PSI - Issue 13

J.-P. Brüggemann et al. / Procedia Structural Integrity 13 (2018) 317–321 J.-P. Brüggemann et al. / Structural Integrity Procedia 00 (2018) 000 – 000

318

2

1. Introduction

Selective Laser Melting (SLM) is an additive manufacturing technology that enables the production of metallic structures with a high complexity, Gebhardt (2016). The parts are made of metal powder with a density of nearly 100%, Leuders et al. (2013), Riemer et al. (2014) and Thöne et al. (2012). It is a layer-wise process in which the three steps of coating, irradiation and lowering are repeated so that the structure grows stepwise, see Fig. 1. One important element in lightweight construction is given by the high freedom of design using additive manufacturing technologies, Gibson et al. (2010). This new technology offers the opportunity to produce complex and delicate structures, e.g. undercuts, lattice structures or topology optimized parts, Gebhardt (2013) and Riemer (2015).

Fig. 1. SLM-process, Brüggemann et al. (2016).

Another element is the use of lightweight materials – materials with low density and good mechanical properties. A typical lightweight material is titanium alloy Ti-6Al-4V. Due to its relatively low density combined with good strength properties and high fatigue strength, the material meets the most important requirements for a lightweight material, Peters and Leyens (2010). Typical application areas are automotive and aircraft industries. Because of the biocompatibility the alloy is also of great importance for medical technology, Jackson and Ahmed (2007) or Schramm et al. (2016). Ti-6Al-4V is already safely processable by SLM and Leuders et al. (2013) as well as Riemer (2015) have already analyzed the material characteristics . The material’s lightweight potential has been shown in the optimization of different bicycle and medical components, Riemer et al. (2015). In addition, the positive influence of the 1073.15 K heat treatment to reduce the process-induced residual stresses is also known. Furthermore, hot-isostatic pressing leads to the reduction of pores and thus to the improvement of material performance. Riemer (2015) also found that the additively processed Ti-6Al-4V alloy has almost isotropic material properties in the heat-treated condition, so that only a slight influence of the building direction can be observed. To use this alloy for the manufacturing of reliable components the influence of varied process parameters on the material characteristics has to be known. In this context the impact of varied powder particle size distribution on the material characteristics of laser-melted Ti-6Al-4V is investigated. In order to increase the bulk density and, thus, to generate a denser powder bed for the manufacturing process, the particle size distribution (PSD) of the powder is changed to lower values. Therefore it is to determine whether a changed particle size distribution has an influence on the material characteristics of Ti-6Al-4V. As a first step in these investigations the particle size distributions (PSDs) of two powder lots are analyzed, see Fig. 2a. Material characteristics for the powder with a median particle size value d (0.5) = 38.9 µm are already determined by Riemer (2015) and Leuders et al. (2013). The new powder lot has got a significantly smaller d (0.5) value of 31.7 µm. Furthermore, the variance in the particle sizes is increased. For the manufacturing of specimens, Ti-6Al-4V powder was produced by gas atomization. The particle shape of the new powder lot is analyzed using a scanning electron microscope (SEM) image, see Fig. 2b. A homogenous spherical particle shape can be detected which influences the processability positively. 2. Experimental details