Electron beam melting of Ti-6Al-4V lattice structures: correlation between post heat treatment and mechanical properties

Giuseppe Del Guercio,Abdollah Saboori,Manuela Galati

doi:10.1007/s00170-021-07619-w

Giuseppe Del Guercio, Abdollah Saboori + Show 1 more

Open Access

https://doi.org/10.1007/s00170-021-07619-w

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Abstract

Additive manufacturing processes are considered advanced manufacturing methods. It would be possible to produce complex shape components from a computer-aided design model in a layer-by-layer manner. As one of the complex geometries, lattice structures could attract lots of attention for both medical and industrial applications. In these structures, besides cell size and cell type, the microstructure of lattice structures can play a key role in these structures’ mechanical performance. On the other hand, heat treatment has a significant influence on the mechanical properties of the material. Therefore, in this work, the effect of the heat treatments on the microstructure and mechanical behaviour of Ti-6Al-4V lattice structures manufactured by electron beam melting was analysed. The main mechanical properties were compared with the Ashby and Gibson model. It is very interesting to notice that a more homogeneous failure mode was found for the heat-treated samples. The structures’ relative density was the main factor influencing the mechanical performance of the heat-treated samples. It is also found that the heat treatments were able to preserve the stiffness and the compressive strength of the lattice structures. Besides, an increment of both the elongation at failure and the absorbed energy was obtained after the heat treatments. Microstructure analysis of the heat-treated samples confirms the increment of ductility of the heat-treated samples with respect to the as-built one.

Highlights

Additive manufacturing (AM) is “a process of joining materials to obtain components from 3D model data using a layer upon layer approach” [1,2,3,4,5]
According to Ashby and Gibson [24], the results showed that three main trends characterize the stress-strain trend: (1) elastic behaviour of the lattice structures, (2) progressive collapse of the layers up to the point where (3) the structure has the same behaviour of the bulk material
The lattice structures manufactured in larger cell sizes showed the worst mechanical performances, in terms of both Young’s modulus and UCS*, with respect to those produced with smaller cell size [38, 41, 43, 44]

Summary

Introduction

Additive manufacturing (AM) is “a process of joining materials to obtain components from 3D model data using a layer upon layer approach” [1,2,3,4,5]. On the other hand, during the production of Ti-6Al-4V alloy via the EBM process due to the presence of a preheating phase before the melting, the temperature inside the building chamber reaches values of 650–750 °C for this specific alloy [16, 18, 19] These working conditions ensure small thermal shrinkages, Int J Adv Manuf Technol (2021) 116:3535–3547 and the powder bed results in enough strength to support the construction of the overhang part and limiting the use of supports [20, 21]. EBM makes possible the production of so-called micro-architectured components These parts, known as cellular structures, are of considerable interest because of the opportunity to achieve a singular combination of lightness and high mechanical properties compared to their corresponding bulk ones [22, 23]. Ashby and Gibson [24] proposed a model to describe the mechanical performances of lattice structures, in which a generic relative property can be expressed, in a bi-logarithmic diagram, as a linear relationship of the lattice relative density

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