Centrifugal Investment Casting of Ti-47Al-6Nb Exhaust Valves

The shell mold filling process for high-Nb TiAl alloy exhaust valve casting prepared by centrifugal investment casting was investigated. Composition of the casting and shell mold was Ti-47Al-6Nb (at%) and zircon sand, respectively. As a comparison and verification of the simulation results, a series of shell mold filling experiments of centrifugal casting were carried out. Simulation results indicate that the shell mold filling time is about 3.8 s; casting defects are distributed along the central line of the exhaust valves, especially in the neck position. The comparison shows that the simulation results agree with experiments. The powder/liquid ratio of 1.5:1 and mixing time of 30 min are identified as the proper process for the inner layer slurry in the process of making shell mold. There are no noticeable interfacial reactions between casting and shell mold according to XRD analysis. The metallurgical analysis results reveal that the lamellar structure is the typical structure of the as-cast exhaust valves, with a grain size of 185~300 μm. Copyright © 2021, Northwest Institute for Nonferrous Metal Research. Published by Science Press. All rights reserved.