The effect of ageing and annealing on shape memory properties of Cu-Al-Ni melt-spun ribbons

P. LA ROCA, C. SOBRERO, J. MALARRÍA, PH. VERMAUT, P. OCHIN, R. PORTIER

Rosario (Argentina)

Congreso; 10th Inter-American Congress of Electron Microscopy CIASEM-09; 2009

Inter-American Committee of Societies for Electron Microscopy - CIASEM

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; mso-hyphenate:none; font-size:12.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES; mso-fareast-language:AR-SA;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Cu-13.5Al-5.5Ni-1Ti tapes with a grain refined microstructure of 3-5 mm were obtained by melt spinning. As result of the rapid solidification process, the martensitic transformation temperatures of this high temperature shape memory alloy shifts below 0 °C. After in-situ ageing experiments in a DSC, combined with microstructure analysis by SEM and TEM this phenomenon was ascribed mainly to short range retained disorder. On the other hand, high temperature treatments as annealing in the range 700°C-900°C leads to marked microstructural changes related with Ostwald ripening of Cu-Al-Ni-Ti precipitates: Fine precipitates are dissolved while medium and coarse precipitates grows up, leading to a microstructure more favorable for moving interfaces. As a consequence, the high temperature martensitic transformation above 70 ºC is recovered and an increase of the fraction of transforming material is observed.