Development and Characterization of Micro-plasma Additive Manufacturing Process for Inconel 718 Superalloy

A micro-plasma process parameters were investigated for its capability in additive manufacturing (AM). In this study, the effects of two arc and wire feed modes on dimensional consistency and hardness were first examined. Subsequently, one set of the specimens was further subjected to oxidation tests and the results were compared to that from conventional wrought Inconel 718. It was found that all four processes could produce crack free samples without measurable distortion. After heat treatment, the hardness of the samples varies from 403 to 440 HV. The oxidation tests at 900°C yielded similar weight change for AM Inconel 718 and its counterpart wrought alloy; however, the rate constant for wrought alloy is slightly higher. Microstructural analysis with SEM and EDS revealed a dendritic structure in the AM Inconel 718 and the presence of Nb-rich compounds in the interdendritic region. The polycrystal grain structure is not delineated in AM material as that in wrought 718. With the increase of exposure time, the oxide layer continues to increase at a higher rate, along with a sublayer of Ni₃Nb above the metal substrate. In addition, after 200 hours, the wrought alloy developed porous chromia while AM material exhibited uneven oxide thickness.