RESUMO
The residual stress generated during heat treatment of nickel-base superalloys will affect their service performance and introduce primary cracks. In a component with high residual stress, a tiny amount of plastic deformation at room temperature can release the stress to a certain extent. However, the stress-releasing mechanism is still unclear. In the present study, the micro-mechanical behavior of the FGH96 nickel-base superalloy during room temperature compression was studied using in situ synchrotron radiation high-energy X-ray diffraction. The in situ evolution of the lattice strain was observed during deformation. The stress distribution mechanism of grains and phases with different orientations was clarified. The results show that at the elastic deformation stage, the (200) lattice plane of γ' phase bears more stress after the stress reaches 900 MPa. When the stress exceeds 1160 MPa, the load is redistributed to the grains with their <200> crystal directions aligned with the loading direction. After yielding, the γ' phase still bears the main stress.
RESUMO
FGH96 is a powder metallurgy Ni-based superalloy used for turbine disks of aero-engines. In the present study, room-temperature pre-tension experiments with various plastic strain were conducted for the P/M FGH96 alloy, and subsequent creep tests were conducted under the test conditions of 700 °C and 690 MPa. The microstructures of the pre-strained specimens after room-temperature pre-strain and after 70 h creep were investigated. A steady-state creep rate model was proposed, considering the micro-twinning mechanism and pre-strain effects. Progressive increases in steady-state creep rate and creep stain within 70 h were found with increasing amounts of pre-strain. Room-temperature pre-tension within 6.04% plastic strain had no obvious influence on the morphology and distribution of γ' precipitates, although the dislocation density continuously increased with the increase in pre-strains. The increase in the density of mobile dislocations introduced by pre-strain was the main reason for the increase in creep rate. The predicted steady-state creep rates showed good agreement with the experiment data; the creep model proposed in this study could capture the pre-strain effect.
RESUMO
In this paper, considering the strength and geometric discrete distribution characteristics of composite reinforcement, by introducing the discrete distribution function of reinforcement, the secondary development of ABAQUS is realized by using the Python language, the parametric automatic generation method of representative volume elements of particle-reinforced composites is established, and the tensile properties of silicon carbide particle-reinforced aluminum matrix composites are analyzed. The effects of particle strength, particle volume fraction, and particle random distribution on the mechanical properties of SiCp/Al composites are studied. The results show that the random distribution of particles and the change in particle strength have no obvious influence on the stress-strain relationship before the beginning of material damage, but have a great influence on the damage stage, maximum strength, and corresponding failure strain. With the increase in particle volume fraction, the damage intensity of the model increases, and the random distribution of particles has a great influence on the model with a large particle volume fraction. The results can provide a reference for the design, preparation, and characterization of particle-reinforced metal matrix composites.
RESUMO
The effect of surface integrity on the hot fatigue performance of Ti2AlNb alloy was investigated. A turning process was used to prepare the standard specimens for hot fatigue tests. The surface integrity characterization and axial fatigue tests were performed. The results show that the influence of surface roughness on the hot fatigue performance of the Ti2AlNb alloy is a secondary factor. The compressive residual stress and enhanced microhardness in the surface layer has a significant effect on the hot fatigue life and they are dominant in the hot fatigue behavior of the Ti2AlNb alloy. Through the investigation on the characteristics of the fatigue fractures, the fatigue propagation process was significantly suppressed because of the strong residual compressive stress and microhardness distribution on the surface layer of the Ti2AlNb specimen.