ATOM-N 2008 4 th edition Advanced Topics in Optoelectronics, Microelectronics and Nanotechnologies A structural-morphological study of a Cu 63 Al 26 Mn

ATOM-N 2008ATOM-N 2008 44thth edition editionAdvanAdvancced Topics in Oed Topics in Opptoelectronics, Microelectronics and toelectronics, Microelectronics and

NanotechnologiesNanotechnologies

A structural-morphological study

of a Cu63Al26Mn11 shape memory alloy

Sergiu Stanciua, Leandru G. Bujoreanua*, Iulian Ioniţăa, Andrei V. Sandub, Alexandru Enachea

a Faculty of Materials Science and Engineering, “Gh. Asachi” Technical University from Iaşi, Bd. D. Mangeron 61A, 70050 Iaşi, Romania;b Romanian Inventors Forum, Str. Sf. P.Movilă, 3, 700089, Iaşi, Romania



1. Introduction1. Introduction

In alloys with In alloys with

(12(12..4-13) % Al, 4-13) % Al,

ββ11(D0(D033)) ordered ordered

austenitaustenitee is a is a

solid solution solid solution

babased on sed on CuCu33AlAl

that transforms that transforms

into into ββ11’ (18R’ (18R11) ) oror

γγ11’(2H)’(2H) martensite martensite



In Cu-Al alloys, MIn Cu-Al alloys, Mss is very elevated and the precipitation of hard is very elevated and the precipitation of hard

γγ22 cannot be suppressed by quenching → cannot be suppressed by quenching → Ni alloyingNi alloying lowers M lowers Mss

down to room temperature. Above 5 %Ni, brittle NiAl precipitates down to room temperature. Above 5 %Ni, brittle NiAl precipitates

can occur.can occur.

Usual concentration of Cu-Al-Ni SMAs is: Usual concentration of Cu-Al-Ni SMAs is: Cu-(10-14) %Al- (2-4) Cu-(10-14) %Al- (2-4)

%Ni%Ni

Typical thermoelastic martensite (martensite plates grow Typical thermoelastic martensite (martensite plates grow

continuously during cooling and shrink continuously during continuously during cooling and shrink continuously during

heating, until complete disappearance, which creates a heating, until complete disappearance, which creates a

continuous balance between thermal and elastic effects continuous balance between thermal and elastic effects

suggesting the term suggesting the term thermoelastic transformation)thermoelastic transformation) is γis γ11’, with the ’, with the

substructure formed by internal twins.substructure formed by internal twins.



Cu–Al–Ni shape memory alloys (SMAs) represent one of the Cu–Al–Ni shape memory alloys (SMAs) represent one of the

systems that have become commercially available due to their systems that have become commercially available due to their

relatively low cost and thermoelastic character of martensitic relatively low cost and thermoelastic character of martensitic

transformation. transformation.

Common alloys contain (10-14) Al – (2-4) Ni – bal. Cu (hereafter Common alloys contain (10-14) Al – (2-4) Ni – bal. Cu (hereafter

all chemical composition will be in mass. %) and are grain refined all chemical composition will be in mass. %) and are grain refined

with Mn, B, Ce, Co, Fe, Ti, V, and Zr. with Mn, B, Ce, Co, Fe, Ti, V, and Zr.

In Cu–Al–Ni-based SMAs up to four martensites (α’In Cu–Al–Ni-based SMAs up to four martensites (α’11, β’, β’11, β”, β”11 and and

γγ’’11) can be observed along with an ordered parent phase, also ) can be observed along with an ordered parent phase, also

called austenite (called austenite (ββ11 based on Cu based on Cu33Al) and three equilibrium phases Al) and three equilibrium phases

((αα, NiAl and , NiAl and γγ22, based on Cu, based on Cu99AlAl44).).

Cu–Al–Ni shape memory alloys (SMAs) represent one of the Cu–Al–Ni shape memory alloys (SMAs) represent one of the

systems that have become commercially available due to their systems that have become commercially available due to their

relatively low cost and thermoelastic character of martensitic relatively low cost and thermoelastic character of martensitic

transformation. transformation.

Common alloys contain (10-14) Al – (2-4) Ni – bal. Cu (hereafter Common alloys contain (10-14) Al – (2-4) Ni – bal. Cu (hereafter

all chemical composition will be in mass. %) and are grain refined all chemical composition will be in mass. %) and are grain refined

with Mn, B, Ce, Co, Fe, Ti, V, and Zr. with Mn, B, Ce, Co, Fe, Ti, V, and Zr.

In Cu–Al–Ni-based SMAs up to four martensites (α’In Cu–Al–Ni-based SMAs up to four martensites (α’11, β’, β’11, β”, β”11 and and

γγ’’11) can be observed along with an ordered parent phase, also ) can be observed along with an ordered parent phase, also

called austenite (called austenite (ββ11 based on Cu based on Cu33Al) and three equilibrium phases Al) and three equilibrium phases

((αα, NiAl and , NiAl and γγ22, based on Cu, based on Cu99AlAl44).).



At rapid cooling At rapid cooling ββ11 (D (D0033) austenite usually transforms into ) austenite usually transforms into γγ’’11

(2H orthorhombic) thermally induced martensite, while the (2H orthorhombic) thermally induced martensite, while the

other three above mentioned martensites are stress-induced other three above mentioned martensites are stress-induced

within specific ranges of chemical compositions and applied within specific ranges of chemical compositions and applied

stress levels. stress levels.

At slow cooling, in equilibrium state, βAt slow cooling, in equilibrium state, β11 ordered austenite ordered austenite

undergoes an undergoes an eutectoid decompositioneutectoid decomposition, into α + γ, into α + γ22. .

When Cu-Al-Ni based SMAs, with thermally induced When Cu-Al-Ni based SMAs, with thermally induced

martensite structure, were subjected to heating, up to four solid martensite structure, were subjected to heating, up to four solid

state transitions were observed.state transitions were observed.



1. 1. RReverse transformation of everse transformation of γγ’’11 martensite to β martensite to β11 (DO (DO33) )

austenite was produced in a single or a double stage.austenite was produced in a single or a double stage.

2.2. EExothermic precipitation of equilibrium α or γxothermic precipitation of equilibrium α or γ22 phases from phases from

ββ11 austenite, at lower or higher aluminum contents, austenite, at lower or higher aluminum contents,

respectively. respectively.

3. 3. ββ11 (DO (DO33) austenite became less ordered and turned to β) austenite became less ordered and turned to β22

(B2) austenite(B2) austenite

4. 4. ββ22 (B2) austenite became completely disordered and (B2) austenite became completely disordered and

turned to β (A2) austenite. turned to β (A2) austenite.



In previous reports the influence of γIn previous reports the influence of γ22 phase precipitation on phase precipitation on

shape memory behavior of Cu-Al-Ni-Mn-Fe SMAs was shape memory behavior of Cu-Al-Ni-Mn-Fe SMAs was

analyzed and no major changes were detected in the analyzed and no major changes were detected in the

subsequent reversion of martensite to austenite, after the subsequent reversion of martensite to austenite, after the

quenching of an alloy in which hard γquenching of an alloy in which hard γ22-phase had -phase had

precipitatedprecipitated 4_MSE_A481-482(2008)494-499.pdf4_MSE_A481-482(2008)494-499.pdf. .

Moreover, no orientation relationship was revealed between Moreover, no orientation relationship was revealed between

austenitic matrix and precipitates although the alloy under austenitic matrix and precipitates although the alloy under

study experienced shape recovery degrees higher than 96 study experienced shape recovery degrees higher than 96

%% 6_JOAM10,6(2008)1365-1369.pdf6_JOAM10,6(2008)1365-1369.pdf. .



Secondary electrons scanning electron miscroscopy detail of one cuboidal region corresponding to dendritic precipitation of γ phase

Condo et al. MSE-A 328(2002), 190-195



On the other hand, in Cu-21.57 Zn-7 Al SMA the precipitation On the other hand, in Cu-21.57 Zn-7 Al SMA the precipitation

of copper-rich equilibrium α-phase did not cause total of copper-rich equilibrium α-phase did not cause total

degradation of shape memory phenomena, even if it shifted degradation of shape memory phenomena, even if it shifted

critical temperatures of reversible martensitic transformation.critical temperatures of reversible martensitic transformation.

Considering the above observations, the present paper aims Considering the above observations, the present paper aims

to bring more evidence on the structural-morphological to bring more evidence on the structural-morphological

connection between connection between equilibrium-equilibrium-phase precipitatesphase precipitates and and

matrixmatrix in a Cu-Al-based SMA in a Cu-Al-based SMA in which Ni has been replaced in which Ni has been replaced

by Mnby Mn..



After casting, hot forging (60 % thickness reduction at 973 K) and After casting, hot forging (60 % thickness reduction at 973 K) and

homogenization (1173 K/ 8∙3.6 ksec/ air), specimens were homogenization (1173 K/ 8∙3.6 ksec/ air), specimens were

prepared from a Cuprepared from a Cu6363AlAl2626MnMn1111 SMA for differential scanning SMA for differential scanning

calorimetry (DSC), and scanning electron microscopy (SEM) calorimetry (DSC), and scanning electron microscopy (SEM)

studies.studies.

DSC measurementsDSC measurements:: 2920 Modulated DSC TA INSTRUMENTS 2920 Modulated DSC TA INSTRUMENTS

unit, with a heating rate of 10 K/minunit, with a heating rate of 10 K/min (RUB) (RUB)

SEM micrographsSEM micrographs:: SEM – VEGA II LSH TESCAN scanning SEM – VEGA II LSH TESCAN scanning

electron microscope, coupled with an EDX – QUANTAX QX2 electron microscope, coupled with an EDX – QUANTAX QX2

ROENTEC detectorROENTEC detector (RIF) (RIF)

2. Methodology2. Methodology



3.1 DSC thermogram3.1 DSC thermogram

3. Results and Discussion3. Results and Discussion

Typical DSC thermogram recorded during the heating of hot forged (60 Typical DSC thermogram recorded during the heating of hot forged (60 % thickness reduction at 973 K) and homogenized (1173 K/ 8∙3.6 ksec/ % thickness reduction at 973 K) and homogenized (1173 K/ 8∙3.6 ksec/ water) Cuwater) Cu6363AlAl2626MnMn1111 SMA revealing three solid state transitions. SMA revealing three solid state transitions.



MMartensite reversion was not detected, and no signs of martensite artensite reversion was not detected, and no signs of martensite

instantaneous stabilization were noticeable instantaneous stabilization were noticeable →→ initial structure may initial structure may

be rather austenitic than martensitic.be rather austenitic than martensitic.CConsidering that Al content is onsidering that Al content is

rather low, α-phase precipitation is expected to occur. rather low, α-phase precipitation is expected to occur.

On the thermogram the corresponding On the thermogram the corresponding startstart and and finishfinish critical critical

temperatures were determined for both temperatures were determined for both experimentalexperimental and and

theoreticaltheoretical transformations, designated with subscripts transformations, designated with subscripts ss and and ff as as

well as well as exex and and thth, respectively. , respectively.

For For α-phase precipitationα-phase precipitation, located around 575 K, these values , located around 575 K, these values

were: αwere: αss((exex)) = 483 K; α = 483 K; αss((thth)) = 524 K; α = 524 K; αff((thth)) = 621 K and α = 621 K and αff((exex)) = 629 K, = 629 K,

while specific enthalpy emission was between 5.48 and 7.34 kJ/ while specific enthalpy emission was between 5.48 and 7.34 kJ/

kg. kg.



Between DBetween Dss((exex)) = 712 K and D = 712 K and Dff((exex)) = 804 K two disordering = 804 K two disordering

transition occur. Theoretical critical temperatures for βtransition occur. Theoretical critical temperatures for β11 (DO3) (DO3)

→ β→ β22 (B2) order-disorder transition were: D (B2) order-disorder transition were: DBBss((thth)) = 747 K and = 747 K and

DDBBff((thth)) = 787 K and for β = 787 K and for β22 (B2) → β (A2) order-disorder (B2) → β (A2) order-disorder

transition were: Dtransition were: DAAss((thth)) = 747 K and D = 747 K and DAAff((thth)) = 797 K. = 797 K.

These results suggest that both transitions start at the same These results suggest that both transitions start at the same

temperature, 747 K.temperature, 747 K.

PPrevious DSC resultsrevious DSC results,, reported by Kustov reported by Kustov et al.et al. on Cu-Al on Cu-Al

based SMAsbased SMAs,, have shown that eutectoid reaction also have shown that eutectoid reaction also

occurred on heating, at about 770 K [7]occurred on heating, at about 770 K [7]..



The typical SEM micrographs of the alloy under study, after The typical SEM micrographs of the alloy under study, after

being subjected to 873 K heating and air quenching show α-being subjected to 873 K heating and air quenching show α-

phase precipitatphase precipitateses locatedlocated both along grain boundaries both along grain boundaries ((primary primary

coarse precipitatescoarse precipitates)) and inside the grains and inside the grains ( (finer secondary-finer secondary-

phase particlesphase particles)). .

Primary α-phase precipitatesPrimary α-phase precipitates:: preferred orientation tendencies preferred orientation tendencies

in neighboring grains, in neighboring grains, iintersectinntersectingg atat about 120 about 12000. Their width is . Their width is

about several μm while their length is between 20-30 μm.about several μm while their length is between 20-30 μm.

Secondary α-phase precipitates are much finer, with width less Secondary α-phase precipitates are much finer, with width less

than 1 μm and are mothan 1 μm and are morre dense.e dense.

3.2 SEM observations3.2 SEM observations



Typical SEM micrographs of hot forged (60 % thickness reduction at 973 K) and homogenized (1173 K/ 8∙3.6 ksec/ water) Cu63Al26Mn11 SMA after 873

K heating and air quenching, etching with 30 % HNO3 aqueous solution:

(a) primary and secondary α-phase precipitates; (b) enlarged view of α-phase precipitates.



The general aspect of the matrix The general aspect of the matrix that contains secondary that contains secondary αα--

phase precipitates, phase precipitates, suggests that it represents an eutectoid.suggests that it represents an eutectoid.

In order to better reveal the morphology of α-phase In order to better reveal the morphology of α-phase

precipitates and to detect chemical composition fluctuations, precipitates and to detect chemical composition fluctuations,

between the component metallographic phases, a detail of between the component metallographic phases, a detail of

the of primary α-phase precipitatesthe of primary α-phase precipitates in micrograph (b) in micrograph (b), is , is

shown and a phase image is illustratedshown and a phase image is illustrated,, as determined by as determined by

means of SEM electron microprobe. means of SEM electron microprobe.



Electron microprobe observations on hot forged (60 % thickness reduc-tion at 973 K) and homogenized (1173 K/ 8∙3.6 ksec/ air) Cu63Al26Mn11 SMA

after 873 K heating and air quenching, etching with 30 % HNO3 aqueous

solution: (a) magnified detail of α-phase precipitates, from previous micrograph; (b) chemical composition variation on α-phase and matrix.



The detail reveals the fact that, after etchingThe detail reveals the fact that, after etching,, α-phase α-phase

appears in relief as compared to the matrix. The composition appears in relief as compared to the matrix. The composition

image shows higher Cu-contents and lower Al-contents, as image shows higher Cu-contents and lower Al-contents, as

compared to the matrix, at the corresponding level of α-compared to the matrix, at the corresponding level of α-

phase precipitates.phase precipitates.

These results agree with theoretical chemical compositions These results agree with theoretical chemical compositions

of α-phase, which is copper-based and of the matrix, which of α-phase, which is copper-based and of the matrix, which

is based on Cuis based on Cu33Al, therefore richer in Al but poorer in Cu.Al, therefore richer in Al but poorer in Cu.



A CuA Cu6363AlAl2626MnMn1111 shape memory alloy with ferromagnetic shape memory alloy with ferromagnetic

properties was analyzed in hot pressed and homogenized properties was analyzed in hot pressed and homogenized

state, revealing austenitic structure. During heating to 873 K, state, revealing austenitic structure. During heating to 873 K,

exothermic α-phase precipitation occurred with 5.48 - 7.34 exothermic α-phase precipitation occurred with 5.48 - 7.34

kJ/ kg specific enthalpy emission.kJ/ kg specific enthalpy emission.

The structure, analyzed after heating to 873 K and The structure, analyzed after heating to 873 K and

subsequent air cooling, revealed the formation of primary subsequent air cooling, revealed the formation of primary

and secondary precipitates which, by electron probe phase and secondary precipitates which, by electron probe phase

imagingimaging,, were ascribed to α-phase. were ascribed to α-phase.

4. Conclusions4. Conclusions



Primary precipitates were formed along grain boundaries Primary precipitates were formed along grain boundaries

while secondary precipitates had very large densities and while secondary precipitates had very large densities and

were observed only inside the grains. The results suggest were observed only inside the grains. The results suggest

that rather eutectoid decomposition than forward martensitic that rather eutectoid decomposition than forward martensitic

transformation occurred during post-precipitation cooling transformation occurred during post-precipitation cooling

from 873 K.from 873 K.



Financial assistance was obtained from Romanian National Financial assistance was obtained from Romanian National

University Research Council under the PCE-IDEI grant 616, University Research Council under the PCE-IDEI grant 616,

project 83/01.10.2007.project 83/01.10.2007.

AcknowledgmentsAcknowledgments



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ATOM-N 2008 4 th edition Advanced Topics in Optoelectronics, Microelectronics and Nanotechnologies A structural-morphological study of a Cu 63 Al 26 Mn