A Specification for Wrought NiTi-based SMA for Actuation

While there exists a broad range of potential applications for SMA actuators, their transition to production is hindered by a lack of standardized material specifications. To address this need, a new specification that evaluates and controls the wrought NiTi-based material for actuation is being developed under ASTM work item WK 82516. It is recognized that, due to chemical composition overlap between the new specification and the specification for Wrought NiTi SMAs for Medical Devices and Surgical Implants (F2063), there is potential for confusion within industry. While the main differentiator can be found within the specifications’ respective scope statements, it is helpful to recognize the fundamental differences in practical application. Use cases in the medical industry predominantly utilize NiTi material for its superelasticity, defined as the materials elastic response to an applied stress. This contrasts with the thermally induced shape memory effect utilized in actuation applications. The draft specification considers several grades of material including ternary alloys and high-transition temperature Ti-rich material. More generally, a grading system has been established to categorize alloys by transition temperature and micro-cleanliness, two key considerations when selecting material for use in actuation applications. While wrought material itself is not suitable for direct use in actuation applications, follow-on specifications covering processed and finished forms are anticipated.