Journal of Materials Science and Engineering B 7 (7-8) (2017) 135-141 doi: 10.17265/2161-6221/2017.7-8.001

The Microstructure of Zr-Based Bulk Metallic Glass and

Glass Matrix Composite

Min-Chi Yeh1, Pei Jen Lo1, Wei-Liang Liu2 and Ker-Chang Hsieh1

1. Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 804, Taiwan

2. Metal Industries Research & Development Center, Kaohsiung 804, Taiwan

Abstract: This study describes the microstructure of a Zr-based alloy (Zr63.36Cu17.22Ni11.47Al7.95, at.%) under different cooling conditions. The Zr-based alloy can obtain completely amorphous structure, amorphous/nanocrystalline droplet and amorphous/crystalline composite structure by fast to slow cooling rate. It is interesting in the amorphous/nanocrystalline droplet composite that the average compositions of the droplet phase and amorphous matrix phase were same as the original alloy composition and the contrasts of BEI (back scatting image) were different. The droplet phase formed with (Al,Ni)2Zr3, and Zr2Ni(Al,Cu) nanocrystalline structures based on the analysis of XRD (X-ray diffractometry), EBSD (electron backscatter diffraction) and TEM (transmission electron microscopy). And Zr2Ni(Al,Cu) nanocrystalline phase transfers to the Zr2Cu(Al,Ni) phase after thermal treatment. The equilibrium phases of the alloy have been identified as Zr2Ni phase, Zr2Cu phase, Al2NiZr6 phase and τ3 (Zr51Cu28Al21, at.%) phase which reach four phases equilibrium at 1,073 K for one week.

Key words: Metallic glass, nanocrystalline, glass-forming ability, droplet phase.

1. Introduction

To solve the problem of limited deformation in

glassy metallic alloys, researchers have recently

developed the concept of heterogeneous materials

including a glassy matrix and various metastable

phases [1, 2]. Investigating the possibility for the

design of a new type of composite structure (i.e.,

amorphous/crystalline or amorphous/nanocrystalline

composites instead of amorphous/amorphous

composites) may be able to improve the ductility of

BMG (bulk metallic glass). Cu-Zr-Al(Ti) composites

have been reported to contain glassy matrix and

droplet phase including metastable crystalline phases

[3-8]. The sizes of droplet phases are from nanometer

to micrometer dimensions. These structural

heterogeneities are beneficial for the enhancement of

macroscopic deformability.

Due to the fact that Zr-based metallic glasses

exhibit excellent GFA (glass forming ability), i.e.,

Corresponding author: Ker-Chang Hsieh, Ph.D., professor,

research fields: alloy, phase diagram.

cooling rates of only about 1 K/s is required to

suppress crystallization and to form a metallic glass

[9]. In current study, we present a Zr-based alloy

(Zr63.36Cu17.22Ni11.47Al7.95, at.%) and different

composite structures can be formed under different

cooling conditions. The relationships between

amorphous, nanocrystalline structure and equilibrium

structure are discussed.

2. Experimental Method

The Zr-based alloys were prepared by arc melting

under an argon atmosphere. An amorphous/crystalline

structure is obtained from the water-quenching

method. The alloy samples were vacuum sealed in

quartz tube and heated at 1,173 K became a liquid

state, and then quenched into water. The medium

cooling rate used the copper-mold casting method to

obtain an amorphous/nanocrystalline droplet structure.

The alloys were cooled directly on the copper-hearth

with cooling water circulation inside the copper-hearth.

Finally, the rapid cooling rate used the copper-mold

suction-casting method to produce a fully amorphous

D DAVID PUBLISHING

The Microstructure of Zr-Based Bulk Metallic Glass and Glass Matrix Composite

136

structure. The alloys directly cast into cylindrical rods

with a 5 mm diameter by suction casting that attached

on the copper-hearth of arc-smelter.

In order to understand the relationship between

nanocrystalline structure and equilibrium structure, we

undergo heat treatment experiments. The alloy

samples with amorphous/nanocrystalline droplet

structure were annealed at 686 K between glass

transition temperature and crystallization temperature.

The phase transformation of nanocrystalline droplet

was examined at 15 minutes, 45 minutes and 120

minutes heat treatment time. One of the samples was

fully annealed at 1,073 K for one week in order to

reach the stable equilibrium phases.

The glass transition temperature, Tg, and the

crystallization onset temperature, Tx, were determined

by DSC (differential scanning calorimetry,

PerkinElmer DSC7) and thermos-gravimetry scanning

calorimetry (STA, NETZSCH STA 409 PC) by using

a constant heating rate of 0.33 K/s. Structural

characterization was performed by XRD (X-ray

diffractometry, Bruker D8) with Co Kα radiation,

EBSD (electron backscatter diffraction), and an

HRTEM (high-resolution transmission electron

microscopy, FEI E.O Tecnai F20 G2 MAT S-TWIN).

The phase composition was examined by using an

EPMA (electron probe micro-analyzer, JEOL

JXA-8900R). The hardness was measured by a micro

Vickers testing machine (SHIMADZU

Micro-hardness Tester) with 100 grams load and 15

seconds holding time.

3. Results and Discussion

3.1 Microstructure and Composition Analysis

Fig. 1 shows the alloy microstructure by using the

water-quenching method. There are black hexagonal

precipitates and dark droplet phase embedded in a

bright matrix. The dark droplets have the size around

10~100 um diameter and droplets occasionally appear

close to each other. The composition of black

hexagonal precipitates is Zr51Cu21Ni7Al21. If the Ni

concentration adds with the Cu concentration, the

black hexagonal precipitates are similar to the τ3

phase with a composition of Zr51Cu28Al21. Yokoyama

et al. [10, 11] proposed that the τ3 crystalline phase

causes embrittlement of the Zr-based bulk amorphous

alloys. Thus, it is important to eliminate τ3 phase from

the molten Zr-based alloy before casting. The other

higher cooling rate samples did not form the τ3

crystalline phase. Fig. 2 shows the alloy

microstructure that cooled on the copper-hearth inside

the arc-smelter. The average compositions of the

droplet phase and the matrix phase are same as the

original alloy composition within the experimental

error of EPMA composition measurement. This

phenomenon is similar to the previous studies [6-8].

Hirotsu et al. [12] propose that there is no clear

compositional variation throughout the specimen

which means that the atomic composition distribution

is almost the same as that in the liquid state, and no

local primary phase nucleation and growth was

occurring during quenching. Therefore, we speculate

that droplet exists in nanocrystalline different which is

Fig. 1 The alloy microstructure by using the water-quenching method. The composition of black hexagonal precipitates is Zr51Cu21Ni7Al21.

Fig. 2 Thcopper-hearthcomposition ooriginal alloy EPMA.

from the am

contrast in b

3.2 Glass-F

Zr63.36Cu17.22

Fig. 3

Zr63.36Cu17.22

glass transit

first crystal

respectively

a supercoole

temperature,

heating rate

reported a Z

622 K and T

ΔTx = 127 K

3.3 Hardnes

Fig. 4 sh

The Micr

e alloy microh inside thof the droplet

composition w

morphous matr

backscattered

Forming Abili

2Ni11.47Al7.95 A

3 shows

2Ni11.47Al7.95

tion temperat

llization, Tx

, at a heating

ed liquid regi

, Tl = 1,103 K

e of 0.33 K/

Zr65Al7.5Ni10C

Tx = 749 K. T

K.

ss Test

hows an SEM

rostructure o

ostructure thahe arc-smelte

and the matrwithin the exp

rix. This diffe

electron mod

ity (GFA) of

Alloy

DSC

full amorph

ture, Tg, and

, are 652

g rate of 0.33

ion, ΔTx = 68

K, was measu

s. The Inoue

Cu17.5 alloy [1

The supercool

M image ob

of Zr-Based B

at cooled on er. The averix is same as

perimental erro

ference causes

de.

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pattern

hous alloy.

the onset of

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btained from

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the

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roup

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uses the pile-

ented area. N

plet phase of

plet phase

pagating to

asured by us

orphous matr

ter than that o

V). They mi

esses for act

orphous matr

umes, which

3 DSC patteper-mold suctio

4 BEI image plet structure a

ass Matrix Co

with amorphou

he hardness t

visible on one

the amorph

he indenter d

-up and over

No shear-band

f the indented

can prevent

the free surf

sing the mic

rix phase is 4

of the nanocr

ight possess

tivating shea

rix phase sho

h benefit the

rn of the full aon-casting meth

of the alloy wiafter hardness t

omposite

us/nanocrysta

test. A semic

e side of the

hous matrix

during the ind

rlapping of l

d travel is app

d area. The na

t the shear

face. The lo

cro-hardness

56 ± 8 HV, w

rystalline drop

different c

ar bands [1

ould have mo

initiation of

amorphous BMhod.

ith amorphous/test.

137

alline droplet

circular shear

e indentation

phase. The

dentation test

layers in the

parent on the

anocrystalline

band from

ocal hardness

test for the

which is 10%

plet (504 ± 8

critical shear

5]. A softer

ore open free

f shear bands

MG by using the

/nanocrystalline

7

t

r

n

e

t

e

e

e

m

s

e

%

8

r

r

e

s

e

e

138

caused by

amorphous

shear-transfo

sites for th

shear bands

regions [16]

3.4 XRD, EB

The XRD

investigate

amorphous/n

pattern of th

matrix are

appears at a

50°, and

nanocrystall

identified a

Zr2Cu(Al,Ni

on the JCP

41-0898 and

Due to the

poor crystal

affected by

false identi

Therefore, t

analysis to id

phase in deta

Fig. 5 The Xamorphous m

The Micr

lower critic

matrix p

ormation zon

he shear ban

are apparent

.

BSD, and TEM

D, EBSD, and

the struct

nanocrystallin

he nanocrysta

shown in Fi

a diffraction a

a few pe

line droplet p

s the (Al,Ni

i) structure-l

PDS file No

d JCPDS fil

fact that the

lline therefor

amorphous

ification of

this study w

dentify nanoc

ail.

XRD pattern omatrix.

rostructure o

cal shear str

phase prefer

nes, which ser

nds. Consequ

t in the soft am

M Analysis

d TEM analys

ture of th

ne droplet p

alline droplet

ig. 5. A broa

angle of appr

aks are ap

phase. These

i)2Zr3, the Z

like crystallin

o. 65-1673,

e No. 18-04

nanocrystall

re the XRD

matrix. It is

the nanocr

ill conduct E

crystalline str

of the nanocrys

of Zr-Based B

resses. A so

rentially fo

rve as nuclea

uently, abun

morphous ma

sis are applie

he alloy w

phase. The X

t and amorph

ad diffuse hu

roximately 35

pparent in

e peaks could

Zr2Ni(Al,Cu)

ne phases b

JCPDS file

466, respectiv

line structure

signals wil

s likely to c

rystalline ph

EBSD and T

ructure of dro

stalline droplet

Bulk Metallic G

ofter

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ation

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atrix

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with

XRD

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ump

5° to

the

d be

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ased

No.

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has

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ause

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the

Fig.

Glass and Gla

n the droplet

identified

ucture-like p

ucture-like ph

stallinity in

icating that

ntrast between

orphous stru

nocrystalline

ntributed by

ase and Zr2Ni

EBSD measu

agonal struc

h-resolution

m the drople

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ne of the Z

ntified as the

and B spot bo

ferent crystal

[311] zone o

. 6 EBSD ana

ass Matrix Co

phase, the K

as the

phase and

hase. In addit

n the brig

the dark-bri

n the nanocry

ucture. From

structure

tetragonal (

(Al,Ni) struc

urements did

cture-like ph

transmissio

t phase. The

of A spot i

Zr2Ni(Al,Cu)

[001] zone o

oth have the s

orientation. T

of the (Al,Ni)2

alysis of the dr

omposite

Kikuchi lines

(Al,Ni)2Zr3

the Zr2Ni(A

tion, there is

ght amorpho

ight contrast

ystalline struc

m the above

of droplet

(Al,Ni)2Zr3 s

ture-like pha

not observe

hase. Fig.

on electron

e selected are

is identified

phase and

of the Zr2Ni(A

same structur

The C spot is

2Zr3 phase. T

roplet phase.

in Fig. 6 can

tetragonal

Al,Ni) cubic

no signal of

ous matrix,

t is a phase

cture and the

results, the

phase is

structure-like

se. However,

Zr2Cu(Al,Cu

7 shows a

microscopy

ea diffraction

as the [125]

d B spot is

Al,Cu) phase.

re and have a

s identified as

TEM analysis

n

l

c

f

,

e

e

e

s

e

,

u)

a

y

n

]

s

.

a

s

Fig. 7 TEMdiffraction pa

did not obse

EBSD and T

are the nano

3.5 Phase Tr

In order

nanocrystall

therefore we

The alloys

phase were a

temperature

thermal trea

120 minut

crystallizatio

thermal tre

stronger cr

annealing s

weaker in

crystalline

stronger.

nanocrystall

phase. Fig.

after therma

droplet regio

the (Al,Ni)2Z

The Micr

M bright field ttern) of the dr

erve Zr2Cu(A

TEM results,

ocrystalline st

Transformation

to understan

line structur

e undergo the

with amorp

annealed at 6

and cryst

atment time is

tes to for

on. Fig. 8 sh

eatment. Th

rystalline si

sample and

the 45 m

signals of Z

This me

line phase ma

9 shows the

al treatment

on, the Kiku

Zr3 tetragona

rostructure o

image and SAroplet phase.

l,Ni) phase. C

(Al,Ni)2Zr3 a

tructures in th

n under Ther

nd the relat

re and equi

e heat treatm

phous/nanocr

686 K betwee

tallization te

s 15 minutes

rm differen

hows the XR

e Zr2Ni(Al,

gnals in th

crystalline

minutes samp

Zr2Cu(Al,Ni)

eans that

ay transfer to

e EBSD patt

for 45 minu

uchi lines can

al structure-li

of Zr-Based B

ADP (selected

Combining X

and Zr2Ni(Al

he droplet pha

rmal Treatmen

ionship betw

ilibrium pha

ment experime

rystalline dro

en glass transi

emperature,

, 45 minutes

nt degrees

RD patterns a

Cu) phase

he 15 min

signals bec

ple instead

) phase bec

Zr2Ni(Al

the Zr2Cu(A

tern of the a

utes. In the d

n be identifie

ike phase and

Bulk Metallic G

area

XRD,

,Cu)

ase.

nt

ween

ases,

ents.

oplet

ition

the

and

of

after

has

nutes

came

the

came

,Cu)

Al,Ni)

alloy

dark

ed as

d the

Zr2C

EBS

Zr2N

in th

the

stru

crys

and

Fig. amo

Fig. amomin

Glass and Gla

Cu(Al,Ni) te

SD analysis r

Ni(Al,Cu) ph

he 45 minute

broad diffra

ucture almos

stalline state

d (Al,Ni)2Zr3

8 XRorphous/nanocr

9 EBorphous/nanocrnutes.

ass Matrix Co

etragonal st

results also c

hase was not

es sample. Aft

action charac

st disappear

e. The dropl

3 phases at

RD pattern rystalline dropl

BSD patternrystalline drop

omposite

tructure-like

onfirm this p

found by EB

fter annealing

cteristic of an

red, and th

let became Z

this therm

of the let after therma

n of the plet after ann

139

phase. The

phase change.

BSD analysis

g 120 minutes

n amorphous

hat is fully

Zr2Cu(Al,Ni)

al treatment

alloy withal treatment.

alloy withnealing for 45

9

e

.

s

s,

s

y

)

t

h

h 5

140

Fig. 10 ThAl2NiZr6 andEPMA after week.

condition.

equilibrium

annealing te

week. Fig.

several crys

equilibrium

Al2NiZr6 ph

alloy reache

one week.

4. Conclus

Both drop

composition

contrast diff

the structu

droplet and a

No shear-

of the indent

than the am

prevent the

surface.

Combinin

(Al,Ni)2Zr3

structures in

nanocrystall

after therma

The equil

identified a

phase and τ

phases equil

The Micr

e four equilibd τ3 (Zr51Cu2

the Zr-based

In order

phases of

emperature is

10a shows th

stalline phase

phases as

hase and τ3

es four phase

sions

plet and amo

n as the orig

ference in ba

ure differenc

amorphous m

-band travel

ted area, whi

morphous ma

shear band

ng XRD, EB

and Zr2Ni(A

n the drople

line phase tra

al treatment.

ibrium phase

as Zr2Ni pha

τ3 (Zr51Cu28A

librium at 1,0

rostructure o

brium phases

8Al21) phase walloy anneal a

to understa

f this Zr-ba

s raising to

he SEI image

es. Fig. 10b

Zr2Ni phase

3 (Zr51Cu28A

es equilibrium

orphous phas

ginal alloy c

ack scattering

ce between

matrix.

appears on t

ich has a 10%

atrix. The dr

from propag

BSD and TE

Al,Cu) are the

et phase. An

ansfers to Zr2

es of Zr-based

ase, Zr2Cu

Al21) phase w

073 K for one

of Zr-Based B

as Zr2Ni, Zrwere identifiedat 1,073 K for

and the st

ased alloy,

1,073 K for

e which pres

shows the st

e, Zr2Cu ph

Al21) phase.

m at 1,073 K

se have the s

composition.

g image is du

nanocrystal

the droplet ph

% higher hard

roplet phase

gating to the

EM results

e nanocrystal

nd Zr2Ni(Al

2Cu(Al,Ni) ph

d alloy have b

phase, Al2N

which reach

e week.

Bulk Metallic G

r2Cu, d by r one

table

the

one

sents

table

hase,

This

K for

same

The

ue to

lline

hase

dness

can

free

that

lline

,Cu)

hase

been

NiZr6

four

Ac

T

fina

Cou

Re

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

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