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Intermetallics 19 (2011) 1586e1593
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Intermetallics
journal homepage: www.elsevier .com/locate/ intermet
Evolution of phases in AlePdeCo alloys
I. �Cerni�cková a,*, P. Priputen a, T.Y. Liu a, A. Zemanová b, E. Illeková c, D. Jani�ckovi�c c, P. �Svec a,c, M. Kusý a,�L. �Caplovi�c a, J. Janovec a
a Institute of Materials Science, Faculty of Materials Science and Technology, Slovak University of Technology, J. Bottu 25, 917 24 Trnava, Slovak Republicb Institute of Physics of Materials, Academy of Sciences of the Czech Republic, v.v.i., �Zi�zkova 22, 616 62 Brno, Czech Republicc Institute of Physics, Slovak Academy of Sciences, Dúbravská 9, 845 11 Bratislava, Slovak Republic
a r t i c l e i n f o
Article history:Received 11 April 2011Received in revised form3 June 2011Accepted 4 June 2011Available online 30 June 2011
Keywords:A. IntermetallicsB. Thernary alloy systemsB. Phase identificationF. DiffractionF. Electron microscopy
* Corresponding author. Tel.: þ421 905 773 063.E-mail address: [emailprotected] (I. �Cern
0966-9795/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.intermet.2011.06.003
a b s t r a c t
The Al68Pd14.6Co17.4 and Al69.8Pd13.8Co16.4 alloys were investigated after continuous cooling and/orannealing at 700 �C for 2000 h. In the investigation light microscopy, scanning electron microscopyincluding energy dispersive X-ray spectroscopy, X-ray diffraction, electron backscatter diffraction, anddifferential thermal analysis were used. In the as-annealed near-equilibrium conditions of theAl68Pd14.6Co17.4 and Al69.8Pd13.8Co16.4 alloys U þ b þ Al5Co2 and U þ Al5Co2 were identified, respectively.The U-phase in a majority of investigated samples was found to consist of 2e3 mutations differing fromeach other in metal composition, but exhibiting the same crystal structure. The mutations showedcompositional features of their parent phases (liquid, V, and b).
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1. Introduction
The AlePdeCo is a suitable system for the formation of complexmetallic alloys (CMAs) defined as crystalline compounds of thefamily of intermetallics that are characterized by large unit cellscontaining often thousands of atoms, by occurrence of well-definedclusters ordinarily of icosahedral symmetry, and by some disorderessentially due to the fact that icosahedra do not fill Euclidian 3-dimensional space [1,2]. From the compositional point of view,CMAs correspond to binary, ternary or quaternary systems based onmetals and occasionally containing also metalloids and/or rareearths. The AleTM alloys, where TM stands for one or severaltransition elements, are ranked between the typical representa-tives of CMAs [3]. CMAs exhibit interesting properties excluded incommon metals, like the presence of a new type of dislocationsinvolving huge amount of atoms (so-called metadislocations)[4e9], the coexistence of good electrical and low thermal conduc-tivities [10], the memory and rejuvenation effects [11], the spinglass-like behaviour [12,13] and others. As follows from the AlePd,AleCo, and AlePdeCo phase diagrams [14e18], both binary andternary phases are present in CMAs corresponding to theAlePdeCo system. For instance, e6 and e28 of the e-family as well as
i�cková).
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b belong between the typical binary phases which can also bealloyed with the third element. However, other two phases of the e-family, e22 and e34, were found in the ternary region only. Besidesthem, six stable ternary compounds denoted asW, Y2, U, V, F, and C2were identified in alloys of the AlePdeCo system [16].
The aim of the present work is to contribute to the betterunderstanding of the phase evolution in the Al68Pd14.6Co17.4 andAl69.8Pd13.8Co16.4 alloys. In Fig. 1 showing the isothermal section ofthe ternary AlePdeCo diagram at 790 �C [18], positions of thealloys are marked with solid circles. The attention is focused on theidentification of phases in the as-cast and the as-annealed (700�C/2000 h) conditions of both alloys. With respect to earlier findings[16], the Al68Pd14.6Co17.4 alloy is expected to contain liquid, V, andb at 1050 �C. These phases are assumed to be replaced with U andb during the cooling from 1050 to 1000 �C. On the continuedcooling to ambient temperature U and b should be stable. More-over, a negligible amount of Al5Co2 can also form. For theAl69.8Pd13.8Co16.4 alloy, liquid, V, and b are expected to occur at1050 �C. At temperatures below 1000 �C the only U-phase isassumed to be stable in this alloy.
2. Experimental procedure
The investigated Al68Pd14.6Co17.4 (denoted also A in this work)and Al69.8Pd13.8Co16.4 (B) alloys were produced by arc melting of
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Fig. 1. Isothermal section of ternary AlePdeCo diagram at 790 �C [18]. Positions of Al68Pd14.6Co17.4 and Al69.8Pd13.8Co16.4 alloys are marked with solid circles. The symbol B2 standsfor b-phase.
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pure components under argon atmosphere. The purity of Al, Co,and Pd was at least 99.95 wt.%. To improve the alloy hom*ogeneity,the alloys were repeatedly re-melted before cast. A part of bothingots was investigated in the as-cast condition (denoted withsymbol 1). Rests of both ingots were cut into smaller samples whichwere placed into silica capsules (each capsule was rinsed withargon before evacuated and sealed up) and subsequently annealedat 700 �C for 2000 h. The as-annealed condition is denoted withsymbol 2 in this work. After annealing the samples were rapidlycooled into water to fix their high-temperature microstructure. Inthe investigation, light microscopy (LM), scanning electronmicroscopy (SEM) including both energy dispersive (EDX) andwavelength dispersive (WDX) X-ray spectroscopies, X-ray diffrac-tion (XRD), electron backscatter diffraction (EBSD), and differentialthermal analysis (DTA) were used. The DTA measurements wereperformed by a DTA7 Perkin Elmer differential thermal analyzercalibrated for heating regime. The DTA runs were done under argonatmosphere from ambient temperature up to 1345 �C and backwith the rate of 10 �C per minute. Altogether three successive runswere applied to each sample. The XRD measurements were carriedout by a Philips PW 1830 diffractometer with Bragg-Brentanogeometry using iron filtered co*ka1 radiation at following condi-tions: scattering angle 2q from 5 to 70�, step size 0.02�, and expo-sure time 10 s per step. The microstructure was studied witha Neophot 30 light microscope. Metal compositions of micro-structure constituents were determined using a JEOL JSM-7600Fscanning electron microscope operating at the accelerationvoltage 20 kV in SEI (secondary electron) and BEI (back-scatteredelectron) regimes. The microscope is equipped with three spec-trometers of Oxford Instruments; the X-max 50 spectrometer for
EDX analysis using INCA software, the INCAWave spectrometer forWDX analysis using the same software, and the Nordlys detector forEBSD using FLAMENCO software. At least 10 measurements perconstituent were used to calculate average values of the metalcomposition. Volume fractions were calculated by means of anImageJ software designed for the precise image analysis.
3. Results
In this work, altogether 8 samples related to 4 conditions of theAl68Pd14.6Co17.4 and Al69.8Pd13.8Co16.4 alloys were investigated(sample/condition denotations are given in Table 1 - the firstcolumn). The as-cast microstructures corresponding to A1 and B1samples are shown in Figs. 2 and 3, respectively. Black areas in allpresented micrographs correspond to pores. Two constituents ofwhite and grey appearance were found in the microstructure of thesample A1 using light microscopy (Fig. 2a). In the grey constituent,two areas showing different colour shades and slightly differentmetal compositions were observed by means of SEM/EDX tech-nique (Fig. 2b, Table 1). The white Pd-rich constituent showedevidently different metal composition as that determined for thegrey constituent (Fig. 2cee). Contrary to the sample A1, themicrostructure of the sample B1 (Fig. 3a and b, Table 1) consists ofaltogether four constituents (white, dark, lighter grey, and darkergrey). Inside the darker grey constituent two types of areas wereobserved differing from each other in metal composition (Table 1).The darker grey areas appearing exclusively around the whiteconstituent contained more palladium and less cobalt than thosesurrounding occasionally the dark constituent (Fig. 3).
Table 1Metal compositions (EDX) and volume fractions (the occurrence of pores was omitted) of the microstructure constituents observed in as-cast (A1), as-cast after DTA (A1-DTA),as-annealed (A2), and as-annealed after DTA (A2-DTA) states of Al68Pd14.6Co17.4 alloy, as well as in as-cast (B1), as-cast after DTA (B1-DTA), as-annealed (B2), and as-annealedafter DTA (B2-DTA) states of Al69.8Pd13.8Co16.4 alloy. The particular microstructure constituents (second column) are coupled with the experimentally identified phases (thirdcolumn).
Condition/sample Microstructure constituent Phase Atomic content in % Volume fraction in %
Al Co Pd
Al68Pd14.6Co17.4A1 Grey U 68.93 17.91 13.16 92.3
Lighter UL 68.67 � 0.55 17.32 � 0.64 14. 01 � 1.14 64.8Darker UV 69.47 � 0.36 19.33 � 0.54 11.20 � 0.31 27.5
White b 54.50 � 1.00 10.71 � 1.39 34.79 � 1.09 7.7A1-DTA Grey U 67.25 18.41 14.34 93.2
Lighter UL 67.14 � 0.40 18.15 � 0.40 14.71 � 0.49 84.0Darker UV 68.19 � 0.39 20.82 � 0.56 10.99 � 0.22 9.2
White b 52.91 � 0.16 13.75 � 0.63 33.34 � 0.68 6.8A2 Grey U 68.85 � 0.12 16.14 � 0.12 15.01 � 0.09 92.8
White b 57.61 � 0.26 8.13 � 0.13 34.26 � 0.18 6.6Dark Al5Co2 72.52 � 0.1 25.42 � 0.11 2.06 � 0.06 0.6
A2-DTA Grey U 68.47 18.02 13.51 91.2Lighter UL 68.41 � 0.29 17.92 � 0.53 13.66 � 0.25 88.1Darker UV 69.66 � 0.21 20.96 � 0.18 9.39 � 0.23 3.1
White b 54.94 � 0.20 16.91 � 0.68 28.16 � 0.52 8.8
Al69.8Pd13.8Co16.4B1 Grey U 69.64 16.11 14.22 91.9
Lighter UL 69.33 � 0.63 16.86 � 1.05 13.81 � 1.67 60.7Darker UV 69.45 � 0.37 18.91 � 0.81 11.64 � 1.07 10.3
Ub 70.69 � 0.31 12.52 � 0.92 16.79 � 1.13 20.9White b 56.87 � 0.15 3.54 � 0.35 39.59 � 0.26 7.5Dark Al5Co2 72.38 � 0.10 22.22 � 0.39 5.40 � 0.11 0.6
B1-DTA Grey U 69.19 14.27 16.54 97.9Lighter UL 67.95 � 0.19 14.54 � 0.68 17.51 � 0.84 79.8Darker UV 69.89 � 0.41 18.01 � 0.54 12.10 � 0.96 5.6
Ub 71.25 � 0.28 11.55 � 0.19 17.20 � 0.28 13.5White b 57.61 � 0.18 4.78 � 0.16 37.61 � 0.28 1.6Dark Al5Co2 72.18 � 0.19 22.86 � 0.15 4.96 � 0.11 0.5
B2 Grey U 69.09 15.13 15.78 99.4Lighter UL 68.12 � 0.23 15.23 � 0.18 16.65 � 0.11 64.9Darker UV 69.91 � 0.13 16.52 � 0.13 13.56 � 0.08 12.7
Ub 71.53 � 0.12 14.02 � 0.11 14.45 � 0.14 21.8Dark Al5Co2 72.47 � 0.19 24.84 � 0.19 2.69 � 0.05 0.6
B2-DTA Grey U 68.94 15.70 15.36 95.2Lighter UL 68.37 � 0.42 15.15 � 0.55 16.48 � 0.95 70.9Darker UV 70.06 � 0.32 17.93 � 0.82 12.01 � 0.99 8.4
Ub 70.93 � 0.14 11.96 � 0.51 17.11 � 0.59 15.9White b 57.88 � 0.09 6.28 � 0.33 35.84 � 0.52 3.9Dark Al5Co2 72.71 � 0.11 22.05 � 0.11 5.24 � 0.08 0.9
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The SEM/BEI micrographs corresponding to the as-annealed A2and B2 samples are presented in Figs. 4 and 5, respectively. In theA2 sample, white, grey, and dark constituents are observable(Fig. 4a) differing from each other in metal composition (Fig. 4b). Inthe micrograph of the B2 sample (Fig. 5a) two constituents (greyand dark) are present, whereas the white constituent is missing.The grey constituent exhibits two colour shades (Fig. 5a) and threevarious metal compositions (Table 1).
In Fig. 6, XRD patterns of the samples A1, A2, B1, and B2 areillustrated. The comparison of the patterns with the diffraction datagiven in refs. [16,17,19] shows that U is the dominant phase in allfour samples. Beside peaks corresponding to this phase two smallpeaks of bwere found in the patterns of the samples A1, A2, and B1.No other phases were identified by XRD. Using EBSD the existenceof b was confirmed and the dark constituent was identified asAl5Co2 (Fig. 7). Lattice parameters of the concerned phases aregiven in Table 2. For U and b phases, the data obtained by therefinement of XRD patterns are present besides the literature data.
The DTA records obtained for as-cast and as-annealed condi-tions of both alloys are illustrated in Fig. 8a and b, respectively. Onerecord per measurement is documented only, because there werenot observed any remarkable differences between the records
corresponding to various runs of the same measurement. Totalenthalpies of transformations for concerned alloys and regimes aresummarized in Table 3. The values corresponding to heating andcooling regimes of the same condition and alloy are comparable.The comparison of the DTA records for Al68Pd14.6Co17.4 andAl69.8Pd13.8Co16.4 alloys shows a difference in the number of peaks.In the records corresponding to the latter alloy one additional peakat about 950 �C was observed. No pronounced differences in theDTA records were observed between as-cast and as-annealedconditions of the same alloy, except for the cooling regime of theAl68Pd14.6Co17.4 alloy. Here, the as-annealed condition compared tothe as-cast condition exhibits a shorter range between onsettemperatures of the solidification and the peritectic reaction, a lesspronounced peak corresponding to the peritectic reaction, as wellas a broader peak at about 1030 �C. Continuously cooled samplescorresponding to the same alloy (e.g. A1, A1-DTA, A2-DTA) showedalso similar microstructures.
4. Discussion
In earlier studies on phase evolution in AlePdeCo alloys[16e18], the equilibrium (near-equilibrium) phases were mostly
Fig. 3. As-cast microstructure of the Al69.8Pd13.8Co16.4 alloy documented by LM (a) and SEM/BEI (b). Results of the EDX analysis along the solid line are illustrated separately foraluminium (c), palladium (d), and cobalt (e). The particular microstructure constituents are coupled with the experimentally identified phases (b).
Fig. 2. As-cast microstructure of the Al68Pd14.6Co17.4 alloy documented by LM (a) and SEM/BEI (b). Results of the EDX analysis along the solid line are illustrated separately foraluminium (c), palladium (d), and cobalt (e). The particular microstructure constituents are coupled with the experimentally identified phases (b).
Fig. 4. SEM/BEI micrograph of the as-annealed Al68Pd14.6Co17.4 alloy (a) and compositional changes along the solid line shown in the small window situated in the upper rightcorner of the overview picture (b).
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Fig. 5. SEM/BEI micrographs of the as-annealed Al69.8Pd13.8Co16.4 alloy (a) and compositional changes along the solid line shown in the small window situated in the upper rightcorner of the overview picture (b).
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characterized after long-term isothermal annealing. The obtainedresults were usually used to update the ternary phase diagram and/or related binaries. In the present work, both near-equilibrium andnon-equilibrium phases were investigated in Al68Pd14.6Co17.4 andAl69.8Pd13.8Co16.4 alloys. The phases identified in samples A2 and B2(Table 1) can be considered as near-equilibrium, because they wereformed on long-term annealing (2000 h at 700 �C).
The annealing resulted in the appearance of near-equilibrium Uand Al5Co2 phases in the B2 sample. However, U (Table 1) wasfound to consist of three mutations varying in metal compositions.Besides EDX, the WDX analysis was also used to determine differ-ences in metal compositions of U mutations in the B2 sample. Theresults obtained by EDX and WDX methods were found to be ingood agreement. On the other hand, compositionally hom*ogeneousnear-equilibrium U, Al5Co2 and b phases were observed in the A2
Fig. 6. Powder X-ray diffraction spectrum corresponding to as-cast (a) and as-annealed (b) cthe Al69.8Pd13.8Co16.4 alloy.
sample. It gives rise to the question why the near-equilibrium Uidentified in the B2 sample shows fluctuations in metal composi-tion resulting in the formation of three mutations of this phase. Thereason can be associated with the absence of b in the near-equilibrium microstructure of the B2 sample. When Pd-richb present in the original as-cast microstructure dissolves onannealing, some localities show enhanced concentration of slowlydiffusing palladium atoms. This results in the heterogeneousdistribution of palladium across the sample and causes theformation of more compositional mutations of the U-phase.Consequently, threemutations of Umarked as UL, UV and Ub appearin the b-free microstructure of the B2 sample.
Al5Co2 as the binary AleCo phase [15,16] showed tendency to bepresent inside and/or close to the areas poor on palladium. This iswell observable in Fig. 3b and Fig. 5a where aggregates of Al5Co2
onditions of the Al68Pd14.6Co17.4 alloy, and as-cast (c) and as-annealed (d) conditions of
Fig. 7. Electron backscatter diffraction images of b (a) and Al5Co2 (b) in microstructureof the as-annealed Al68Pd14.6Co17.4 alloy.
Fig. 8. DTA records obtained for as-cast and as-annealed conditions of theAl68Pd14.6Co17.4 (a) and Al69.8Pd13.8Co16.4 (b) alloys.
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appear inside the UV areas containing less palladium than othertwo mutations of U (Table 1). The metal composition of Al5Co2shows a minimal scatter across the phase. The average aluminiumcontent (about 72.5 at.% (Table 1) is comparable with that calcu-lated for the binary constitution of this phase (71.4 at.% [17]). Yur-echko [17] stated the solubility limit of palladium in Al5Co2 at thelevel of 3 at.% at 790 �C. The average palladium contents in Al5Co2determined for the samples A2 (2.06 at.%, Table 1) and B2 (2.69 at.%)annealed at 700 �C fulfill this limit very well. On the other hand,palladium contents in the non-equilibrium Al5Co2 (the averagevalues range between 4.96 and 5.40) exceed slightly the above limitvalue. This finding can be explained by the formation of Al5Co2 fromUV containing up to 14 at.% of palladium (Table 1). A decrease of thepalladium content in this originally supersaturated Al5Co2 to theequilibrium value (about 3 at.%) is hardly possible during thecontinuous cooling applied.
The U-phase showing observable fluctuations in metal compo-sition was found in all samples investigated, except for the A2sample. In the latter sample, the hom*ogenous near-equilibrium Uwas identified exhibiting XRD pattern (Fig. 6b) similar to thosepublished in literature [16,17]. For thementioned patterns, the ratiobetween 54.8� (2Q) and 53.7� (2Q) peak heights is between 1.3 and1.4. According to ref. [19] these peaks correspond to the reflections(�8 6 5), and (�8 8 3) and thementioned ratio is approximately 1.3.The XRD patterns (Fig. 6a, c, d) corresponding to heterogeneous U(consisting of UL, UV and/or Ub) exhibit lower values of this ratiothan unity. Thus, the obtained results point to the correlationbetween the chemical hom*ogeneity of U, the proximity of thecorresponding alloy system to equilibrium, and the ratio between54.8�(2Q) and 53.7�(2Q) peak heights in the XRD pattern. It couldbe a way how to distinguish between the near-equilibrium and thenon-equilibrium U if the corresponding XRD patterns are available.
Moreover, the enhanced intensities of some peaks correspond-ing to U are observable in the XRD patterns of the A1, B1, and B2samples if compared to the A2 sample (see for instance the range of25e35�(2Q)). It could be explained by the appearance of more
Table 2Lattice parameters and space groups of experimentally identified phases [16].
Phase Space group Lattice parameters References
a [nm] b [nm] c [nm] b [�]
U C121, C1m1 or C12/m1 1.9024 2.9000 1.3140 117.26 [16]1.8950 2.8920 1.3154 116.954 This work/A11.9005 2.8976 1.3209 117.009 This work/A21.8921 2.8892 1.3125 116.925 This work/B11.9007 2.8978 1.3211 117.011 This work/B2
b Pm3m 0.3036 e e e [16]0.2960 e e e This work/A10.2970 e e e This work/A20.2961 e e e This work/B1
Al5Co2 P63/mmc 0.76717 e 0.76052 e [16]
mutations of the U-phase in the former samples exhibiting slightdifferences in lattice parameters and positions of atoms in thelattice.
The final microstructures of all continuously cooled samples(they are denoted as A1, A1-DTA, A2-DTA, B1, B1-DTA, B2-DTA inTable 1) consist of non-equilibrium phases. The interpretation of
Table 3Values of transformation enthalpies determined from DTA records for theAl68Pd14.6Co17.4 and Al69.8Pd13.8Co16.4 alloys.
Alloy/condition Temperaturerange [�C]
Total enthalpy oftransformations[J g�1]
Heatingregime
Coolingregime
Al68Pd14.6Co17.4/as-cast 1023.1e1075.5 210.51058.1e1004.6 �214.4
Al68Pd14.6Co17.4/as-annealed
1016.2e1080.3 264.21050.4e989.5 �269.7
Al69.8Pd13.8Co16.4/as-cast 985.9e1069.8 228.81055.4e950.9 �224.9
Al69.8Pd13.8Co16.4/as-annealed
990.6e1078.4 331.91056.8e944.6 �339.6
Fig. 9. SEM micrographs of the as-cast Al69.8Pd13.8Co16.4 alloy after DTA documented in BEI (a) and SEI (b) regimes. Compositional changes along the solid line are shown in therightehand diagram (c). The particular microstructure constituents are coupled with the experimentally identified phases (a).
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concerned microstructures and DTA records (Fig. 8) makes possibleto suggest the temperature dependent evolution of these phases.The values of the total enthalpy of transformations correspondingto heating and cooling regimes (Table 3, Fig. 8) of the identical runare comparable. It enables to use the more readable “cooling”curves for the description of sequences of phase transformations.The “cooling” curves of the as-cast Al68Pd14.6Co17.4 alloy (Fig. 8a)between about 1058 and 1026 �C contain two closely overlappedpeaks corresponding probably to the formation of b and V fromliquid (L). At about 1037 �C started the invariant peritectic reactionwhere parts of liquid and b as well as the whole volume of V areparticipating in the formation of UV. Subsequently, the rest of theliquid transformed into UL. At about 1004 �C liquid phase dis-appeared from the system. It was not formed any other phaseduring the cooling from 1004 �C to ambient temperature and thefinal microstructure consisted of UV, UL, and b phases. In themicrostructures of non-equilibrium samples A1, A1-DTA, and A2-DTA the same phases were found after the cooling was finished(Fig. 2b). Contrary to the as-annealed A2 sample, Al5Co2 was notpresent in the non-equilibrium samples due to the insufficient timefor its formation. The differences in shapes of cooling curves(Fig. 8a) could be explained by a limited formation of V-phase in theoriginally as-annealed sample. Thus, lower amounts of solid andliquid phases participated in the peritectic reaction (the corre-sponding peak is lower) and the preserved liquid in a higherquantity transformed subsequently into UL (the peak at about1030 �C is broader). A slightly different sequence of transformationscan be attributed to the Al69.8Pd13.8Co16.4 alloy. As follows from the“cooling” curves in Fig. 8b double peak between about 1055 and1029 �C should correspond to the formation of b and V from liquid.At about 1029 �C the invariant peritectic reaction started and it wasfollowed immediately with the transformation of the rest of liquidinto UL. At about 1009 �C the solidification was finished and thesolid state consisted of UV, UL, and b phases. In the temperaturerange 962e950 �C, a part of b transformed into Ub. Finally, a smallamount of Al5Co2 formed probably fromUV. The last transformationis not observable in the DTA record (Fig. 8b), however, the presenceof Al5Co2 was evidenced experimentally (Fig. 7b). The high-temperature parts of the transformation sequences were found tobe very similar for both alloys. Differences concern the low-temperature parts where Ub and Al5Co2 were formed additionallyto UV, UL, and b on cooling of the Al69.8Pd13.8Co16.4 alloy.
Except for the as-annealed A2 sample, the microstructures ofother samples contain 2 or 3 mutations of U differing from eachother in metal composition (Table 1), but exhibiting the same
crystal structure (Fig. 6). Particular mutations of U were found toexhibit compositional features of their mostly high-temperatureparent phases (i.e. phases which they were formed from). Forinstance, UV contains more Co and less Pd (Table 1) as it is alsotypical for its parent V-phase [17]. The same correlation wasobserved between Ub and b (parent). The parent phase for UL isliquid, so it is difficult to determine a compositional correlationbetween these phases. Differences in metal composition along thesolid line intersecting five co-existing phases (b, Ub, UL, UV, andAl5Co2) in the B2-DTA sample (Fig. 9) show that compositionalchanges did not follow immediately the structural changes in thenewly formed phases. This is typical for the paratransformation[20]. The chemical fluctuations were not observed in minor phases(b, Al5Co2), but only in the dominant U-phase forming more than90% of the microstructure (Table 1). The open question is if alsoother dominant phases in the AlePdeCo alloys exhibit similarheterogeneity in metal composition under non-equilibriumconditions as it is evidenced for U in the present work.
Larger pores and smaller voids observable in the microstruc-tures of both alloys originated from the alloy processing and theetching procedure, respectively.
5. Conclusions
The results of the investigation of as-cast and as-annealed(700 �C/2000 h) conditions of Al68Pd14.6Co17.4 and Al69.8Pd13.8Co16.4alloys before and after DTA can be summarized as follows:
� Chemically hom*ogeneous U, b, and Al5Co2 were identified inthe as-annealed near-equilibrium condition of theAl68Pd14.6Co17.4 alloy. The volume fraction of the dominant U-phase was 92.8%.
� In the as-annealed near-equilibrium condition of theAl69.8Pd13.8Co16.4 alloy the minor Al5Co2 and the dominant Uwere identified. The U-phase was found to consist of threemutations differing from each other in metal composition, butexhibiting the same crystal structure.
� In continuously cooled non-equilibrium conditions, b (in bothalloys) and Al5Co2 (in the Al69.8Pd13.8Co16.4 alloy only) wereclassified as chemically hom*ogeneous minor phases. Thedominant U-phase was found to consist of two (forAl68Pd14.6Co17.4) or three (for Al69.8Pd13.8Co16.4) mutationsexhibiting compositional features of their parent phases(liquid, V, b).
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Acknowledgement
The authors wish to thank to the European Regional Develop-ment Fund (ERDF) for financial support of the projectITMS:26220120014 “Center for development and application ofadvanced diagnostic methods in processing of metallic and non-metallic materials” funded within the Research & DevelopmentOperational Programme, as well as to the Grant Agency of theMinistry of Education of the Slovak Republic and the SlovakAcademy of Sciences (VEGA) for financial support under thecontracts No. 1/0011/10, 2/0111/11, and 1/0339/11.
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