Large-area surface topography analysis of additively manufactured metallic materials using directional reflectance microscopy

Abstract

The surface topography of additively manufactured metals carries valuable information about the mechanisms involved during materials formation. As such, it may be used as an indirect measure of materials quality, both during and after production. Standard surface analysis techniques, however, are characterized by narrow field of view and low data acquisition rate, making them unsuited to rapidly characterize large areas. In this work, we describe a novel method to quantify the three-dimensional surface topography of a 1 cm3 metal sample produced by selective laser melting. The method relies on directional reflectance microscopy—an optical technique that quantifies surface reflectance as a function of the illumination angle. By fitting the directional reflectance measurements with a reflection model, we map the surface normal orientation and microscopic surface roughness over the entire sample surface at a spatial resolution of ~5.3μm. We also discuss the possibility of integrating our method within the additive process by reducing the number of measurements required to reconstruct surface topography. Because of the inexpensive equipment employed, the large field of view measurements, and rapid data acquisition speed, we believe that our method is a competitive alternative for analysing the surface topography—and thus the quality—of additively manufactured metals both during and after production.