In Situ Observation of γ′ Phase Transformation Dynamics During Selective Laser Melting of CMSX‐4

Benjamin Wahlmann,Eckart Uhlmann,Erwin Krohmer,Carolin Körner,Christoph Breuning,Peter Staron,Norbert Schell

doi:10.1002/adem.202100112

Abstract

Additive manufacturing (AM) of superalloys has been attracting increasing interest. While most studies focus on the processability and mechanical properties of the finished product, it is also necessary to understand the phase transformations during the consecutive melting processes. Herein, the precipitation and dissolution of the γ′ phase in the Ni‐base superalloy CMSX‐4 in a selective laser melting process is reported. These phase transformations are studied in situ by small‐angle X‐ray scattering (SAXS) during AM. Concurrent wide‐angle X‐ray scattering (WAXS) provides information on the evolution of lattice parameters and temperature during the process. Additional thermal and thermodynamic simulations are carried out to support the experiments. The investigations are focused on the influence of different beam scanning strategies as well as the effect of laser power and scanning speed on the phase transformation dynamics. Due to the high cooling and heating rates inherent to AM, phase transformations occur far off equilibrium. Both precipitation and dissolution of γ′ phase are observed. The scan strategies are shown to have a considerable effect on the phase transformation dynamics, which exceed the impact of the beam parameters. The capability of combined SAXS and WAXS for the in situ study of phase transformations in AM processes is demonstrated.

Highlights

Introduction interestWhile most studies focus on the processability and mechanical properties of the finished product, it is necessary to understand the phase transformations during the consecutive melting processes
We investigated the transformation dynamics of the γ 0 phase in the nickel-base superalloy CMSX-4 while imposing a thermal profile similar to that occurring in SEBM, but with lower heating and cooling speed.[21]
We varied three parameters: beam power P, scan speed vs, and the scanning pattern. These governed the thermal history of the process and, the kinetics and dynamics of phase transformations

Summary

Introduction

Introduction interestWhile most studies focus on the processability and mechanical properties of the finished product, it is necessary to understand the phase transformations during the consecutive melting processes. The precipitation and dissolution of the γ 0 phase in the Ni-base superalloy CMSX-4 in a selective laser melting process is reported. These phase transformations are Additive manufacturing (AM) offers new ways to fabricate high-performance alloys, e.g., nickel-base superalloys, for application in the hottest sections of jet engines or gas turbines. Powder-bed-based techniques such as selective electron beam melting studied in situ by small-angle X-ray scattering (SAXS) during AM. The investigations are focused on the influence of different beam scanning strategies as well as the effect of laser power and scanning speed on the phase transallow great geometric design freedom and provide the ability to fine-tune microstructural properties by intelligent beam deflection and heat management. Due to the high cooling and heating rates inherent to AM, beam energies, and deflection speeds

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