5
PHYSICAL REVIEW B VOLUME 49, NUMBER 5 1 FEBRUARY 1994-I Annealing-induced icosahedral glass yhase in melt-syun Al-Cu-V and Al-Si-Mn alloys A. P. Tsai, K. Hiraga, A. Inoue, and T. Masumoto Institute for Materials Research, Tohoku University, Sendai 980, Japan H. S. Chen AT& T Bell Laboratories, Murray Hill, New Jersey 07974-5000 (Received 25 October 1993) Structures of amorphous and icosahedral phases in A175Cul5Vlp and A153Si27Mnzp alloys have been studied by x-ray and electron diffraction, and high-resolution electron microscopy. X-ray peak widths of the icosahedral phase in both alloys show a linear dependence on phason momentum. The high- resolution image of the icosahedral phase of Al»Cu»Vip shows an atomic arrangement similar to that described by the icosahedral-glass (IG) model. The lattice image shows a two-dimensional tiling pattern comprised mainly of pentagons joined together side by side randomly and filled with unique tearlike and cracklike defects exhibited in the IG model. Despite the high degree of structural defects of the IG phase, the characteristic physical properties of quasiperiodic lattices such as high electrical resistivity, high hardness, and large elastic modulus strongly persist in the IG phase. The quasicrystalline state characterized by long-range icosahedral order in melt-quenched A186Mn&4 was report- ed by Shechtman et al. ' Since then, studies dealing with the formation, structure, physical, and electrical proper- ties have followed, and great progress has been achieved in the understanding of quasicrystals. The structure of a quasicrystal is different from those of crystals and disor- dered solids in a unique way. It is nonperiodic but not disordered. Specifically, its key characteristic is the self- similarity of the structure. The proposed structural order for the quasicrystalline phases ranges from that of icosahedral glass to the random tiling quasilattice to the highly ordered quasilattice. Since the discovery of the stable icosahedral Al-Cu-Fe, which exhibits sharp diffraction peaks comparable to those in a highly ordered crystal, the realistic structure of icosahedral quasicrystal is believed to have a perfect quasiperiodic or random til- ing lattice and most works on the structure of interest then have been focused on these two models. Although the icosahedral-glass (IG) model failed to in- terpret the sharp diffraction peaks observed in many quasicrystals, the idea still prevails that there exists a correlation in structure between amorphous and icosahedral phases. A molecular-dynamics simulation of an undercooled Lennard-Jones liquid, has revealed a structure with an icosahedral bond-orientational order and its structure factors rejecting those of metallic glasses and the icosahedral solid. A structure compar- ison of amorphous and quasicrystalline has also been made in sputtered A172Mn22Si6. The amorphous metal was concluded to be a highly defective quasicrystal in which the orientation order was lost through random orientation of the local unit. An isothermal calorimeter experiment concluded that the amorphous Al-Mn has a microquasicrystalline structure as evidenced by the ob- served icosahedral-amorphous phase transformation which proceeds through a grain-growth process without nucleation. On the other hand, the single icosahedral- phases in Al-Cu-V and Al-Si-Mn (Ref. 9) alloys, which are converted from the amorphous phase through a nucleation-growth process, warrant further investigation on that whether there are similarities in structure and physical properties between icosahedral and amorphous phases. In this paper, we have studied the structures and some physical properties of amorphous and icosahedral phases in A175Cu$5Vio and A153Si27Mn20 alloys. The structure similarity between the two phases has been observed in both alloys. A linear dependence of peak width on phason momentum (Gi) was seen for the two icosahedral phases. Observation of high-resolution transmission elec- tron microscopy for the icosahedral Al-Cu-V reveals a til- ing pattern which can be described by an IG model. In comparison with the amorphous phase, the two icosahedral alloys show higher resistivity and hardness which are characteristics of quasiperiodic materials. Ternary alloys of A175Cu»V&0, A175Cu20V5, A153Si27Mn20, and A160Si30Mn&0 were melted in an argon atmosphere using an arc furnace. Amorphous samples were prepared by using a single roller of 20 cm diam ro- tating at 6000 rpm and the icosahedral phase was an- nealed from the amorphous alloys. All samples were carefully powdered for x-ray-diffraction measurements. X-ray-diffraction spectra were measured precisely by the use of a rotating anode x-ray generator (Cu Ka 40 kV, 150 mA) with a graphite (002) monochrometer. Samples were scanned between 10-100 degrees in 28 with a step size of 0. 02'. The instrumental resolution was evaluated from the Si powder pattern to be about 2.5X10 A Microstructure observations were examined on JEM (EX-200) and (JEM4000-EX) transmission electron mi- croscopy. To illustrate the evolution of the icosahedral phase from the amorphous phase, we show in Fig. 1 the diffraction patterns of amorphous (a)(c) and icosahedral (b, d) in A17&Cu&sV&o (a, b) and Als3Siz7Mnzo (c, d) alloys. The transition of amorphous to icosahedral phase in A175Cu, 5V&0 and A155Si25Mn2p has been shown previous- ly to proceed via a nucleation-growth process. The 0163-1829/94/49(5)/3569(4)/$06. 00 49 3569 1994 The American Physical Society

Annealing-induced icosahedral glass phase in melt-spun Al-Cu-V and Al-Si-Mn alloys

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Page 1: Annealing-induced icosahedral glass phase in melt-spun Al-Cu-V and Al-Si-Mn alloys

PHYSICAL REVIEW B VOLUME 49, NUMBER 5 1 FEBRUARY 1994-I

Annealing-induced icosahedral glass yhase in melt-syun Al-Cu-V and Al-Si-Mn alloys

A. P. Tsai, K. Hiraga, A. Inoue, and T. MasumotoInstitute for Materials Research, Tohoku University, Sendai 980, Japan

H. S. ChenAT& TBell Laboratories, Murray Hill, New Jersey 07974-5000

(Received 25 October 1993)

Structures of amorphous and icosahedral phases in A175Cul5Vlp and A153Si27Mnzp alloys have been

studied by x-ray and electron diffraction, and high-resolution electron microscopy. X-ray peak widths ofthe icosahedral phase in both alloys show a linear dependence on phason momentum. The high-

resolution image of the icosahedral phase of Al»Cu»Vip shows an atomic arrangement similar to that

described by the icosahedral-glass (IG) model. The lattice image shows a two-dimensional tiling pattern

comprised mainly of pentagons joined together side by side randomly and filled with unique tearlike and

cracklike defects exhibited in the IG model. Despite the high degree of structural defects of the IGphase, the characteristic physical properties of quasiperiodic lattices such as high electrical resistivity,

high hardness, and large elastic modulus strongly persist in the IG phase.

The quasicrystalline state characterized by long-rangeicosahedral order in melt-quenched A186Mn&4 was report-ed by Shechtman et al. ' Since then, studies dealing withthe formation, structure, physical, and electrical proper-ties have followed, and great progress has been achievedin the understanding of quasicrystals. The structure of aquasicrystal is different from those of crystals and disor-dered solids in a unique way. It is nonperiodic but notdisordered. Specifically, its key characteristic is the self-similarity of the structure. The proposed structural orderfor the quasicrystalline phases ranges from that oficosahedral glass to the random tiling quasilattice to thehighly ordered quasilattice. Since the discovery of thestable icosahedral Al-Cu-Fe, which exhibits sharpdiffraction peaks comparable to those in a highly orderedcrystal, the realistic structure of icosahedral quasicrystalis believed to have a perfect quasiperiodic or random til-ing lattice and most works on the structure of interestthen have been focused on these two models.

Although the icosahedral-glass (IG) model failed to in-

terpret the sharp diffraction peaks observed in manyquasicrystals, the idea still prevails that there exists acorrelation in structure between amorphous andicosahedral phases. A molecular-dynamics simulation ofan undercooled Lennard-Jones liquid, has revealed astructure with an icosahedral bond-orientational orderand its structure factors rejecting those of metallicglasses and the icosahedral solid. A structure compar-ison of amorphous and quasicrystalline has also beenmade in sputtered A172Mn22Si6. The amorphous metalwas concluded to be a highly defective quasicrystal inwhich the orientation order was lost through randomorientation of the local unit. An isothermal calorimeterexperiment concluded that the amorphous Al-Mn has amicroquasicrystalline structure as evidenced by the ob-served icosahedral-amorphous phase transformationwhich proceeds through a grain-growth process withoutnucleation. On the other hand, the single icosahedral-phases in Al-Cu-V and Al-Si-Mn (Ref. 9) alloys, whichare converted from the amorphous phase through a

nucleation-growth process, warrant further investigationon that whether there are similarities in structure andphysical properties between icosahedral and amorphousphases.

In this paper, we have studied the structures and somephysical properties of amorphous and icosahedral phasesin A175Cu$5Vio and A153Si27Mn20 alloys. The structuresimilarity between the two phases has been observed inboth alloys. A linear dependence of peak width onphason momentum (Gi) was seen for the two icosahedralphases. Observation of high-resolution transmission elec-tron microscopy for the icosahedral Al-Cu-V reveals a til-ing pattern which can be described by an IG model. Incomparison with the amorphous phase, the twoicosahedral alloys show higher resistivity and hardnesswhich are characteristics of quasiperiodic materials.

Ternary alloys of A175Cu»V&0, A175Cu20V5,

A153Si27Mn20, and A160Si30Mn&0 were melted in an argonatmosphere using an arc furnace. Amorphous sampleswere prepared by using a single roller of 20 cm diam ro-tating at 6000 rpm and the icosahedral phase was an-nealed from the amorphous alloys. All samples werecarefully powdered for x-ray-diffraction measurements.X-ray-diffraction spectra were measured precisely by theuse of a rotating anode x-ray generator (Cu Ka 40 kV,150 mA) with a graphite (002) monochrometer. Sampleswere scanned between 10-100 degrees in 28 with a stepsize of 0.02'. The instrumental resolution was evaluatedfrom the Si powder pattern to be about 2.5X10 AMicrostructure observations were examined on JEM(EX-200) and (JEM4000-EX) transmission electron mi-croscopy.

To illustrate the evolution of the icosahedral phasefrom the amorphous phase, we show in Fig. 1 thediffraction patterns of amorphous (a)(c) and icosahedral(b, d) in A17&Cu&sV&o (a, b) and Als3Siz7Mnzo (c,d) alloys.The transition of amorphous to icosahedral phase inA175Cu, 5V&0 and A155Si25Mn2p has been shown previous-ly to proceed via a nucleation-growth process. The

0163-1829/94/49(5)/3569(4)/$06. 00 49 3569 1994 The American Physical Society

Page 2: Annealing-induced icosahedral glass phase in melt-spun Al-Cu-V and Al-Si-Mn alloys

3570 BRIEF REPORTS

significant features exhibited in the amorphousA175Cu»V&0 and A153Si27Mn20 alloys are (1) the appear-ance of pronounced prepeaks at Q=1.5 and1. 6 A ' and(2) marked shoulders at the low Q of the main peaks.The presence of a prepeak is a strong evidence of chemi-cal short-range order in the sense of compound forma-tion. The prepeak occurs with the partial functions, S„in the Bhatia-Thornton formalism and with S„„orSzzin the Faber-Ziman formalism. The interatomic dis-tances can be derived using the Ehrenfest relation Q„s=I 23[.2n ld„~]and the correlation length computedfrom b,Q=aIL„. It has been indicated by Chen,Koskenmaki, and Chen' that the prepeak may be associ-ated with Mn-Mn correlation (-4.65 A) and the appear-ance of the distinct shoulder attributed to the existence oftwo groups of atomic pairs Al-Al (-2.82 A) and Al-Mn(-2.65 A), which are originated from the structure ofaA1-Si-Mn. " As in the case of the Al-Mn-Si, the appear-ance of a shoulder at low Q of the main peak in theAl-Cu-V [Fig. 1(a)] can be attributed to the icosahedralshort-range order existing in Al-rich crystalline A14,V7compounds. The average interatomic distances for Al-Vand Al-V were determined to be 2.72 and 2.86 A, respec-tively. ' The prepeak at Q=1.5 A ' corresponds to adistance of -5.1 A, which is close to the distance be-tween V(0) and V(1) atoms which locate at the center of

A175Cu(5VIo

icosahedron in an aA1-V compound. ' Furthermorewhen V was substituted by 5 at % Cu the prepeak disap-peared (not shown). These results indicate that theprepeak could be associated with the V-V correlation.X-ray-diffraction studies have indicated that the struc-ture of the icosahedral phase is indeed identical to that ofthe amorphous phase within 6 A at the same compositionfor Pdz&UzoSizo (Ref. 13) and A175Cu»V, 0 (Ref. 14).

One approach to understanding the universal phasondisorder can be found in accretion models for the growthof the icosahedral phase. In these models, localicosahedral units are excreted by the attachment of anicosahedron to a randomly chosen vertex or face of anicosahedral seed. To ensure orientational order, adjacenticosahedra are given the same orientation. The resultingstructure is highly defective but has a macroscopic orien-tation order. It was predicted that the peak widthsshould be a function of G~ and -G~ for theicosahedral-glass model and —G~ for the phason strainmodel. ' However, it is difficult if not impossible experi-mentally to distinguish them. Figure 2 shows experimen-tal data for the x-ray linewidth as a function of phasonmomentum (G~) for an icosahedral Al-Cu-V and anicosahedral Al-Si-Mn annealed from amorphous state.The x-ray linewidths correlate strongly with G~ andvary almost linearly with a slight scatter is seen in theAl-Cu-V. It suggests that the IG model is a possiblemodel for these two icosahedral alloys.

Figure 3 shows (a) the high-resolution image and (b)selected area diffraction pattern taken with an incident

0.04 I I

i-A175Cu15 v I p

1x10 0.03—

g 0.02

Ns0 ~ 01

Alq3Si27Mn2o

O. OO

0.03

~ 0.02

i-A153Si27Mn2p

0.01

FIG. l. Powder x-ray-diffraction patterns from amorphous(a, c) and icosahedral phases (b, d) in A175Cu»V, o and

A153Si»Mn» alloys. The icosahedral phases were obtained byannealed amorphous phase at 693 K for 1 h for the former andat 660 K for 10 min for the latter.

00

I

0.2I

0 ' 4

+per

FIG. 2. Results of x-ray study of peak widths, half width athalf maximum (HWHM) as a function of G~ for i-A175Cu15V, o

and i-A153Mn&oSip7.

Page 3: Annealing-induced icosahedral glass phase in melt-spun Al-Cu-V and Al-Si-Mn alloys

49 BRIEF REPORTS 3571

beam along fivefold axis, (c) the corresponding pattern il-lustrated by connecting the bright dots in the image of anicosahedral Al-Cu-V obtained by annealing the arnor-phous phase at 693 K for 1 h, and (d) the bright-field im-

age taken with an incident beam along a fivefold axis ofan icosahedral grain aged at 300 K for 17 880 h. One cannotice that the fringes in the photograph reveal mismatchalong various directions which suggests a random distri-bution of the phason disorder. The image lattice [Fig.3(c)] shows a two-dimensional structure consisting ofpentagons stuck together, side by side, in a random way.Besides the "diamonds" and "boats" often exhibited inan ideal Penrose tiling (PT) or a random tiling models(RT), the image lattice reveals unique tearlike or crack-like defects, shown dark, being similar to the IG patternschemed by simulation. ' We also note that the "stars"seen in the PT and RT models are absent in the imagelattice and IG patterns. As shown in Fig. 3(b), althoughbroadening appeared in spots, the distortion and dis-placement in spots are absent. Furthermore, convergentbeam electron-diffraction patterns from the 10-nm-diamarea do not show the deviation from the fivefold symme-try in spot positions (not shown), implying that the wave-length of the "phason" is much smaller than 10 nm.These results suggest the existence of isotropic strains inthe icosahedral phase. These observations assert than anicosahedral structure with higher density of random

I I I I '? lt I I

phase strains could be similar to that of an IG model. InFig. 3(d), a random network structure with "tears" is ob-served nearby the interface.

As mentioned previously, the icosahedral chemicalshort-range order existing in aA1-Si-Mn and aAl-V per-sists in the two amorphous alloys. Moreover, it wasverified that the structural unit in the icosahedral phaseof Al-Mn-Si is the Mackay icosahedron. ' It is worthnoting that the icosahedral unit is a Mackay icosahedronof —10 A in size for aA1-Si-Mn and is based on a regularicosahedron with a size of -6 A for aA1-V. Icosahedralstructures for these two alloys are described by the sameIG model but decorated by different icosahedral units. Ithas been theoretically undertaken to test the viability ofthe glass model in which the icosahedral phase is a net-work of linked atomic clusters and growth of this phaseinvolves the creation of new clusters from the liquid andtheir addition to the network. In the simulation, it wasindicated that a parameter b(-EQ/G~) depends on thegrowth conditions, in particular, is larger at low veloci-ty. ' Growth velocity of our IG phases is examined to beapproximately 10 ' cm/s. The data in Fig. 2 give thevalue of b-0.05. This value is much larger than thevalue observed in the melt-quenched sample (-0.02)with high growth velocity approximately —10 cm/s. ' Inaddition, the IG phase in Fig. 3(d) with a growth velocityapproximately -10 ' cm/s reveals a network morphol-

.ogy with tears, in accordance with the prediction of thesimulation in which tears were only observed in theicosahedral phase with low-growth velocity. A criticalcooling rate for forming the amorphous phase in thepresent two alloys is about 10 K/s and there is only oneway to form a single icosahedral phase by annealing theamorphous phase. Only by slowing down the coolingrate can a mixture of icosahedral and crystalline phasesbe obtained. Obviously, the IG phase formed from theamorphous solid is different from the icosahedral phasedirectly created from liquid in two ways, i.e., compositionand growth velocity. This was reflected in terms of thephason strain in previous studies. These results suggestthat our IG phase is the one observed in a sample which

e

/

/

JAW ~ . I ~

",„Yj%g~"j"?

/

-$.

/??

?

.a'

-@,,$:5 pg.

SO nm

I I

' Phgqee &e~0&c 10.

Cy~~ ~ g 0$ —~--

& 00 i50 200 250 XSTem perdu/e (K)

A oem /I

Cry. 470 pQCm

FICx. 3. High-resolution image (a), electron-diffraction pat-tern (b), and corresponding illustration (c) schemed from (a)with an incident beam along a Svefold axis of an icosahedralAl-Cu-V obtained by annealing the amorphous phase at 693 Kfor 1 h. The dark area in (c) represents the defects in a pentagontiling. (d) is the bright-Seld image taken along a 6vefold axis ofan icosahedral grain aged at 300 K for 17880 h. Note that theicosahedral grain is precipitated in the amorphous matrix.

0300

I

400 500 600

Temperature (Kj

700 800 900

FIG. 4. Temperature dependence of resistivity above roomtemperature of amorphous, icosahedral, and crystalline phasesin A153Si»Mn2O alloy from the same specimen. The inset showsthe temperature dependence of resistivity below temperature.

Page 4: Annealing-induced icosahedral glass phase in melt-spun Al-Cu-V and Al-Si-Mn alloys

3572 BRIEF REPORTS 49

TABLE I. Hardness (H„),Young's Modulus (E), low-temperature specific heat (y), resistivity (p), and transformation heat (H, ) ofamorphous and icosahedral phases in A175Cu&sV&o and A153Si»Mn2o alloys.

Al sCuisVio

A153Si27Mn2o

'Reference 21.

Amicosahedral phase

Amicosahedral phase

H„(DPN)

700870

11001500

E4„„(GPa)7486

y (mJmol 'K )

1 30'0.92'

p3oo ~ {pQcm)

151'221'950

1820

H, (kJ/mol)

1.4

1.6

can be described by the network of linked icosahedralclusters.

Figure 4 shows the temperature dependence of electri-cal resistivity p for amorphous, icosahedral, and crystal-line phases for A153Si27Mn20. The p and its dependenceon temperature dR /dT in the icosahedral phase are near-ly double that in the amorphous phase for both alloys(also see Table I). The crystalline Al-Mn-Si consisting ofcubic A15Mn&2Si7, hexagonal A19Mn3Si, and hexagonalA13Mn4Si5 shows a much lower resistivity than that inthe icosahedral and amorphous phases. The increase inresistivity upon an amorphous-icosahedral phase trans-formation is rather unique. It contrasts with the drasticdecrease in resistivity generally observed upon crystalli-zation of amorphous alloys due to structural ordering.The results of recent transport measurements on quasi-crystals indeed indicate that quasicrystal electrical resis-tivities are high compared with related crystalline phases,even with the corresponding amorphous phases. ' Thequasicrystals are more analogous to crystalline semi-insulators. The higher crystalline order, the higher isthe electrical resistivity. The anomalous high resistivityin quasicrystals comes from its quasiperiodicity and in-creases with the degree of quasiperiodic order. Besides

the high resistivity, as compared with either the corre-sponding amorphous or the crystalline phases, theicosahedral phases exhibit high hardness, high modulus,and a small coeIcient of low-temperature specific-heat(y) characteristics of the quasiperiodic lattice. '

Despite the presence of a high degree of phason dis-order in the so-called icosahedral-glass phase, i.e.,i-A175Cu&5V&0 and i-A153Mn20Si27, the nature of the quasi-periodic lattice strongly persisted in the IG model asreflected in physical properties. The IG phase may be akey point in understanding the inter-related structure andproperties of th quasicrystalline and amorphous phases.To date, the IG phase was only observed in a very slowgrowth rate, i.e., transition from the amorphous phase.It raises a question whether an IG phase can be formed ina melt-quenched state. In a simulation of strain accumu-lation in quasicrystalline solids, a dependence of thestrain accumulation on the cooling rate was observed.

This work has been supported by Iketani Science andTechnology Foundation. We are grateful to ProfessorMizutani of Nagoya University and Professor Matsuda ofAichi University of Education for the measurements ofresistivity.

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Page 5: Annealing-induced icosahedral glass phase in melt-spun Al-Cu-V and Al-Si-Mn alloys