Chin. Phys. B, 2011, Vol. 20(4): 046102    DOI: 10.1088/1674-1056/20/4/046102
 CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES Prev   Next

# The effect of Si content on the martensitic transfor-mation temperature of Ni55.5e18Ga26.5–xSix alloys

Shen Hua-Hai(申华海)a),Yu Hua-Jun(余华军)b), Fu Hao(付浩)a), Guo Yuan-Jun(郭袁俊) a), Fu Yong-Qing(傅永庆)c),and Zu Xiao-Tao(祖小涛)a)
a Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, China; b The College of Physics and Electronic Information, Gannan Normal University, Ganzhou 314000, Jiangxi Province, China; c School of Engineering and Physical Sciences, Heriot Watt University, Edinburgh, EH14 4AS, UK
Abstract  This paper investigates the effects of substitution of Si for Ga on the martensitic transformation behaviours in Ni--Fe--Ga alloys by  using optical metallographic microscope and differential scanning calorimetry (DSC) methods. The structure type of Ni$_{55.5}$Fe$_{18}$Ga$_{26.5 - x}$Si$_{x}$ alloys is determined by x-ray diffraction (XRD), and the XRD patterns show the microstructure of Ni--Fe--Ga--Si alloys transformed  from body-centred tetragonal martensite (with Si content $x = 0$) to body-centred cubic austenite (with $x = 2$) at room temperature. The  martensitic transformation temperatures of the Ni$_{55.5}$Fe$_{18}$Ga$_{26.5 - x}$Si$_{x}$ alloys decrease almost linearly with increasing Si  content in the Si content range of $x \le 3$. Thermal treatment also plays an important role on martensitic transformation temperatures in the Ni--Fe--Ga--Si alloy. The valence electronic concentrations, size factor, L2$_{1}$ degree of order and strength of parent phase influence the  martensitic transformation temperatures of the Ni--Fe--Ga--Si alloys. An understanding of the relationship between martensitic transformation  temperatures and Si content will be significant for designing an appropriate Ni--Fe--Ga--Si alloy for a specific application at a given  temperature.
Keywords:  Ni–Fe–Ga alloys      ferromagnetic shape memory alloys      martensitic transformation      thermal treatment
Received:  18 June 2010      Revised:  22 November 2010      Accepted manuscript online:
 PACS: 61.66.Dk (Alloys ) 81.30.Kf (Martensitic transformations) 75.10.-b (General theory and models of magnetic ordering) 81.40.Ef (Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization)
Fund: Project supported by the National Natural Science Foundation of China (Grant No. 10976007), the Fundamental Research Funds for the Central Universities (Grant Nos. ZYGX2009J046 and ZYGX2009X007) and Royal Academy of Engineering-Research Exchanges with China and India Awards in UK.