Effect of build thickness and geometry on quasi-static and fatigue behavior of Ti-6Al-4V produced by Electron Beam Melting

N Razavi,B Van Hooreweder,F Berto

doi:10.1016/j.addma.2020.101426

N Razavi, B Van Hooreweder + Show 1 more

Open Access

https://doi.org/10.1016/j.addma.2020.101426

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Abstract

The geometry and material properties of additively manufactured (AM) parts are closely related in a way that any alteration in geometry of the part will change the underlying manufacturing strategy. This in turn, affects the microstructure and consequently, the mechanical behavior of material. This paper aims to evaluate the effect of the AM part’s thickness and geometry on microstructure, surface roughness, and mechanical properties under quasi-static and fatigue loading conditions by performing experimental tests. A series of Ti-6Al-4V specimens with three different thicknesses and two different geometries were fabricated using electron beam melting (EBM). The results of microstructural analyses revealed that specimens with lower build thickness experience finer grain size, higher microhardness, and lower elongation at failure. Although the microstructure of the produced parts was strongly affected by the build thickness, different surface to volume ratios eliminated the effect of microstructural differences and governed the fatigue properties of the parts. The size effect on the microstructural features, geometrical appearance, mechanical properties of the AM parts should be considered for the design and failure analysis of complex structures.

Highlights

Additive Manufacturing (AM) technology allows direct conversion of digital unprecedented complex designs into physical products within one completely autonomous production step while avoiding setup time and the use of tools
According to the optical images, the lamellar grains mainly exist around the boundary of the prior beta grains, while the basketweave and equiaxed grains were mostly observed in the inner region of the prior grains
Fatigue behavior of electron beam melting (EBM) Ti-6Al-4V specimens with different build thicknesses and in the presence of geometrical discontinuities has been evaluated in this study

Summary

Introduction

Additive Manufacturing (AM) technology allows direct conversion of digital unprecedented complex designs into physical products within one completely autonomous production step while avoiding setup time and the use of tools. Despite the ability of AM technology in fabrication of geometrically complex components, the material properties of the produced AM parts are closely associated with the input geometry. Different geometries or scales of the given geometry change the way that the AM machine performs its building routine, affecting the printing strategy and, the microstructure and mechanical properties of the resulting solid [4]. On the other hand, depending on the underlying manufacturing strategy, anisotropy, presence of residual stresses, geometrical imperfections, and poor surface conditions are commonly reported for AM parts, which can be largely eliminated using different post-processing techniques [5,6,7,8,9]. Two main categories of AM technologies have been developed, namely Powder Bed Fusion (PBF) [10] (e.g. Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), and Electron Beam Melting (EBM)) and Direct Energy Deposition (DED) [11] (e.g. Laser Engineered Net Shaping (LENS), Directed Light Fabrication (DLF), Direct Metal Deposition (DMD), and Laser Cladding (LC))

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