V.S.Tsepelev, B.A.Baum, G.V.Tjagunov, V.I.Ladjanov, K.Y.Shmakova, A.N.Vloh
Institut of Liquid Metal Physics, Urals State Technical University,
19 Mira str., Yekaterinburg, 620002, Russia
ABSTRACT
The physical properties of liquid alloy Finemet type has been investigated. The melting regimes of alloy has been proposed on the base of liquid metal properties analysis. The first regime is the heating to the temperature below t c
and further amorphisation. The second regime is the heating to the temperature above t c
, then amorphisation by the first regime. The third regime is the heating to the temperature above t c
. The amorphisation temperature is below then by the first regime. The physical characteristics of amorphous and nanocrystalline ribbons were tabulated. The best service properties of ribbons were obtained by the third regime.
It has been established by the x-ray difraction and magnetometry that nanocrystalline layer of boron and silicon solid solutions in

-Fe is formed on the specimen surface during amorphisation. The polyterms of magnetic anisotropy effective field (H a
) have nonmonotonic type. The physical motive of such H a behaviour is the competition of main processes: the quenching stress relaxation, the composition of nanocrystalline phase changing, surface and body crystallisation.
Such melt preparing leads to account of plane nanocrystalline phase on the surface change in a nonannealed specimens.The means of H a
is changed and its polyterm extremum position is moved out on temperature scale. The elimination of plane nanocrystals from specimen surface by the chemical etching tends to double decreasing of anisotropy effective field.
1. INTRODUCTION
The preparation technology of a commercial melt of specific chemical composition can have many variants. For a given set of production conditions, the optimal variant can be selected out of them only on a scientific basis by taking into accoun the formation of the structure and properties of the liquid multicomponent system during the course of melting. In a well prepared melt, there must not be any traces of prehistory and it must be in equilibrium, i.e., under the given conditions, it must have the maximum amount of homogeneity possible. The microinhomogeneity existing in such a melt is determined only by the differences in the interaction energies of particles (1).
The question arises then as to what model concepts can adequately describe the structure of a melt, which has the aforementioned features, and is it correct to consider the interrelationship found in the experiments between liquid and solid states of the same real substance? In our opinion, the most complete answer to the problem is the quasichemical model of the microinhomogeneous structure of liquids, which is result of development of the views of Stuart, Frenkel, and Eyring (2).
The model essentially consists of the following. The melt is composed of extended regions (cybotaxes or clusters), the atomic arrangement inside which is distinguished by a certain order (short-range). Owing to relatively strong thermal
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motion of the particles, the clusters do not have any clear boundaries. The predominant atomic coordination is continuously replased by other arrangements as the distance from the core of the cluster increases. For the same reason, the lifetime of the clusters is limited and depends on the energy of the chemical bonds in them as well as temperature.
2. EXPERIMENTAL PROCEDURES
The main advantage of complex is the ability of simultaneous stadyng of structure, electron and kinetic characteristics of liquid and solidifyed metals in the wide temperature interval up to 1900°C. Obtaining absolute values of phisicochemical properties of metal melts. The most of the units work in the automatic regimes, it improve the results reliability. Metrological attestation of complex's unit is carried out. Unique of the complex is in absence of analogies in the world practice.
Measurements of the strength
 f
were carried out at 27 and -196 o
C with the extension rate 1.5 x 10
-4
s
-1
using a deformation machine with a rigidity of 25 kN/mm.
Each experimental point of the strength was obtained by averaging the results of measurements on five samples. The spread in values
 f measurements of the anisotropy of
 f
was 3-5%. Samples for were cut out from a "wide" ribbon at angles
 of 0, 22.5, 45, 67.5 and 90° to the ribbons length axis. Their width and gauge length were 5-6 mm and 15-20 mm, respectively. Fracture toughness K
1C
was measured under uniaxial tension of samples with a transversal crack made beforehand on the axis of the sample. The failure surfaces of the samples were studied by means of a
JSM-T20 scanning electron microscope, surfaces of the samples were studied using an optical microscope. The kinematic viscosity of melts was measured by the method of damping of torsional vibrations of the crucible with the melt suspended on elastic fibre (3).
At present time the fundamental properties and structural changes investigations of the Fe-C-Si, Fe-B, Ni-B, Co-B alloys cany out on the units of the complex. The composition and melt technology this alloys are improved.
It may be additionally carry out the investigations of the amorphous alloys on the iron, nickel and cobalt base and wide range of alumin alloys.
3. EXPERIMENTAL RESULTS AND DISCUSSION
Investigations of physical properties of liquid alloys based on iron, nickel and cobalt that are designated for producing amorphous materials deserve to be paid special attention. This is related, on the one hand, to the high crystallization rates and retention of the structural features of the liquid metal in the solid state and, on the other hahd, to the substantial effect of the kinematic viscosity and surface properties on the production technology of amorphous ribbons.
The reason of anomaly forming on the properties polyterms may be follows.
Alloys for amorphization have as a rule the eutectic composition or close to it. The phases that forming eutectic are bordered in the solid state. After melting the liquid metal inherites their local structure. The physical properties polyterms anomalys are determined by the intensive destruction of this microregions where internal interatomic interaction in the region is stronger than outside. Upon heating to the critical temperature (or tan) the energy of the thermal motion of the particles in the melt becomes comparable to the bond-breaking energy of the strongest interatomic
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interaction in the nonequilibrium atomic clusters. The heat motion destroys clusters, the melt loses its heredity.
The destruction of strong microregions leads to significant melt overcooling during solidification, that increases its glassforming ability and gives the possibility to stabilize production technology and to get the more amorphous straps.
So, the kinematik viscosity ( Fig.l
) of nanocristalline magnetic alloy Finemet type, has been studied (4). The first regime is heating to the temperature belove t
C
, and fumer amorphisation. The second regime is heating to the temperature above t
C
, then amorphisation by the first regime. The third regime is heating to the temperature above t
C
, then overcooling and further amorphisation. The physical characteristics of amorphous ribbons were tabulated. The best service properties of ribbons were obtained by the third regime.
Fig. 1.
The politerm of kinematic viscosity of the amorphous solder Finemet type:

- heating; o - cooling; t
C
- critical temperature. The numbers about the curves are the termal diagrams of three regims
Quantitative study of the melt thermal treatment influence on mechanical properties of metallic glass ribbons (MGRs) had begun in the early 1990s (5). It had
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turned out that the ductile shear failure stress
 f and the fracture toughness K
1C
of the
MGRs obtained after the melt heating above the melt critical temperature t
C
are higher than those obtained from the melts that were not heated above t
C
.
The critical temperatures t
C
were determined from the measurements of the temperature dependence of the melt kinematic viscosity under heating and cooling.
Results are clear from the Table 1 and Fig. 2 where
 f values are indicated for the Fe
73.5
Nb
3
Cu
1
Si
13.5
B
9 metallic glass obtained from the melt after its different thermal treatments.
Table 1
Dependence of strength of the Fe
73.5
Nb
3
Cu
1
Si
13.5
B
9 ribbons on the thermal treatment of the melt before quenching
Termal treatment
 f
(GPa)
27 o C -196 o C
Regime 1
Regime 2
1.43
1.10
1.13
0.97
Fig. 2.
The polar of strength diagrams

f
(

) /
 f
(0 о
) of the Fe
73.5
Nb
3
Cu
1
Si
13.5
B
9 ribbons 1 - regime 1, 2 - regime 2
It is well known that the temperature of the beginning crystallization of the amorphous alloys increases with the growth of heating rate. For the comparision of the regimes the annealing in the temperature region from 250 to 600°C during 1 hour.
The minimal DC coercive force (H
C
) 1,04-1,20 A/m is reached after annealing at 500-
520°C in comparision with nonannealed spesimens that have H
C
= 28,8-36,0 A/m .
The rapid crystallization during 2,5,10 second at 620°C made by the method of Physic
Metal Institute of Urals departament of Russian Academy of Science gives the opportunity to reach the values H
C
= 1,20 A/m. Holding time after annealing (to 10 days and in the initial state to 1 year) and melting regime does not influence on H
C
.
The typical temperature dependences of kinematic viscosity (

), electrical resistivity (

), magnetic sucsecibility (

), surface tension (

) and density (d) of the melt containing high amount of element - amorphizator is shoun on Fig. 3 . It is founded that the special critical temperatures named t are determined on the base of
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such data. The heating above t leads to more homogenous melt state and, as a rule to forming the physical properties hysteresis (2). The overcooling value
 t is measured for this equilibrium melt. The presence of hysteresis is indicated the differencies between the initial and finished melt state and wishes to each the t
C
during melting.
Some times the melt may be heated only to the anomaly temperatures t an
. The melt holding time at the maximal heating temperature is experimentally determined during the investigation of the time dependence of properties changes at this temperature.
Fig. 3.
The typical politerms of physical properties of amorphous alloys:
 t - a value of overcooling; t an
- the temperature of anomalies; t h
- the temperature of hysteresis; t
C
- the critical temperature
It has been established by the x-ray difraction and magnetometry that nanocrystalline layer of boron and silicon solid solutions in

-Fe is formed on the specimen surface during amorphisation. The polyterms of magnetic anisotropy effective field (H a
) have nonmonotonic type. The physical motive of such H a behaviour is the competition of main processes: the quenching stress relaxation, the composition of nanocrystalline phase changing, surface and body crystallisation.
650

Such melt preparing leads to account of plane nanocrystalline phase on the surface change in a nonannealed specimens.The means of H a
is changed and its polyterm extremum position is moved out on temperature scale. The elimination of plane nanocrystals from specimen surface by the chemical etching tends to double decreasing of anisotropy effective field.
In cooperation with GAMMAMET Research & Production Enterprise soft magnetic alloy has been developed on a basis of GM 411 alloy which has found a wide application in the field of magnetic core materials for high frequency transformers, current transformers and measuring transformers.
4. CONCLUSION
An analysis of polytherms of properties in the crystal-liquid phase-transition region shows that melting in metallic melts is not accompanied by a substantial restructuring of their electronic structure or interatomic inteaction. While heating the melt, discontinuous structural changes can take place in them.
While studying questions of the interrelationships between the properties and structure of real iron-based melts, which differ in terms of their complex ratios of the localized and collectivizedvalence electrons, whith properties and structures of the corresponding solid substances, the quasichemical model seems to be the most satisfactory among the models or the ingomogeneous structural state of the melt. The usefulness of the latter is caused by its retention of information regarding the real bond between liquid and solid states and consists of the possibility of predicting the results of physicochemical effects affecting the melts and the properties of the final solid product.
Regularities of low temperature mechanical properties of metallic glass ribbons are determined both by their atomic structure and by peculiarities of their macroscopic stressed state and macroscopic defects (inclusions, surface caverns etc). The properties that find their explanation on the basis of knowledge of peculiarities of clusterous atomic structure of metallic glasses are considered in this review. It turned out that the theory of polycluster amorphous solids (5) is a satisfactory basis for understanding mechanical properties of metallic glasses that enables the extension of the 'structure-properties' conception to amorphous state of solids.
In all technologies investigated, the preparation of a melt toward amorphization by its temperature-time treatment leads not only to improvement but also to stabilization of the structure and properties of the metal from melt to melt.
AKNOWLEDGEMENTS
The work has been made thanks to finansial help of Russian Ministry of science on the "Unical units for investigation of structure and physical properties of metal melts. Melt. Registration number 06-02".
REFERENCES
1. Baum B.A: Metallic Liquids. Moscow, Sciens, 1979.
2. Baum B.A., Khasin G.A., Tyagunov G.V. et al.: Liquid Steel. Moscow,
Metallurgiya, 1984.
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3. Egorov D.V., Tsepelev V.S., Tjagunov G.V., Pastuchov S.V: 'The automated system of determinations of the kinematic viscosity of melts'. Industrial laboratory.
Diagnostics of materials 1998 (11) 46-48.
4. Tsepelev V.S., Baum B.A., Tjagunov G.V., Kulechov B.M:'The new technology of melt preparing to amorphization'.14
nd
Int Scient Conference, Poland, Zakopane,1995.
5. Tabachnikova E.D., Bengus V.Z., Egorov D.V., Tsepelev V.S., Ocelik V:
'Mechanical properties of amorphous alloys ribbons prepared by rapid quenching of the melt after different thermal treatments before quenching'. 9 th
Int Conf
Proceedings, Bratislava, Elsevier, 1997.
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