Mössbauer Spectroscopy for Additive Manufacturing by Selective Laser Melting

Abstract

Selective laser melting (SLM) is a technology of layer-by-layer additive manufacturing using a laser. This technology allows one to get complex-shaped, three-dimensional (3D) specimens directly from metal powder. In this technology, various metal powders are used, including different steels. Stainless steel 1.4404 (CL20ES) and maraging steel 1.2709 (CL50WS) have been investigated. The surface of samples manufactured from CL20ES and CL50WS powders by SLM (with and without combination sandblasting and annealing) was studied by conversion X-ray Mössbauer spectroscopy (CXMS) and conversion electron Mössbauer spectroscopy (CEMS). The surface morphology, elemental composition, and structure were examined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD). Samples with sandblasted (corundum powder) and non-sandblasted surfaces were annealed at 540 °C (CL50WS) or 550 °C (CL20ES) for 6 h in air. Oxidation processes on surfaces of samples manufactured from both initial powders were observed after post-process annealing by CEMS and CXMS, as well as confirmed by XRD. The transformation of the austenitic to ferritic phase was observed in a sandblasted and annealed CL20ES sample by CEMS and XRD.