ABSTRACT
The dynamic means of affecting solidification were briefly discussed in Section 2.1. The main contributions to this topic are summarized in the literature [1-7]. One may recall that two main mechanisms were considered: (a) undercooling of the cavitation bubble surface during the expansion phase of oscillations and (b) undercooling of the liquid phase resulting from the instantaneous increase of pressure during cavitation bubble collapse (according to the Clapeyron equation). The latter mechanism seems most probable, as the decrease of bubble surface temperature does not exceed 1 K, while the change of the melting point as a result of bubble collapse can reach tens of degrees and approach 0.2Tm [4]. For example, for 99.99% pure aluminum, the increase in melting temperature changes with the pressure as shown in the following grid:
In addition to dynamic nucleation, multiplication of solidification nuclei by activation of heterogeneous substrates was suggested in the 1930s-1950s [8-11], involving improved wetting, decreased surface tension, and enhanced heterogeneous nucleation in the available insoluble substrates such as oxides, carbides, etc.
