Oxidation Behavior of Ni-Based Alloys Fabricated by Additive Manufacturing

Abstract

Additive manufacturing (AM) allows for the fabrication of complex near net shape components, leading to new design opportunities and significant savings, for example by decreasing tooling and materials cost or by accelerating prototype development. New Ni-based alloy heat exchangers with thin-walled areas exposed to hot gases will, however, suffer from corrosion degradation, and the high temperature oxidation performance of AM alloys needs to be addressed. Alloy N06002 (Ni-22Cr-18Fe-9Mo) fabricated by electron beam melting (EBM) and selective laser melting (SLM) along with EBM-fabricated N07247 and modified N07247 were cyclic oxidation tested at 950°C in air and humid air for durations ranging from 100 h to 5000 h. Increased spallation rates were observed initially for the AM N06002 alloys in comparison with wrought N06002 alloy because of the AM alloy specific microstructures. After ∼2000 h, the situation was reversed with significant spallation observed for the wrought HX alloy only. Low mass gains were observed for the EBM N07247 alloys at 950°C, but thick oxide scales were observed locally due to the presence of oxidized cracks. Massive oxidation of these cracks led to fast oxidation rates at 1100°C.