Mechanical strain and temperature annealing effect on structural relaxation kinetics of the Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy

Structural changes of amorphous ribbon Fe89.8Ni1.5Si5.2B3C0.5, causing its isothermal expansion, were investigated by sensitive dilatation method and X-ray analysis. The measurements were carried out concerning ribbon samples thermal expansion, having been exposed to constant strain degrees of sigma1 = 130 MPa, sigma2 = 300 MPa and sigma3 = 475 MPa at temperatures T1 = 653 K, T2 = 673 K and T3 = 693 K. It has been determined that isothermal ribbon expansion is caused by the structural relaxation process. It has been shown that structural relaxation process occurs in two stages. In initial time interval linear logarithmic dependence of isothermal ribbon expansion upon time exists. This leads to a conclusion that activationally-controlled process is carried out in this time interval. The process time decreases with the increase in annealing temperature. The second time interval of structural relaxation process is characterized by linear dependence of isothermal expansion upon the square root of process time. Such time dependence of isothermal expansion shows that this time interval of structural relaxation process is a slow diffuse process. The results of X-ray analysis show that during these processes the ribbon preserves its amorphous structure with reduced defects density and reduced internal strain. The paper shows that dilatation method may be successfully used in analysis of structural relaxation process kinetics, which, on the other hand, is not possible by means of DSC and X-ray analyses.