 1340 °C was determined to be the optimal processing condition. This study demonstrates that the MEX process is a reliable method for fabricating 316L/17-4PH multi-material structures via controlled solid-state sintering.
Go et al. (Sun,) studied this question.