Peritectic Solidification Path of the La(Fe,Si) 13 Phase in Dual-Phase Directionally Solidified La-Fe-Si Magnetocaloric
- PDF / 3,311,914 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 12 Downloads / 162 Views
ON
SOLID refrigeration has the potential to replace conventional gas compression/expansion refrigeration as a result of the increasing environmental concern.[1–3] In this case, La-Fe-Si alloy, with NaZn13-type La(Fe,Si)13 phase, has been reported as a promising candidate for magnetic refrigerants.[4,5] La(Fe,Si)13 alloy exhibits a giant magnetocaloric effect (MCE, which refers to the heating or cooling of magnetic materials due to a varying magnetic field) due to a magnetic field-induced, first-order itinerant electron metamagnetic (IEM) transition above the Curie temperature (TC).[6] La(Fe,Si)13 alloy displays a small hysteresis and an isotropic magnetovolume effect accompanied by the phase transition.[7–9] These properties are beneficial for a cyclic use of La-Fe-Si alloys because of the existing giant magnetocaloric effect. Several attempts have been made to improve the properties of La(Fe,Si)13 magnetocaloric alloys, such as partial element substitution, atom
LIANG YANG, ZHENNI ZHOU, JIANGRUI QIAN, XUAN GE, JUN LI, QIAODAN HU and JIANGUO LI are with the School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China. Contact e-mails: [email protected], [email protected] Manuscript submitted November 18, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS A
insertion, and applying extra pressure by using hydrogenation.[10–14] NaZn13-type La(Fe,Si)13 phase (1:13 phase) is a peritectic phase that is formed by a peritectic solidification reaction. However, the 1:13 phase was not observed using conventional techniques, such as arc-melting. Instead, the as-cast La-Fe-Si alloys show a two-phase structure composed of a-(Fe,Si) and La-Fe-Si (Cu2 Sb-type: P4/nmm) phases. According to the phase diagram, during equilibrium solidification, the a-Fe phase (primary phase) dendrites first grow from the liquid. Once the prime phase forms, a peritectic reaction with the surrounding liquid forms the peritectic phase. Once the peritectic phase appears at the junction of the prime phase and surrounding liquid, the peritectic solidification will be blocked.[15] It has been reported that a dual-phase structure containing both a-Fe and La(Fe,Si)13 shows an enhanced thermal conductivity and mechanical property compared with the single-phase structure.[16] The existence of the a-Fe phase can improve the mechanical properties, particularly, the ductility of La-Fe-Si alloys due to the internal brittleness of the La(Fe,Si)13 phase. However, this dual-phase microstructure is achieved by high-temperature annealing of the non-stoichiometric La(Fe,Si)13 alloy for an extended period of time.[16] To our knowledge, bulk casting of the La(Fe,Si)13 alloy is currently unavailable. Other novel methods have been used, such as melt-spun to refine the prime a-Fe phase and powder metallurgy
(HDSH) to insert H atoms; however, the alloys are prepared in powder and/or ribbon form.[17–19] Directional solidification has been used in the production of peritectic functional alloys and can tailor the microstructure, morp
Data Loading...
