Theoretical description of slow non-monotonic relaxation processes in Al–Y melts

Temperature and time dependent structure of the molten Ni81P19 alloy by neutron diffraction

“…Furthermore, it was also shown that the viscosity in Al-rich melts of Al-Y during isothermal holding for several hours at temperatures more than 100 degrees above liquidus increases significantly before a subsequent exponential decay [44]. This increase in viscosity was explained by the temporal competition of two simultaneous effects, an Ostwald ripening effect in which large heterogeneities present in the melt after melting grow and a general slow dissolution of the heterogeneities resulting in a homogenization of the melt [45].…”

“…Another measurement has shown that a PbSn melt after an ultrasonic pulse needs several hours in order to return to its initial state [43]. A time of the same order of magnitude needed to reach a steady state in other molten alloys was found, for example, in the Al95Y5 alloy [44,45]. Furthermore, similar behavior was observed in measurements of the kinematic viscosity, for example, in Al-rich Al-Fe melts [46], in FeB [47] as well as in BiZn melts [48].…”

To understanding of slow and non-monotonic relaxation in Al–Y eutectic melts

“…As an example we consider the post melting relaxation of Al-Y-based melts. The initial inhomogeneities Al 3 Y and Al 2 Y have characteristic size order 10 −5 m. Estimation of characteristic dissolution time these inhomogeneities was done in the paper [3] and is 10 −2 s, which is many fewer than the relaxation time, observed on the experiment: τ ≈ 10 4 s. It ity behavior is observed both in the presence of other solutes and without them. One can assume that the nature of this unusual phenomenon is mainly related to the peculiarities of Al-Y melt relaxation.…”

“…The instability can explain not only slow relaxation of the eutectic melts, but also its nonmonotonic character. In order to illustrate our statement we use results of the fluctuation dynamic theory of phase transition applied to the "toy model" of a system undergoing an weak first order phase transition [3]. For this we firstly write the time-dependent correlation function corresponding to equation ( 5):.…”

“…Therefore, initially for its description, we can limit ourselves to the consideration of the binary melt. As a possible explanation of the abnormally slow relaxation and non-monotonic dependence of viscosity on time in [3] it was assumed that they are related with nonlinearity of the concentration dependence of the system chemical potential near the liquidus line. Indeed, the melts right after melting are non-homogenous because of non-homogeneity of initial solid alloy (see Fig.…”