Metallography of Biomedical Nitinol

Metallography is the oldest imaging technique for analyzing the microstructure of metallic materials. Specimens are potted, cross sectioned, polished and imaged using light microscopy or scanning electron microscopy (SEM) to reveal microstructural features. Despite the history and widespread use of metallography, there is no comprehensive guide to performing practical metallography on Nitinol especially for its use in biomedical applications. A guide is necessary as performing metallography on Nitinol can be very challenging due to its corrosion resistance and phase transforming properties.

For this study, we aim to provide a comprehensive guide to performing metallographic analysis on Nitinol used in biomedical applications. The guide will cover metallographic examples from three main categories: Prior austenite grain structure and precipitate formation in raw material, HAZ microstructure from laser cutting and EDM, and lastly weld microstructure and defects. These categories and examples represent the majority of microstructural imaging needs in biomedical Nitinol. Metallography will be performed using a modified Beraha tint etchant with light microscopy and electron channeling contrast imaging (ECCI) with SEM. Best practices for sample polishing and imaging between the two techniques will be demonstrated highlighting which imaging techniques are best suited for each category of microstructural investigation.