Effect of different heat treatments on the microstructure of In718 processed by additive manufacturing

Tuesday, May 5, 2020: 5:00 PM
Pasadena (Palm Springs Convention Center)
Dr. J. A. Villada , CIDESI, Queretaro, Mexico
Mr. Julio Cesar Franco , CIDESI, Queretaro, QA, Mexico
Dr. E. Martinez-Franco , CIDESI, Queretaro, QA, Mexico
Dr. D. G. Espinosa-Arbelaez , CIDESI, Queretaro, QA, Mexico
Dr. J.M. Alvarado-Orozco , Centro de Ingeniería y Desarrollo Industrial, Queretaro, QA, Mexico
Currently, additive manufacturing (AM) technologies are using, as feedstock, alloys that have been designed for conventional processes such as wrought or casting. Contrary to these processes, AM processes are typically associated with rapid cooling rates, large thermal gradients and multiple reheat cycles. Under these conditions, the behavior of conventional materials could be quite different, giving rise to problems such as high levels of residual stress and microsegregation during solidification, leading local inhomogeneities in the alloys composition. In addition, heat treatment processes, also designed for conventionally manufactured parts, are currently applied to AM pieces, As a result, problems such as deleterious phases forming during a heat treatment may result.

To reveal the inherent differences between the microstructure of parts manufactured by conventional and AM process, in the present work, systematic studies on the element segregation, phase formation and mechanical properties of In718, manufactured by AM, are provided. In718 is a Ni-based superalloy with excellent high yield tensile and creep-rupture properties, used in parts for jet engines such as wheels and buckets. The phase that is responsible for high mechanical properties of alloy IN718 is the γ″ (Ni3Nb, D022) phase. This phase is metastable with respect to the detrimental phase δ (Ni3Nb, D0a). Due to the Nb is the most important element controlling the formation of the γ″ and δ phases, it was used as the tracer element for the evaluation of the element segregation and phase formation.

The Thermo-Calc software and its modules (Dictra and TCPrisma) were used to discuss the microstructure observed. The TTT diagrams and volume fraction of the most important phase were obtained. From the results modifications to the standard heat treatment are proposed. The effects of conventional and modified heat treatments on the microstructure are evaluated.

See more of: Additive Manufacturing IV-b
See more of: Technical Program