Nitinol sheets develop various crystallographic textures during the rolling process. The crystallographic texture results in orientation-dependent mechanical response variability, such as plateau stress, plateau strain and residual strain. These anisotropic mechanical responses may cause a non-uniformity of deformation in engineering components and increase a risk of structure failure and material damage, particularly for those products involving large crimping strain in medical device fabrication.

There is an increasing demand for high quality Nitinol medical devices and implants to accommodate to the rapid growth in the biomedical market. Extensive studies have confirmed the significant impact of micro-cleanliness of Nitinol on fatigue life. Ultra-clean Nitinol material is required for most critical medical applications such as cardiovascular and neurovascular devices for which integrity and durability are critical. This poses challenges for upstream manufacturers to consistently produce ultra-low inclusion Nitinol mill products. This work is a comprehensive to evaluate hot rolled bars and coils of a new commercial scale ultra-clean Nitinol alloy. The robustness of the alloy production process and stability of product properties was confirmed by examining a large number of mill products manufactured in different campaigns. Extensive characterization and multiple approaches of inclusion analysis demonstrated the consistent ultra-high cleanliness of the products.