The fatigue behavior of 30 WGP1600 non-oriented electrical steel, which is generally used in the motors for electrical vehicles, was investigated. The detailed microstructure and dislocation configurations of the fati...The fatigue behavior of 30 WGP1600 non-oriented electrical steel, which is generally used in the motors for electrical vehicles, was investigated. The detailed microstructure and dislocation configurations of the fatigue specimens were examined by OM, SEM, and TEM. The test results showed that fatigue cracks were commonly initiated from the surface grain boundaries, crystals plane, and inclusions. The rapid fatigue crack propagation was characterized by transgranular cleavage fracture, while most transient fracture exhibited ductile tearing characteristics. After cyclic deformation of the non-oriented electrical steels, various dislocation structures, such as short and thick lines, veins, persistent slip bands, cells, and labyrinth, were observed.展开更多
High temperature low cycle fatigue tests on GH4742 superalloy were studied under the total strain-con- trolled conditions at 650 ℃. Combined with fatigue test data, fatigue properties of the alloy were analyzed. Frac...High temperature low cycle fatigue tests on GH4742 superalloy were studied under the total strain-con- trolled conditions at 650 ℃. Combined with fatigue test data, fatigue properties of the alloy were analyzed. Fracture morphology and dislocation structure were observed by scanning electron microscopy and transmission electron mi- croscopy. The results showed that fatigue life and fatigue resistance of GH4742 alloy decreased significantly with in- creasing total strain amplitude. The cyclic hardening, cyclic softening and cyclic stability phenomena of the alloy oc- curred during the low cycle fatigue process. The increasing total strain amplitude is conducive to the formation of γ1 phase. Fatigue crack propagation is controlled jointly by ductile and brittle fracture. Inhomogeneous deformation and deformation restricted in slip bands are the main reasons for the reduction of fatigue life of GH4742 alloy.展开更多
Ultrafine grained(UFG) materials have attracted considerable attention owing to their unique microstructure and mechanical properties.However,the easy formation of large-scale shear bands and severe grain coarsening d...Ultrafine grained(UFG) materials have attracted considerable attention owing to their unique microstructure and mechanical properties.However,the easy formation of large-scale shear bands and severe grain coarsening during cyclic deformation gives rise to enormous difficulties when investigating the intrinsic fatigue behavior of UFG materials.Herein,we discuss the fabrication of an ideal model material,based on pure Cu,by friction stir processing(FSP),which exhibits equiaxed ultrafine grains,low dislocation density,and a high ratio of high-angle grain boundaries.This model material was used to investigate the intrinsic high cycle fatigue behavior of UFG material.It was found that an enhanced fatigue limit and fatigue ratio can be achieved by FSP Cu due to its uniform and stable UFG structure.Instead of traditional large-scale shear bands,protrusion was found to be the main surface damage morphology for FSP Cu during high cycle fatigue deformation,and no obvious grain coarsening was observed.Dislocation related activity also dominated,but was limited to the ultrafine grains without the formation of regular dislocation structures.展开更多
基金Funded by the High Technology Research and Development Program of China(2011AA11A238)
文摘The fatigue behavior of 30 WGP1600 non-oriented electrical steel, which is generally used in the motors for electrical vehicles, was investigated. The detailed microstructure and dislocation configurations of the fatigue specimens were examined by OM, SEM, and TEM. The test results showed that fatigue cracks were commonly initiated from the surface grain boundaries, crystals plane, and inclusions. The rapid fatigue crack propagation was characterized by transgranular cleavage fracture, while most transient fracture exhibited ductile tearing characteristics. After cyclic deformation of the non-oriented electrical steels, various dislocation structures, such as short and thick lines, veins, persistent slip bands, cells, and labyrinth, were observed.
基金Sponsored by Major National Science and Technology Project of High-end CNC Machine Tools and Basic Manufacturing Equipments of China(2012ZX04010081)
文摘High temperature low cycle fatigue tests on GH4742 superalloy were studied under the total strain-con- trolled conditions at 650 ℃. Combined with fatigue test data, fatigue properties of the alloy were analyzed. Fracture morphology and dislocation structure were observed by scanning electron microscopy and transmission electron mi- croscopy. The results showed that fatigue life and fatigue resistance of GH4742 alloy decreased significantly with in- creasing total strain amplitude. The cyclic hardening, cyclic softening and cyclic stability phenomena of the alloy oc- curred during the low cycle fatigue process. The increasing total strain amplitude is conducive to the formation of γ1 phase. Fatigue crack propagation is controlled jointly by ductile and brittle fracture. Inhomogeneous deformation and deformation restricted in slip bands are the main reasons for the reduction of fatigue life of GH4742 alloy.
基金supported by the National Natural Science Foundation of China(51301178 and 51331008)
文摘Ultrafine grained(UFG) materials have attracted considerable attention owing to their unique microstructure and mechanical properties.However,the easy formation of large-scale shear bands and severe grain coarsening during cyclic deformation gives rise to enormous difficulties when investigating the intrinsic fatigue behavior of UFG materials.Herein,we discuss the fabrication of an ideal model material,based on pure Cu,by friction stir processing(FSP),which exhibits equiaxed ultrafine grains,low dislocation density,and a high ratio of high-angle grain boundaries.This model material was used to investigate the intrinsic high cycle fatigue behavior of UFG material.It was found that an enhanced fatigue limit and fatigue ratio can be achieved by FSP Cu due to its uniform and stable UFG structure.Instead of traditional large-scale shear bands,protrusion was found to be the main surface damage morphology for FSP Cu during high cycle fatigue deformation,and no obvious grain coarsening was observed.Dislocation related activity also dominated,but was limited to the ultrafine grains without the formation of regular dislocation structures.