Thermo mechanical properties of Ni_(60 weight) Ti _(40 weight)

摘要

60-NiTinol (60% Nickel 40% Titanium content by weight) was developed by the US Naval Ordnance Laboratory in the 1960s as a structural form of NiTinol. Due to 60-NiTinol's extreme brittleness application development was abandoned. NiTinol Technologies Inc. successfully produced cutting instruments with this material in the early 90's. Subsequent work demonstrated that with proper heat treatment the material exhibits a strong, stable, shape memory response. Unlike other NiTinol alloys, 60-Nitinol does not require cold work. Initial testing of this material shows that the transition temperature is a strong function of the heat treatment. Therefore the same ingot of material can produce samples with superelastic and shape memory effect. Samples with different heat treats exhibited transition temperatures varying from -55 C to +60 C. Additionally, appropriate heat treatment allows the material to exhibit extreme hardness (Re 62) or a two-way shape memory effect. This paper provides the first study of the thermomechanical properties, including stress-strain curves and thermal cycling of axially loaded slender 60-Nitinol samples. The samples were tested at extremely high stress levels greater than 695 MPa (100 ksi) with recoverable strain of 2.5%. In addition, flexures designed with potential for aerospace applications were tested. This initial research shows that 60-Nitinol has some enticing advantages over 55 NiTinol, however further study is required.