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Study of order—disorder transformation of copper—gold alloys by means of differential thermal analysis
77zcrdca Acra, 25 (1978) 143-153 @ Ekevim sdcntifk Publishing Companx
Amsterdam
-
Printed in The Netherlands
STUDY OF ORDER-DISORDER TRANSFORMATION ALLOYS BY MEANS OF DIFFERENTIAL THERMAL
P. TISSOT
ASD
OF COPPER-GOLD ANALYSIS
R. DALLENBACH
D&m~emmt & chimie MiniraZe, ArJprmcr.
Adyfique Z2ZZ Cefu?ke 4 (SwifzrZandJ
(Rtodvai
4 octobez
et AppZiqke,
LQzircrsirtf de GCRC?W, 30, quai Emesr
19n)
ABsr5mc-r
Several copper-Sold alloys, with compositions of between IO and SO atomic percent of gold, were examined by quantitative DTA from 25 to 5fKl”C. The results are in good agreement with those obtained by other less rapid, but more accurate, methods. All the reactions observed were first-order transformations. A latent heat (180 & 40 cal g-at- ‘) was measured at 405’C for the 9; + cri transformation of the alloy containing 50% of gold. An endothermic effec& corresponding to an orderdisorder readon, was detected for all alloys, up to a composition of over 90 atomic percent of gold. I?.XRODUCIlON
An abundant literature has been devoted from many years to the study of order-disorder transformations, but it is clear that differential thermal analysis (DTA) is a technique not often used ’ - ‘_ As indicated by Castenet and Urbain”, this method is interesting because complete information on the structural transformations of an alloy may be rapidly obtained_ However, this dynamic method can only be used to study phenomena which are sufficiently rapid with respect to the heating rate used.
, We have studied the well kuown copper-gold system, which shows a continuous substitution solid solution (aD) and many ordered phases (a’, z:, 4, a“) (see Fig. I)_ Ail the solid St&e transformations take place between 200 and 4oocC All measurements were made using a Mettkr quantitative DTA apparatus, type TA 2000.
Samples were prepared by.melting capper and gold (Baker Coating Quality, 99.99 %) in graphite crucibks. Samp1e.weight.s were 50 &- -2 mg for compositions over 65. atom&percent (at* 76) copper,. and 980 5 20 mg- for compositions lower than 65 at % copper. For thermal analysis; ahtminiurn crucibles were -uw and the
Fig
1.3-k
cmppcr-gotd q-stanT.
60 mia 1 1660 2 E 3 E +o E
‘i0 #rpin-’
1 7
240 min
f-L /
1 i
I
/
lOVnin-
{
f
0 ;/
I
0
, 100
s 200
. 300
i 400
I Time
Cmh)
-
so0
rcfkrena was tie same weight of pure gold; the heating rate was 4 deg min- ‘. -ration of alloys, thermal trcatmcntsand difikrcntiaithermal anaiysis wexc performed under a nitrogenatmosphere!(99.995%). The formation of an or&red phase is g~~~raIiyassumedto proceed by nucleationand growth- This mechanism kads to the formationof antiphasedomains,theslow growth of thee domainsbeing the limitingfactorof thedegreeof or&r. The methodof preparationof thesamplesis thus ~a--- important_ and we used the treatment indicated in Fig_ 2, which seems to @v-c the best resoWion and rcproducibiiity of DTA peaks_The smallspheresobtained ~~~p~bttwcentwo~plattstomakta~tsurfaccof1mm,tocnsurt
145 good contact with the aluminum crucible- The composition of the aIloys was checked by neutron activation and analysis of 66Cu and “*Au content. Ali the heat treatments were performed under nitrogen, in Pyrex tubes heated in a smali electrical furnace. RESULTS AND DISCUSSION
In order to determine the optimum duration of annealing to obtain ordered ailoys, we quenched a line of samples AuCu and AuCu, beginning at 450°C. These samples were annealed at 370°C for different periods. Some DTA curves obtained are shown in Fig. 3. We observe an evolution of the peak shape, of the area and of the temperature, ali as functions of the annealing time. This evolution is particularly striking for AuCu, for which the first peak, corresponding to the transformation $’ -+ ai appears only after an annealing time of several minutes at 370°C; the second peak, corresponding to the transformation z;I + zD, is doubled when the annealing lasts less than ten hours. We have never observed an evo!ution after 24 hours at 37O”C, and we decided to anneal each sample for at least 60 hours at a temperature 10 de_below the transformation temprature. For transitions occurring at temperatures beiow 22O”C, the thermal treatment was extended to 100 hours. We have also studied the influence of the heating rate, between 2 and 15 deg min- ‘. on the temperature and the area of the peaks. We observed a steady increase in the temperature; on the other hand, the peak area remains roughly constant_ For the alloys near AuCu, which present two peaks, we also observed a constant total area, although the first peak increases and the second decreases with increasing heating rate_ We chose, for all DTA measurements, a heating rate of 4 deg min-‘_ In TabIe I, we list the onset- and maximum-peak temperature for all the samples_ These results can be divided in three groups, corresponding to the composi-
1
400 .
.
420 .
1
Temperctore 440 320 . I
PC) 340 I .
Au Cul
I
01-c
Fig. 3. Influa~ctof the annealingduration,
r
360 I
I)
156 35.m
330 320. :62 330,378 Ho.r402 370,-a I 9 3t?S.‘~21 4@_419 365,‘-%35 360 325
401 41-I 443 463 48.6 49-9 (Aucu) 5I.9 W.l
_%9 _w.9
335 337 372 380 560 325
69.1 71-l 724 7-a (.&Cat) n-1 792 -
365 356 398 394 387 3GO
169 197 226 289 250 239
Lions on &-her side of each ideaf composition Au,Cu, AuCu and AuCu3. The curves obtained for each group are shown in Fis_ 4, 5 and 6. The temperatures of the superhttice boundaries (see Fig_ 1) are indicated on each curve; the ageement is qui:e good, and it is clear tit DTA affords rapidly, and to z good degree of approximation, the general apprana cf the order disorder transformations of this binary system. In a!1w the shape of the peaks is characteristic of a first order transformation_ The difkrena betweco first and second order transformations is clurly demonstrated by comparison phase
with Fig_ 7, uhich illustrates, the transformation
of the /?
of the alloy Cu-2x1, which is considered to proceed by a second order reaction s*g_ The peaks of the gold-rich alloys (Fi_e 3) are quite broad, due to the relatively
low temperature of the trapsformation cxpcri-menr4 conditions,
and to the sample weight (-
1 g)_ Within our
the transformation extends over 40-50 degees. equivalent
to 10 minutes at a heztin,orate of -%de% min- I_ The enthalpy variation measured for xu,cu (4H,,_,, = 172 cal z-at- ’ ) is in good agreement with the calorimetric measurements of D’ Heurle and Gordon ’ o who report a value of 180 cai g-at- ’ for an alloy quench& from 500 to IS7 T_ Ko maximum value is observed for the ideal comgosi-
until 90 at oAgold, Jtirough Batterusing X-ray anaIysis. did not observe a superstructure with alloys richer than
Lion Xu,Cu.
Inann”,
We have measured a rhermal
effect
147
250
F&F_
Temperature
PC) 300
4_ J3TA curser nea.r Aud3.
75 at % gold. The alloys near AuCu (Fig. 5) show two peaks. The smaller corresponds to the transformation EX; + 2;; the larger, very sharp peak, corresponds to the formation of the disordered alloy. According to theory, the enthalpy variation decreases on either side of the ideal composition AuCu (see Fig. S), where the degree of order is at a maximum. Figure 9 depicts the enthalpy variation of formation for AuCu as a function of temperature ‘_ This value varies progressively up to 410°C; no-one has yet succeeded in showing the presence of a jump near 38O”C, which may correspond to the transformation z; -+ z,~_Xt410~C,theAHvalueis390ca1g-at-’_ Fi_eure 9 also shows the values obtained by DTA. Between 385 and 435°C two jumps are observed: the first one (405°C 180 cal g-at- *) corresponds to the transformation cx; -+ z;; the second one (420X, 385 cal g-at- ‘) corresponds to the transformation 3; + zu_ We hzve calculated for these two reactions the vaiues AS = O-27 and dS = 0.56 Cal g-at- t deg- r, r espectively. All these values are in good agreement with those indicated in the literature’. Copper-rich alloys (Fig_ 6) also show a maximum of enthalpy variation for the ideal composition AuCu, (Fig 8). As before, we compared the enthalpy of formation of AuCu, with the results obtained in this work (Fig. 10): our measurements a_pee quite well with those reported in the literature’, and the calculated variation of entropy is AS = 0.44 cal g-at- ’ deg- I_ For all compositions, good reproducibility during several successive thermal treatments and DTA measurements was, in general, observed- This means that the ,erowth of antiphase domains does not play an important role; on the other hand, the effects measured by DTA represent the establishment of surstructure in each antiphase domain.
Temrxrature 3uo
356
PC1 400
450 rC
of the order-disorder reaction during several 5uccessive heating and cooling cycles In the case of AU&U, the transformation is prxticalIy irreversibl t under these conditions L)uring the cooling, we did not We
0-e
have also studied the rwetibility
any thermal effa&
thermic peak was observd Figs, 1 I sod
I2
For AuCu,
and during the second heating, only a very small endoThe resu!ts obtained with AuCu wz obsczx
the disappearance
and AuCu,
are shown in
of the first peak OQ the
cooling tune;
it dues not appear a-tin during the successive heating but the second peak shows a double maximum- The reaction disorder + order seems to be more
rapid or complete obsaved
dtig
tbzm the rcymc
the cooling
reaction,
as shown
In the case of AuCu,,
by ti
higher value of AH
the thermal efT&ts on cooling and
heating art approximatiuely the same after the first cyc2e.
149 Temperature 300
PC) 409
350
I
I
L ____-_--
-
is.2
--
-xl
325
72.4
I
O.lOC
Fig_
420 I
6. DTA culvcs near AuCw.
.
Temperature PC)
440 ,
,
LSO ,
)
,,.
(
480 ,
(
440 ,
,
420 ,
: -
Fig.7, DTA-
haathg
+Jdi”O
-
for /Hxas.s: sample, 26 rn~ 47 at yO Zn, refereoa 50 ma pure copper.
600.
Fig. 13 shows two curves obtained with alloys quenched in cold water from S0”C_ The formation of sustructuie begins near 6O”C_ At 35O”C, the s@ of order formation diminishes, and the disapmnnce of order takes place. The area on each side of the base line gives the following results: AuCu fftd+: -490 cal g-at --I &-GE)-- 315 cal g-at-’ AuCu3 HId_,r -560 ul g-at-’ 205 Cal g-at-’ &V-*,I The dificrence observed between the two reverse reactions may be attributed to the formation of short range order, which does not disappear during the formation at the disordered phase zD12_
The use ofa sensitive DTA deviaz, such as the ,Mettler TA uloo, is very useful for studying the phase transformations of materials, One of the advantages is the rapidity of measurement, although the accuracy is not very high_ With this technique, we have shown all the known transformations of the system copper-gold; we have dearly
demonstratrd
that all these transformations
are first-order reactions and have
detrrmimd the associated AH values Finally, we have studied the reversibiity of
151
Temperature
Fig. 9. - AHrand
‘L 200
Fig_
10. - dHr and dHt_~)
as
300
PC)
a function of temperature
Temperature
PC)
as a function of tempemturc.f~~
AuCh.
.
.-
AUCUS-
c
. .
heath1
-
F
$~~Iiag . I
I_jj3]
.
... . .
I
Fig_ 11. Rcwrsi‘bility
380
400
Sal
12
Tempercture 400 :
hc8tiag
c-
Fs
of the tramforfn8tiott
Rnusitility
:cooI~
of the
for AuCh.
PC) 380
-
360
e+-
tt-ansfortmtioo
for AuCut
Tempercture 200
110 I
1
543
400 i
153 some of these transformations; DTA allows one to show the difference between AuCu and Au0.1~. In particular, the transformation aI --, Q;Iappears to be compIetely irreversible within our experimental conditions. ACKEiOWLEDGMENT
Our thanks arc due to Miss H. Lartigue who performed the greatest part of the experimental work. REFERENCES
1 2 3 4 5
M. Ganto’k, A Piielli and R Faivre. CR. AC&_ Ski_. 260 (1965) 3643. G. Moraglio, Limei Rend_ Sci. Fir. Mut. Nat., 43 (1967) 558. H Luthy, C. Islcr and P. Tit, f?efv. Claim. Acfa, 54 (1971) 2194. H. Luthy and P. Tit, WeZv. Chirrr.Acxa_ 10 (1974) 279_ P_ Tit and R DalIenbach, in D. Dollimore (Ed.). Proceedirrgs of the First ESTA Syrrzposium, Heyden and Son, London, 1976, pm410. 6 R Castenet and G. Urhain. Ci~lk~q.Inr_ CNRS. No. 201. p_ 329. 7 R Hukren, R L Orr. P_ D. Anderson and K K_ Keiky (Eds.), Selecfed Values of l7wmodynamic Properties of l etaLs and Alloys, John Wiley. New York, 1963, p_ 456. 8 L_ Guttman. Solid St&e Phys_, 3 (1956) 145_ 9 R. W. C&n (Ed.), Physical Metallurgy, North Holland Publishing Co., Amsterdam, 1970. 10 F. M. D~curic and P. Gordon, Rcru Mettall., 9 (1961) 304. 11 B.W.Bzttt amann. J. Appl. Phys_, 28 (1957) 556. 12 A_ Van dcr BeurW, A. P. Matthijsen, J. M. J. Ritzn and R. Den Buurman, Acta Me:all., 16 (196Q 435.
Amsterdam
-
Printed in The Netherlands
STUDY OF ORDER-DISORDER TRANSFORMATION ALLOYS BY MEANS OF DIFFERENTIAL THERMAL
P. TISSOT
ASD
OF COPPER-GOLD ANALYSIS
R. DALLENBACH
D&m~emmt & chimie MiniraZe, ArJprmcr.
Adyfique Z2ZZ Cefu?ke 4 (SwifzrZandJ
(Rtodvai
4 octobez
et AppZiqke,
LQzircrsirtf de GCRC?W, 30, quai Emesr
19n)
ABsr5mc-r
Several copper-Sold alloys, with compositions of between IO and SO atomic percent of gold, were examined by quantitative DTA from 25 to 5fKl”C. The results are in good agreement with those obtained by other less rapid, but more accurate, methods. All the reactions observed were first-order transformations. A latent heat (180 & 40 cal g-at- ‘) was measured at 405’C for the 9; + cri transformation of the alloy containing 50% of gold. An endothermic effec& corresponding to an orderdisorder readon, was detected for all alloys, up to a composition of over 90 atomic percent of gold. I?.XRODUCIlON
An abundant literature has been devoted from many years to the study of order-disorder transformations, but it is clear that differential thermal analysis (DTA) is a technique not often used ’ - ‘_ As indicated by Castenet and Urbain”, this method is interesting because complete information on the structural transformations of an alloy may be rapidly obtained_ However, this dynamic method can only be used to study phenomena which are sufficiently rapid with respect to the heating rate used.
, We have studied the well kuown copper-gold system, which shows a continuous substitution solid solution (aD) and many ordered phases (a’, z:, 4, a“) (see Fig. I)_ Ail the solid St&e transformations take place between 200 and 4oocC All measurements were made using a Mettkr quantitative DTA apparatus, type TA 2000.
Samples were prepared by.melting capper and gold (Baker Coating Quality, 99.99 %) in graphite crucibks. Samp1e.weight.s were 50 &- -2 mg for compositions over 65. atom&percent (at* 76) copper,. and 980 5 20 mg- for compositions lower than 65 at % copper. For thermal analysis; ahtminiurn crucibles were -uw and the
Fig
1.3-k
cmppcr-gotd q-stanT.
60 mia 1 1660 2 E 3 E +o E
‘i0 #rpin-’
1 7
240 min
f-L /
1 i
I
/
lOVnin-
{
f
0 ;/
I
0
, 100
s 200
. 300
i 400
I Time
Cmh)
-
so0
rcfkrena was tie same weight of pure gold; the heating rate was 4 deg min- ‘. -ration of alloys, thermal trcatmcntsand difikrcntiaithermal anaiysis wexc performed under a nitrogenatmosphere!(99.995%). The formation of an or&red phase is g~~~raIiyassumedto proceed by nucleationand growth- This mechanism kads to the formationof antiphasedomains,theslow growth of thee domainsbeing the limitingfactorof thedegreeof or&r. The methodof preparationof thesamplesis thus ~a--- important_ and we used the treatment indicated in Fig_ 2, which seems to @v-c the best resoWion and rcproducibiiity of DTA peaks_The smallspheresobtained ~~~p~bttwcentwo~plattstomakta~tsurfaccof1mm,tocnsurt
145 good contact with the aluminum crucible- The composition of the aIloys was checked by neutron activation and analysis of 66Cu and “*Au content. Ali the heat treatments were performed under nitrogen, in Pyrex tubes heated in a smali electrical furnace. RESULTS AND DISCUSSION
In order to determine the optimum duration of annealing to obtain ordered ailoys, we quenched a line of samples AuCu and AuCu, beginning at 450°C. These samples were annealed at 370°C for different periods. Some DTA curves obtained are shown in Fig. 3. We observe an evolution of the peak shape, of the area and of the temperature, ali as functions of the annealing time. This evolution is particularly striking for AuCu, for which the first peak, corresponding to the transformation $’ -+ ai appears only after an annealing time of several minutes at 370°C; the second peak, corresponding to the transformation z;I + zD, is doubled when the annealing lasts less than ten hours. We have never observed an evo!ution after 24 hours at 37O”C, and we decided to anneal each sample for at least 60 hours at a temperature 10 de_below the transformation temprature. For transitions occurring at temperatures beiow 22O”C, the thermal treatment was extended to 100 hours. We have also studied the influence of the heating rate, between 2 and 15 deg min- ‘. on the temperature and the area of the peaks. We observed a steady increase in the temperature; on the other hand, the peak area remains roughly constant_ For the alloys near AuCu, which present two peaks, we also observed a constant total area, although the first peak increases and the second decreases with increasing heating rate_ We chose, for all DTA measurements, a heating rate of 4 deg min-‘_ In TabIe I, we list the onset- and maximum-peak temperature for all the samples_ These results can be divided in three groups, corresponding to the composi-
1
400 .
.
420 .
1
Temperctore 440 320 . I
PC) 340 I .
Au Cul
I
01-c
Fig. 3. Influa~ctof the annealingduration,
r
360 I
I)
156 35.m
330 320. :62 330,378 Ho.r402 370,-a I 9 3t?S.‘~21 4@_419 365,‘-%35 360 325
401 41-I 443 463 48.6 49-9 (Aucu) 5I.9 W.l
_%9 _w.9
335 337 372 380 560 325
69.1 71-l 724 7-a (.&Cat) n-1 792 -
365 356 398 394 387 3GO
169 197 226 289 250 239
Lions on &-her side of each ideaf composition Au,Cu, AuCu and AuCu3. The curves obtained for each group are shown in Fis_ 4, 5 and 6. The temperatures of the superhttice boundaries (see Fig_ 1) are indicated on each curve; the ageement is qui:e good, and it is clear tit DTA affords rapidly, and to z good degree of approximation, the general apprana cf the order disorder transformations of this binary system. In a!1w the shape of the peaks is characteristic of a first order transformation_ The difkrena betweco first and second order transformations is clurly demonstrated by comparison phase
with Fig_ 7, uhich illustrates, the transformation
of the /?
of the alloy Cu-2x1, which is considered to proceed by a second order reaction s*g_ The peaks of the gold-rich alloys (Fi_e 3) are quite broad, due to the relatively
low temperature of the trapsformation cxpcri-menr4 conditions,
and to the sample weight (-
1 g)_ Within our
the transformation extends over 40-50 degees. equivalent
to 10 minutes at a heztin,orate of -%de% min- I_ The enthalpy variation measured for xu,cu (4H,,_,, = 172 cal z-at- ’ ) is in good agreement with the calorimetric measurements of D’ Heurle and Gordon ’ o who report a value of 180 cai g-at- ’ for an alloy quench& from 500 to IS7 T_ Ko maximum value is observed for the ideal comgosi-
until 90 at oAgold, Jtirough Batterusing X-ray anaIysis. did not observe a superstructure with alloys richer than
Lion Xu,Cu.
Inann”,
We have measured a rhermal
effect
147
250
F&F_
Temperature
PC) 300
4_ J3TA curser nea.r Aud3.
75 at % gold. The alloys near AuCu (Fig. 5) show two peaks. The smaller corresponds to the transformation EX; + 2;; the larger, very sharp peak, corresponds to the formation of the disordered alloy. According to theory, the enthalpy variation decreases on either side of the ideal composition AuCu (see Fig. S), where the degree of order is at a maximum. Figure 9 depicts the enthalpy variation of formation for AuCu as a function of temperature ‘_ This value varies progressively up to 410°C; no-one has yet succeeded in showing the presence of a jump near 38O”C, which may correspond to the transformation z; -+ z,~_Xt410~C,theAHvalueis390ca1g-at-’_ Fi_eure 9 also shows the values obtained by DTA. Between 385 and 435°C two jumps are observed: the first one (405°C 180 cal g-at- *) corresponds to the transformation cx; -+ z;; the second one (420X, 385 cal g-at- ‘) corresponds to the transformation 3; + zu_ We hzve calculated for these two reactions the vaiues AS = O-27 and dS = 0.56 Cal g-at- t deg- r, r espectively. All these values are in good agreement with those indicated in the literature’. Copper-rich alloys (Fig_ 6) also show a maximum of enthalpy variation for the ideal composition AuCu, (Fig 8). As before, we compared the enthalpy of formation of AuCu, with the results obtained in this work (Fig. 10): our measurements a_pee quite well with those reported in the literature’, and the calculated variation of entropy is AS = 0.44 cal g-at- ’ deg- I_ For all compositions, good reproducibility during several successive thermal treatments and DTA measurements was, in general, observed- This means that the ,erowth of antiphase domains does not play an important role; on the other hand, the effects measured by DTA represent the establishment of surstructure in each antiphase domain.
Temrxrature 3uo
356
PC1 400
450 rC
of the order-disorder reaction during several 5uccessive heating and cooling cycles In the case of AU&U, the transformation is prxticalIy irreversibl t under these conditions L)uring the cooling, we did not We
0-e
have also studied the rwetibility
any thermal effa&
thermic peak was observd Figs, 1 I sod
I2
For AuCu,
and during the second heating, only a very small endoThe resu!ts obtained with AuCu wz obsczx
the disappearance
and AuCu,
are shown in
of the first peak OQ the
cooling tune;
it dues not appear a-tin during the successive heating but the second peak shows a double maximum- The reaction disorder + order seems to be more
rapid or complete obsaved
dtig
tbzm the rcymc
the cooling
reaction,
as shown
In the case of AuCu,,
by ti
higher value of AH
the thermal efT&ts on cooling and
heating art approximatiuely the same after the first cyc2e.
149 Temperature 300
PC) 409
350
I
I
L ____-_--
-
is.2
--
-xl
325
72.4
I
O.lOC
Fig_
420 I
6. DTA culvcs near AuCw.
.
Temperature PC)
440 ,
,
LSO ,
)
,,.
(
480 ,
(
440 ,
,
420 ,
: -
Fig.7, DTA-
haathg
+Jdi”O
-
for /Hxas.s: sample, 26 rn~ 47 at yO Zn, refereoa 50 ma pure copper.
600.
Fig. 13 shows two curves obtained with alloys quenched in cold water from S0”C_ The formation of sustructuie begins near 6O”C_ At 35O”C, the s@ of order formation diminishes, and the disapmnnce of order takes place. The area on each side of the base line gives the following results: AuCu fftd+: -490 cal g-at --I &-GE)-- 315 cal g-at-’ AuCu3 HId_,r -560 ul g-at-’ 205 Cal g-at-’ &V-*,I The dificrence observed between the two reverse reactions may be attributed to the formation of short range order, which does not disappear during the formation at the disordered phase zD12_
The use ofa sensitive DTA deviaz, such as the ,Mettler TA uloo, is very useful for studying the phase transformations of materials, One of the advantages is the rapidity of measurement, although the accuracy is not very high_ With this technique, we have shown all the known transformations of the system copper-gold; we have dearly
demonstratrd
that all these transformations
are first-order reactions and have
detrrmimd the associated AH values Finally, we have studied the reversibiity of
151
Temperature
Fig. 9. - AHrand
‘L 200
Fig_
10. - dHr and dHt_~)
as
300
PC)
a function of temperature
Temperature
PC)
as a function of tempemturc.f~~
AuCh.
.
.-
AUCUS-
c
. .
heath1
-
F
$~~Iiag . I
I_jj3]
.
... . .
I
Fig_ 11. Rcwrsi‘bility
380
400
Sal
12
Tempercture 400 :
hc8tiag
c-
Fs
of the tramforfn8tiott
Rnusitility
:cooI~
of the
for AuCh.
PC) 380
-
360
e+-
tt-ansfortmtioo
for AuCut
Tempercture 200
110 I
1
543
400 i
153 some of these transformations; DTA allows one to show the difference between AuCu and Au0.1~. In particular, the transformation aI --, Q;Iappears to be compIetely irreversible within our experimental conditions. ACKEiOWLEDGMENT
Our thanks arc due to Miss H. Lartigue who performed the greatest part of the experimental work. REFERENCES
1 2 3 4 5
M. Ganto’k, A Piielli and R Faivre. CR. AC&_ Ski_. 260 (1965) 3643. G. Moraglio, Limei Rend_ Sci. Fir. Mut. Nat., 43 (1967) 558. H Luthy, C. Islcr and P. Tit, f?efv. Claim. Acfa, 54 (1971) 2194. H. Luthy and P. Tit, WeZv. Chirrr.Acxa_ 10 (1974) 279_ P_ Tit and R DalIenbach, in D. Dollimore (Ed.). Proceedirrgs of the First ESTA Syrrzposium, Heyden and Son, London, 1976, pm410. 6 R Castenet and G. Urhain. Ci~lk~q.Inr_ CNRS. No. 201. p_ 329. 7 R Hukren, R L Orr. P_ D. Anderson and K K_ Keiky (Eds.), Selecfed Values of l7wmodynamic Properties of l etaLs and Alloys, John Wiley. New York, 1963, p_ 456. 8 L_ Guttman. Solid St&e Phys_, 3 (1956) 145_ 9 R. W. C&n (Ed.), Physical Metallurgy, North Holland Publishing Co., Amsterdam, 1970. 10 F. M. D~curic and P. Gordon, Rcru Mettall., 9 (1961) 304. 11 B.W.Bzttt amann. J. Appl. Phys_, 28 (1957) 556. 12 A_ Van dcr BeurW, A. P. Matthijsen, J. M. J. Ritzn and R. Den Buurman, Acta Me:all., 16 (196Q 435.