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Effect of allyying on composition, structure and properties of powders of alloy AlCuFe, containing quasi-crystalline PHASE.

One of the methods of improving quality of materials and coatings, which contain quasi-crystalline phase, including alloys of system Al--Cu--Fe, is their alloying by one or a complex of elements. At present there are about a dozen of foreign patents, in which various schemes of alloying powders of the alloy AlCuFe are proposed, depending upon functional designation of produced from them coatings.

For increasing resistance of coatings from alloy AlCuFe to oxidation composition is proposed, containing up to 6 at.% Cr. Thermal coating from powder [Al.sub.65.6][Cu.sub.18.5][Fe.sub.8][Cr.sub.6] is used as a sublayer in making heat-protection coatings from Zr[O.sub.2] [1]. For ensuring efficient heat-barrier protection material of the sublayer should contain at least 80 vol.% of quasicrystalline phase. Application of such material, which has low heat conductivity, instead of traditional MeCrAlY (Me--Ni, Co, CoNi) should improve protection properties of the double-layer heat-barrier coating.

For the purpose of increasing hardness and wear resistance of coatings from AlCuFe alloys it is proposed to alloy them by refractory metals (chromium, molybdenum, tungsten, etc.), as well as boron and silicon in small amounts [2].

In patent [3] mixture of powders AlCuFe and FeAlCrB, containing brittle and ductile components, is proposed. Coating of such composition is characterized by increased resistance to abrasive wear.

For producing wear-resistant coatings it was proposed to introduce into AlCuFe-base alloy soft particles, such as polymers BN, clad BN, and Ni-graphite [4].

A number of multicomponent alloys with general formula [Al.sub.a][Cu.sub.b][Co.sub.b]-[(B, C).sub.c][M.sub.dNe[I.sub.f] (M--iron, chromium, manganese, nickel, ruthenium, osmium, molybdenum, vanadium, manganese, zinc, palladium; N--tungsten, titanium, zirconium, hafnium, rhodium, niobium, tantalum, yttrium, silicon, germa nium, rare-earth metals; [I.sub.f]--unavoidable impurities), in which one of the main components (iron) is replaced by cobalt, was patented [5]. Refractory, rareearth and other metals, boron and carbon act as alloying elements.

The alloys contain 30 wt.% of one or several quasi-crystalline phases. They are divided into seven groups depending upon their designation: for operation in acid and alkaline atmospheres, resistant to oxidation, grain-growth-resistant alloys, alloys with increased hardness, toughness, etc. Despite high number of various versions of doping alloys AlCuFe, works are continued in this direction.

In this article for additional alloying scandium and chromium are selected on the basis of analysis of diagrams of state of aluminium alloys and literature data.

Information on influence of alloying by scandium on structure and properties of the Al--Cu--Fe system alloys is absent in the literature. At the same time it was established in the course of investigations of aluminium alloys, carried out within the last 20 years, that alloying by 0.25--0.50 wt.% Sc exerts positive influence on mechanical and corrosion properties of aluminium alloys [6]. Production of the alloy AlCuFe powders, alloyed by scandium for application of coatings using the method of thermal spraying, is proposed in [7].

Alloys AlCuFe, alloyed by chromium, are already used as heat protection coatings in production of household utensils (frying pans, irons, etc.) due to their low heat conductivity and high corrosion resistance [8]. However, data on study of powders from the alloy AlCuFe, alloyed by chromium, are absent. Alloyed powders, investigated in this work, were produced by developed in the Institute for Materials Science Problems of NASU new original method of the alloy spraying by high-pressure water on experimental technological line by Dr. O.D. Nejkov.

Chemical compositions of investigated alloys are as follows:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.]

In the course of investigation complex methodology was used, which included metallography (optical microscope <<Neophot-32>> with attachment for digital photographing); scanning electron microscopy (scanning electron microscope JSM-840); X-ray spectral microanalysis (microanalyser <<Camebax>> SX-50).

X-ray diffraction phase analysis was carried out on diffractometer Dron-UM1 in monochromatized radiation Cu[K.sub.a]. Investigations were carried out both at room temperature and at heating within temperature range 20--900 [degrees]C in helium using high-temperature attachment UVD-2000. Amount of [psi]-phase was determined using methodology described in [9]. For this purpose recording of radiograms was performed within angle interval, in which the most strong diffraction maximums of main phases were located: 40 <20 <50.

In addition, resistance of powders to oxidation in air was studied using thermography. Experiments were carried out on derivatograph Q-1500 within temperature range 20--1000 [degrees]C at heating rate 10 K/min. Phase transformations during heating in helium up to the temperature 1500 [degrees]C were studied using method of differential thermal analysis (DTA).

Technological properties of powders (flow and bulk density) were determined according to GOST 20899--75 and GOST 19440--74. Before investigation powders were classified by fractions on vibratory sieves (GOST 18318--73), and each fraction was investigated separately.

It was established as a result of investigation of granulometrtic composition of atomized powders and construction of bar graphs of particle distribution by sizes that more than 70 wt.% of particles related to the fraction 25--100 [micro]m, i.e. were fit for application of coatings by the method of thermal spraying (plasma, micro-plasma or detonation one). More coarse fraction of the powder (100--200 [micro]m), content of which in the mixture is about 25 wt.%, may be used as a filler of flux-cored wires for application of coatings by the method of electric arc plating, and amount of fine powder (<25 [micro]m), unfit for application of coatings because of high losses of aluminum during heating of the powder up to the melting state, does not exceed 2--5 wt.%.

Appearance of powders of doped alloys (Figure 1) is practically the same for all compositions. Particles of the powders have irregular, sometimes elongated shape with molten surface. Occasionally particles with sharpened edges and internal pores occur.

Metallographic analysis of the powder particles showed their fine and multi-phase structure (Figure 2), which mainly represents mixture of two phases: crystalline (light, more soft) and quasi-crystalline (dark, more hard and brittle) ones.

Phase composition of the powders was investigated in more detail by radiographic method. So, on radiograms of powders of the alloys with scandium, especially with a highest content (Figure 3), near reflexes of [psi]- and [beta]-phases system of additional low-intensity lines was registered at diffraction angles 20.5; 29.05; 41.53 and 46.71. Analysis of angular position of these peeks showed their good coincidence with diffraction spectrum lines of equilibrium triple W-phase of the Al--Cu--Sc system with tetragonal lattice of the ThMn12 type [10]: experimental peeks of W-phase in our case correspond to values of the lattice parameters a = 0.8688 nm, c = 0.5029 nm and insignificantly differ from a = 0.855 nm, c = 0.506 nm for W-phase in the Al--Cu--Sc system with the composition [Al.sub.51.4][Cu.sub.39.7][Sc.sub.8.9] [11].

Disregarding small amount of W-phase, one may estimate content of [psi]-phase in powders according to the methodology of [9]. The results obtained prove that doping of the alloy AlCuFe with 0.265 and 0.440 at.% Sc essentially increases content of quasicrystalline icosahedron [psi]-phase, whereby, like in case of non-alloyed powders, content of [psi]-phase increases by means of size of the particles reduction (Figure 4).

For precision investigation of temperature influence on phase transformations of the alloy AlCuFe powder, alloyed by scandium, powder of the [Al.sub.62.56][Cu.sub.25][Fe.sub.12][Sc.sub.0] 44 composition and fraction 25-40 [micro]m with content of [psi]-phase about 78 wt.% selected. It was established that introduction into alloy of 0.44 at.% Sc causes certain reduction of the period of lattice of [psi]- and [beta]-phases (Table 1) in comparison with non-alloyed powder AlCuFe, for which [a.sub.[psi]] = = 0.63466(7) nm, and [a.sub.beta] = 0.29270(9) nm, which may be the evidence of scandium dissolution in lattices of [psi]- and [beta]-phases or of the change in them of the content of base elements.

As a result of seasoning the powder alloyed by 0.44 at.% Sc at temperature 600 [degrees]C for 1 h transforms practically completely into single-phase [psi]-state (Figure 5), whereby lines of [psi]-phase noticeably narrow down, i.e. the crystalline lattice improves. Cooling down to room temperature does not change singlephase state of the annealed powder, whereby period of crystalline lattice of [psi]-phase is less than in initial powder (see Table 1).

At the temperature 700 [degrees]C lines of [beta]-phase are registered again on the radiogram, whereby their intensity increases by means of temperature increase (see Table 1). At the temperature 900 [degrees]C in addition to lines of [beta]-phase peaks of [lambda]-phase are registered on the radiogram.

Formed at the temperature above 700 [degrees]C [beta]-phase preserves during cooling down up to the room temperature, whereby parameter of its lattice does not remain constant (see Table 1).

Diffractogram of the powder, alloyed by chromium, contains in initial state [psi]- and [beta]-phases (Figure 6, curve 1), whereby periods of the lattices of mentioned phases are as follows: [a.sub.[psi]] = 0.64860(9) nm but [a.sub.[beta]] = 0.29144(4) nm. This causes superimposition of the peak (110) p (28 = 43.9[degrees]) on more intensive peak of [psi]-phase with Kahn indices (20/32). Heating of the powder up to the temperature 600--800 [degrees]C enables increase of the [beta]-phase period ([a.sub.[beta]] = 0.29460(9) nm) and formation instead of y-phase of crystalline approximant of decagonal quasi-crystal--phase [O.sub.1] (Figure 6, curve 2). Phase [O.sub.1] of the Al--Cu--Fe--Cr system alloys is analyzed in detail in [12, 13].

[FIGURE 1 OMITTED]

In Figure 7 calculated diffractogram of orthorhombic phase [O.sub.1] (spatial group B, [micro][m.sup.2], a = 3.254 nm, b = 1.237 nm, c = 2.357 nm) is presented, which contains 660 atoms in the elementary cell. Very good coincidence of calculated and experimental diffractograms is registered.

Radiographic investigation of the alloy AlCuFe powders, annealed within 1 h in vacuum furnace and then cooled down to room temperature, showed that although after annealing at 500 [degrees]C new phase [O.sub.1] appears, significant amount of [psi]-phase continues to exist, while after annealing at 550 [degrees]C practically the whole [psi]-phase converts into [O.sub.1].

Influence of alloying on resistance to oxidation was studied in relation to powders with size of particles 80--100 [micro]m. For comparison non-alloyed powders, produced by spraying with water and argon, were investigated under the same conditions. Analysis of the data (Figure 8) shows that temperature of initiation of nonalloyed powder oxidation (about 600 [degrees]C) does not depend upon the method of its production, while by means of temperature increase oxidation intensity of the powders, produced by spraying with water, increases in comparison with the powder, produced by spraying with argon. This is connected with higher specific surface of powder particles in the first case.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

Oxidation initiation temperature of the powders, alloyed by scandium and chromium, somewhat increases (from 600 to 680 [degrees]C) in comparison with nonalloyed powders. As heating proceeds, intensity of oxidation of powder with chromium differs little from that of non-alloyed powder sprayed with water.

Powder, alloyed by scandium, is least resistant to oxidation. The same regularity is noted in [14]. Introduction of rare-earth metals in quasi-crystal [Al.sub.63][Cu.sub.25][Fe.sub.12] accelerates oxidation of iron and copper with formation of nano-dimensional structure of oxides.

Results of investigation of powders by DTA method are presented in Figure 9.

As far as preliminary investigations showed that size of the powder particles does not effect character of curves (DTA), we limited ourselves by investigation of the powder with size of particles 80--100 [micro]m.

Comparison of curves (DTA) of the powders, alloyed by scandium, with curves of the unalloyed powder shows that scandium just insignificantly reduces temperature of initiation of phase transformation both during heating (curves 1, 2) and during cooling (curves 1', 2').

First endothermic effects (810--900 and 820-890 [degrees]C) for non-alloyed and alloyed alloys, respectively, may be referred to the melting point of [psi]-phase, which, according to literature data, equals 870 [degrees]C (Figure 10).

Character of the curves within this range is, evidently, influenced by the effects connected with [beta][right arrow][psi] transformation, which were established in in vestigation of powders by the method of high-temperature radiography (see Table 1).

[FIGURE 8 OMITTED]

Second endothermic effect (930--1010 and 930-1000 [degrees]C) for the same compositions relates to the area L + [lambda] + [beta] on the diagram of the Al--Cu--Fe system phase equilibriums (Figure 10). Lines of [lambda]-phase together with [beta]-phase are registered on radiograms at temperature 900 [degrees]C. The process terminates by formation of the melt at temperature above 1000 [degrees]C with subsequent two-stage solidification during cooling (Figure 9, curves V, 2'). It is characteristic that ingots after DTA had spherical form, which proved absence of wetting by the crucible material melt (Zr[O.sub.2]).

[FIGURE 9 OMITTED]

[FIGURE 10 OMITTED]

Structure of ingots is rather course-grain (Figure 11, a, b) because of lower rate of solidification (80 K/s) in comparison with solidification rate of sprayed powders ([approximately or equal to] [1.10.sup.5] K/s), which allowed measuring microhardness of the main phase components. In the ingot from non-alloyed powder light [beta]-phase had microhardness value of (7.5 [+ or -] 0.5) GPa, while in the ingot from alloyed powder it was somewhat lower--(7.32 [+ or -] 0.3) GPa. Detailed investigation inside p-phase grains allows differing rare dendrites of [lambda]-phase of dark-grey color with microhardness (8.0 [+ or -] [+ or -] 1.5) GPa.

Microhardness of quasi-crystalline [psi]-phase in the ingot from non-alloyed powder achieved 10 GPa, while in the powder alloyed by 0.44 at.% Sc it was (9.36 [+ or -] 0.5) GPa. Content of [psi]-phase in the first case equaled, approximately, 22, in the second case was [approximately or equal to] 29 wt.%.

Alloying by chromium is reflected on the character of curves in DTA more essentially: their view changes within the whole temperate range and area of thermal effects shifts into the area of lower temperatures.

On the heating curve 3 (Figure 9) flexes (790, 830, and 890 [degrees]C) are noted, which proves multistage character of phase transformations that precede liquid phase formation (970 [degrees]C). Solidification process covers wide temperature range, which may indicate overlapping of temperature ranges of phase transitions and high degree of the ingot chemical inhomogeneity.

Although in X-ray diffraction phase analysis two phases were detected (solid solution on the basis of orthorhombic VCC-lattice [O.sub.1] and cubic VCC-lattice [beta]), significant chemical inhomogeneity was registered in the process of the ingot etching, especially over edges of the phase [O.sub.1] grains (Figure 11, c). Microhardness of the main structural components varies within wider range than in previous cases. For [beta]-phase it is (6.35 [+ or -] 7.0) GPa, for phase [O.sub.1]--(7.96 [+ or -] 1.25) GPa.

[FIGURE 11 OMITTED]

Investigation of technological properties of powders (Table 2) showed that doping of alloy AlCuFe by scandium and chromium increases flow of the powder fine fractions. While in non-alloyed powder flow was absent when size of particles was 63--80 [micro]m and less, in alloyed powder it disappeared when size of particles was 40--63 [micro]m. Inherent to the powders with higher content of scandium (0.44 at.%) is also higher flow in the fraction 63--80 [micro]m and rather good flow in powders of more coarse fraction (more than 200 [micro]m). However, technological properties of powders, produced by spraying with water, are inferior to those of powders, produced by spraying with argon, having spherical shape of particles and flow 35-60 s/50 g for wide range of size of particles--from <25 to >160 [micro]m.

CONCLUSIONS

1. It is established that doping of alloy [Al.sub.63][Cu.sub.25][Fe.sub.12] with 0.265 and 0.440 at.% Sc allows significant increasing content of icosahedron [psi]-phase in powders from this alloy. In addition to crystalline [beta]- and quasicrystalline y-phases forms crystalline W-phase, which is stable up to the temperature 600 [degrees]C. After annealing, powder with 0.440 at.% Sc completely transits at 600 [degrees]C within 1 h into single-phase [psi]-state.

2. It is shown that in powders from alloy [Al.sub.66][Cu.sub.18][Fe.sub.8][Cr.sub.8] form [psi]- and [beta]-phases in, approximately, the same amount. After annealing at 550 [degrees]C within 1 h the whole quasi-crystalline phase transforms into phase [O.sub.1], which represents crystalline approximate of decagonal quasi-crystalline phase.

3. It is determined that doping of alloy AlCuFe by scandium and chromium practically does not change qualitative phase composition of the powders, but significantly increases in them content of quasi crystalline phases without exerting significant influence on thermal stability thereof.

4. It is established that oxidation initiation temperature of alloyed powders increases, in comparison with non-alloyed powders, from 600 to 680 [degrees]C, while alloying with scandium significantly increases oxidation intensity at higher temperatures.

Authors express their gratitude to the National Technical Center in Ukraine for financial support of this work carried out within the framework of project 1630.

[1.] Dubois, J.-M., Archambault, P., Colleret, B. Quasicrystalline aluminum heat protection element and thermal spray method to form elements. Pat. 5888661 US. Publ. 30.04.99.

[2.] Shield, J.E., Goldman, I., Anderson, I.E. et al. Method of making quasicrystal alloy powder, protective coatings and articles. Pat. 5433978 US. Int. Cl. B22F9/08. Publ. 18.07.95.

[3.] Sordelet, D.J., Besser, M.F. Abrasion resistant coating and method of making the same. Pat. 6242108 B1 US. Publ. 05.07.2001.

[4.] Hermanek, F.J. Abradable quasicrystalline coating. Pat. 6254700 B1 US. Publ. 03.07.2001.

[5.] Dubois, J.M., Pianelli, A. Aluminum alloys, substrates coated with these alloys and their applications. Pat. 5432011 US. Publ. 11.07.95.

[6.] Milman, Yu.V., Lotsko, D.V., Sirko, O.I. (2000) Sc effect of improving mechanical properties in aluminum alloys. Mater. Sci. Forum, 331--337, 1107 -1112.

[7.] Milman, Yu.V., Lotsko, D.V., Efimov, N.A. et al. (2005) Sc alloying effect in cast Al--Cu--Fe quasicrystals. In: Abstr. of Pap. of Int. Conf. on Current Materials Science: Achievements and Problems (Kiev, Sept. 26--30, 2005).

[8.] Dubois, J.-M., Proner, A., Bucaille, B. et al. (1994) Quasicrystalline coatings with reduced adhesion for cookware. Ann. Chem. Fr., 19, 3 -25.

[9.] Sordelet, D.J., Besser, M.F., Anderson, I.E. (1996) Particle size effects on chemistry and structure of Al--Cu--Fe quasicrystalline coatings. J. Thermal Spray Technology, 5(2), 161--174.

[10.] Kharakterova, M.L., Dobatkina, T.V. (1988) Polymetric sections of Al--Cu--Sc system. Izvestiya AN SSSR. Metally, 6, 180 -182.

[11.] Kharakterova, M.L. (1991) Phase composition of Al--Cu-Sc alloys at temperatures of 450 and 500 [degrees]C. Metally, 4, 191-194.

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[13.] Dong, C., Dubois, J.-M. (1995) Structural study of crystalline approximants of the Al--Cu--Fe--Cr decagonal quasicrystal. J. Appl. Cryst., 28, 96--104.

[14.] Yamasaki, M., Tsai, P. (2002) Oxidation behavior of quasicrystalline [Al.sub.63][Cu.sub.25][Fe.sub.12] alloys with additional elements. J. Alloys and Compounds, 342, 473--476.

[15.] Quiguandon, M., Calvayrac, Y., Quivy, A. et al. (1999) Phase diagrams and approximants. Quasicrystals: MRS Symp. Proc., 553, 95--106.

A.L. BORISOVA, Yu.S. BORISOV, L.I. ADEEVA, A.Yu. TUNIK, M.V. KARPETS and L.K. DOROSHENKO

E.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine
Table 1. Dependence of intensity I, half-width B, main parameters of
X-ray peaks and lattice parameters of [psi]- and [beta]-phases of
[Al.sub.62.56][Cu.sub.25][Fe.sub.12][Sc.sub.0.44]

Filming temperature, [degrees]C [psi]-phase

 I, rel. un A, deg

20, initial 38373 0.28
600 after seasoning for 1 h 42528 0.22
20 after 600 45944 0.22
200 44375 0.22
400 42430 0.22
600 40865 0.21
700 38514 0.18
800 35145 0.16
600 after 800 37950 0.16
600 after 850 28290 0.15
600 after 900 29115 0.20
20 after 900 31792 0.23

Filming temperature, [degrees]C [beta]-phase

 I, rel. un A, deg

20, initial 15500 0.28
600 after seasoning for 1 h -- --
20 after 600 -- --
200 -- --
400 -- --
600 -- --
700 3486 0.17
800 5264 0.17
600 after 800 5493 0.18
600 after 850 8354 0.14
600 after 900 23228 0.24
20 after 900 30905 0.26

Filming temperature, [degrees]C Period of lattice, nm

 [a.sub.[psi]] [a.sub.[beta]]

20, initial 0.63298 (3) 0.29237 (3)
600 after seasoning for 1 h 0.63774 (3) --
20 after 600 0.63149 (4) --
200 0.63322 (1) --
400 0.63522 (2) --
600 0.63728 (3) --
700 0.63832 (4) 0.29674 (5)
800 0.63998 (3) 0.29719 (7)
600 after 800 0.63696 (5) 0.29633 (4)
600 after 850 0.64137 (6) 0.29754 (7)
600 after 900 0.63160 (9) 0.29650 (8)
20 after 900 0.62740 (8) 0.29390 (6)

Table 2. Effect of alloying by scandium and chromium on technological
properties of the alloy AlCuFe-base powders

 Chemical composition of alloy

Powder fraction, [Al.sub.62.735]
[micro]m [Cu.sub.25][Fe.sub.12]
 [Sc.sub.0.265]

 Flow, s/50 g Bulk density,
 g/[cm.sup.3]

> 200 Not flowing 1.15 [+ or -] 0.01
160-200 80 1.11 [+ or -] 0.01
120-160 81 1.19 [+ or -] 0.01
100-120 76 1.26 [+ or -] 0.01
80-100 86 1.29 [+ or -] 0.01
63-80 101 1.34 [+ or -] 0.01
40-63 Not flowing 1.42 [+ or -] 0.02
25-40 Same 1.45 [+ or -] 0.02

Powder fraction, [Al6.sub.2.56]
[micro]m [Cu.sub.25]
 [Fe.sub.12]
 [Sc.sub.0.44]

 Flow, s/50 g Bulk density,
 g/[cm.sup.3]

> 200 149 1.08 [+ or -] 0.01
160-200 95 1.10 [+ or -] 0.01
120-160 70 1.25 [+ or -] 0.01
100-120 85 1.30 [+ or -] 0.01
80-100 68 1.34 [+ or -] 0.01
63-80 74 1.42 [+ or -] 0.01
40-63 Not flowing 1.52 [+ or -] 0.02
25-40 Same 1.57 [+ or -] 0.02

Powder fraction, [Al.sub.66]
[micro]m [Cu.sub.18]
 [Feg.sub.8]
 [Cr.sub.8]

 Flow, s/50 g Bulk density,
 g/[cm.sup.3]

> 200 Not flowing 1.10 + 0.01
160-200 105 1.11 [+ or -] 0.01
120-160 82 1.14 [+ or -] 0.01
100-120 77 1.18 [+ or -] 0.01
80-100 74 1.23 [+ or -] 0.01
63-80 73 1.29 [+ or -] 0.01
40-63 Not flowing 1.37 [+ or -] 0.01
25-40 Same 1.38 [+ or -] 0.01

 [Al.sub.63]
 [Cu.sub.25]
 [Fe.sub.12]

 Flow, s/50 g Bulk density,
 g/[cm.sup.3]

> 200 N/D
160-200 Same
120-160 >>
100-120 >>
80-100 63 1.38 [+ or -] 0.02
63-80 Not flowing 1.33 [+ or -] 0.01
40-63 Same 1.36 [+ or -] 0.01
25-40 >> 1.30 [+ or -] 0.02
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Title Annotation:GENERAL PROBLEMS OF METALLURGY
Author:Borisova, A.L.; Borisov, L.I.; Adeeva, A.Yu; Tunik, M.V. Karpets; Doroshenko, L.K.
Publication:Advances in Electrometallurgy
Article Type:Report
Date:Apr 1, 2006
Words:3919
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