The effects of strain rate on the dislocation type and dislocation configure of TA15 alloy were investigated.The experimental results show that the operating dislocation type changes from c type to c and a＋ c type wi...The effects of strain rate on the dislocation type and dislocation configure of TA15 alloy were investigated.The experimental results show that the operating dislocation type changes from c type to c and a＋ c type with increasing strain rate under the deformation condition of 900℃,60% strain.Under the condition of 900℃,60% strain and 0.001/s strain rate,lots of orientate dislocation cellular configurations and sub-grains,many dislocations pile up before sub boundary.When the strain rate increases to 0.1/s,some dislocations exhibit curved and dislocation tangles and pile-ups can be found,suggesting more dislocations and much stronger interactions among dislocations.展开更多
The evolution of dislocation structures in 6% prestrained steel 1018 during fatigue has been studied by TEM.The dislocations are quite movable,the loose cells quickly change to “checkboard”structures,in which the ma...The evolution of dislocation structures in 6% prestrained steel 1018 during fatigue has been studied by TEM.The dislocations are quite movable,the loose cells quickly change to “checkboard”structures,in which the main cell walls lie about {100}.Then,the low energy dislocation structures i.e.dipolar walls and abyrinth structures are evolved.The characteristic of labyrinth and the orientation of dipolar walls are quite similar to fcc crystal.This indicates the energy state of system and the moving ability of dislocations are important factors affect- ing softening process,rather than the slip geometric characteristic of dislocations and details of dislocations.The decreasing in misorientation between adjoining cells and internal stress are discussed.展开更多
Microstructure evolution and damping capacities of Mg–Ce binary alloys with three different Ce contents（0.5, 1, or 2 wt%） have been systematically investigated in this work. Numerous fine parallel second phases in...Microstructure evolution and damping capacities of Mg–Ce binary alloys with three different Ce contents（0.5, 1, or 2 wt%） have been systematically investigated in this work. Numerous fine parallel second phases in Mg–2Ce alloy are obtained, as well as a large number of dislocations around them, but few dislocations appear around the reticular second phase in the Mg–1Ce alloy. Among the three alloys, two internal friction peaks（P;and P;） are detected at about 78 and 167?C in both the Mg–0.5Ce and Mg–1Ce alloys.In addition, the alloy with special parallel second phase structure exhibits excellent damping capacity in both strain amplitude and temperature-dependent regions. These results may be ascribed to the stress concentration and the formation of abundant parallel and uniform dislocation configurations in the ?-Mg matrix without the influence of crystal orientation. The obtained results may provide a novel idea to prepare high-damping magnesium alloys by tailoring their microstructure.展开更多
In this study, we used the stop-action technique to experimentally investigate the material flow and microstructural evolution of alclad 2A12-T4 aluminum alloy during refill friction stir spot welding.There are two ma...In this study, we used the stop-action technique to experimentally investigate the material flow and microstructural evolution of alclad 2A12-T4 aluminum alloy during refill friction stir spot welding.There are two material flow components, i.e., the inward-or outward-directed spiral flow on the horizontal plane and the upward-or downward-directed flow on the vertical plane.In the plunge stage, the flow of plasticized metal into the cavity is similar to that of a stack, whereby the upper layer is pushed upward by the lower layer.In the refill stage, this is process reversed.As such, there is no obvious vertical plasticized metal flow between adjacent layers.Welding leads to the coarsening of S(Al2CuMg) in the thermo-mechanically affected zone and the diminishing of S in the stir zone.Continuous dynamic recrystallization results in the formation of fine equiaxed grains in the stir zone, but this process becomes difficult in the thermo-mechanically affected zone due to the lower deformation rate and the pinning action of S precipitates on the dislocations and sub-grain boundaries, which leads to a high fraction of low-angle grain boundaries in this zone.展开更多
The development of dislocation structures in the plastic zone ahead of a crack tip has been in- vestigated in a duplex stainless steel during in-situ deformation experiments in a scanning transmission electron microsc...The development of dislocation structures in the plastic zone ahead of a crack tip has been in- vestigated in a duplex stainless steel during in-situ deformation experiments in a scanning transmission electron microscope.It was found that the dislocation distribution was significantly different in the ferrite and in the austenite.In the ferrite grains,the dislocations emitted by the crack tip may cross-slip out of the original slip planes and form a broad plastic zone.However,in the austenite,the dislocation free zone is small and the dislocations emitted by the crack pile up in its slip plane.The selection of slip systems at the crack tip depends on the crack tip Schmid factors in both phases.But after large deformation,the selection of the second slip systems at the craek tip in austenite does not depend on the Schmid factors.展开更多
Fatigue lifetime curves of Zircaloy-4 at different temperatures were measured, and the fatigued dislocation configurations were investigated using transmission electron microscopy. Ii was found that prismatic slip is ...Fatigue lifetime curves of Zircaloy-4 at different temperatures were measured, and the fatigued dislocation configurations were investigated using transmission electron microscopy. Ii was found that prismatic slip is the primary deformation mode. for Zircaloy-4fatigued at RT prismatic plus Pyramidal slip at 400℃,and prismatic plus (0001) basic slip at 600℃. The corresponding dislocation configurations are parallel dislocation lines al RT, elongated cells at 400℃ and two sets of mutually Perpendicular dislocation bands at 600℃.respectively. The relationship among. fatigue deformation mode, dislocation configuration and lifetime is discussed.展开更多
The microstructure of Ti-24Al-14NB-3V intermetallic alloy with solution treated was investigated by trans mission electron microscopy (TEM) and selected area electron diffraction (SAD) in conjunction with X-ray energy...The microstructure of Ti-24Al-14NB-3V intermetallic alloy with solution treated was investigated by trans mission electron microscopy (TEM) and selected area electron diffraction (SAD) in conjunction with X-ray energydispersive spectroscopy (EDS) techniques. It shown that =50% ductile βo-phase and small amount of O phase,and α2 with the number of dislocations having c-component resulted in increasing slip system of the material, havecontributed to a good combination of strength and ductility at room temperature. Owing to some reciprocal planes ofsimilarity between α2 and O Phases, to distinguish both of two phases, a series of diffraction patterns obtained bytilting around one reciprocal direction of the phase are needed based on the systematic extinction and reciprocalplanes sequences occurred in the diffraction patterns, if those patterns are not containing one of three reciprocal unitvectors, a*, b*, c* in terms of the crystal unit cell, a, b, c.展开更多
文摘The effects of strain rate on the dislocation type and dislocation configure of TA15 alloy were investigated.The experimental results show that the operating dislocation type changes from c type to c and a＋ c type with increasing strain rate under the deformation condition of 900℃,60% strain.Under the condition of 900℃,60% strain and 0.001/s strain rate,lots of orientate dislocation cellular configurations and sub-grains,many dislocations pile up before sub boundary.When the strain rate increases to 0.1/s,some dislocations exhibit curved and dislocation tangles and pile-ups can be found,suggesting more dislocations and much stronger interactions among dislocations.
文摘The evolution of dislocation structures in 6% prestrained steel 1018 during fatigue has been studied by TEM.The dislocations are quite movable,the loose cells quickly change to “checkboard”structures,in which the main cell walls lie about {100}.Then,the low energy dislocation structures i.e.dipolar walls and abyrinth structures are evolved.The characteristic of labyrinth and the orientation of dipolar walls are quite similar to fcc crystal.This indicates the energy state of system and the moving ability of dislocations are important factors affect- ing softening process,rather than the slip geometric characteristic of dislocations and details of dislocations.The decreasing in misorientation between adjoining cells and internal stress are discussed.
基金financially supported by the National Natural Science Foundation of China (No. 51271206, No. 51571044)the National Basic Research Program of China (No. 2013CB632201)+1 种基金the Basic Research Project of Chongqing (cstc2015jcyj BX0081)National Key Research and Development Program (No. 2016YFB0301102)
文摘Microstructure evolution and damping capacities of Mg–Ce binary alloys with three different Ce contents（0.5, 1, or 2 wt%） have been systematically investigated in this work. Numerous fine parallel second phases in Mg–2Ce alloy are obtained, as well as a large number of dislocations around them, but few dislocations appear around the reticular second phase in the Mg–1Ce alloy. Among the three alloys, two internal friction peaks（P;and P;） are detected at about 78 and 167?C in both the Mg–0.5Ce and Mg–1Ce alloys.In addition, the alloy with special parallel second phase structure exhibits excellent damping capacity in both strain amplitude and temperature-dependent regions. These results may be ascribed to the stress concentration and the formation of abundant parallel and uniform dislocation configurations in the ?-Mg matrix without the influence of crystal orientation. The obtained results may provide a novel idea to prepare high-damping magnesium alloys by tailoring their microstructure.
基金financially supported by the National Science and Technology Major Project of China (No.2017ZX04005001)the Key Research & Development program of Shandong Province (2018GGX103053)。
文摘In this study, we used the stop-action technique to experimentally investigate the material flow and microstructural evolution of alclad 2A12-T4 aluminum alloy during refill friction stir spot welding.There are two material flow components, i.e., the inward-or outward-directed spiral flow on the horizontal plane and the upward-or downward-directed flow on the vertical plane.In the plunge stage, the flow of plasticized metal into the cavity is similar to that of a stack, whereby the upper layer is pushed upward by the lower layer.In the refill stage, this is process reversed.As such, there is no obvious vertical plasticized metal flow between adjacent layers.Welding leads to the coarsening of S(Al2CuMg) in the thermo-mechanically affected zone and the diminishing of S in the stir zone.Continuous dynamic recrystallization results in the formation of fine equiaxed grains in the stir zone, but this process becomes difficult in the thermo-mechanically affected zone due to the lower deformation rate and the pinning action of S precipitates on the dislocations and sub-grain boundaries, which leads to a high fraction of low-angle grain boundaries in this zone.
文摘The development of dislocation structures in the plastic zone ahead of a crack tip has been in- vestigated in a duplex stainless steel during in-situ deformation experiments in a scanning transmission electron microscope.It was found that the dislocation distribution was significantly different in the ferrite and in the austenite.In the ferrite grains,the dislocations emitted by the crack tip may cross-slip out of the original slip planes and form a broad plastic zone.However,in the austenite,the dislocation free zone is small and the dislocations emitted by the crack pile up in its slip plane.The selection of slip systems at the crack tip depends on the crack tip Schmid factors in both phases.But after large deformation,the selection of the second slip systems at the craek tip in austenite does not depend on the Schmid factors.
文摘Fatigue lifetime curves of Zircaloy-4 at different temperatures were measured, and the fatigued dislocation configurations were investigated using transmission electron microscopy. Ii was found that prismatic slip is the primary deformation mode. for Zircaloy-4fatigued at RT prismatic plus Pyramidal slip at 400℃,and prismatic plus (0001) basic slip at 600℃. The corresponding dislocation configurations are parallel dislocation lines al RT, elongated cells at 400℃ and two sets of mutually Perpendicular dislocation bands at 600℃.respectively. The relationship among. fatigue deformation mode, dislocation configuration and lifetime is discussed.
文摘The microstructure of Ti-24Al-14NB-3V intermetallic alloy with solution treated was investigated by trans mission electron microscopy (TEM) and selected area electron diffraction (SAD) in conjunction with X-ray energydispersive spectroscopy (EDS) techniques. It shown that =50% ductile βo-phase and small amount of O phase,and α2 with the number of dislocations having c-component resulted in increasing slip system of the material, havecontributed to a good combination of strength and ductility at room temperature. Owing to some reciprocal planes ofsimilarity between α2 and O Phases, to distinguish both of two phases, a series of diffraction patterns obtained bytilting around one reciprocal direction of the phase are needed based on the systematic extinction and reciprocalplanes sequences occurred in the diffraction patterns, if those patterns are not containing one of three reciprocal unitvectors, a*, b*, c* in terms of the crystal unit cell, a, b, c.
