Electron beam-powder bed fusion of Alloy 718: Effect of hot isostatic pressing and thermal spraying on microstructural characteristics and oxidation performance

Abstract

Alloy 718 manufactured via electron beam-powder bed fusion (EB-PBF) was coated with a thermally- sprayed NiCoCrAlY coating for enhanced oxidation protection. A high-velocity air fuel technique was used to deposit the coating. The specimens were then subjected to hot isostatic pressing (HIP). Oxidation of the specimens was undertaken in an ambient air environment at 650 and 800 °C for 168 h. The oxidation performance of EB-PBF-built Alloy 718 was improved after the deposition of the coating, particularly at 800 °C. In this temperature, a thick Cr-rich oxide scale was found on the uncoated Alloy 718 specimen, whereas a thin and stable Al-rich oxide scale was formed on the surface of the coated specimen. HIPing enhanced the oxidation resistance of uncoated Alloy 718; however, the oxidation behavior of coated Alloy 718 was negatively affected by HIPing.