Factors Affecting the Ms Temperature of nitinol alloy

The difference in the composition range of nitinol alloys is very small. The proportion of components determines whether the component is super elastic or temperature-controlled.

The difference in composition of only 0.1% may cause the transition temperature to become 10℃. Basically, the higher the nickel content,the lower the transition temperature.

The use of heat treatment can finely adjust its conversion temperature,which will be explained in the later part. In addition to intentionally changing the composition, impurities in the alloy may also affect the transition temperature. Impurities such as carbon and oxygen combine with titanium, resulting in depletion of titanium in the bulk alloy, so the transition temperature is reduced.

For super elastic nitinol, three specified properties are appropriate:

• Upper platform stress
• Ultimate tensile stress
• Af temperature range is much lower than body temperature to ensure superelastic behavior

When the specifications are tested at a temperature between 20℃and 25℃, the upper platform stress should be between 450 and 500MPa. The ultimate tensile stress should be higher than 1300MPa. The temperature range of Af is between 25℃and 30℃.

For thermal nitinol shape memory, the following properties are appropriate:

• Ultimate tensile stress
• Af temperature range above body temperature37℃ and below 50℃

The ultimate tensile stress should be higher than 1000OMPa,and the Af temperature range should be between 45℃and 50℃.

There are other factors that will affect the final measurement performance and performance of Nitinol products. Use the heat to“set”the shape of the final product. Typically, the heat treatment is carried out at a temperature of 450℃to 550℃. The heat treatment causes changes in the microstructure of nitinol, and changes the mechanical properties and transition temperature accordingly.

The initial state of the alloy will also have a great impact on the final performance. Typically, nitinol alloys can be“directly annealed state “or“drawn state”.

Straight annealing means that when the wire leaves the drawing table, the shape of the wire is basically straight. To achieve this purpose, the wire passes through the continuous wire straightening furnace before winding onto the spool. ”Drawing state”means that the wire is wound directly from the final stretching step.