Correlation between composition and phase transformation temperatures in Ni–Mn–Ga–Co ferromagnetic shape memory alloys

✍ Scribed by V. Sánchez-Alarcos; J.I. Pérez-Landazábal; V. Recarte; C. Gómez-Polo; J.A. Rodríguez-Velamazán

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 435 KB
• Volume: 56
• Category: Article
• ISSN: 1359-6454
• DOI: 10.1016/j.actamat.2008.07.017

✦ Synopsis

The effect of Co addition on the phase transformation temperatures (martensitic and Curie point) and crystal structure of Ni-Mn-Ga-Co shape memory alloys has been investigated on (Ni 50.26 Mn 27.30 Ga 22.44 ) 100Àx Co x (x = 0, 2, 4, 6) alloys as well as on alloys having different Ni/Mn/Ga ratios and a fixed amount of Co. Alloying by Co affects the martensitic transformation temperature and the transformation enthalpy change mainly through the change on the valence electron concentration (e/a), but the transformation entropy is almost unaffected. On the other hand, the composition (analyzed through the e/a ratio) shows a different influence on the Curie temperature depending on the crystallographic phase (austenite or martensite) in which the magnetic ordering takes place. It is also reported that in Ni-Mn-Ga-Co alloys the Curie temperature of the martensitic phase is lower than that of the austenitic phase, opposite to what occurs in ternary Ni-Mn-Ga alloys.