INFLUENCE OF RELAXATION PROCESSES ON MECHANICAL STRESS SHIFTS IN AMORPHOUS AND NANOCRYSTALLINE RIBBON ALLOYS AT ELECTROPULSE EXPOSURE

Abstract

Relaxation processes in amorphous and nanocrystalline alloys in temperature range of –196 ÷ 80 °C have been studied. It was established that in amorphous alloy stress relaxation occurs in two stages. At the same time, decrease in initial mechanical stress in the sample by 5 % only occurs during the holding time of at least 1 hour. An increase in temperature of the sample leads to more intensive relaxation, which is manifested in an increase in rate of mechanical stress decrease. At the temperature of liquid nitrogen, stress relaxation is not observed. It has been established that in nanocrystalline alloy relaxation processes proceed in a similar manner, but relaxation rate is much lower. Dependences of residual mechanical stress on temperature and holding time were studied. It was found that in amorphous and nanocrystalline alloys, areas of stabilization of residual mechanical stresses are observed at small holding time (less than 5 min) in temperature ranges of 50 – 60 and 40 – 50 °C. Increase in holding time leadsto monotonousfall in residual mechanical stresses. Heating up to 40 °C results in complete relaxation of mechanical stresses in the sample 15 minutes after the start of the testing. It is shown that preliminary relaxation of stresses in amorphous alloy leads to decrease in value of mechanical stress relieving during electropulse ipmact in samples subjected to stretching. In nanocrystalline alloy, value of relieving remains practically unchanged under the indicated impact. It is also shown that the observed effect occurs due not only to thermal expansion, but also to change in the value of reversible component of directed structural relaxation. In the course of work it was established that value of mechanical stress relieving in amorphous alloy depends on medium in which electric current impulse is supplied. In particular, in liquid nitrogen medium, decrease in value of relieving is observed. Such a decrease is not observed in nanocrystalline alloy.