Machine Design for Multiscale Nitinol Annealment Process and End Product Performance Analysis

Abstract The functional properties of Nitinol (NiTi) are set by composition, production process, and post-production heat treatment and cold working. Post-production heat treating is dependent on two main parameters: anneal temperature and aging time. Most heat-treating processes performed by researchers generally consist of simple temperature soaks at specified aging times. However, there are drawbacks to this method. More complex heat treatments can result in performance improvements, but they are difficult to implement and often proprietary to manufacturers and therefore not widely used by researchers. By designing a Continuously-Fed heat treatment System (CFS), this work demystifies this complex heat-treatment process by rapidly heat-treating NiTi wire samples across a range of annealing temperatures, soak times, and tensions with little human intervention. This automated process ensures samples are created in a consistent manner and results in a much more consistent end-product when compared to conventional heat-treating methods. Using the CFS, a gamut of samples with varying annealing temperatures (400–550°C) and aging times (1–3 minutes) were created with 0.25mm diameter high-temperature actuator wire initially in the ‘as-drawn’ condition. Differential Scanning Calorimetry (DSC) analysis was performed to determine how the transition temperature(s) change with the various heat-treating parameters and the mechanical properties of the wire were determined utilizing a tensile test. The experimental results demonstrate the benefits of the CFS and are compared to those of a more conventional heat treatment process. Experimental results show that high-performance Nitinol actuator behavior can consistently be achieved using the CFS. Optimal heat treatment processes can be determined quickly experimentally.