GlassGlass--formation formation in Mgin Mg--CuCu--Y Y alloysalloys

M.Satta, M.Palumbo,P. Rizzi, M.BariccoDipartimento di Chimica NIS, IFM/CNISM

Università degli Studi di Torino

BMGs:Mg-based alloysPROPERTIESMg-based alloy shows both high strenght to weight ratio and a low glass transition temperature

Good corrosion resistance

Low cost and ability to be recycled so Mg alloys should be highly desiderable for applications

APPLICATIONS

European School-BMGs/13-16 Sept ’06, Turin,ITALY

Synthesis of BMGs

T -T -T c u rv e s fo r a m o rp h o u s a llo y s

c a s tin gra p id

s o lid if ic a t io n

ln t im e

Tem

pera

ture

h ig h G F Alo w G F A

T g

T f

105-106

K/s 50 K/s

Mg-based glass forming alloys have a relatively large G.F.A.Samples up to 4 and 9 mm in diameter were obtained in Mg65Cu25Y10alloys by copper mould castingZhang Y, Tan H, Kong HZ, Yao B, Li Y. JMater Res 2003;18:664.

H.Ma, Q.Zheng, J.Xu, Y.Li, E.Ma; “J.Mater.Res,Vol20,No9 Sep2005 pag-2252-2255

How can we reach a high G.F.A?

Large G.F.A. obtained simultaneously with high value of Trg(Tg/Tm) and ΔTx(Tx-Tg)

The largest G.F.A. lies really at the eutectic point?

Which eutectic is involved for the system Mg-Cu-Y?

European School-BMGs/13-16 Sept ’06, Turin,ITALY

Calculated ternary systemDescription of the liquid ternary phase has been carried out by extrapolation from the assessed binary parameters. The aim of the work is to know:

The eutectic position

Ternary compounds, one or more?

G.F.R.

(1)

(3) (2)

Extrapolation from binary diagrams at different temperature leads to a different eutectic point.

x(C

U)

x(MG)

0.0

0.2

0.3

0.5

0.7

0.9

0.0 0.2 0.4 0.6 0.8 1.00 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

x(MG)

x(CU

)

Y

CU

MG

liquid->Cu fcc+Cu2Mg+Cu6Y

liquid->Mg2Y+CuMg2+Culiquid->Mg2Y+CuMg2+Cu2Y

From the calculation of the liquidus surface it is possible to obtain 3 eutectic points.

The (2)Mg45Cu33Y22 is the more close but not the same present in literature

European School-BMGs/13-16 Sept ’06, Turin,ITALY

1

2

3

Mg45Cu33Y22

Mg45Cu33Y22

Mg65Cu25Y10

Best Glass forming composition

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.00 0.00

0.25

0.50

0.75

1.00

Amorphous Part.amorphous Amorphous Inoue Part.amorphous Inoue Cristall. Inoue

Y

MgCu

X(Y)

X(Cu

)

X(Mg)

Experimental G.F.R. (Glass Forming Range)

Mg65Cu25Y10 was determined to be at a eutectic composition,but recently the best BMG former in the Mg-Cu-Y system was found to be located at the off- eutectic composition Mg58.5Cu30.5Y11 and Mg58Cu30.5Y11.5. The critical size for BMG formation now has been more than double from 4 to 9 mm. H.Ma, Q.Zheng, J.Xu, Y.Li, E.Ma; “J.Mater.Res,Vol20,No9 Sep2005 pag-2252-2255

Q.Zheng, H.Ma, E Ma, J.Xu; “Scripta Materialia”, In press

Xrd patterns show for both alloys phase unknown,no phase diagram or XRD standard for ternary phases

Improvement in the value of the undercooled liquid region (ΔTx)

Mg65Cu25Y10

Mg58Cu30.5Y11.5

European School-BMGs/13-16 Sept ’06, Turin,ITALY

Mg-Cu-RE (La,Y) systemNo thermodynamic assessment of the ternary Mg-Cu-Y system available.

Other systems that should present similarities with our system (Mg-Cu-La and Mg-Cu-Y)

Searching for…

European School-BMGs/13-16 Sept ’06, Turin,ITALY

A ternary intermetallic compound (MgCu2Y2) has been reported in the literature .

R. Mishra et al. Z. Naturforsch. 56b 2001 239-244

Mg-Cu-Y

Phase Crystal structure a(nm) b(nm) c(nm)MgCu2Y2 Mo2FeB2 0.76265 0.37409

Mg-Cu-La In the Mg-Cu-La system several ternary phases were found.A lot of intermetallics compounds were found to exist along the line corresponding to the Cu/lLa equiatomic ratio.S. De Negri, M. Giovannini, A.Saccone; “J.of Alloys and Compounds”,In Press.

Phase Crystal structure a(nm)LaCuMg (τ2) hP9-ZrNiAl 0.7732LaCuMg3 (τ4) UnknownLaCuMg4 (τ5) Unknown

Mg27Cu38Y35 (LM1)

40 60 80 100 120

Master alloy LM1 MgCu2Y2 MgCuY Mg2Y

Kα=Cu

Inte

nsity

LM1

2 θ

A

B

C

XRD pattern show 3 phases,one binary and two ternary.

The presence of three phases seems to be confirmed by the SEM and EDS: (A)MgCu2Y2; (B)MgCuY and (C)Mg2Y

No amorphous samples with this composition are obtained not a good glass former composition

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.00 0.00

0.25

0.50

0.75

1.00 LM1 Mg65Cu25Y10 Inoue Mg58Cu30.5Y11.5 Ma

Y

MgCu

X(Y)

X(Cu

)

X(Mg)

European School-BMGs/13-16 Sept ’06, Turin,ITALY

Mg 18%

Cu 42%

Y 40%

Mg 32%

Cu 35%

Y 33%

Mg61Cu28Y11 (LM2)

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.00 0.00

0.25

0.50

0.75

1.00

LM2 Mg65Cu25Y10 Inoue Mg58Cu30.5Y11.5 Ma

Y

MgCu

X(Y)

X(Cu

)

X(Mg)

Master alloy annealed at 713 K for two weeks

20 40 60 80 100

???

?

?

??

? ?

?

?

???

Inte

nsity

LM2 Annealed at 713 K for two weeks Mg2Cu

? Phases unknown (Mg4CuY;τ5)(Mg3CuY;τ4)

Kα=Cu

LM2 annealed at 713 K for two weeks

2 θ

A

B

C

Annealing is useful to obtain equilibrium phases

XRD pattern show one binary phase (A)(Mg2Cu)and two ternary unknown phases (B e C)

After EDS analysis we may propose two phases not reported: (B) Mg3CuY and (C) Mg4CuY

Easy to obtain amorphous ribbonsEuropean School-BMGs/13-16 Sept ’06, Turin,ITALY

Mg 59%

Cu 21%

Y 20%

Mg 67%

Cu 17%

Y 16%

Mg 64%

Cu 36%

Conclusions I

0.00 0.25 0.50 0.75 1.00

0.00

0.25

0.50

0.75

1.00 0.00

0.25

0.50

0.75

1.00

Mg2Y

Mg2Cu

LM1LM2Mg3CuY; Mg 4 CuY MgCuY and MgCu 2Y2Mg65Cu25Y10 InoueMg58Cu30.5Y11.5 Ma

Y

MgCu

X(Y)

X(Cu

)

X(Mg)Eutectic should be formed also by ternary phases.

Suggested ternary compounds lie on a Cu:Y 1:1 line as for Mg-La-Cu. Strcutures unknown

A thermodynamic assessment has been carried out for understanding the Glass Formation in this ternary system. M.Palumbo, M.Satta, G. Cacciamani, M Baricco; Thermodynamic Analysis of the Undercooled Liquid and Glass Transition in the Cu-Mg-Y System to appear in Mater.

Transaction

In order to understand the full thermodynamics of the system thermochimical properties of compunds are necessary.

A)MgCu2Y2

B)MgCuY

C)Mg3CuY (τ4)

D)Mg4CuY (τ5)

A

B CD

European School-BMGs/13-16 Sept ’06, Turin,ITALY

Mg-Cu SystemIn order to describe the ternary Cu-Mg-Y system, binary parameters have to be known.

Binary system shows amorphous phases G.F.R is around the eutectic between hcp-Mg and Mg2Cu phases

In order to determine experimental values of thermodynamic properties related to the amorphous phase, glassy ribbons have been prepared.

Composition studied:

Eutectic Mg85Cu15

Ipo-eutectic: Mg80Cu20, Mg75Cu25

Iper-eutectic: Mg87Cu13

Phase Pearson Space Lattice Coordinates Occupancy WyckoffName Symbol and Group and Parameters Positions

Prototype Number (nm)

CuMg2 oF48 Fddd a=0.9070 0,0,.128 Cu 16gCuMg2 70 b=0.5284 .161, 0, 0 Mg 16f

c=1.8250 0, 0, .411 Mg 16g

Cu2Mg cF24 Fd-3m a=0.7048 625, .625, .625 Cu 16d(C15 Laves) Cu2Mg 227 0,0,0 Mg 8a

Mg-Cu phase diagram has two intermetallic phases: Cu2Mg (Laves phase) and Mg2Cu

T[K

]

x(MG)

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

x(MG)

T[K]

CU MG

LIQUID

FCC

CU2MG

CUMG2

HCP

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1300

400

500

600

700

800

900

1000

1100

1200

1300

1400

G.F.R.

European School-BMGs/13-16 Sept ’06, Turin,ITALY

XRD/DSC of master alloys and melt-spun

European School-BMGs/13-16 Sept ’06, Turin,ITALY

2 3 4 5

D)

C)

B)

A)

A) Mg75Cu25B) Mg80Cu20C) Mg85Cu15D) Mg87Cu13

Mg

Inte

nsity

vettore di scattering s/Å-1

2 3 4 5 6

D)

C)

B)

A)

Inte

nsity

vettore di scattering s/Å-1

A) LM Mg75Cu25B) LM Mg80Cu20C) LM Mg85Cu15D) LM Mg87Cu13

Mg2Cu Mg

Master alloys haveshown the presence of the intermetallic phase Mg2Cu and hcp-Mg phase

XRD analysis confirm the appearance of a fully amorphous phase up to 85%Mg.

Crystallization behavior depends on composition, but in all cases crystallization products appear as Mg and Mg2Cu.

Evidence of Glass transition at 401K (scanning rate 40K/min) in good agreement with the value proposedby Sommer (Tg=380K at 20K/min) .F.Sommer, G.Bucher, B.Predel, J. De Phys.Colloque C8,suppl 8, 41 (1980) C8-563

Tx1(K) Tx2(K) Tx3(K) Tg(K) ΔHx (kJ/mol)Spin Mg75Cu25 422 444 3.8Spin Mg80Cu20 396 451 195 4.3Spin Mg85Cu15 413 453 401 3.9Spin Mg87Cu13 397 415 2

360 400 440 480 520

A) Mg75Cu25B) Mg80Cu20C) Mg85Cu15D) Mg87Cu13

DSC of melt-spun Cu-Mg alloys 273-->523K; 40 K/min

D

C

B

A

exo

2 W/g

Hea

t Flo

w

Temperature / K

European School-BMGs/13-16 Sept ’06, Turin,ITALY

20 40 60 80

Spin1 Spin2 Spin3 Spin4(partially amorphous) CuY Cu2Y

Melt-spun Cu58Y42

Inte

nsity

2θ

Cu-Y SystemSeveral intermetallic phases are present in

this system: CuY, Cu2Y, Cu7Y2, Cu4Y, Cu6Y. High ductilities in RM intermetallic

compounds (r=rare earth and M=main group or transition metal)

RM (CuY) crystallize in the CsCl (B2)-type structure.

Amorphous alloys can be prepared for 0.20<x<0.75 in the CuxY1-x system

Phase Pearson Space Lattice Coordinates Occupancy WyckoffName Symbol and Group and Parameters Positions

Prototype Number (nm)

Cu5Y hP6 P6/mmm a=0.5005 1/3, 2/3, 0 Cu 2c(or Cu6Y) CaCu5 191 c=0.4097 .5,0,.5 Cu 3g

0,0,0 Y 1a

Cu2Y oI12 Imma a=0.4308 0, .052, .162 Cu 8hCeCu2 74 b=0.6891 0, .25, .546 Y 4e

c=0.7303

CuY cP2 Pm-3m a=0.3479 0,0,0 Cu 1aClCs 221 .5, .5, .5 Y 1b

Cu4Y ???? ? ? ? ? ?

Cu7Y2 ???? ? ? ? ? ?

T[K

]

x(Y)

300

1150

2000

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

x(Y)

T[K

]

CU Y

LIQUID

FCC_A1

Cu6YCu7Y2

Cu4Y

Cu2Y

Cu2Y

HCP

BCC

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1300

1150

2000

G.F.R.

CuY

European School-BMGs/13-16 Sept ’06, Turin,ITALY

Conclusions IIThe calculated equilibrium phase diagram

is in good agreement with experimental values.

Results are comparable with a deviation of the eutectic temperatures of 15 K.

Experimental evidence of Tg is possible,but only at high scanning rates.

0.0 0.2 0.4 0.6 0.8 1.0

400

600

800

1000

1200

1400 this work Liang et al. CALPHAD 22 (1998) 527-544

Tem

pera

ture

/ K

Mole fraction MgFuture works,planning to…

DMA (dynamic mechanical analyzer) analysis to pinpoint Tg at low scanning rates for all compositions.

Try to obtain fully amorphous samples for Cu-Y system in view of study the CuY phase (ClCS structure).

CuY phase presents high ductility and high fracture-thoughness at room temperature that give an improvement of the mechanical properties.

European School-BMGs/13-16 Sept ’06, Turin,ITALY

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