Effect of heat treatment and madrel material on precision tube drawing of Ni-Ti shape memory alloy

Abstract

The Ni-Ti shape memory alloy (NITINOL) was known as one of difficult materials to meet the dimensional accuracy because of the complex phase transformation and the shape recovery characteristics. In this study, a tube drawing process with mandrel was numerically and experimentally investigated for manufacturing precision NITINOL tube to identify the stable phase transformation condition to remove the R-phase by differential scanning calorimeter. To study the non-linear material and shape recovery behavior of the NITINOL, tension and loading-unloading tests were conducted with three test velocities of 1, 5, and 10 mm/min. The three dimensional finite element (FE) analyses were carried out using the ABAQUS with hyperelastic and Mullins effect model. The amount of the shape recovery was checked for the drawn tubes compared to the numerical results. According to the present investigation, it was found out that the stable phase transformation which improved the ductility and reduced the effect of shape recovery was occurred under the condition of the heat treatment at 700˚C for 30 min and the tensile test velocity of 10 mm/min. The FE results showed similar tendency of the stress-strain curves obtained from the experiments. Moreover, the amount of the shape recovery of the NITINOL could be predicted by the FE analysis. From the results of the FE analysis and the tube drawing with red copper and brass mandrel, the dimensional accuracy was found to be improved by using the brass mandrel, but the drawing stress was somewhat higher for the brass mandrel than the case using the red copper mandrel. In conclusion, the shape recovery effect of the NITINOL could be predicted by the FE analysis and the process condition determined by the current experiments could be helpful for the precision tube drawing of the NITINOL shape memory alloy tube.