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MATERIALS SCIENCE AND ENGINEERING

SEMINAR

 

Macrosegregation and Shrinkage Pipe Formation in Static Castings

 

By:

Sailei Zhang

 

Ph.D. Final Examination

 

Co-Advisors:

Prof. M. J. Krane and Prof. D. R. Johnson

 

ABSTRACT

 

Both macrosegregation and shrinkage defects are common problems in static castings. However these two aspects were usually studied separately in earlier research. In this presentation, a single-domain multi-phase model is developed for macrosegregation evolution and shrinkage pipe formation in static castings, as functions of buoyancy- and shrinkage-induced flow. Using a volume-of-fluid (VOF) method, both the air/liquid and air/solid interfaces are tracked during shrinkage pipe formation.

The model is applied to binary Ti-48Al (at.%) and ternary Ti-46.6Al-8.6Nb (at.%) alloys in a cylindrical mould (R = 3.5 cm, H = 15 cm). Experiments to investigate macrosegregation and shrinkage pipe formation are performed by casting both alloys in an induction skull melting (ISM) furnace, using tilt-casting method in investment moulds. No significant exchange of fluid that is not at nominal composition between the riser and the part is found. However, the macrosegregation level is increased in a larger scale casting (R = 30 cm, H = 50 cm), which can potentially change the primary solidification phase and the local microstructure of the ã-TiAl alloy in the final cast.

 

To study the influence of the riser on flow exchange between riser and cast part as well as the macrosegregation development in static castings, an Al-5wt. % Cu alloy system is used. An ingot with the riser designed based on Chvorinov’s rule is performed in a slab mould, which is used as a standard case for this study. The results show that a wider riser is able to provide a barrier and prevent the solute-rich interdendritic liquid in the riser from flowing into cast part. For the castings with the riser shape being fixed, the average composition in the cast part is smaller at a higher solidification rate.

 

 

Date:         Friday, April 18, 2013

Time:      9:30 A.M.

Place:        FRNY B124

 

 

 

Lisa Stacey

Secretary/Development Assistant

Purdue University

School of Materials Engineering

765/494-4100