Additive Manufacturing (AM) gets increasing attention for Nitinol processing for medical devices because it provides the opportunity to circumvent many of the challenges associated with conventional machining of Nitinol as well as the tailoring of patient-specific implants. Frequently used AM techniques for Nitinol are powder-bed technologies such as Selective Laser Melting (SLM) which is a suitable method for creating complex parts. However, functional Nitinol parts are strongly influenced by the powder properties. In particular, the oxygen content is a critical factor when components with medical grade Nitinol are required. Trace amounts of oxygen form an oxide covering the powder surface with a nanometric thickness as well as complex structure and composition due to the high specific surface energy of the powder. The oxide layer is depending on ambient conditions during powder manufacturing as well as powder handling. The present work provides characterization of the oxide layer and the microstructure for a pseudoelastic Ni 50.8 Ti 49.2 Nitinol alloy powder for AM by TEM investigations. Furthermore, for an estimation of the powder oxide layer thickness, the calculated oxide layer thickness resulting from the oxygen content and the particle size is compared with the measured oxide layer thickness by an EDX line-scan.

Transcatheter heart valve replacement is a key advancement in the cardiovascular device industry and provides an alternative to open surgical procedures for patients that suffer from severe symptomatic stenosis and/or regurgitation. The functions and boundary conditions of the four heart valves are unique and must be considered separately. It is essential that the structural durability of these high-risk valve replacement implants is thoroughly assessed through testing and analysis. As such, ISO 5840 outlines a comprehensive device durability approach that incorporates worst-case boundary conditions, computational stress/strain analyses, and benchtop fatigue testing. The present study is focussed on 100,000,000-cycle fatigue testing of custom-designed “diamond-shaped” coupons of process-optimized high purity VAR/EBR Nitinol. Benchtop testing was coupled with finite element analysis (FEA) and microstructural characterization to provide an in-depth understanding of durability.

The continuous rolling of Nitinol alloys is a metalworking process with the ability to produce large quantities of sheet with uniform properties for the use in actuation applications in motion systems with cyclic loads. Great advantages of continuous rolling in comparison with other manufacturing methods are the cold work and heat treatment steps and their ability to influence the properties of the product and keep them in a very tight window over the width and the length of the process. Those tightly controlled properties are key-requirements to use the continuous rolled Nitinol material for subsequent automated processes like stamping in progressive dies or deep- drawing. It is also required for efficient reel-to-reel laser or EDM cutting. The primary objective of this work is to evaluate and obtain the properties of Nitinol continuously flat-rolled sheets and optimization of the process parameters by fatigue evaluation.