The Influence of Ingot Transformation Temperatures on Plateau Strain and Stress of Nitinol Tubes

Earlier investigations (O.Tych et al. 2016) have shown the influence of the degree of cold work and heat treatment on the plateau strain and fatigue properties of Nickel-Titanium thin wires. Recently, the interest on the influence of the plateau strain on the mechanical properties of Nitinol tubes and subsequently their potential impact on fatigue properties increasingly gain in importance. The aim of this work is to analyze the influence of ingot transformation temperature on the mechanical properties of Nickel-Titanium tubes. For this study, materials with two different ingot transformation temperatures were selected and uniformly processed to final tubing with an outer diameter of 7 mm and a wall thickness of 0.5 mm. Moreover, the tubes have undergone consistent final heat treatment. Experiments have been verified with two different material grades. In order to analyze mechanical properties and the transformation behavior, extensive tensile testing, bend and free recovery testing and differential scanning calorimetric measurements were part of this study. The comparison of these results with fatigue data provides great insight into potential effects of plateau strain on fatigue behavior.