Papers by Keyword: TCP Phase

Abstract: The coarsening behavior of γ' phase and precipitation behavior of TCP phase in a Ni₃Al based single crystal superalloy were investigated by experimental and calculation. The Re-containing and Mo-rich single crystal superalloy used in this study exhibit good high-temperature strength and oxidation resistance. After fully heat-treated, the experimental superalloys were aged at 1050°C and 1150°C for different time periods from 50h to 1000h. The microstructure after thermal exposure was examined by field emission-scanning electron microscopy (FE-SEM). The results indicated that the coarsening behavior of γ' phase agrees well with the typical Lifshitz-Slyozov-Wagner (LSW) theory. After thermal exposure, both the size and the volume fraction of the TCP phase changed perceptibly.

Abstract: The effect of aging time at 980°C on the microstructures and mechanic properties for a single crystal Ni-based superalloy was investigated in this paper. The results showed that γ’ size distribution portrayed a low growth rate and maintained well cubic during aging for 0~1000h at 980°C. However, γ’ phase was gradually coarsened directionally during the aging for 1000~2500h at 980°C, indicating that the γ’ phase coarsening was controlled by diffusion during aging for 0~1000h at 980°C. In addition, the γ’ phase coarsening was also susceptible to the interface reaction during aging for 1000~2500h at 980°C. Furthermore the precipitated phase was analyzed, and the results showed that only slightly Topologically Close-Packed (TCP) phase was precipitated after aging for 1500h at 980°C which indicates that the microstructures of alloy were stable during aging for up to 1500 hours. At the same time, stress rupture life decreased rapidly for 0~250h, but basically kept constant value when aged for 250~1500h, then decreased rapidly again aging for 1500~2000h.

Abstract: The effect of Ru addition (0 wt.%, 3 wt.%, 5 wt.%), on γ morphology, elemental segregation, microstructural stability under long-term thermal exposure at 980 and stress rupture properties at 1100°C/130MPa have been studied. The results showed that with the increase of Ru content, the γ/γ eutectic volume fraction and the dendrite arm spacing decreased gradually. The γ' phase mean size in three alloys decreased with the increase of the Ru content. On the other hand, the dendrite segregation of Al, Ta towards interdendrite area and ReW towards dendrite core area was alleviated gradually with the increase of the Ru content. The increase of Ru content from 0 wt.% to 5 wt.% pronouncedly enhanced the stress rupture properties by suppressing the precipitation of TCP phases effectively at high temperature.

Abstract: Addition of Ru in Ni-base single crystal superalloys had been used to improve the elevated temperature strength and other multiple properties. Significant decreases in stacking fault energy of the γ phase and the volume fraction of γ′ phase are observed with the addition of Ru. As well as serving as an effective solid-solution strengthening element in high refractory content Ni-base single crystal superalloys, Ru additions are able to effectively strengthen both the γ and γ′ phases and suppress the formation of TCP phases. Due to the changes in the partitioning behavior of elements and the slight decrease in the supersaturation of refractory elements in γ phase associated with Ru additions, high temperature creep resistance and the microstructural stability of the alloy are improved remarkable. The influence of Ru on the microstructure of Ni-base single crystal superalloys is reviewed.

Abstract: The effect and the ways of removal of the segregation of alloying elements within the dendrite cell in single-crystal nickel-base superalloys are discussed. The peculiar features of Re and Ru behavior are underlined.

Abstract: The microstructures evolution of a new type Ni-base superalloy has been investigated after long-term aging at 750°C for 2000h. The results indicate that TCP, a harmful phase greatly affects the mechanical properties of the alloy, is un-precipitated in the aging process. γ´ phase is precipitated in two kinds of sizes during long-term aging. The shape of larger one is transit from spherical to cubic with prolonging of aging time. The M23C6 carbide formed mainly by Cr, and other elements such as Al, Ti, Co and Mo is also precipitated in both γ matrix and grain boundaries, and the quantities of the carbide increase gradually with the increasing of aging time.

Abstract: The effects of ruthenium and chromium contents have been investigated on phase transformation temperatures and the morphology of γ’ precipitates as well as microstructural stability in high refractory Ni-base superalloys. The solidus and liquidus temperatures were determined by differential scanning calorimetry (DSC), suggesting that the addition of Cr resulted in a decrease in solidus/liquidus temperatures while the Ru addition (3.5 at.%) had the neutral effect. The morphology of γ’ precipitates in the heat-treated microstructure was changed under the influence of the Cr and Ru additions, suggesting that Ru and Cr contents affected the γ−γ’ lattice misfit through changes in the associated partitioning to the constituent phases. The microstructural instability has been investigated at 1000 oC. High levels of Cr addition (8 at.%) strongly promoted the formation of TCP phases, while Ru improved the microstructural stability to some extent.

Abstract: The effect of Ru on the microstructure of a high content refractory elements nickel base Superalloy has been studied in the present investigation. The results showed that, the adding of 3%Ru did not prevent the precipitation of TCP phase during high temperature exposure, and even accelerated the formation of TCP phase,however the addition of Ru decreased the growth rate of μ phase significantly. In addition, the adding of Ru decreased the solving temperature of γ/γ′ eutectic by 5°C, and increased the tendency of γ′ rafting during high temperature exposure.