Influence Of Microstructure On Mechanical Properties and Fatigue Behavior On Next Generation Nitino! Materials

摘要

It is well known in the industry, that Ti-rich secondary phases, generated in the solidification processes, are influencing the fatigue behavior of the final product [1,2]. On the other side microstructure, namely grain size has a significant influence on the mechanical behavior of metals as well. This dependency is described in the so called Hall-Petch equation, with increasing grain size, yield strength is decreasing, although the equation is only valid till the micrometer range [3]. In conventional materials like stainless steel or Titanium based alloys, the reduction of grain size has a positive impact on the fatigue behavior. In case the grain sizes become smaller than 1 μm the Hall-Petch equation is not longer valid. Based on the two know properties, fatigue behavior dependency from secondary faces and yield strength dependency from grain size, it will be shown, that also with higher yield strength the fatigue behavior is influenced in a positive way. To exclude the effect of secondary phases on fatigue from grain size dependencies on fatigue, Standard Nitinol materials as well as next generation clean Nitinol materials were used to prove the influence of grain size in Rotary Bending Tests.