Mathematical and Physical Modelling of Directional Solidification of Aerospace Alloys

Defect formation in aerospace components is studied, particularly in regions of directionally solidified casting with stepwise increase in cross-section, which is a typical geometric configuration for such components as turbine blades. Given the fact that the geometry of a casting is directly related to probability of defect formation, special attention was paid to grain defects in regions of cross-sectional change (platform regions). Mathematical and physical modelling were employed to describe directional solidification and to obtain overall understanding of different or key aspects involved in the directional solidification process. Aluminum-4.5wt%Copper alloy was used for physical modelling; mathematical models were made both of the Al-Cu system (for correlation to the physical model) and of In718, a nickel-based superalloy (for correlation to actual defective parts examined). Although characteristically different, analysis of the solidification pattern of the two materials showed some commonalities, such as primary dendritic growth orientation and location of defect formation. The combination approach to modelling, employing both mathematical and physical methods, led to a good understanding of the process, and increased the ability to design new configurations whose solidification patterns promote single crystals with minimum defects. Thesis Supervisor: Title: Julian Szekely Professor of Materials Science and Engineering In Loving Memory of Professor Szekely