Formation of nanocrystals by crystallisation of Zr-Al-Cu-Ni-Fe metallic glasses

Citation
N. Mattern et al., Formation of nanocrystals by crystallisation of Zr-Al-Cu-Ni-Fe metallic glasses, MATER TRANS, 42(8), 2001, pp. 1509-1516
Citations number
16
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Material Science & Engineering
Journal title
MATERIALS TRANSACTIONS
ISSN journal
1345-9678 → ACNP
Volume
42
Issue
8
Year of publication
2001
Pages
1509 - 1516
Database
ISI
SICI code
1345-9678(200108)42:8<1509:FONBCO>2.0.ZU;2-M
Abstract
The influence of iron addition on the crystallisation behaviour of Zr65Al7. 5Cu17.5Ni10 bulk metallic glass was investigated by differential scanning c alorimetry, (DSC), X-ray diffraction, (XRD), transmission electron microsco py, (TEM) and magnetisation measurements. The amorphous Zr65Al7.5Cu17.5Ni10 alloy crystallises eatectically into CuZr2 and Zr6NiAl2. Addition of iron in amorphous (Zr65Al7.5Cu17.5Ni10)(100-x)Fe-x (0 less than or equal to x le ss than or equal to 20) leads to a changed crystallisation sequence and to the formation of nanocrystals. The formation of a cubic NiTi2-type Phase (S .G. Fd (3) over barm, a(0) = 1.22 nm) is the first step of crystallisation in amorphous alloys with iron contents x greater than or equal to 1. Depend ing on the iron content the average crystallite size decreases to the nanom eter regime. Ultrafine nanoclusters of down to 2 nm in size are formed as t he first step of crystallisation for amorphous Zr52Al6Cu14Ni8Fe20 due to a high nucleation rate combined with a low growth velocity. The clusters grow by Ostwald ripening during isothermal annealing up to 5 nm average crystal lite size. The magnetic behaviour of the (Zr65Al7.5Cu17.5Ni10)(100-x)Fe-x a lloys is dominated by temperature-independent Pauli paramagnetism for x les s than or equal to 15. For x = 20, a small contribution of magnetic cluster s is observed. These ferromagnetic clusters are in accordance with statisti c composition fluctuations within the homogeneous amorphous phase. With the formation of nanocrystals the size of the magnetic clusters increases to t he same order of magnitude.