Nickel titanium and nickel titanium hafnium shape memory alloy thin films

Show simple item record Rao, Jeff - Roberts, T, - Lawson, K. J. - Nicholls, John R. - 2011-02-07T23:11:44Z 2011-02-07T23:11:44Z 2010-04-01T00:00:00Z -
dc.identifier.citation J. Rao, T. Roberts, K. Lawson, J. Nicholls, Nickel titanium and nickel titanium hafnium shape memory alloy thin films, Surface and Coatings Technology, Volume 204, Issue 15, 25 April 2010, Pages 2331-2336 en_UK
dc.identifier.issn 0257-8972 -
dc.identifier.uri -
dc.description.abstract Shape memory alloy (SMA) coatings of NiTi and NiTiHf have been deposited onto Si substrates using pulse DC sputtering. Coatings of NiTi with compositions containing 45 to 65 at.% Ti have been fabricated by co-sputtering NiTi with Ti. NiTiHf coatings with Hf compositions ranging from 2 to 30 at.% Hf have been fabricated by co-sputtering NiTi with Hf. XRD results reveal the as-deposited coatings as amorphous. A high temperature, 1100 à °C anneal followed by a low temperature, 550 à °C anneal was employed to crystallise the coatings. The XRD then shows the coatings to be martensitic at room temperature. Two sets of samples were produced for characterisation; one set was used for indentation studies and the other set used to prepare freestanding films required for differential scanning calorimetry (DSC) studies. Using the DSC, a NiTi coating containing 52 at.% Ti shows an endothermic austenite peak phase transformation, (Ap) at around 105 à °C and an exothermic peak martensite phase transformation, (Mp) at 65 à °C, resulting in a hysteresis of 40 à °C. For a NiTi coating containing 65 at.% Ti the hysteresis remained unchanged at 40 à °C, but there was a decrease in the phase transformation enthalpies when compared with the coatings containing 52 at.% Ti. Calculated phase transformation enthalpies in the NiTi coatings ranged from 6 to 13 J/g for the austenite phase and â  8 to â  11 J/g for the martensite phase. The NiTiHf coating shows SMA behaviour for a film containing 30 at.% Hf. DSC reveals an â  Râ  phase transition in this film. It is understood that this phase is present in films that have high internal stresses and is understood to nucleate near Ti3Ni4 precipitates. Phase transformation temperatures occur at 98 à °C and 149 à °C during heating and occur at 99 à °C during cooling. Phase transformation enthalpies range between 2 and 3 J/g for the austenite phase and â  7 J/g for the martensite phase. A scratch tester equipped with a 5 mm spherical tip has been utilised with loads ranging from 1 to 5 N to determine the recovery properties of the films. The results in this study conclude that NiTi films containing 65 at.% Ti deform 3 times more than films containing 52 at.% Ti. For NiTiHf thin films, increasing the Hf composition from 2 at.% to 30 at.%, doubled the deformation measur en_UK
dc.language.iso en_UK en_UK
dc.publisher Elsevier Science B.V., Amsterdam. en_UK
dc.subject SMA en_UK
dc.subject NiTi en_UK
dc.subject NiTiHf en_UK
dc.subject Sputtering en_UK
dc.subject Thin films en_UK
dc.title Nickel titanium and nickel titanium hafnium shape memory alloy thin films en_UK
dc.type Article en_UK

Files in this item

This item appears in the following Collection(s)

Show simple item record

Search CERES


My Account