The Influence of Annealing Temperature and Time on the Formation of delta-Phase in Additively-Manufactured Inconel 625

Published: May 10, 2018

Author(s)

Mark R. Stoudt, Eric Lass, Daniel S. Ng, Maureen E. Williams, Fan Zhang, Carelyn E. Campbell, Greta Lindwall, Lyle E. Levine

Abstract

This research evaluated the kinetics of delta-phase growth in laser powder bed additively- manufactured (AM) Inconel 625 during post-build stress-relief heat treatments. The temperatures ranged between 650 °C to 1050 °C, and the times from 0.25 h to 168 h. The presence of delta-phase was verified for each temperature/time combination through multiple techniques. A conventional TTT diagram was constructed from the time-temperature data. Comparison to the growth in wrought IN625 with a similar nominal composition revealed that delta-phase formation occurred at least two orders of magnitude faster in the AM IN625. The results of this study also revealed that the segregated microstructure in the as-built condition has a strong influence on the kinetics of delta-phase formation in AM IN625 as compared to a homogenized material. Since control of the delta-phase growth is essential for reliable prediction of the performance of IN625 components in service, avoiding heat treatments that promote the formation of delta-phase in AM components that are not homogenized is highly recommended. This will be particularly true at elevated temperatures where the microstructural stability and the consistency of mechanical properties are more likely to be affected by the presence of delta-phase.
Citation: Metallurgical Transactions A-Physical Metallurgy and Materials Science
Volume: 49
Issue: 7
Pub Type: Journals

Keywords

Additive manufacturing, Ni-based alloys, Inconel 625, Time-temperature-transformation diagram
Created May 10, 2018, Updated November 10, 2018