Emissivity Measurements of Metals Used in Wire-Arc-Directed Energy Deposition Processes

Accurate temperature measurement is a key parameter that determines the quality of additive manufactured components in directed energy deposition processes. Optical pyrometers which are used to provide in-process temperature data require accurate emissivity data of the metal surface. Process-specific emissivity data for metals used in these processes is not readily available. This paper provides the emissivity of a variety of metals used in wire-arc directed energy deposition processes. For the first time, the test samples were fabricated using typical deposition processes and systems. The metals evaluated were titanium alloy (Ti-6Al-4V), Inconel 718, mild steel, aluminum alloy 2319, and nickel aluminum bronze. At ambient temperature, the measured normal emissivity was 0.26–0.28 for Ti-6Al-4V; for Inconel 718, it was 0.45–0.54; for mild steel, it was 0.4–0.72; for aluminum 2319, it was 0.14; and for nickel aluminum bronze, it was 0.35. The approximate emissivity values are also given over the temperature range 20–1400 °C. The effect of residual oxygen in the shield gas on emissivity is explored for the first time. The spectrophotometric technique was used to measure the metal thermo-optical properties.