dc Joule heating of amorphous metallic ribbons: Experimental aspects and model

Abstract

A fluidflowtemperature model for the casting of amorphous metal ribbon by melt extraction A dc technique of Joule heating has been developed with the purpose of developing unconventional crystallization products in amorphous metallic ribbons. The thermal effects of a continuous current flow on Fe,ONi,B,O and FesOSilOB1O amorphous ribbon strips are examined. The evolution of the temperature in samples submitted to different values of electrical current is followed by measuring the variations in the electrical resistance of the ribbon strips. A model of sample heating is developed and shown to predict both the steady-state temperature of the ribbon strips and the law of approach to the steady state. A number of experimental data, obtained from multiple-thermocouple measurements, x-ray diffractometry, and differential scanning calorimetry, support the model's assumptions. The effect of fluctuations in the room-temperature resistance is discussed. The temperature behavior of samples submitted to free cooling after a Joule-heating treatment is considered.

A model concerning the environmental factors that modify the nanocrystallization of current-annealed samples

“…If we consider a thin differential strip of the sample along the y-axis, we obtain the differential equation (having the same expression as Allia et al [12]): (8) is the boundary condition.…”

“…Allia et al [12] already solved the equation numerically considering that there are no temperature differences over the width of the sample…”

“…Aştefǎnoei et al [11] developed a complete model considering convection to calculate the temperature distribution in the thickness of the sample. Allia et al [12] calculated numerically the temperature distribution along a sample in vacuum during annealing. They also obtained an expression of the temperature in the central part of the sample.…”

Development of granular structure in Cu/sub 90/Co/sub 10/ ribbons through furnace and current annealing

“…J OULE heating techniques, based on thermal effects of an electrical current flowing through a metallic ribbon or wire, are conceptually simple and experimentally versatile [1]. These unconventional thermal treatments are very useful to produce a great quantity of samples in order to make a systematic investigation on the development of the materials microstructure.…”

“…Typcally, a pulse of electrical current is applied through the sample where a great fraction of the heat released by the Joule power increases sample's temperature. Depending on the current amplitude and its time duration, the sample can undergo structural transformations [1]. When current is varied rather slowly, it allows one to control, for example, these transformations through on-line monitoring of the resistance of the materials while current is increasing [2].…”