The mechanical properties of welded joints in resistance spot welding of DP780 steel were tested,and three different types of welding cracks in welded joints were investigated by optical microscopy,scanning electron m...The mechanical properties of welded joints in resistance spot welding of DP780 steel were tested,and three different types of welding cracks in welded joints were investigated by optical microscopy,scanning electron microscopy and electron back-scattered diffraction.Finally,the failure mode of the welded joints in shear tensile test was discussed.It is found the shear tensile strength of welded joints can be greatly improved by adding preheating current or tempering current.The surface crack in welded joint is intergranular fracture,while the inner crack in welded joint is transgranular fracture,and the surface crack on the edge of the electrode imprint can be improved by adding preheating current or tempering current.The traditional failure mode criterion advised by American Welding Society is no longer suitable for DP780 spot welds and the critical nugget size suggested by Pouranvari is overestimated.展开更多
Titanium alloys play an important role in aerospace and other fields.However,after precision forging and cold rolling process,some defects will appear on the subsurface of titanium alloy bars,thus reducing the surface...Titanium alloys play an important role in aerospace and other fields.However,after precision forging and cold rolling process,some defects will appear on the subsurface of titanium alloy bars,thus reducing the surface quality and precision of turning process.This study aimed at exploring the effect of crack defects on TC4 cutting.Firstly,the finite element cutting simulation model of TC4 material with crack defects was established in ABAQUS.Then,the cutting parameters such as cutting force,stress concentration,chip morphology,residual stress were obtained by changing the variables such as the size and height of crack defects.Finally,the turning experiment was carried out on centerless lathe.The results show that the cutting force changes abruptly when the defect position is located on the cutting path,the maximal stress occurs at the tip of the defect,and the mutation of stress value is more serious with the increase of defect size;the buckling deformation of chip morphology occurs and becomes less serious with the increase of the distance between the defect position and the workpiece surface;the surface residual stress near the defect is related to the stress when the tool is close to the defect,the larger defect size and the closer to the machined surface,the greater the residual stress.Therefore,under certain processing conditions,the TC4 material should avoid large size defects or increase the distance between defects and the machined surface,so as to obtain better and stable surface quality.展开更多
Intermetallic alloys offer exceptional high-temperature mechanical properties and low densities,thus rendering them suitable for a wide range of applications in aviation and spacecraft.However,their inherent brittlene...Intermetallic alloys offer exceptional high-temperature mechanical properties and low densities,thus rendering them suitable for a wide range of applications in aviation and spacecraft.However,their inherent brittleness at room temperature poses challenges in the manufacture of complex geometries.Hence,Laser additive manufacturing(LAM)has emerged as a promising approach to investigate the potential limitations of these materials.This review discusses the key findings and challenges associated with the LAM of intermetallic alloys,particu-larly NiAl,Ni_(3)Al,and TiAl,whose engineering applications are substantial.It provides an overview of typical defect morphologies,formation mechanisms,and strategies to prevent cracks and pores.Additionally,it presents an analysis of the microstructural characteristics of as-built and post-treated samples compared with those of samples prepared conventionally.Furthermore,the mechanical properties of the above-mentioned alloys at both room and high temperatures are reviewed,thus highlighting the effects of post-treatment processes.This review concludes with summary tables detailing the mechanical properties,which serve as useful references for researchers.展开更多
The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects...The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects are prone to occur.This leads to an increase in the scrap rate of casings,causing significant resource wastage.Additionally,the presence of cracks poses a significant safety hazard after the casings are put into service.The generation of different types of crack defects in stainless steel casings is closely related to casting stress and the high-temperature concession of the sand mold.Therefore,the types and causes of cracks in stainless steel casing products,based on their structural characteristics,were systematically analyzed.Various sand molds with different internal topology designs were printed using the 3DP technology to investigate the impact of sand mold structures on high-temperature concession.The optimal sand mold structure was used to cast casings,and the crack suppression effect was verified by analyzing its eddy current testing results.The experimental results indicate that the skeleton structure has an excellent effect on suppressing cracks in the casing.This research holds important theoretical and engineering significance in improving the quality of casing castings and reducing production costs.展开更多
In order to know the cause of cracks in cold rolling of QSn6.5 0.1 copper alloy strip, a lot of experiments and analysis were done. The microstructure changes of QSn6.5 0.1 were investigated by means of metallurgical ...In order to know the cause of cracks in cold rolling of QSn6.5 0.1 copper alloy strip, a lot of experiments and analysis were done. The microstructure changes of QSn6.5 0.1 were investigated by means of metallurgical microscope. The morphology of cracks and surface defects were examined using scanning electron microscope. Macroscopic residual stresses produced in every process during manufacturing in the QSn6.5 0.1 strip were measured by X ray diffraction method and hole drilling method. The results show that the cracks in the QSn6.5 0.1 cold rolling strip were caused due to the derivation of metallurgical defects, such as SnO 2, S, fine looses,the inverse segregation unable to clear up when milling, and the accumulation of all kinds of resi dual stresses. When the accumulation of the residual stress reaches the material′s breaking strength, the cracks will be generated. Several measures to avoid the development of these kinds of cracks were put forward, such as: controlling the casting technology, improving homogenization annealing procedure (680 ℃/7 h) and milling quality(using the second milling when necessary), working out a more reasonable rolling technology to ensure intermediate annealing in time.展开更多
文摘The mechanical properties of welded joints in resistance spot welding of DP780 steel were tested,and three different types of welding cracks in welded joints were investigated by optical microscopy,scanning electron microscopy and electron back-scattered diffraction.Finally,the failure mode of the welded joints in shear tensile test was discussed.It is found the shear tensile strength of welded joints can be greatly improved by adding preheating current or tempering current.The surface crack in welded joint is intergranular fracture,while the inner crack in welded joint is transgranular fracture,and the surface crack on the edge of the electrode imprint can be improved by adding preheating current or tempering current.The traditional failure mode criterion advised by American Welding Society is no longer suitable for DP780 spot welds and the critical nugget size suggested by Pouranvari is overestimated.
基金supported by Key Research and Development Program of Shaanxi Province(No.2023-YBGY-386)Natural Science and Technology Fund General Program of Shaanxi Province(No.2021JM-599).
文摘Titanium alloys play an important role in aerospace and other fields.However,after precision forging and cold rolling process,some defects will appear on the subsurface of titanium alloy bars,thus reducing the surface quality and precision of turning process.This study aimed at exploring the effect of crack defects on TC4 cutting.Firstly,the finite element cutting simulation model of TC4 material with crack defects was established in ABAQUS.Then,the cutting parameters such as cutting force,stress concentration,chip morphology,residual stress were obtained by changing the variables such as the size and height of crack defects.Finally,the turning experiment was carried out on centerless lathe.The results show that the cutting force changes abruptly when the defect position is located on the cutting path,the maximal stress occurs at the tip of the defect,and the mutation of stress value is more serious with the increase of defect size;the buckling deformation of chip morphology occurs and becomes less serious with the increase of the distance between the defect position and the workpiece surface;the surface residual stress near the defect is related to the stress when the tool is close to the defect,the larger defect size and the closer to the machined surface,the greater the residual stress.Therefore,under certain processing conditions,the TC4 material should avoid large size defects or increase the distance between defects and the machined surface,so as to obtain better and stable surface quality.
基金supported by National Key Research and Development Program of China(Grant No.2021YFB3702502)National Natural Science Foundation of China(Grant Nos.52271035,and 52474412)+1 种基金Natural Science Foundation of Shanghai,China(Grant No.23ZR1421500)the SPMI Project from Shanghai Academy of Spaceflight Technology(Grant No.SPMI2022-06).
文摘Intermetallic alloys offer exceptional high-temperature mechanical properties and low densities,thus rendering them suitable for a wide range of applications in aviation and spacecraft.However,their inherent brittleness at room temperature poses challenges in the manufacture of complex geometries.Hence,Laser additive manufacturing(LAM)has emerged as a promising approach to investigate the potential limitations of these materials.This review discusses the key findings and challenges associated with the LAM of intermetallic alloys,particu-larly NiAl,Ni_(3)Al,and TiAl,whose engineering applications are substantial.It provides an overview of typical defect morphologies,formation mechanisms,and strategies to prevent cracks and pores.Additionally,it presents an analysis of the microstructural characteristics of as-built and post-treated samples compared with those of samples prepared conventionally.Furthermore,the mechanical properties of the above-mentioned alloys at both room and high temperatures are reviewed,thus highlighting the effects of post-treatment processes.This review concludes with summary tables detailing the mechanical properties,which serve as useful references for researchers.
基金financially supported by the National Natural Science Foundation of China(No.52175352)the Xing Liao Ying Cai Project of Liaoning Province(No.XLYC2008036)the Shenyang Youth Innovation Talent Support Program(No.RC220429)。
文摘The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects are prone to occur.This leads to an increase in the scrap rate of casings,causing significant resource wastage.Additionally,the presence of cracks poses a significant safety hazard after the casings are put into service.The generation of different types of crack defects in stainless steel casings is closely related to casting stress and the high-temperature concession of the sand mold.Therefore,the types and causes of cracks in stainless steel casing products,based on their structural characteristics,were systematically analyzed.Various sand molds with different internal topology designs were printed using the 3DP technology to investigate the impact of sand mold structures on high-temperature concession.The optimal sand mold structure was used to cast casings,and the crack suppression effect was verified by analyzing its eddy current testing results.The experimental results indicate that the skeleton structure has an excellent effect on suppressing cracks in the casing.This research holds important theoretical and engineering significance in improving the quality of casing castings and reducing production costs.
文摘In order to know the cause of cracks in cold rolling of QSn6.5 0.1 copper alloy strip, a lot of experiments and analysis were done. The microstructure changes of QSn6.5 0.1 were investigated by means of metallurgical microscope. The morphology of cracks and surface defects were examined using scanning electron microscope. Macroscopic residual stresses produced in every process during manufacturing in the QSn6.5 0.1 strip were measured by X ray diffraction method and hole drilling method. The results show that the cracks in the QSn6.5 0.1 cold rolling strip were caused due to the derivation of metallurgical defects, such as SnO 2, S, fine looses,the inverse segregation unable to clear up when milling, and the accumulation of all kinds of resi dual stresses. When the accumulation of the residual stress reaches the material′s breaking strength, the cracks will be generated. Several measures to avoid the development of these kinds of cracks were put forward, such as: controlling the casting technology, improving homogenization annealing procedure (680 ℃/7 h) and milling quality(using the second milling when necessary), working out a more reasonable rolling technology to ensure intermediate annealing in time.
