Characterisation of additively manufactured Inconel 718 alloy by using electrolytic extraction

Abstract: The formation of non-metallic inclusions (NMIs) are common in all steel grades and it is not possible  as  of  today  to  be able  to  remove  all  of them.  The  inclusions  are  categorised  into endogenous (oxides, nitrides, sulfides, carbides, and phosphides), and exogenous (entrapment of  nonmetals:  slag, mold).  Their  morphology,  size,  number,  chemical  composition,  and location are  important  parameters  which need to be classified and controlled as they have a big impact on the final properties of steel grades. In this study, only endogenous NMIs for the superalloy  Inconel  718 were  investigated.  An electrolytic extraction (EE) was performed to see if this was a suitable method to be used for the study of the NMIs in powder particles, and in a metal sample produced from metal powder. The results were compared with NMIs found in conventional  Inconel  718.  The  powder  particles  and  the  NMIs  were investigated  on  a scanning  electron  microscope  (SEM)  for  mentioned parameters.  When  the  NMIs  were classified,  it  was  found  that  four inclusions  (Al2O3,TiNb-N,  NbTi-C,  NbTiCrMo-C) were found in the metal sample produced by the powder and three (TiNb-N, NbTi-C, NbTiCr-C) in the conventional  sample.  Two  inclusion  types  were  the  same  for  both  alloy 718  metal samples,  but all inclusions differed in number, size, morphology, and location. Furthermore, the  EE  method  did  not  work for  the powder particles themselves, it was concluded that the EE method was suitable for the metal sample made out of metal powder, but not the powder particles.  The  EE method  needs  to  be  further  developed  and  adapted  for  metal powder analysis.