Determination of the depth of the shrinkage cavity in ingots of Ti-6Al-4V alloy produced by electron-beam remelting with an intermediate crucible

摘要

One of the main defects in an billet associated with its solidification in electron beam remelting is the shrinkage cavity. This defect forms as a result of the nonuniform cooling of the upper end of the billet after switching off the external heating source. In this case, the surface of the billet cools at a higher rate than the deep layers of the metal as a result of radiant heat exchange with the environment, and the thermal centre of the temperature field of the billet is displaced from its upper end into the depth. On the level of distribution of the thermal centre in final solidification of the ingot, the shrinkage cavity or scattered porosity forms as a result of compression due to solidification. In ingots of the titanium and its alloys, the shrinkage cavity is a cavity or a set of cells and pores, concentrated in the top part of the billet and isolated from the surrounding environment by means of a 'bridge', i.e. it is the skin of dense metal free from any discontinuity [1].