Jinguo Li

Effects of melt treatment on the cast structure of M963 superalloy

Abstract The cast structure of M963 superalloy is greatly affected by the melt superheating treatment. Melt superheating treatment (below 1923 K) coarsens the grain structure and transforms the blocky MC carbide into Chinese-script one that mostly distributed in dendrite. However, when the melt superheating temperature reaches 2123 K, the grain structure becomes very fine equiaxed, and the morphology of MC carbide changes back to the blocky appearance.

Evolution of Grain Selection in Spiral Selector during Directional Solidification of Nickel-base Superalloys

The modes of grain selection in spiral selector were investigated by both a ProCAST simulation and experimental confirmation. The results show that the efficiency of grain selection in starter block is associated with the geometry shape. At the early stage of grain selection, the optimization of grain orientation is dominated by competitive grain growth, but the optimization of grain orientation in starter block is gradually dominated by geometry shape at the later stage of grain selection. Besides, the spiral part could also optimize the orientation of the selected single crystal when the initial angle is large enough, and the single crystal selection in spiral parts with different pitch lengths and initial angles is dominated by different modes. The simulation results agree well with experimental ones.

Effect of Solidification Parameters on the Microstructure and Creep Property of a Single Crystal Ni-base Superalloy

A single crystal Ni-base superalloy was processed with withdrawal rates between 2 and 7 mm/min. The as-cast microstructures, heat treatment response and creep property have been characterized as a function of the withdrawal rate. As expected, the primary and secondary dendrite arm spacing decreased with increasing withdrawal rate; microsegregation degree and porosity distribution were also varied with different withdrawal rates. The withdrawal rate of 2 mm/min resulted in a noticeable residual microsegregation even after full heat treatment. The samples solidified at 7 mm/min exhibited a high density of cast porosities, and this led to a dramatical decline of the creep strain. 4 or 6 mm/min appeared to be the optimum withdrawal rate in the present study, which resulted in a uniform microstructure and an optimum density of cast porosity.

Preparation of a (Ti, Nb, W)C particulate reinforced nickel-base superalloy via super-high temperature treatment of melt

A well-dispersed (Ti,Nb,W)C particulate reinforced nickel-base superalloy was prepared via super-high temperature (above 2123 K) treatment of melt. Scanning electron microscope (SEM) observation and energy dispersive X-ray spectroscopy (EDS) results show that most of the (Ti,Nb,W)C particles have a carbonitride core. Gas analysis shows that nitrogen content in the alloy with super-high temperature treatment of melt is much higher than that in the conventional cast superalloy. The welldispersed (Ti,Nb,W)C particles could be attributed that nitrogen combines with Ti in the alloy melt to produce TiN, which acts as the nucleator to form (Ti,Nb,W)C. This work provided a new way to prepare the TiC particulate strengthened composites

Method of Stray Grain Inhibition in the Platforms with Different Dimensions During Directional Solidification of a Ni-Base Superalloy

A model of typical turbine blade shape with different platforms was designed to study the method of stray grain inhibition in the platforms by both experimental investigation and a ProCAST simulation based on a Cellular Automaton Finite Element model. The results show that stray grains with random orientations increasingly nucleate and grow in these platforms with the increase of platform dimension. To inhibit these stray grains, assistant bars are designed to introduce the primary grain into these platforms according to the theory of seeding method. The results indicate by the help of these assistant bars, the primary grain is introduced to the large dimensional platforms by developing secondary and tertiary dendrites, which form “crisscross” structure in these platforms. And, the stray grains in the large dimensional platforms are successfully and effectively inhibited. Further more, it is found that the thermal condition and the solidification sequence are changed in the large dimensional platforms by the use of assistant bars, which result in the introduction of primary grain and the inhibition of stray grains. Besides, the simulation results are in accordance with experimental findings.