The process parameters were optimized by simulation and verification experiments using orthogonal experimental design and the Taguchi method to lessen the tendency of significant shrinkage porosity in the centrifugal cast ring parts of K417 nickel-based superalloy. Advanced Porosity Model (APM) in ProCAST was used to predict the shrinkage porosity of centrifugal castings, and the effects of centrifugal speed, pouring speed, pouring temperature and preheating temperature of the mold were investigated on the shrinkage porosity ratio of the castings. According to the results, the parameter that has the greatest influence on the shrinkage porosity ratio of centrifugal casting is the centrifuge speed, followed by the preheating temperature of the mold, and the pouring temperature and pouring speed have relatively small effects on it. The optimized parameters were proposed as follows: centrifugal speed of 500 r/min, pouring speed of 225 mm/s, pouring temperature of 1400[Formula: see text], and mold preheating temperature of 50[Formula: see text], which could effectively reduce the formation of shrinkage porosity of the K417 centrifugal casting rings.

The effects of the package materials on the hot workability and stress-strain characteristics of high-Nb TiAl alloy with a nominal composition of Ti-46Al-8Nb (in at.%) were systematically studied via “sandwich structure” hot compression. TiAl sheet fabrication was conducted by hot pack rolling, and the microstructural characteristics and deformation mechanisms were investigated. Based on the analysis of compressed samples and stress-strain curves, the stainless steel/TiAl structure showed better deformation compatibility with homogeneous deformation and decreasing resistance. However, severe interfacial reactions were inevitable. Meanwhile, for the titanium alloy/TiAl structure, few interfacial reactions happened, but wavy deformation and high resistance complicated the compression process. Finally, a package structure with an outer stainless steel isolation layer and inner titanium alloy was determined for the pack rolling process. A TiAl sheet with no crack defects was obtained with 80% reduction. The pack-rolled TiAl sheet took on alternate microstructure of the grain-boundary Al-enriched ribbons and elongated lamellar colonies ribbons. The grain-boundary recrystallized α2 phase, lumpy γ phase, and massive α2/γ lamellae could be observed, which led to the scatter microstructure. The microstructural characteristics mainly resulted from the solute segregations of as-cast Ti-46Al-8Nb alloys, which triggered the local flow softening and deformation incompatibility during hot pack rolling.