Roughness Analysis of Powder-Bed Fused Nickel–Titanium Surfaces with Chemical Etching Enhancement by a Safe Aqueous Fluoride Solution

Surface treatments for metal additive manufacturing have been increasingly explored to remedy undesired high surface roughness in as-printed components, which can hinder intended performance. Chemical etching is a simple method of improving surface quality in mechanically inaccessible, internal, delicate, or otherwise complex regions in such parts. In this work, the chemical etching effectiveness of the sodium fluoride and ammonium persulfate solution, known as Multi-Etch , was explored on printed nickel–titanium shape memory alloy surfaces at various exposure temperatures and times. Titanium-containing alloys often require solutions of extremely hazardous hydrofluoric acid (HF), which prompts specialized safety infrastructure; in contrast, the etchant herein is a substantially safer titanium etchant alternative. Nickel–titanium parts were generated via laser powder-bed fusion (LPBF) with geometries consisting of exterior surfaces, unsupported overhangs, and internal channels. Surface morphologies were investigated with scanning electron microscopy and optical surface profilometers. A particle size analysis of partially fused particles on as-printed surfaces was performed. Various areal surface texture parameters were considered to properly compare the as-printed and etched surfaces, of which the density of peaks ( S pd ), peak curvature ( S pc ), slope ( S dq ), and developed interfacial area ratio ( S dr ) were drastically reduced. An effective reduction of surface roughness, without detrimental loss in mass and spatial dimensions, was developed by etching at temperatures ranging from 40 to 60 °C for at least one hour. Metallurgical inclusions and melt track borders were preferentially etched at lower temperatures. The etching treatment herein represents an effective process for improving the surface quality of powder-bed fused nickel–titanium.