TY  - THES
T1  - Development of copper-zinc-tin shape memory alloy by electroless plating
A1  - Alarcon, Maria Celine Poblete
LA  - English
YR  - 2006
UL  - https://tuklas.up.edu.ph/Record/UP-99796217609926710
AB  - Metal alloys which have the ability to return to their previous shape after application of heat are termed shape memory alloys (SMA). This phenomenon is driven by what is called a thermoelastic martensitic transformation, causing the crystal structure to undergo change at a certain temperature. At low temperatures, the crystal structure is twinned martensite. Upon deformation, the twinned martensite de-twins then transforms to austenite; this austenite phase has the same shape as that of the twinned martensite when sufficient heat is applied. The most common shape memory alloys are the nickel titanium and copper based alloys. Ni-Ti shape memory alloys, more frequently known as Nitinol, have superior mechanical properties but are expensive, which makes copper base alloys the more practical choice. Of the many possible copper based SMAs, the Cu-Zn, Sn system has been given relatively little attention. This research is therefore focused on the Cu-Zn-Sn system and aspires to develop a shape memory alloy through the relatively less common yet uncomplicated method of electroless plating, as opposed to a study which previously successfully fabricated Cu-Zn-Sn SMA by DC electroplating process.
AB  - For this study, the Cu-Zn-Sn shape memory alloy was fabricated through electroless Sn plating of 70 um thick common brass strips that were alloyed at 300 degree celcius and annealed in a quartz tube furnace at 700 degree celcius/850 degree celcius and quenched in water (with ice/room temperature). The samples were preliminarily checked for shape memory behavior by exposing the samples to blue flame. The extent of shape memory effect was also determined through this test and results indicated presence of high temperature two way shape memory behavior in certain samples. Characterization of the Cu-Zn-Sn shape memory alloys was accomplished with the use of SEM and EDS for weight percent composition determination, DSC and TMA for transformation temperature determination, Van der Pauw Analysis for resistivity measurements, and XRD for analysis of the crystal structure of the samples.
AB  - Changes in the microstructure from the initial brass sample to the final SMA were evident; evidence of twinned structures and presence of cubic shaped etch pits and step like appearance became very prominent. The optimal compositions of the Cu-Zn-Sn shape memory alloys in weight % among those tested in this research was 67.1+1.17% Cu, 32.4+1.14% Zn and 0.63+0.12 Sn. DSC analysis showed a defined endothermic peak at 252 degree celcius marking the austenite transformation temperature. TMA plots revealed large changes in the slopes at 253 degree celcius+14.79865 degree celcius and 364 degree celcius+9.53939 degree celcius indicating the start (As) and end (Af) of austenitic transformations respectively. XRD plots showed additional peaks in the Cu-Zn-Sn SMA not present in the initial brass sample which points out that there was a change in crystal structure and/or phases within the alloy. Compared to the resistivities of the component metals, the resistivity of the SMA was found to greater than pure metals as calculated from the Van der Pauw method of computing for resistivity.
CN  - LG 995 2006 M37 A43
KW  - Alloys : Thermomechanical properties.
KW  - Electroless plating.
KW  - Martensite : Thermomechanical properties.
KW  - Shape memory alloys.
KW  - Martensitic transformations.
KW  - Shape memory effect.
ER  -