The additive manufacturing technology is applied for producing complexly shaped components by melting fine metal powders layer by layer according to a computer-aided design (CAD) model. The three dimensional (3D) printed end-use parts have unique properties due to the layered creation. Compared to the machining, casting or forging metals, the mechanical properties, material density, and residual stress more performant in the parts fabricated by 3D printing.

Nowadays, there are a number of different technologies, such as directed energy deposition and powder bed fusion, are applied for metal 3D printing. Nowadays, the laser powder bed fusion (LPBF) process is one of the advanced powder bed fusion methods for additive manufacturing of small-sized parts instead of conventional metal forming methods. In particular, the LPBF process is attractive for the aerospace and biomedical industries offering a unique perspective [1–3]. The complexly shaped metal components can be fabricated directly using CAD model reducing material waste and lead times.

It should also be noted that the application of the LPBF technique for manufacturing biomedical metal components still requires a large range of research and tests to confirm the stability of the characteristics of the LPBF-built metals. Generally, the cardiovascular stents are made of stainless steel, cobalt‑chromium alloy, nickel‑titanium alloy, and other metal alloys [4, 5]. Recently, Demir et al. fabricated prototype stents of cobalt‑chromium alloy using the LPBF method as an alternative method to the conventional manufacturing [5]. They have shown that the surface roughness (Ra parameter) and microhardness were respectively approx. 12 μm and 320 HV_0.5 for the LPBF-built stents with hatching strategy, and 9 μm and 345 HV_0.5 for the LPBF-built stents with concentric scanning strategy.

This work aims to design the solid model of the cardiovascular stent prototype and to fabricate the designed stent by the selective laser melting process using a single-exposure strategy.

The cardiovascular stent test parts were fabricated using a nickel-based pre-alloyed Inconel (IN) 718 powder. The chemical composition of the LPBF‑built specimens was the following (wt.%): Ni 51.34, Cr 19.08, Nb 5.33, Mo 3.28, Ti 0.98, Al 0.46, Mn 0.27, Si 0.18, C 0.08, and Fe balance.

The laser powder bed fusion (LPBF) process was implemented using an industrial Renishaw AM400 machine, which was equipped with an ytterbium fiber laser and scanning optics [6]. The cardiovascular stent test parts were manufactured using a single-exposure (points) strategy (Fig. 1). The powder layers with a thickness of 30 μm were melted at a laser power of 100 W with a laser beam diameter of 70 μm and an exposure time of 30 μs.

Fig. 1. General view of Renishaw AM400 machine used and scheme for the LPBF process.

The CAD model of cardiovascular stent prototype and LPBF-built IN 718 alloy stent are given in Fig. 2. The 3D model of cardiovascular stent test part was designed in the SolidWorks program based on similar designs presented in the literature [5]. The stent shown in Fig. 2a was designed with a length of ~19 mm and diameter of 2 mm. The strut thickness for this build was set to ~200 μm.

Fig. 2. CAD model of cardiovascular stent test part (a) and LPBF-built IN 718 stent (b).

As seen in Fig. 2 the surface of LPBF-built stents has remarkably large surface roughness due to unmelted powder particles. It is well known that a large number of manufacturing defects are ordinarily formed on the surface components fabricated by the LPBF technique [5, 6]. As a consequence, post-chemical or electrochemical surface treatments of LPBF-built cardiovascular stents are required to reduce the surface roughness parameters to meet clinical requirements. Application of Zn alloy powders allows getting a higher mechanical performance in the LPBF-built stents [2]. On the other hand, to improve both surface quality and mechanical properties of LPBF-built stents, post-mechanical surface treatments can be applied as well.

The LPBF technique applied in this study to fabricate the cardiovascular stent prototype parts using a nickel-based pre-alloyed IN 718 powder. The following conclusions can be drawn:

1. 3D printing of cardiovascular stents by the LPBF process can replace the conventional manufacturing techniques;

2. The stent geometry and scanning strategy should be optimized;

3. To reduce the surface roughness and subsurface porosity, post-processing surface modification techniques are required.