Phase formation of rapidly quenched Cu–Si alloys

doi:10.1016/j.jallcom.2006.04.046

Journal of Alloys and Compounds

Volume 429, Issues 1–2, 21 February 2007, Pages 211-215

Dedicated to Prof. Dr.-Ing. Dr.h.c. Hartmut Fueß in occasion of his 65th birthday.

https://doi.org/10.1016/j.jallcom.2006.04.046 Get rights and content

Abstract

The influence of rapid quenching on the phase formation of Cu–Si alloys was investigated for silicon contents between 10 and 30 at.%. Rapid quenching leads to formation of different meta-stable states depending on the chemical composition. High temperature phases η, δ and κ can be preserved at room temperature. The formation of the room temperature phase ɛ can be suppressed by rapid quenching from the melt. The crystal structure of the high temperature phases was analysed by X-ray powder diffraction. Annealing of the rapidly quenched alloys at T = 500 °C leads to the transformations of the meta-stable phases. The equilibrium states exhibit phase compositions, which are in agreement with the generally accepted phase diagram.

Introduction

The Cu–Si binary phase diagram is well established [1]. A thermodynamic description of the phase diagram is assessed in [2], [3]. Several inter-metallic phases are formed at the Cu-rich side. Three inter-metallic phases exist at room temperature: η″ (Cu₃Si), ɛ (Cu₁₅Si₄), and γ (Cu₅Si). The room temperature Cu₃Si-phase η″ has two high temperature modifications η′ and η. Furthermore there are three high temperature phases in the system: δ, β, and κ (Cu₇Si). The solubility of Si in fcc-Cu extents to 11.25 at.% at T = 842 °C. On the other side, Cu is soluble only to a very low degree in Si (0.003 at.% at T = 1300 °C).

The crystal structures of the η″, η′, η and δ-phase are not known. Rapid quenching enables to prepare meta-stable states like frozen in high temperature phases or supersaturated solid solutions. Electrical resistivity and hardness of rapidly solidified binary Cu–Si alloys were reported in [4]. A refined microstructure is observed, but no information on the structure of the formed silicide phases was given. The aim of this work was to analyse the influence of rapid quenching on the phase formation of Cu–Si alloys within the range of the inter-metallic compounds from 10 to 30 at.% Si and to determine the crystal structure of the high temperature phases at room temperature.

Section snippets

Experimental

Ingots with nominal composition of Cu_100−xSi_x (Table 1) were prepared by arc melting of the pure elements on a water-cooled copper mold under a high purity argon atmosphere. The ingots were remelted at least three times to obtain a macroscopic homogeneous distribution. Ribbons, 5 mm in width and about 30 μm in thickness, were prepared by means of rapid quenching from the melt using a single-roller melt-spinner under argon atmosphere. Chemical compositions were analysed by titration technique.

Phase formation

Fig. 1 shows as an example the XRD patterns of the as-quenched ribbons of Cu₇₇Si₂₃ and Cu_81.5Si_18.5 together with the corresponding equilibrium states after annealing the samples at T = 500 °C for 1 h. The comparison indicates that rapid quenching of the Cu–Si alloys leads to several changes in the phase compositions. The Cu₃Si phase is observed in the as-quenched ribbons with 25 ≥ x ≥ 23 as a single phase, and for x > 25 together with Si. For the rapidly quenched ribbons the mean crystal structure of

Conclusions

Rapidly quenching of Cu–Si alloys leads to formation of different metastable states depending on the chemical composition. High temperature phases η, δ and κ can be preserved at room temperature. On the other hand, the formation of the room temperature phase ɛ can be completely suppressed. During annealing at elevated temperatures the rapidly quenched material transforms into the equilibrium state showing phase compositions, which are in agreement with the generally accepted phase diagram.

Acknowledgements

The authors wish to thank S. Kuszinski, A. Ostwaldt and B. Opitz for their assistance in the sample preparation.

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Phase formation of rapidly quenched Cu–Si alloys

Abstract

Introduction

Section snippets

Experimental

Phase formation

Conclusions

Acknowledgements

CALPHAD

Mater. Lett.

J. Alloys Compd.

Acta Cryst.