Taiwen Huang

Interaction between Re and W on the microstructural stability of Ni-based single-crystal superalloys

The influences of Re and W as well as their interaction on γ′ and topologically close-packed (TCP) phases have been investigated in seven kinds of Ni-based single-crystal superalloys. The results show that after full heat treatment, the γ′ size is reduced with increasing Re, but does not change with increasing W. After thermal exposure at 1000°C for 1000 h, the TCP phase is dramatically increased with increasing Re, but increased slightly with increasing W. The TCP phase volume fraction in higher Re alloys is much more than that in lower Re alloys which have the same total content of Re and W. This indicates that W instead of Re could effectively improve the microstructural stability of Ni-based single-crystal superalloys.

Effects of spiral geometries on grain selection during casting of single crystal superalloys

Abstract Grain texture evolution in starter block during single crystal (SX) casting with a grain selector had been investigated. Several spiral grain selectors with different spiral geometries were designed to investigate the effects of spiral geometries on grain selection in spiral passage. The results indicated that the percentage of grains with a deviation angle of <10° from the axial orientation increased simultaneously with distance from the chill plate. When the distance reached 36·1 mm, nearly 90% of the grains’ misorientations were <10°, and the minor grains deviated >12°. As the spiral angle θ and the spiral thickness T decrease, the SX structure occurred at the lower position of the grain selector. In addition, it was concluded that the SX structure cannot be selected when the spiral angle is <15°. Moreover, the effect of spiral geometries on grain selection has also been discussed.

Grain Refinement on Microstructure and Mechanical Properties of IN718 Superalloy

The mixed refiner of Co3FeNb2 and CrFeNb ternary intermetallic compounds and melt superheating treatment under the modified thermally-controlled solidification (TCS) process have been designed to achieve grain refinement and further improve mechanical properties of IN718 superalloy. It is found that the refinement effect of addition grain refiners under TCS process is quite superior to that by convention casting (CC) process with refiner, as experiment results show that the grain size is refined from 3340 to 126 μm and greatly reduce the amount of porosity, during the refinement process. In addition, the applied melt treatment can refine grain size from 6420 to 89 μm and greatly reduce the amount of porosity. Meanwhile, after grain refinement, the stress rupture property under 650 °C/620 MPa is significantly improved. Grain refinement mechanisms are also discussed.