Liquid-phase-separation-in-Gd-Ti-and-Gd-Zr-melts_2010_Interm

Liquid phase separation in Gd e Ti and Gd e Zr melts

Steffen Schmitz *,Hans-Günther Lindenkreuz,Norbert Mattern,Wolfgang L?ser,Bernd Büchner

IFW Dresden,PO Box 270116,D-01171Dresden,Germany

a r t i c l e i n f o

Article history:

Received 13November 2009Received in revised form 25January 2010

Accepted 27February 2010

Available online 25March 2010Keywords:

A.Rare-earth intermetallics

B.Phase diagrams B.Glasses,metallic

a b s t r a c t

Liquid phase separation in two binary melt systems,Gd e Zr and Gd e Ti,related to phase separated metallic glasses are investigated by electromagnetic levitation experiments.Gd e Ti samples quenched onto a copper chill substrate from temperatures below the binodal line exhibit typical coarse phase separated microstructures,assigning melt immiscibility.The miscibility gap of Gd e Ti melts extends at least from 10to 80at.%Gd,much wider than reported previously.The critical temperature is about 1580 C at Gd 20Ti 80.In the Gd e Zr system no indication of a stable liquid miscibility gap was detected.However,melt droplets quenched from the undercooled state exhibit concurrent coarse Gd and Zr primary phase constituents suggesting a metastable miscibility gap.

ó2010Elsevier Ltd.All rights reserved.

1.Introduction

Phase separated metallic glasses can be produced from complex alloys involving binary terminal systems with both negative and positive heats of mixing.It was ?rst shown by Kündig et al.that phase separation of the supercooled liquid state into two different glasses occurred in the as-melt-spun Zr e La e Cu e Ni e Al alloy due to the positive heat of mixing in the liquid state for Zr e La [1].Later on,phase separated metallic glasses were successfully prepared in various alloy systems:Y e Ti e Al e Co [2],Ni e Nb e Y [3],Zr e Nd e Al e Co [4],Cu e (Zr,Hf)e (Gd,Y)e Al [5],Zr e (Ce,Pr,Nd)e Al e Ni [6].Fu et al.[7]have improved the glass forming ability of Cu e Zr e Al if Gd is added,a rare-earth element which has a positive heat of mixing with Zr.

Liquid phase separation below a critical temperature T c can principally occur within either a stable or a metastable miscibility gap (MG).While the former is an equilibrium phase diagram feature,the latter one,lying beneath the liquidus curve (T c

For understanding phase separation processes in complex glass forming alloys such as Gd e Zr e Cu e Al or Gd e Ti e Cu e Al experi-mental data on Gd e Ti and Gd e Zr binary melts are an urgent need.

The calculated Gd e Ti phase diagram predicts monotectic solidi ?-cation behavior with a stable MG between 35and 87at.%Gd and a critical temperature T c z 1520 C (cf.Fig.3)[11].Gd e Zr phase diagram assessments do not envisage liquid immiscibility,but a wide miscibility gap in the solid state.Predicted eutectic compositions,near Gd e 27.5at.%Zr [12]and Gd e 11at.%Zr [13],respectively,are at variance in different assessments.

The present work is a study of phase separation of Gd e Ti and Gd e Zr binary melts by electromagnetic levitation experiments.Microstructure analysis of levitated melt droplets quenched from de ?nite temperatures,which also comprise the supercooled state,will reveal the stable or metastable character of liquid immiscibility and the width and the critical temperature of the MG.2.Experimental

Master alloy ingots of Gd x Ti 100àx (5

*Corresponding author.Tel.:t493514659762;fax:t493514659313.E-mail address:s.schmitz@ifw-dresden.de (S.

Schmitz).Contents lists available at ScienceDirect

Intermetallics

jou rn al homepage:

30a48d29bc64783e0912a21614791711cc797957/locate/intermet

0966-9795/$e see front matter ó2010Elsevier Ltd.All rights reserved.doi:10.1016/j.intermet.2010.02.030

Intermetallics 18(2010)1941e 1945

Quenched splats with approx.1e3mm thickness were prepared for metallographic examination by polishing the resin-mounted specimens with diamond pastes.The microstructure was analyzed by scanning electron microscopy(SEM)in the backscattered elec-tron(BSE)mode using a Philips XL30device.The chemical composition of the phases was measured by electron probe X-ray microanalysis(EPMA)in the energy dispersive mode(EDS). Differential scanning calorimetry(DSC)studies of annealed samples were accomplished up to1500 C in an argon atmosphere using a Netzsch DSC404device at a heating rate of20K/min.

3.Liquid phase separation in Gd e Ti

Levitated Gd e Ti melt droplets are heated above the melting temperature,slowly cooled down,and held at a given temperature. After switching off the power the sample falls down to be quenched by heat transfer to the copper chill substrate.The temperature of the mel …… 此处隐藏：15040字，全部文档内容请下载后查看。喜欢就下载吧 ……