EFFECT OF INCREASING ELECTRICAL RESISTANCE OF ALLOYS OF VARIOUS COMPOSITIONS

Summary: The electrical resistance of undeformed samples hardened in water gradually increases to 300-400 °C due to the positive temperature coefficient of resistance. The progression of the curve from 400 to 700 °C indicates the development of the K-state. In the temperature range 700- 925 °C, the solid solution decomposes with the formation of particles of a strengthening phase, which leads to a decrease in electrical resistance. The rise of the curve above 950 °C is associated with the dissolution of previously released particles of the second phase. The heating curve indicates the occurrence of the mentioned processes in reverse order. In deformed samples, the formation of the K-state during heating occurs in a wider temperature range (from 100 to 700 °C) and is much more intense than in undeformed samples. The course of the cooling curve is similar to the cooling curve of samples quenched in water [1]. The cooling curve in the temperature range 775-500 °C is slightly higher than the heating curve, which is associated with different degrees of formation of the K-state due to different “initial” structures [2]. After cooling, the electrical resistance of undeformed samples cooled in a furnace returns to its original value. In deformed samples it is 5% higher than before heating, which indicates a stable influence of deformation on subsequent transformations. The magnitude of the change in electrical resistance after cooling depends on the previous treatment. For samples quenched only in water, it is 3.5% higher, for samples with a reduction of 50% - by 8.7%, for samples with a reduction of 75% - by 10.5%. This increase in electrical resistance is determined by the occurrence of the K-state during cooling, and the different magnitude of the increase is associated with the influence of the deformation energy (preserved even after high heating) on the development of the process of formation of the K-state during cooling. An increase in the electrical resistance of samples cooled with the furnace from the quenching temperature is observed only up to 550 0C, regardless of whether the samples were subjected to work hardening or not, and this increase is significantly less than that of the same samples, but quenched in water [1, 3]. When cooling with the furnace from the quenching temperature, some development of the K-state already occurs in the samples, which is probably not completely destroyed even with a reduction of 50%. This determines a smaller increase in electrical resistance during subsequent heating and shifts the maximum to a temperature of 550 °C [2, 5]. In addition, a distinctive feature of the heating curves of the samples is a two-stage drop in electrical resistance in the temperature range of 550-950 °C.