In-situ tensile testing of notched poly- and oligocrystalline 316L wires
Mitevski, Bojan and Weiss, Sabine and Fischer, Alfons
Volume: 59 Pages: 130--135
Published: feb 2017
In-situ testing inside a scanning electron microscope is a helpful tool for detailed analyses of small sized specimens with respect to their mechanical properties and the correlated microstructural alterations. Thus, this test method is used to analyze the tensional properties of thin 316L (1.4441) wires used for microscale components, e. g., like coronary artery stents. Tensile tests were conducted on unnotched and circularly notched 316L wires (phi 0.95 mm) with a special focus on the number of grains within the cross section as well as the notch geometry. Four combinations of notch width (2 and 4 mm) and notch depth (diameter at notch root: 0.5 and 0.75 mm) were chosen. Notch depth and notch shape were adjusted by means of electrochemical polishing. Previous investigations showed, that oligocrystalline structures exhibit a different mechanical behavior compared to polycrystalline ones or single crystals. There are only a few data available on mechanical testing of oligocrystalline structures with respect to varying notch geometries. Depending on the notch geometry, grain size and, therefore, the number of grains within the notch cross section widely scattering yield-and tensile strength as well as failure elongation values were measured. However, the transition criterion between poly-and oligocrystalline behavior could be quantified to be 6 to 7 grains within the cross section.