Influences of Reduction Ratio on Mechanical Properties and Transformation Temperature of NiTi Drawn Wires

NiTi alloy wires are widely used in many applications for examples, orthodontic arch wires, mini screw implant, sensors, etc. Usually, wire drawing process is chosen to produce arch wires because of its high productivity as well as superior surface quality of the drawn wire surface. In the case of NITI arch wire, the cold work occurred during wire drawing operation also plays important role to control mechanical properties and transformation behavior of the wires. Thus, the purpose of this work is to study the influences of reduction ratio of cross sectional area and annealing temperature on transformation and mechanical behavior of the drawn wires. The wire materials used in the experiment are Ni51.4Ti48.6 (atomic percentage) with initial wire diameter of 0.64 mm. The die tip is made of tungsten carbide which is inserted into the steel case made of tool steel. The reduction ratios of cross sectional area (%Re) are varied at three different levels, i.e., 10, 20 and 30%, respectively. In order to study the influences of post heat treatment temperature, the drawn wires are annealed for 3,600 sec at two different levels; 400 and 600C. The lubricant used in the experiments is sodium stearate powder. From the results, drawing force and surface roughness of the drawn wire strongly depend on %Re. in addition; tensile properties and phase transformation temperature noticeably depend on heat treatment temperature. Keyword: NiTi arch wire, Wire drawing, Reduction ratio, Heat treatment temperature, Phase Transformation temperature, Shape memory alloy