Variation of texture anisotropy and hardness with build parameters and wall height in directed-energy-deposited 316L steel

Lova Chechik,Felicity Freeman,Peter Honniball,Jon Raffe Willmott,Iain Todd,Leigh Russell Stanger,Nicholas Andrew Boone,Gavin Baxter

doi:10.1016/j.addma.2020.101806

Lova Chechik, Felicity Freeman + Show 6 more

Open Access

https://doi.org/10.1016/j.addma.2020.101806

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Abstract

Directed energy deposition (DED) is an emerging technology with repair applications in critical aerospace components. Mechanical properties of DED components have been shown to vary significantly through a part, making it difficult to achieve the level of process control required for these applications. Using thermal data captured in-situ, cooling rates and melt pool dimensions were calculated and related to the final grain structure, captured by EBSD. The changes in cooling rate explain the microstructural variation between different processing parameters and through the build height. A new approach, using a cumulative anisotropy factor was implemented and correlates the variation in hardness with grain structure. Two regimes were found depending on the linear heat input in 316L, with high linear heat input resulting in great amounts of mechanical anisotropy on the component level. The relationships between thermal signature and mechanical properties suggest close control of anisotropy could be achieved by monitoring and controlling the melt pool size using a coaxial camera. • Walls built with high heat input shown to have significantly increased grain structure anisotropy. • Grain structure explained through cooling rate and melt pool size, varying with both processing parameters and build height. • Hardness shown to be directly related to grain structure, suggesting it can be controlled using the thermal signature.

Highlights

Laser Directed Energy Deposition (DED), is a branch of metal additive manufacturing (AM) where components are created layer-by-layer
DED has been implemented with a range of alloys, including Inconel 718 [2], Al 4047 [3] and 316L stainless steel [4,5], the latter being the focus of this paper
There is a large variation in grain size between samples, Walls A1 and B have smaller average grain size and less variation than high H walls (Table 3)

Summary

Introduction

Laser Directed Energy Deposition (DED), is a branch of metal additive manufacturing (AM) where components are created layer-by-layer. The focus of this paper will be on blown powder laser DED in which a powder feedstock is deposited into a molten pool created by a laser. This process experiences rapid cooling, with cooling rates estimated on the order of 103–104 K/s, significantly quicker than traditional manufacturing processes [1]. DED has been implemented with a range of alloys, including Inconel 718 [2], Al 4047 [3] and 316L stainless steel [4,5], the latter being the focus of this paper. The microstructure depends on the cooling rate and the thermal gradient; slight variations in the process or part geometry make it difficult to achieve the high level of microstructural control required [9]

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Discussion

Conclusion