High temperature oxidation behaviors of FGH96 P/M superalloy have been studied in air at temperatures ranging from 600 to 1000℃. By means of isothermal oxidation testing,X-ray diffraction,SEM(scanning electron microscopy),and EDS(energy dispersive X-ray spectroscopy) analyses,the oxidation kinetics as well as the composition and morphology of scales were investigated. Thermodynamic calculations were used to explain the oxidation mechanism. The results showed that as the oxidation temperature increased,the oxidation rate,the scale thickness,and scale spallation increased. FGH96 P/M superalloy exhibits good oxidation resistance at temperature below 800℃. The oxidation kinetics follows an approximately parabolic rate law,and the oxide layer was mainly composed of Cr2O3,TiO2,and a little amount of NiCr2O4. The oxidation is controlled by the transmission of chromium,titanium,and oxygen through the oxide scale. 相似文献
Recently,theγ’-strengthened superalloys are of great interests in high temperature applications due to their excellent high temperature strength which is derived from theγ’strengthening phase.For theseγ’-strengthened superalloys,the changes in morphology,size and distribution ofγ’precipitates due to coarsening during thermal exposure have a significant impact on the properties of alloys.This article briefly summarizes the recent advances on the coarsening behavior of gamma prime precipitates in the recently-developedγ’-strengthened superalloys and its effects on the hot deformation behavior of superalloys,drawing specific examples on Allvac■718 Plus TM and Ni3 Al-based intermetallic superalloys.It is found that the particle size plays an important role in morphological evolution ofγ’precipitates.For instance,the morphology ofγ’precipitates evolves from cuboidal to strip-like or other complex structures in Ni3 Al-based intermetallic alloys,while theγ’precipitates in Allvac■718 Plus alloy always present nearspherical morphology due to the relatively small initial particle size.The Lifshitz-Slyozof-Wagner(LSW)theory and its modifications,as well as Trans-Interface Diffusion Controlled(TIDC)theory have been applied to describing the coarsening kinetics ofγ’precipitates.Additionally,the hot deformation behavior ofγ’-strengthened superalloy is found to be greatly influenced by the coarsening ofγ’precipitates. 相似文献
K416B Ni-based superalloy with high W content has good high temperature properties and low cost, which has a great development potential. To investigate the room temperature tensile property and the deformation feature of K416B superalloy, tensile testing at room temperature was carried out, and optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the deformation and damage mechanisms. Results show that the main room temperature tensile deformation features of the K416B nickel-based superalloy are dislocations slipping in the matrix and shearing into γ′ phase. The <110> super-dislocations shearing into γ′ phase can form the anti-phase boundary two coupled (a/2)<110> partial-dislocations or decompose into the configuration of two (a/3)<112> partial dislocations plus stacking fault. In the later stage of tensile testing, the slip-lines with different orientations are activated in the grain, causing the stress concentration in the regions of block carbide or the porosity, and cracks initiate and propagate along these regions.
The hot deformation behavior of a nickel-based superalloy was investigated by means of isothermal compression tests in the strain rate range of 0.001–10 s−1 at 1110 °C. Transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) technique were used to study the effect of strain rate on the microstructure evolution of the alloy during hot deformation. The results revealed that the dynamic recrystallization (DRX) process was stimulated at high strain rates () due to the high dislocation density and adiabatic temperature rise. Meanwhile, high nucleation of DRX and low grain growth led to the fine DRX grains. In the strain rate rage of 0.001–1 s−1, the volume fraction of DRX grains increased with the decreasing strain rate, and the grain growth gradually governed the DRX process. Moreover, the strain rate has an important effect on DDRX and CDRX during hot deformation. On the other hand, particular attention was also paid to the evolution of twin boundaries during hot deformation. It was found that there was a lower fraction of Σ3 boundaries at the intermediate strain rate of 1 s−1, while the fractions of Σ3 boundaries were much higher at both the lower strain rates () and higher strain rates (). 相似文献
The present work reviews previous research on the evolution of porosity. It presents new results from a detailed study on the evolution of porosity during casting, heat treatment and creep of a single crystal Ni‐base superalloy subjected to uniaxial tensile creep at 1050 °C and 160 MPa in [001] and [110] directions. A quantitative metallographic study was performed on carefully polished metallographic cross sections, monitoring sampling fields of 4500 × 1000 µm2 using the back scatter contrast of an analytical scanning electron microscope; evolutions of pore sizes and pore form factors were analyzed and all important details which were previously revealed in a synchrotron study could be reproduced. In addition, it was observed that micro cracks form at larger cast pores. They interlink and thus initiate final rupture. The [110] tensile creep tests showed lower rupture strains than the [001] experiments. In agreement with earlier work, this can be rationalized on the basis of aligned porosity along primary dendrites. 相似文献