LPBF Ti–6Al–4V cellular materials with hierarchical porosity

Details

Supervisors

Hannard, Florent ; Simar, Aude

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil biomédical, à finalité spécialisée

Abstract

Lattice structures can be used for multiple applications as for example as bone implants. The development of such implants remains challenging as they must present several important properties such as high fatigue resistance, be non-toxic, non-carcinogenic and promote osseointegration [1, 2]. Metallic implants are commonly used, especially titanium based ones and are fabricated using additive manufacturing such as Laser Powder Bed Fusion. The development is still limited due to uncontrollable AM defects such as internal pores. While the traditional approach consists in fighting against these defects, a porosity engineering approach i.e. generating porosity at selected locations, will be applied in this thesis. The goal is to build cellular structures with a porosity hierarchy, i.e. a structure with two porosity scales. This porosity is achieved by the use of a set of two printing parameters, where one is at the beginning of keyhole mode. Such an intentional introduction of defects may seem controversial, but could in the end even have a positive effect on the mechanical behaviour of lattice structures. These structures mainly fail by two main failure modes: layer-by-layer and diagonal shear band [3]. For both failure modes, only struts in the localization band participate in the deformation and buckle under the localised stress concentration. The goal is to add weaker zones throughout the structure in order to postpone structure collapse by introducing a programmed deformation pattern. This project concentrates first on the print of architectured struts, simple cylindrical structural element of a lattice structure. The resulting porosity will be characterized using different microstructural characterization methods as for example scanning electron microscopy and tomography. Additionally, the architectured struts are tested mechanically under compression. Finally, a first lattice structure will be printed and tested under compression as a proof of concept. Indeed, the addition of weaker zones seems to alter the mechanical response in the single struts and even in the lattice structures. Although, the effect in the lattice structure is masked by the nodes which still govern the failure mode, this project allows to draw first positive conclusions regarding voluntarily introduction of pores in lattice structures.