Diffusion Module (DICTRA) and TCNI8 Used in Assessment of Additive Manufacturing

A new publication in the May issue of Acta Materialia uses the Diffusion Module (DICTRA) with TCNI8, the Ni-based superalloys database, to investigate how additive manufacturing can improve heat treatment processes in the Ni-based superalloy Inconel 625. 

The article, Application of finite element, phase-field, and CALPHAD-based methods to additive manufacturing of Ni-based superalloys, uses three numerical simulation methods to test different aspects of additive manufacturing in heat treatment and compares the results against experimental observations. Thermo-Calc’s Diffusion Module (DICTRA), along with the Ni-based superalloys database, TCNI8, is used to predict microsegregation during solidification.

Additive manufacturing has shown a lot of promise in materials science over the past few years to improve development processes and bring down costs of development and manufacturing, but, as the paper points out in its introduction, Finding suitable stress-relieving and homogenizing heat treatments without sacrificing strength is an iterative process”, making it slow and costly, but, as the paper goes on, “numerical modeling can help narrow the search.”

The paper was written by Trevor Kellera, Greta Lindwalla, Supriyo Ghosha, Li Maa, Brandon M. Lanec, Fan Zhangd, Ursula R. Kattnera, Eric A. Lassa, Jarred C. Heigelc, Yaakov Idella, Maureen E. Williamsa, Andrew J. Allend, Jonathan E. Guyera and Lyle E. Levinea.

Abstract

Numerical simulations are used in this work to investigate aspects of microstructure and microsegregation during rapid solidification of a Ni-based superalloy in a laser powder bed fusion additive manufacturing process. Thermal modeling by finite element analysis simulates the laser melt pool, with surface temperatures in agreement with in situ thermographic measurements on Inconel 625. Geometric and thermal features of the simulated melt pools are extracted and used in subsequent mesoscale simulations. Solidification in the melt pool is simulated on two length scales. For the multicomponent alloy Inconel 625, microsegregation between dendrite arms is calculated using the Scheil-Gulliver solidification model and DICTRA software. Phase-field simulations, using Ni–Nb as a binary analogue to Inconel 625, produced microstructures with primary cellular/dendritic arm spacings in agreement with measured spacings in experimentally observed microstructures and a lesser extent of microsegregation than predicted by DICTRA simulations. The composition profiles are used to compare thermodynamic driving forces for nucleation against experimentally observed precipitates identified by electron and X-ray diffraction analyses. Our analysis lists the precipitates that may form from FCC phase of enriched interdendritic compositions and compares these against experimentally observed phases from 1 h heat treatments at two temperatures: stress relief at 1143 K (870° C) or homogenization at 1423 K (1150° C).