In situ microstructure analysis of Inconel 625 during laser powder bed fusion

Felix Schmeiser,Christian Wagner,Walter Reimers,Eckart Uhlmann,Erwin Krohmer,Norbert Schell

doi:10.1007/s10853-021-06577-8

Abstract

Laser powder bed fusion is an additive manufacturing process that employs highly focused laser radiation for selective melting of a metal powder bed. This process entails a complex heat flow and thermal management that results in characteristic, often highly textured microstructures, which lead to mechanical anisotropy. In this study, high-energy X-ray diffraction experiments were carried out to illuminate the formation and evolution of microstructural features during LPBF. The nickel-base alloy Inconel 625 was used for in situ experiments using a custom LPBF system designed for these investigations. The diffraction patterns yielded results regarding texture, lattice defects, recrystallization, and chemical segregation. A combination of high laser power and scanning speed results in a strong preferred crystallographic orientation, while low laser power and scanning speed showed no clear texture. The observation of a constant gauge volume revealed solid-state texture changes without remelting. They were related to in situ recrystallization processes caused by the repeated laser scanning. After recrystallization, the formation and growth of segregations were deduced from an increasing diffraction peak asymmetry and confirmed by ex situ scanning transmission electron microscopy.Graphical

Highlights

Additive manufacturing facilitates the fabrication of arbitrarily complex geometries and tailored material properties using a range of different materials
Azimuths of 0°, 180°, and 360° correspond to transverse direction (TD), while 90° and 270° correspond to building direction (BD)
This study shows that in situ diffraction experiments are a viable tool for texture analysis during laser powder bed fusion

Summary

Introduction

Additive manufacturing facilitates the fabrication of arbitrarily complex geometries and tailored material properties using a range of different materials. Laser powder bed fusion (LPBF) is a process especially suited for the production of metal parts. LPBF employs focused laser radiation to melt a powder bed selectively. The material solidifies immediately, and a new powder layer is applied, resulting in the layer-wise fabrication of the desired geometry. The selective and both locally and temporally varying energy input leads to a complex heat flow and temperature distribution, which govern the solidification and grain growth regime. Precise knowledge of the interaction of laser parameters and microstructural response within the workpiece opens up the prospect of tailored microstructure design

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Discussion

Conclusion