Effect of Annealing on the Structural and Magnetic Properties of CoNiAl FSMA

Abstract

A ferromagnetic shape memory alloy is a very interesting system that has various structural transformation, microstructural phases and magnetic properties, and interplays among them. The system studied here is Co39Ni34Al27 that comprises a mixture of β (body‐centered cubic) and γ (face‐centered cubic) structural phases. Here the β phase is responsible for the FSMA behavior and the γ phase improves the mechanical properties necessary for practical applications. Herein, it is showed through resistivity and magnetization measurements that post‐annealing to a higher temperature significantly alters the ratio of β and γ phases in the system, resulting in increasing the austenite to martensite transition temperature and significantly modifying the magnetic properties. Additionally, it is also shown that the low‐temperature magnetic phase of this FSMA system is a disordered magnetic system.

Structure Evolution of Ni36Al27Co37 Alloy in the Process of Mechanical Alloying and Plasma Spheroidization

“…Coercivity depends heavily on the structural state of a material, and as a consequence, a method of its manufacture and the following treatment is capable of changing this property in a quite significant way. The alloys of close to Ni 36 Al 27 Co 37 compositions obtained by conventional methods of arc melting and subsequent heat treatment show the coercivity from 0.7 to 60 Oe [33][34][35]. Thin ribbons of the alloys obtained by rapid quenching show the coercivity from 100 to 2000 Oe [36], and the alloys obtained by conventional methods of powder metallurgy such as sintering the powders show the coercivity of about 160 to 190 Oe [37].…”