Process mechanics and surface integrity of low plasticity burnishing of SE508 Nitinol alloy
Superelastic Nitinol and shape memory alloys have attracted growing attentions over the recent years in the areas of biomedical and aerospace applications. Surface integrity of Nitinol devices by various fabrication processes is critical for their functionality and performance. Low plasticity burnishing (LPB) is a surface enhancement process to improve surface integrity due to its unique capability to plastically deform material in the deep subsurface on the order of a 500-1000ìm. This thesis focuses on the dynamic mechanical behavior of SE508 Nitinol (NiTi) alloy and process mechanics and surface integrity by ball burnishing of the material. The stress-strain behaviors of SE508 NiTi alloy at quasi-static and high strain rates were experimentally determined using a series of compression testing. Then, the experimentally determined stress-strain behavior was used in correlation with Hertzian theory of contact mechanics in ball burnishing of the material. It was found that quasi-static compressive stress-strain behavior correlates well with Hertzian peak pressure. This serves as a basis to select burnishing loads. The effects of LPB parameters, i.e. burnishing pressure, feed, speed, number of path, and pattern on surface integrity characteristics such as surface topography, roughness, microhardness, and microstructure are investigated.