MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Evaluation of Glass-Forming Ability for Metallic Glasses from Time-Reduced Temperature-Transformation Diagram
Akira TakeuchiAkihisa Inoue
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2001 Volume 42 Issue 11 Pages 2374-2381

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Abstract

An equation expressing the transformation curve for crystallization of metallic glasses has been proposed by using two parameters, viscosity and melting temperature (Tm). The Vogel-Fulcher-Tammann (VFT) equation, η=η0exp(B⁄(TT0)) where η0, B and T0 (ideal glass transition temperature) are empirical parameters, was used for expressing the viscosity. A Time-reduced Temperature-Transformation (T-Tr-T) diagram was calculated using the following five quantities: reduced temperature (Tr=TTm), three reduced viscosity parameters (η0r0Tm, Br=BTm and T0r=T0Tm), and reduced critical cooling rate (Rcr=RcTm) for formation of the glassy phase. The Rcr in the T-Tr-T diagram was calculated for Ni, metallic glasses and SiO2. The glass-forming ability (GFA) was estimated from T0rRcr(Rcr=RcTm) diagrams corresponding to TgTmRc diagrams obtained experimentally. The metallic glasses with T0r of 0.55 are calculated to have Rcr ranging from 10−5 to 100 s−1, which agrees with the experimental data that metallic glasses with TgTm of 0.6 or more have Rc of less than 103 K/s. The following three points are clarified: (1) the higher GFA of metallic glass is achieved because of higher viscosity, (2) higher viscosity causes both the homogeneous nucleation frequency (Ivhom) and the ratio (INImax), at reduced nose temperature against the maximum of Ivhom, to decrease, and (3) the Rcr is numerically derived from reduced viscosity parameters.

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© 2001 The Japan Institute of Metals and Materials
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