Structure transformations in amorphous Fe,Co, and Pd based alloys during crystallization to the nanocrystalline state

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Pergamon

Maaaqals, Vol. 9, pp. 379-382.1997 ElsevierScience Ltd © 1997 Aeta Metallurgim In~ Prinled in the USA. All rights res~ved 09659773/97 $17.00 + .00

PH S0965-9773(97)00088-3

STRUCTURE TRANSFORMATIONS IN AMORPHOUS Fe,Co, AND Pd BASED ALLOYS DURING CRYSTALLIZATION TO THE NANOCRYSTALLINE STATE NJ. Noskova, E.G. Ponomareva Institute of Metal Physics, Ural Division, Russian Academy of Sciences, Kovalevskoi Str. 18, Ekaterinburg, 620219 Russia

Abstract -- Amorphous Fe73.jCulNb3Si13jB9, FesCoToSilsBIo and Pd81CuTSi12 alloys, produced by superfast quenchingfrom the meltfollowed byfast heating to 723-923 K and soaking for 10 s in vacuum wereinvestigated. The crystallization of an amorphousFe73NiojCUlNb3Si13jB 9 alloy was determined by methods of transmission electron microscopy (in situ). The F e73.~CulNb3Si I3.sB9alloy annealed at 923 Kfor 10 s produces a grain size of 6 nm, with phases ot-FeSil3 at.%, (FeNb)2B, and (FeNb)B. An FesCoToSilsBlo alloy annealed at 923 K for 10 s produces a grain size of 25 nm, with phases - ot-Fe, a-Co, ~-Co, Fe3Si, Co2Si, and (FeCo)2B. A Pd81CuTSi12 alloy annealed at 823 K for 10 s produces a grain size of 25 nm, with phases - Pd, Pd-Cu( ~, PdjSi, i-PdaSi. ©1997 Acta Metallurgica Inc. INTRODUCTION A recently rapid quenched F e 7 3 , s C u l N b 3 S i 1 3 , 5 B 9 , alloy has been the subject of intensive investigations. Amorphous in its initial state, the alloy crystallized into a nanocrystallme material. The ahoy has two crystallization temperatures, 783 and 843 K. At temperatures higher than 783 K nanocrystalline grams form. Above 843 K the Nb enriched environment of these nanoerystalline grains undergoes crystallization;the grains quickly grow in size while magnetic properties deteriorate [l].Earlier, when producing a nanocrystalline state in Fe73,sCulNb3Sij3,sB9 alloy, we found that rapid cristallization at an elevated temperature (rapid heating and short soaking) produced grains of a smaller size and phases that are slightly different from those obtained upon long annealing at the crystallization point [2]. We applied the same procedure to refine grains in an FesCoToSitsBto ahoy [3]. The PdslCu7Sil2 ahoy selected for the present study has a crystallization temperature of 733 K. This was determined from the variation of the electric resistivity during heating at a rate of 20 K/rain. A goal of the present work is to investigate the effect of increasing the temperature and of a required holding at a given temperature of crystallization annealing on the phase composition, the size of nanograins of the alloys crystallized by a conventional technique by rapid crystallization, and by methods of transmission electron microscopy (in situ). 379

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EXPERIMENTAL

The alloys Fe73.sCulNb3Si13,sB9, FesCoToSilsBl0 and PdgICu7SiI2 were prepared by melt quenching and by the annealing (see Table l). A JEM- 200CX electron microscope was used for structural investigations. We determined the nanoerystalline-grain sizes in alloys from electron micrographs ( used from 500 to 3000 grams when calculating the number of large, medium, and small grains).Phases in the nanocrystalline alloys were determined from electron diffraction patterns.

RESULTS AND DISCUSSION The results are presented m Table 1 and Fig. 1, and Fig.2 a,b. As can be seen from the size distribution of crystallites (Table l and Fig.l) the most common crystallite size m the alloy annealed at 923 K for 0,003 h is 5-6 nm. In the alloy annealed at 813 K for l h, it is 8l0 nm. Calculation the interplanar spacings derived from the electron diffraction patterns were made of the phases in the nanocrystallme alloys[3,4]. As to prove interplanar spacings characteristic of a Fe-Si solid solution tend to approach, in the rapidly crystallized sample of the alloy Fe73,5CulNb3Si13,5B9,the values typical of a Fe-Si solid solution with a smaller Si content, about 13% Si, as compared to 15 % Si in the sample crystallized at 813 K. Moreover to lay open FeaSi,(FeNb)2B,FeNbB,Fe2B phases (see Table l). An analysis of the data in the FesCo70SilsBl0 alloy, showed that a-Fe,a-Co, ~-Co, Fe3Si, CoESi and (Fe,Co)2B phases would exist m the alloy after rapid crystallization, where as or-Co, 13-Co, Co2Si, and CoB would exist after slow crystallization. In PdslCuTSit2 alloy annealing at 823 K for 0,003 h produces grain size is 25 nm, phases - Pd, Pd-Cu0,),PdsSi,i-PdxSi, after annealing at 773 K for l h produces grain size is l 0 , 5 0 rim, phases - Pd,Pd-Cu(y),PdsSi. TABLE 1 The temperature of annealing Tc,the gram size D and phases in alloys Composition Fe73,sCulNb3Si13,5B9

Fe5Co70Si15B10 PdglCu7Sil2 ............ ""- . . . . . . . . . . . . .

Tc Ok')

813 923 1123 873 923 773 823

t (h) l 0.003 l 1 0.003 I 0.003

D,nm

8- l0 5- 6 200 50-200 15 - 50 10, 50 25

Phases c~-(Fe+15%Si),(FeNb)2B,FeNbB,Fe2B ~-(Fe+I3%Si),(FeNb)EB,FeNbB,FeaSi o~-(Fe+ 18°/aSi),FeEB,FeNbB t~-Co,~-Co, Co2Si, CoB ct-Fe,a-Co,fi-Co,FmSi,Co2Si,(FeCo)2B Pd, Pd-Cu('/),PdsSi Pd,Pd-Cu(7 ),PdsSi,i-PdxSi

STRUCTURETRANSFORMATIONSINAMORPHOUSFe, Co, AND Pd BASEDALLOYS

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a grain size Fig. 1. Grain size distribution in various nanocrystalline alloys: I-Fe73.sCulNb3SiI3.5B 9 annealed at 813 K for I h, 2 - Fe73.sCulN'b3Si13.sB 9 alloy annealed at 923 K for 0,003 H; 3 Feq3.sCulNb3Sil 3.5B9 alloy annealed at 1123 K for I h; 4 - Fe5Co7oSil5B 10alloy annealed at 873 K for 1 h; 5 - FesCOToSi 15B l0 alloy annealed at 923 K for 0,003 h; 6 - Pd s iCuTSil2alloy annealed at 773 K for I h; 7 - PdslCUTSil2alloy annealed at 823 K for 0,003 h.

Amorphous alloy

a

Deformation amorphous alloy

773 K

853 K

933 K 5nm

Fig. 2. The microstrueture for a sample of alloy Fe73,sCulNbaSija,sB9 immediately after the rapid quenching and sample of l:Ze73,sCulNb3Si13,sB9 alloy after the rapid quenching and deformation (tension from crack) by crystallization m situ on a electron microscope (a) and the schema of crystallization according to Fig.2 a Co).

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Fig. 2 a shows the microstructure for a sample of alloy Fe73,sCulNb3Si13,sB9 immediately after the rapid quenching and sample of Fe73,sCutNb3Sit3,sB9 alloy after the rapid quenching and deformation (tension from crack) by crystallization in situ on a electron microscope. Fig.2 b shows the scheme of Fig. 2 a. On the scheme showed phases would exist at an elevated temperature under heatmg (kept in the furnace from 0,003h to 0,01 h),and cooling alloy[4]. CONCLUSION Rapid crystalfization at an elevated temperature (rapid heating and short soaking) produced grains and nanophases whose sizes were smaller than in the case of the usual crystalfized alloy. The effects of rapid crystallization at an elevated temperature on the changes in phase composition of the Fe73.5CulNb3Si13.sB9 alloy were repeatable, and in all probability were dependent on the preliminary state of the metallic glass. REFERENCES .

2. 3. 4.

Yoshizawa Y., and Yamauchi K. Mater. Trans. JIM, 31,307 (1990). Glazer A.A., Lttkshina V.A., Potapov A.P., and Noskova N.I. Phys. Met. Metallogr., 74, 163 (1992). Noskova N.I.,Ponomareva E.G.,Lukshina V.A. and Potapov A. P. ,J. Nanostruetured materials,6, 969, (1995). Noskova N.I. and Ponomareva E.G. Phys.Met.MetaUogr.,8_22,(1996),m presse.