# Evaluating the Reliability of Powder Bed Fusion for Biomedical Materials: An Experimental Approach
## 2 Materials and Methods  
### Materials  
This study focuses on the following biomaterial powders: pure titanium, Ti6 Al7 Nb, CoCr, and CoCrWMo. These materials are widely used in medical applications. All these powders were obtained by gas-atomization process, and most of the particles are nearly spherical. Their size distribution was calculated according to ISO 13320 [26], and d-value indicates that 90% of particles are finer than this diameter (d90). Also, the flowability of powder was measured using a hall flowmeter funnel with an orifice of 2.5 mm and calculating the flow rate (s/50 g). The hall flow rate was expressed as the time required for a 50 g powder sample to be discharged by gravitational force through the flowmeter funnel (ASTM B213 [27]). The first material considered was pure titanium (Ti) powder named TILOP 45, provided by Osaka Titanium Technologies (Amagasaki, Japan). This material has 90% of particles finer than 46 um (d90), and its melting point is 1670 \({}^{\circ}\)C, which is included in the Titanium Grade I category (99.5% Ti). The follow ability of this powder was 29.1 s per 50 g.  
Further experimental investigations were undertaken for the other materials. The Ti6 Al7 Nb alloy was developed in 1977 by a team of researchers at Gebruder Sulzer in Winterthur, Switzerland [28]. This alloy is mainly used for orthopedic applications, such as total hip replacement systems, fracture fixation plates, intramedullary rods and nails, spinal devices, screws, and wires. The major benefits of this Ti alloy are its high tensile strength and good biocompatibility. The chemical composition of Ti6 Al7 Nb powder, supplied by TLS Spezialpulver Technik (Niedernberg, Germany), is presented in Table 1. The diameter of 90% of granules was lower than 43 um (d90), and the hall flow rate was 33.7 s per 50 g.  
Cobalt-based alloys have been extensively used in cast and hard-facing forms over the last decades due to their excellent corrosion resistance, biocompatibility, and mechanical strength [29]. Among them, cobalt-chromium (CoCr) alloys have shown remarkable versatility and durability, making them a popular choice for orthopedic implants [4]. Additionally, CoCr alloys are widely used in dental restorations, including customized abutments, crowns, and bridges in both anterior and posterior regions, as well as in telescope or conical crowns and screw-retained restorations [29; 30; 31].  
\begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline
**Chemical Element** & **Al** & **Nb** & **Ta** & **Fe** & **O** & **C** & **N** & **H** & **Ti** \\ \hline Maximum weight percentage [\%] & 6.5 & 7.5 & 0.5 & 0.25 & 0.20 & 0.08 & 0.05 & 0.009 & 84.9 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition of the Ti6 Al7 Nb powder.  
The specific chemical composition of the CoCr powder discussed in this study (CoCr28 Mo6) complies with the ASTM F75 standard [32]. Details regarding the mass percentages of each chemical element are provided in Table 2. This powder was supplied by MCP HEK Tooling (Lubeck, Germany), with particle diameter lower than 45 \(\upmu\)m (d90). The followability of this powder was 35.7 s per 50 g.  
The CoCrWMo powder used in this study complies with the chemical composition requirements specified in ISO 22674 [33] (Dentistry--Metallic materials for restoration and fixed or mobile devices). The mass percentages of each chemical component are listed in Table 3. Commercially known as Starbond CoS 55, this powder is supplied by ReLaizer BmpH (Borchen, Germany--since 2017, ReaLizer GmbH has been acquired by DMG MORI, Bielefeld, Germany). The grain size of the 90% of them was finer than 50 \(\upmu\)m, and the hall flow rate was 23.9 s per 50 g.