A mechanism of intergranular fracture of as-quenched martensite in high carbon steels has been proposed.When coarse grains of austenite transform to martensite,the grain plays a role of the unit of volume dilation,inh...A mechanism of intergranular fracture of as-quenched martensite in high carbon steels has been proposed.When coarse grains of austenite transform to martensite,the grain plays a role of the unit of volume dilation,inhomogeneous strains necessarily produce and local microscop- ic stress concentrations create at grain boundaries.This reduces the intergration of the grains, sometimes intergranular cracks may produce.Under the action of first kind hardening stress or external force,the intergranular cracks propagated along the grain boundaries will form. This results in the candy-like fracture.展开更多
In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequen...In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequently so as to study the grain boundary (GB) cracking behaviour by the surface observation. The results show that crack initiation at GB was a process controlled by multi-factors, such as boundary structure, GB-slip interaction, GB sliding and so on. If these factors are varied so that the incompati- bility at a GB increased, the possibility of cyacking at the boundary will be raised. Some inteygranular cracking phenomena are not able to be explained by the GB stepping mechanism.展开更多
The residual stress in the D019-α2 phase is known to be significantly higher than that in the L10-γphase in TiAl alloys after deformation due to the poor plasticity and strong mechanical anisotropy of theα2 phase.H...The residual stress in the D019-α2 phase is known to be significantly higher than that in the L10-γphase in TiAl alloys after deformation due to the poor plasticity and strong mechanical anisotropy of theα2 phase.However,the internal stress accumulation and relaxation in theα2 phase during high-temperature deformation and annealing are scarcely investigated.In this study,for the first time,the internal strain evolution and load partitioning between theα2 andγphases at high temperatures are characterized by in-situ synchrotron high energy X-ray diffraction(HEXRD)technique.The plastic deformation is at least initiated at a stress of roughly 200 MPa in theγphase and 775 MPa in theα2 phase.The intergranular strains in theα2 phase are generated by the onset of dislocation glide in theγphase,and accentuated with the accumulated dislocations and the ensuing twinning activity.After unloading,great intergranular strains are preserved in theα2 phase constrained by the heavily plastically deformedγphase.During subsequent heating from 400 to 1000℃,the internal strains in theα2 phase are almost fully relaxed by substantial dislocation annihilation and rearrangement in theγphase.During annealing at 800℃,the internal strain relaxation is rapid in the initial 10 min,whereas considerably retarded subsequently.The extent of relaxation after holding at 800℃for 1 h is equivalent to that of heating in an effective temperature range of 680-880℃for 10 min.The in-situ lattice strain measurements with various thermal relaxation schemes provide guidance for the stress relief annealing of TiAl components.展开更多
文摘A mechanism of intergranular fracture of as-quenched martensite in high carbon steels has been proposed.When coarse grains of austenite transform to martensite,the grain plays a role of the unit of volume dilation,inhomogeneous strains necessarily produce and local microscop- ic stress concentrations create at grain boundaries.This reduces the intergration of the grains, sometimes intergranular cracks may produce.Under the action of first kind hardening stress or external force,the intergranular cracks propagated along the grain boundaries will form. This results in the candy-like fracture.
文摘In order to understand the basic mechanism of intergranular cracking in pure metals during fatigue, stress-controlled push-pull fatigue tests were carried out with high purity aluminium. Tests were interrupted frequently so as to study the grain boundary (GB) cracking behaviour by the surface observation. The results show that crack initiation at GB was a process controlled by multi-factors, such as boundary structure, GB-slip interaction, GB sliding and so on. If these factors are varied so that the incompati- bility at a GB increased, the possibility of cyacking at the boundary will be raised. Some inteygranular cracking phenomena are not able to be explained by the GB stepping mechanism.
基金the National Natural Science Foundation of China(No.51971175)Natural Science Foundation of Shanghai(No.22ZR1467400)+1 种基金Chongqing(No.CSTB2022NSCQMSX1113)the“111”Project(No.B20028).
文摘The residual stress in the D019-α2 phase is known to be significantly higher than that in the L10-γphase in TiAl alloys after deformation due to the poor plasticity and strong mechanical anisotropy of theα2 phase.However,the internal stress accumulation and relaxation in theα2 phase during high-temperature deformation and annealing are scarcely investigated.In this study,for the first time,the internal strain evolution and load partitioning between theα2 andγphases at high temperatures are characterized by in-situ synchrotron high energy X-ray diffraction(HEXRD)technique.The plastic deformation is at least initiated at a stress of roughly 200 MPa in theγphase and 775 MPa in theα2 phase.The intergranular strains in theα2 phase are generated by the onset of dislocation glide in theγphase,and accentuated with the accumulated dislocations and the ensuing twinning activity.After unloading,great intergranular strains are preserved in theα2 phase constrained by the heavily plastically deformedγphase.During subsequent heating from 400 to 1000℃,the internal strains in theα2 phase are almost fully relaxed by substantial dislocation annihilation and rearrangement in theγphase.During annealing at 800℃,the internal strain relaxation is rapid in the initial 10 min,whereas considerably retarded subsequently.The extent of relaxation after holding at 800℃for 1 h is equivalent to that of heating in an effective temperature range of 680-880℃for 10 min.The in-situ lattice strain measurements with various thermal relaxation schemes provide guidance for the stress relief annealing of TiAl components.
