Effect of variation of proton beam energy on the martensitic transformation temperature of shape memory nitinol alloy

Specimens of shape memory nitinol alloy (T-c = 323 K) were irradiated with 1.5-2 MeV protons with a fluence of 6.6 x 10(15) protons cm(-2) over a period of 6 h. The electrical resistivity of the specimens was measured under similar conditions before and after proton irradiation in the temperature range 233-350 K. In addition to the sharp rise in the electrical resistivity of the specimens at the martensitic transformation temperature T-c after proton irradiation, a considerable gradual decrease in T-c was seen as the energy of protons increased over 1.75 MeV. T-c decreased from 323 K for the virgin sample to 302 K when the proton energy was 2 MeV. This is an indication that increasing the proton energy enhances the creation of defects and the production of lattice disorder by proton irradiation, which consequently increases the anti-phase boundaries brought about by the particular co-operative shear movement of atoms that takes place, causing T-c to be lower than that of the virgin specimen. This shows that proton beam energy plays an important role in lowering the martensitic transformation temperature T-c. This result provides a new method of producing SMA materials of low T-c and seems to have an important application in the robots industry, controls, sensors etc. In addition, it appears that the results of this work will extend the applications of the shape memory alloys (SMA) of low martensitic transition temperatures.