Beta fleck and segregation in titanium alloy ingots

The segregation defect known industrially as "betafleck" occurs in most of the beta and alpha/beta alloys of titanium, arising in segregation during the solidification of the final vacuum arc remelted (VAR) ingot. In this work we use the data generated in Part I of this study to investigate the possible causes of the defect. We conclude that more than one mechanism is potentially operative. In highly alloyed material the defect mechanism is likely to be caused by a similar flow system to that responsible for the "freckle" defect in steels and superalloys: in the lower alloyed materials, it is more likely that the defect arises in the redistribution of equiaxial crystals in the large VAR final ingot liquid pool volume which is solidifying under low temperature gradients. In either case, the industrially-practical solution to the problem appears to lie in VAR melting with steeper temperature gradients at the solidifying interface. We also outline the future need for alloy design to take into account the difference in defect-forming potential of the different beta-stabilizing elements available for alloy formulation.