Simulating Macrosegregation in Var Ingots of Titanium Alloy During Solidification

摘要

Simulations of VAR-ingots of Ti-6A1-4V, with emphasis on predicting macrosegregation of oxygen, are presented. MULTIA simulations showed that segregation patterns in the ingots result largely from the strong convection in the melt pool. Permeabilities in the mushy zones were less important. Simulations revealed more details in the macrosegregation patterns when the element-size selected for the calculation was reduced to 7.2 mm x 10.8 mm. the extent of the segregation, as the difference between the maximum (=0.22 wt.%) and minimum (=0.15 wt.%) concentrations of oxygen were about the same for both element sizes. A band of negative segregation near and running parallel to the ingot-surface was simulated, but the finer sized elements revealed a more intense band. Since primary arm spacings in titanium alloys are not available, primary dendrite arm spacings in Ti-6A1-4V were estimated. A summary-status of the use of software by VAR titanium-ingot producers in the USA is also given. In its initial stages, the research was on 'Formation of Microporosity in Nickel-Base Thin Wall Casings,' so a brief summary of microporosity in experimental castings is presented.