The growth of Nitinol element has expanded tremendously in the past ten years. Today, super-elastic nitinol is a well known, common engineering material in the medical industry. These devices are long used in stents for different vascular applications, and for other medical applications such as spinal instruments to provide less-invasive procedures, arthroscopic devices, and interventional guide wires, and so on.
Nitinol comprises of two elements together, namely 50% nickel and 50% titanium alloys. These allow displaying unusual shape memory and super-elastic properties that make dramatic changes in the operating ways of the alloy. It is slightly because of nickel-rich alloys the effect of super-elasticity is noticed in nitinol devices. Nonetheless, this phenomenon has been widely used in majority of medical applications across the globe.
Defining: Nitinol Shape Setting and the Various Specifications Involved in the Process
It is a process that is used to program the desired shape of a Nitinol device. In this process, the final desired specific shape of the metal is programmed and configured using special thermal physics for every device. Such programming and configuration totally depends on the end use and end-use environment. When one speaks of shape setting, one should also take into account the type of nitinol that is to be used. Nitinol shape memory and super-elastic type are normally available in Nitinol ribbon, wire, Nitinol sheet, strip, tubing, or bar form. These forms help to set custom shape in a piece of Nitinol. As shape setting often refers to the process used to create Nitinol, whether this element is shape memory or super-elastic, in the straightened or cold work condition, it is quite necessary to form the material in a new ‘memory’ shape. Hence, the process is performed by firmly constraining the material into a new shape, fixture or on a mandrel, and then perform heat treatment.
Shape setting may require different processing temperatures and exhibiting characteristics too. The heating method can be executed in a number of ways such as, air or vacuum furnace, sand bath, salt bath, heated die, and other different methods. However, while adapting any of these techniques and performing the nitinol shape setting process, one has to make sure the temperature range is of 500-550 C with higher temperatures that comfortably result in lower tensile strengths. In addition, the heat treatment time should be able to reach the desired temperature throughout the cross-section. This process depends on the material, mass of the fixture, and the heating method.
The key to designing various parts with Nitinol is to access the material and perform the tests as soon as possible. Nitinol is really not an easy material to work on and design with because it does not have a linear stress-strain curve like other metals such as stainless steel. Therefore, most design formulas and techniques are not applicable. With nitinol shape setting, the aging time must be determined observationally because these processes depend on the heating method, temperature, and history of the material. Nevertheless, it is a quick method to perform provided you have the right equipment available for use.