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A novel technique for dynamic observations of the annealing process in metallic glasses
Surface and Coatings Technology
91-95
(1997) 676-680
A novel technique for dynamic observations of the annealing process in metallic glasses Bozena Todorow*,
Othmar von Bogen
Abstract A new apparatus design is proposed for determining the annealing point temperature of metallic glasses. The new equipment provides more precise results and far better time management than other methods. In essence, the annealing point temperature is experimentally derived as the temperature where the electrical conductivity of the sample changes precipitously. In practice, the procedure is unique in continuously monitoring the annealing process parameters of metallic glasses as a function of time. A computer controlled test stage regulates the direct Joule heating of the sample, processes the data, and yields a resistivity-versus-temperature display and thereby the annealing point temperature. 0 1997 Elsevier Science S.A. Keywords;
Metallic
1. Introduction:
glass; Annealing
structural
point temperature; Structural relaxation
relaxation
in metallic
glasses
The physical properties of a metallic glass depend on its atomic structure which can change according to the production process, composition, ‘aging’ and storage conditions.
As heat is first added to a metallic glass somewhat well below the annealing point temperature. the electrical resistivity, elastic modulus, Hall voltage and specific heat change by an order of 1% [ 1,2]. Structural relaxation during annealing in metallic glasses is caused by modifications in the TSR0 (topological short range ordering) and the CSRO (chemical short range ordering). During the production of a metallic glass sample, ‘free volumes’ are inevitably created. The irreversible decrease in these free volumes (TSRO) during an annealing process can be expressed by [2]: exp(x-‘)
-exp(si’)
= C, f exp
where x = V,I(yV*) Vi, = free volume per atomic volume yV* = const. - 0.01 R = Boltzmann const. Co = const. Ei = activation energy * Comsponding
author.
02.57.89723973$17.00 0 1997 Elsevier Science S&. All rights reserved PII SO257-8972(97)00512-d
During annealing there is a decrease in the atomic degree of freedom which increases the CSRO. There is substantial confirmation [3] that immediately after annealing has taken place the CSRO attains a new equilibrium level. The equilibrium level thereafter varies inversely with temperature. Van den Beukel [ 1,3] analyzed the electrical resistivity of F1lNIOBZOmetallic glass in an attempt to distinguish reversible changes due to structural relaxation from those that are irreversible. According to Cost et al. [4], the increase in the CSRO during annealing is due to a large number of defects (traps) that coexist with the free volumes and that modify the mobility of the atoms in the amorphous phase. An analysis [5] of changes in electrical resistivity as a function of time, for amorphous metallic glasses that are being annealed at various fixed temperatures (see Figs. 1 and 2). indicated some important tendencies:
1. For alloys containing Ni or Co, there was a tendency for the electrical resistivity (relative to that in an unannealed sample) to decrease as the time of the isothermal annealing progressed. 2. For alloys without Ni or Co, being annealed at a fixed low temperature. the relative resistivity increased with time during the oven immersion, whereas at a fixed higher temperature the relative resistivity tended to decrease after long immersion times. Any decreases in resistance (R), for the alloys without Ni or Co, can be interpreted as being due to the formation of
Fig. 1. Changes in resistance AR/R” =J7”J (T = temperature) %r amorphous metallic glasses with 4% of Fe replaced by Co or Ni (1 or V, Cr, Mn c---j.
clusters. For alloys with Ni or Co the decrease in resistance is enhanced by the more collective TSR0 isothermal annealing. The crystallization of metallic glasses is a two-step process [6,7]: 1. Due to the precipitation of components from a saturated solution during ‘aging’ of the glass, whether in a low or high temperature environment, the matrix is enriched by the formation of small polycrystallines (see Fig. 3), leading to more stable compositions (see plateau in Fig. 4) and an initial increase in resistivity (Fig. 1). 2. At higher isothermal temperatures, or for longer annealing times, the number of atoms from the original solution becomes ‘exhausted’, so further clustering is impossible and the resistance decreases (see Figs. l-4). In summary, it seems that during the thermal process the amorphous structure evolves into a more stable sort of structure due to a thermal activation that depends on the chemical composition of the sample. Any analysis of the observed
Fig. 3. Crystallized
volume fraction for Albb Nil0 2,
Fig. 2. The relative electrical resistivity ApIp ing temperature) for Fels Co,” SiY B13.
=J(T,.,j. (T,,
= the anneal-
physical properties should be confirmed by means of Xray diffractogaphy. Peaks in the spectrum indicative of pYWip&Bions of clusters of one element (for temperature T < Tan&: or peaks indicative of crystalline structure (with T > T,,,,,,), can be correlated with observed changes in the sample’s physical properties (see Fig. 5).
2. Methodology
of annealing
2.1. The conventionnl
method
of mnraling
In the conventional method for determining the annealing point temperature of a metallic glass,thqsarnple is placed in an inert gas set at a fixed temperature inside an oven. After some arbitrarily set time the sample is removed and subjected to X-ray diffractography to determine the ex@n-/f any, of the annealing. This procedure is repeated at succes-
versus annealing time at 210°C (TEM):
(a) 10 min? (b) 20 min, (c) 10 h, (d) 193 h.
3. Torloro~~~, 0. I:L)II Bogm / Sutfk~
cud Codngs
Techrzology 93-95
(1997) 676-650
3. Description of the novel annealing dynamical observations
apparatus
for
The test set-up is basically comprised of four parts: 1. 2. 3. 3.
9
I-
-
-
-
1C6
5x10' t (5)
Fig. 4. Crystalline \rolume fraction versus annealing time for different temperatures: (m) ISOT, (0) ISOT, (A) 2lO”C, (*) 240°C. Inset is enlargement for 240°C.
sively higher temperatures until the X-rays indicate that annealing is complete, i.e. until the annealing point temperature is reached. Thus readings are intermittent and time consuming, as well as lacking somewhat in precision relative to the new method. 2.2. New technique of annecrling of mtnllic
sample test stage and vacuum system DC power supply microcontroller computer system.
The sample test stage maintains the sample in a constant pressure inert atmosphere (argon) during the annealing process. The flask is evacuated by means of a single-stage roughing pump to approximately 7 kPa and then refilled with 99.999% pure argon to a pressure of one atmosphere. It is then evacuated again to 7 kPa and refilled once more with argon to flush out any oxygen until remaining amounts can be considered negligible. Argon is used to maintain the system at 1 atm pressure to prevent leakage into the flask. The vacuum system (Fig. 6) contains a mounting stage for the sample. This stage consists of two ceramic supports, two aluminum headers and two carbon clamps to hold the sample. Two electrical feed-throughs supply DC current to the sample via the aluminum headers and the carbon clamps. In addition, the flask contains an ‘R’ type thermocouple
glasses
With the new apparatus the sample is heated electrically and the parameters are monitored continuously. There is a continuous plot in time of electrical resistivity versus temperature, and the annealing point is noted as that temperature where the resistivity changes rapidly. This determination is fast, efficient, precise and under computerized regulation (see Section 3). The procedure is dynamical in that experimental observations and calculations are made by the computer while the annealing process is ‘in progress’. Incidental to determining the annealing point. it was noted that the resistivity depended on the rate of Joule heating (dQ/dt) , yet the annealing always seemed to occur at the same temperature. The implication is that the electronic structure, and hence any physical property of the annealed sample, such as electrical resistivity in this case, can be predetermined by the heating rate; however, the heating rate does not appear to alter the annealing point. This predetermination of physical properties will be the subject of ongoing investigations. Continuous monitoring of the annealing process has shown the need for a new technique and new apparatus. The subject of this paper is the description of the new apparatus and the methods used to determine the annealing point of metallic glasses.
Fig. 5. X-ray diffraction different temperatures.
pattern for samples of Fq$o,,$i~B
I3 annealed at
@&negative temperature coefficient;f the carbon clamps partially offsets the positive value in the remainder of the support stage.
The DC power supply (Fig. 7) is a standard laboratory bench type, with a 12-V DC, 20-A capacity, was designed and built by the authors of this paper. It has been designed to allow the output current to be regulated by an external microcontroller. The power supply, in this case, is utilized in the external current source mode. This source supplies the current required for the Joule heating ._~i_~____.___-=~.-~ ~~ of th~~~~mpl~. It ha> outputs for both the sample voltage and the current which are read digitally by the microcontroller. In addition, the power supply has digital readouts for monitoring the sample heating rate. 3.3. The microcontroller
Fig. 6. Test vessel.
which is electrically isolated from, but in contact with, the sample. The thermocouple is connected to a cold junction compensator and to a linearized thermocouple amplifier calibrated to output 5 V DC at 1000°C. With 256 conversion steps this yields a basic precision of i4”C, or kO.4% over the entire temperature range. The thermocouple system is certified to calibration standard by an independent test and measurement service supplier. By concentrating the analysis near the annealing point, much greater precision is possible compared to ‘batch methods of testing’. The sample size is approximately 1 cm in width by 7.5 cm in length. Carbon clamps were selected because of their relatively low thermal conductivity which yields a close to isothermal electrical connection to the sample. It has been found that metallic clamps would cause a very large temperature gradient at the clamp-sample interface, resulting in serious deformation of the sample during the heating process. The use of carbon clamps has essentially eliminated this problem. Due to the substantial mass of the support stage relative to the mass of the metallic sample, heating of the support is minimal. The change in electrical resistivity of the support stage is negligible. Furthermore,
sJstern
The microcontroller system (Fig. 7): designed and built by the authors of this paper, has several functions. Primarily it is the interface between the computer system and the test apparatus. The microcontroller receives test parameter inputs from the computer and in turn controls the heating rate of the sample via the DC power supply. The microcontroller is an S-bit device and therefore allows 256 (28) incremental steps in the output from the power supply which also means 256 controlled steps in the heating rate (dQ/dt). This results in sufficiently small steps so that the temperature is nearly a linear function of time (T vs. t). The time interval between steps can be chosen to permit observations to be made of changes in electrical resi&Ay-3s a function of either temperature or time. The inference here is that in the standard function for resistivity, (p), i.e. p = pu [I + 01A T], the coefficient of resistivity may be a function of time, i.e., CY= e(t). Moreover,thisisthe-ultimate electronic structure- ofthe-mmatecial in thesample and its physical properties can be predetermined by the heating
Fig. 7. Tesr
set-up:block diagram.
680
B. Todoro~v, 0. van Bogen / Sufuce and Comings Techndogy
94-93
(1997) 676480
rate (dQ/dT) leading up to the annealing point. This feature can contribute to a better understanding of the annealing process at the microscopic electron level. The microcontroller also serves as an analogue to digital converter which monitors the output voltage and current of the power supply. This digitized data is sent to the computer in real-time and subsequently is converted to a real-time ‘resistivity versus temperature’ display. In addition, the microcontroller reads the thermocouple output which it digitizes for reading and logging by the computer. 3.4. The computer system The computer system consists of a 120-MHz Pentium processor platform with 32 Mb RAM, a 1.2-Gb hard drive, a super VGA monitor and an Okidata laser printer. It uses Lotus 123 software to log and to analyze the data as well as to generate the appropriate graphical plots. The computer is also utilized to set the test parameters such as the annealing time, temperature, etc. Of particular interest is the control of the heating rate to determine the affect of the annealing rate on the ultimate properties of the metallic glass. Real-time analysis of the data will permit the change in electrical resistivity during the annealing process to be observed, which will be of assistance in determining the annealing point with precision. As mentioned earlier, the affect of the heating rate on the ultimate electrical resistivity and other properties of the sample can be determined as well.
4. Conclusion Our new apparatus performed as predicted. We were able to determine the annealing point of a sample of metallic glass by automatic computerized means. As can be seen in the accompanying graph of R vs. t for metallic glasses (see Fig. 8 for Fe66Co&B13), the resistance of the sample decreases as its tetnperature increases. The form of the graph is typical of the resistivity versus temperature char-
Fig. 8. Changes in resistance R =flr): (r, temperature) during heating of a sample of Fe&o$iQB,? metallic glass. The point of the sudden drop in resistance indicates the annealing of the sample.
acteristic of metallic glasses. As the temperature approaches the annealing point, the resistance drops suddenly, indicating that annealing is taking place and thereby indicating the annealing temperature. Since the tests are conducted by automatic computer control, the results are repeatable. Contrary to the conventional oven methods of annealing, our new apparatus facilitates very fast and accurate determination of the annealing point as well as real-time observation of the annealing process.
References [II A. Van den Beukel and S. Radelaar, Acrn Merclll., 31 (1989) 419. [?I E. Jakubczyk, Z. Mandecki and J. Filipecki, Key EQ. Mnrer., 81-83 (1993) 383. [3] E. Kokmeijer, E. Huizer, B.J. Thijsse and A. van den Beukel, Morel: Sri. Eng., 97 (1988) 505.
[j.] J.R. Cost, J.T. Stanley and B.J. Thijsse, Mum. Sci. Eng., 97 (1988) 50.5.
[51 C. Antonoine, G. Della Gratta, A. Lucci, G. Rionto and G. Venture110,Aciu Merull., I8 (1970) 1969. 161 T. Egami, ~w&r. Res. Bull., 13 (1978) 557. [71 M. Blank, 5ewersdorSS, Sulzer - Innotec Division 1511, Sulzer Brothers Ltd., CH-8404, Winterhur, Switzerland.
91-95
(1997) 676-680
A novel technique for dynamic observations of the annealing process in metallic glasses Bozena Todorow*,
Othmar von Bogen
Abstract A new apparatus design is proposed for determining the annealing point temperature of metallic glasses. The new equipment provides more precise results and far better time management than other methods. In essence, the annealing point temperature is experimentally derived as the temperature where the electrical conductivity of the sample changes precipitously. In practice, the procedure is unique in continuously monitoring the annealing process parameters of metallic glasses as a function of time. A computer controlled test stage regulates the direct Joule heating of the sample, processes the data, and yields a resistivity-versus-temperature display and thereby the annealing point temperature. 0 1997 Elsevier Science S.A. Keywords;
Metallic
1. Introduction:
glass; Annealing
structural
point temperature; Structural relaxation
relaxation
in metallic
glasses
The physical properties of a metallic glass depend on its atomic structure which can change according to the production process, composition, ‘aging’ and storage conditions.
As heat is first added to a metallic glass somewhat well below the annealing point temperature. the electrical resistivity, elastic modulus, Hall voltage and specific heat change by an order of 1% [ 1,2]. Structural relaxation during annealing in metallic glasses is caused by modifications in the TSR0 (topological short range ordering) and the CSRO (chemical short range ordering). During the production of a metallic glass sample, ‘free volumes’ are inevitably created. The irreversible decrease in these free volumes (TSRO) during an annealing process can be expressed by [2]: exp(x-‘)
-exp(si’)
= C, f exp
where x = V,I(yV*) Vi, = free volume per atomic volume yV* = const. - 0.01 R = Boltzmann const. Co = const. Ei = activation energy * Comsponding
author.
02.57.89723973$17.00 0 1997 Elsevier Science S&. All rights reserved PII SO257-8972(97)00512-d
During annealing there is a decrease in the atomic degree of freedom which increases the CSRO. There is substantial confirmation [3] that immediately after annealing has taken place the CSRO attains a new equilibrium level. The equilibrium level thereafter varies inversely with temperature. Van den Beukel [ 1,3] analyzed the electrical resistivity of F1lNIOBZOmetallic glass in an attempt to distinguish reversible changes due to structural relaxation from those that are irreversible. According to Cost et al. [4], the increase in the CSRO during annealing is due to a large number of defects (traps) that coexist with the free volumes and that modify the mobility of the atoms in the amorphous phase. An analysis [5] of changes in electrical resistivity as a function of time, for amorphous metallic glasses that are being annealed at various fixed temperatures (see Figs. 1 and 2). indicated some important tendencies:
1. For alloys containing Ni or Co, there was a tendency for the electrical resistivity (relative to that in an unannealed sample) to decrease as the time of the isothermal annealing progressed. 2. For alloys without Ni or Co, being annealed at a fixed low temperature. the relative resistivity increased with time during the oven immersion, whereas at a fixed higher temperature the relative resistivity tended to decrease after long immersion times. Any decreases in resistance (R), for the alloys without Ni or Co, can be interpreted as being due to the formation of
Fig. 1. Changes in resistance AR/R” =J7”J (T = temperature) %r amorphous metallic glasses with 4% of Fe replaced by Co or Ni (1 or V, Cr, Mn c---j.
clusters. For alloys with Ni or Co the decrease in resistance is enhanced by the more collective TSR0 isothermal annealing. The crystallization of metallic glasses is a two-step process [6,7]: 1. Due to the precipitation of components from a saturated solution during ‘aging’ of the glass, whether in a low or high temperature environment, the matrix is enriched by the formation of small polycrystallines (see Fig. 3), leading to more stable compositions (see plateau in Fig. 4) and an initial increase in resistivity (Fig. 1). 2. At higher isothermal temperatures, or for longer annealing times, the number of atoms from the original solution becomes ‘exhausted’, so further clustering is impossible and the resistance decreases (see Figs. l-4). In summary, it seems that during the thermal process the amorphous structure evolves into a more stable sort of structure due to a thermal activation that depends on the chemical composition of the sample. Any analysis of the observed
Fig. 3. Crystallized
volume fraction for Albb Nil0 2,
Fig. 2. The relative electrical resistivity ApIp ing temperature) for Fels Co,” SiY B13.
=J(T,.,j. (T,,
= the anneal-
physical properties should be confirmed by means of Xray diffractogaphy. Peaks in the spectrum indicative of pYWip&Bions of clusters of one element (for temperature T < Tan&: or peaks indicative of crystalline structure (with T > T,,,,,,), can be correlated with observed changes in the sample’s physical properties (see Fig. 5).
2. Methodology
of annealing
2.1. The conventionnl
method
of mnraling
In the conventional method for determining the annealing point temperature of a metallic glass,thqsarnple is placed in an inert gas set at a fixed temperature inside an oven. After some arbitrarily set time the sample is removed and subjected to X-ray diffractography to determine the ex@n-/f any, of the annealing. This procedure is repeated at succes-
versus annealing time at 210°C (TEM):
(a) 10 min? (b) 20 min, (c) 10 h, (d) 193 h.
3. Torloro~~~, 0. I:L)II Bogm / Sutfk~
cud Codngs
Techrzology 93-95
(1997) 676-650
3. Description of the novel annealing dynamical observations
apparatus
for
The test set-up is basically comprised of four parts: 1. 2. 3. 3.
9
I-
-
-
-
1C6
5x10' t (5)
Fig. 4. Crystalline \rolume fraction versus annealing time for different temperatures: (m) ISOT, (0) ISOT, (A) 2lO”C, (*) 240°C. Inset is enlargement for 240°C.
sively higher temperatures until the X-rays indicate that annealing is complete, i.e. until the annealing point temperature is reached. Thus readings are intermittent and time consuming, as well as lacking somewhat in precision relative to the new method. 2.2. New technique of annecrling of mtnllic
sample test stage and vacuum system DC power supply microcontroller computer system.
The sample test stage maintains the sample in a constant pressure inert atmosphere (argon) during the annealing process. The flask is evacuated by means of a single-stage roughing pump to approximately 7 kPa and then refilled with 99.999% pure argon to a pressure of one atmosphere. It is then evacuated again to 7 kPa and refilled once more with argon to flush out any oxygen until remaining amounts can be considered negligible. Argon is used to maintain the system at 1 atm pressure to prevent leakage into the flask. The vacuum system (Fig. 6) contains a mounting stage for the sample. This stage consists of two ceramic supports, two aluminum headers and two carbon clamps to hold the sample. Two electrical feed-throughs supply DC current to the sample via the aluminum headers and the carbon clamps. In addition, the flask contains an ‘R’ type thermocouple
glasses
With the new apparatus the sample is heated electrically and the parameters are monitored continuously. There is a continuous plot in time of electrical resistivity versus temperature, and the annealing point is noted as that temperature where the resistivity changes rapidly. This determination is fast, efficient, precise and under computerized regulation (see Section 3). The procedure is dynamical in that experimental observations and calculations are made by the computer while the annealing process is ‘in progress’. Incidental to determining the annealing point. it was noted that the resistivity depended on the rate of Joule heating (dQ/dt) , yet the annealing always seemed to occur at the same temperature. The implication is that the electronic structure, and hence any physical property of the annealed sample, such as electrical resistivity in this case, can be predetermined by the heating rate; however, the heating rate does not appear to alter the annealing point. This predetermination of physical properties will be the subject of ongoing investigations. Continuous monitoring of the annealing process has shown the need for a new technique and new apparatus. The subject of this paper is the description of the new apparatus and the methods used to determine the annealing point of metallic glasses.
Fig. 5. X-ray diffraction different temperatures.
pattern for samples of Fq$o,,$i~B
I3 annealed at
@&negative temperature coefficient;f the carbon clamps partially offsets the positive value in the remainder of the support stage.
The DC power supply (Fig. 7) is a standard laboratory bench type, with a 12-V DC, 20-A capacity, was designed and built by the authors of this paper. It has been designed to allow the output current to be regulated by an external microcontroller. The power supply, in this case, is utilized in the external current source mode. This source supplies the current required for the Joule heating ._~i_~____.___-=~.-~ ~~ of th~~~~mpl~. It ha> outputs for both the sample voltage and the current which are read digitally by the microcontroller. In addition, the power supply has digital readouts for monitoring the sample heating rate. 3.3. The microcontroller
Fig. 6. Test vessel.
which is electrically isolated from, but in contact with, the sample. The thermocouple is connected to a cold junction compensator and to a linearized thermocouple amplifier calibrated to output 5 V DC at 1000°C. With 256 conversion steps this yields a basic precision of i4”C, or kO.4% over the entire temperature range. The thermocouple system is certified to calibration standard by an independent test and measurement service supplier. By concentrating the analysis near the annealing point, much greater precision is possible compared to ‘batch methods of testing’. The sample size is approximately 1 cm in width by 7.5 cm in length. Carbon clamps were selected because of their relatively low thermal conductivity which yields a close to isothermal electrical connection to the sample. It has been found that metallic clamps would cause a very large temperature gradient at the clamp-sample interface, resulting in serious deformation of the sample during the heating process. The use of carbon clamps has essentially eliminated this problem. Due to the substantial mass of the support stage relative to the mass of the metallic sample, heating of the support is minimal. The change in electrical resistivity of the support stage is negligible. Furthermore,
sJstern
The microcontroller system (Fig. 7): designed and built by the authors of this paper, has several functions. Primarily it is the interface between the computer system and the test apparatus. The microcontroller receives test parameter inputs from the computer and in turn controls the heating rate of the sample via the DC power supply. The microcontroller is an S-bit device and therefore allows 256 (28) incremental steps in the output from the power supply which also means 256 controlled steps in the heating rate (dQ/dt). This results in sufficiently small steps so that the temperature is nearly a linear function of time (T vs. t). The time interval between steps can be chosen to permit observations to be made of changes in electrical resi&Ay-3s a function of either temperature or time. The inference here is that in the standard function for resistivity, (p), i.e. p = pu [I + 01A T], the coefficient of resistivity may be a function of time, i.e., CY= e(t). Moreover,thisisthe-ultimate electronic structure- ofthe-mmatecial in thesample and its physical properties can be predetermined by the heating
Fig. 7. Tesr
set-up:block diagram.
680
B. Todoro~v, 0. van Bogen / Sufuce and Comings Techndogy
94-93
(1997) 676480
rate (dQ/dT) leading up to the annealing point. This feature can contribute to a better understanding of the annealing process at the microscopic electron level. The microcontroller also serves as an analogue to digital converter which monitors the output voltage and current of the power supply. This digitized data is sent to the computer in real-time and subsequently is converted to a real-time ‘resistivity versus temperature’ display. In addition, the microcontroller reads the thermocouple output which it digitizes for reading and logging by the computer. 3.4. The computer system The computer system consists of a 120-MHz Pentium processor platform with 32 Mb RAM, a 1.2-Gb hard drive, a super VGA monitor and an Okidata laser printer. It uses Lotus 123 software to log and to analyze the data as well as to generate the appropriate graphical plots. The computer is also utilized to set the test parameters such as the annealing time, temperature, etc. Of particular interest is the control of the heating rate to determine the affect of the annealing rate on the ultimate properties of the metallic glass. Real-time analysis of the data will permit the change in electrical resistivity during the annealing process to be observed, which will be of assistance in determining the annealing point with precision. As mentioned earlier, the affect of the heating rate on the ultimate electrical resistivity and other properties of the sample can be determined as well.
4. Conclusion Our new apparatus performed as predicted. We were able to determine the annealing point of a sample of metallic glass by automatic computerized means. As can be seen in the accompanying graph of R vs. t for metallic glasses (see Fig. 8 for Fe66Co&B13), the resistance of the sample decreases as its tetnperature increases. The form of the graph is typical of the resistivity versus temperature char-
Fig. 8. Changes in resistance R =flr): (r, temperature) during heating of a sample of Fe&o$iQB,? metallic glass. The point of the sudden drop in resistance indicates the annealing of the sample.
acteristic of metallic glasses. As the temperature approaches the annealing point, the resistance drops suddenly, indicating that annealing is taking place and thereby indicating the annealing temperature. Since the tests are conducted by automatic computer control, the results are repeatable. Contrary to the conventional oven methods of annealing, our new apparatus facilitates very fast and accurate determination of the annealing point as well as real-time observation of the annealing process.
References [II A. Van den Beukel and S. Radelaar, Acrn Merclll., 31 (1989) 419. [?I E. Jakubczyk, Z. Mandecki and J. Filipecki, Key EQ. Mnrer., 81-83 (1993) 383. [3] E. Kokmeijer, E. Huizer, B.J. Thijsse and A. van den Beukel, Morel: Sri. Eng., 97 (1988) 505.
[j.] J.R. Cost, J.T. Stanley and B.J. Thijsse, Mum. Sci. Eng., 97 (1988) 50.5.
[51 C. Antonoine, G. Della Gratta, A. Lucci, G. Rionto and G. Venture110,Aciu Merull., I8 (1970) 1969. 161 T. Egami, ~w&r. Res. Bull., 13 (1978) 557. [71 M. Blank, 5ewersdorSS, Sulzer - Innotec Division 1511, Sulzer Brothers Ltd., CH-8404, Winterhur, Switzerland.