Development and characterization of AISI 316L micro parts produced by metal powder hot embossing

Abstract

Metal powder hot embossing (MPHE) is a low-cost micromanufacturing technique that can produce metallic parts with aspects in micron scale. In this study, scanning electron microscopy (SEM) is employed for evaluating the shape retention and the homogeneity of microstructure of replicated geometries into AISI 316L powder feedstock by the secondary electron imaging (SEI) and the backscattered electron imaging modes, the distribution of chemical composition by the electron-dispersive spectroscopy (EDS) mapping, and grain structures by the electron backscatter diffraction technique. Moreover, the SEI and EDS techniques completed the failure analysis of tensile tests. Nanoindentations were also performed to assist phase identification analysis in the densified microstructure. Different geometries in the micron scale (micro wall half-reservoirs, micro channel half-flanges, convex and concave micro gear configurations, and micro tensile specimens) were selected for replication. Shaping limitations were attributed to the geometry, convex or concave, and the stiffness of the die. Micro gear and micro wall configurations were shaped using a stiffer elastomer (T = 230 °C and P = 11.3 to 14 MPa for 45 min) and a metallic die (T = 170 °C and P = 11.3 MPa for 10 min), respectively. The shaping of concave geometries was achieved regardless of the metal powder concentration, 60 and 65 vol.%. Densified parts retained the replicated micro configurations after long periods of thermal debinding and sintering, with densification above 95%. The chemical composition in sintered parts was homogeneous. The microstructure was principally composed of austenitic grains. The 316L stainless steel sintered part produced through MPHE presented an ultimate tensile strength of 458 ± 15 MPa, similar to that of a wrought AISI 316L alloy; the fracture type in the micro tensile specimen was ductile.