The distinctive distribution of acoustic emission(AE)characteristic parameters generated during tensile testing of low-temperature tempered AISI 4140 steel was investigated.Two clusters of acoustic emission signals we...The distinctive distribution of acoustic emission(AE)characteristic parameters generated during tensile testing of low-temperature tempered AISI 4140 steel was investigated.Two clusters of acoustic emission signals were distinguished using power-law distribution fitting and k-means clustering methods.These clusters were identified as resulting from dislocation motion during yielding and dislocation entanglement during uniform plastic deformation.The conclusion is further confirmed by transmission electron microscopy images at different strains.In particular,the unique"arch-shaped"distribution of the acoustic emission energy during yielding implies a change in unusual dislocation motion modes.The effect of carbide precipitation was qualitatively discussed as not considering the primary cause of the formation of this arch-shaped distribution.The evolution of dislocation motion modes during yielding of low-temperature tempered martensite was elucidated by comparing the significant difference in cumulative energy values during yielding of annealed and low-temperature tempered specimens.Dislocations emit from Frank–Read or grain boundary sources and slip along short free paths,contributing to the initial increase in AE signals energy.Subsequently,the primary source of acoustic emission energy“arch-shaped”peak during yielding was generated by the avalanche behavior of accumulated dislocations,leading to the accelerated dislocation motion.展开更多
In this study,the effects of various surface treatments on the friction and wear behavior of AISI 4140 steel have been evaluated.Sample surfaces of AISI 4140 steel were treated by quenching,carburizing,boronizing and ...In this study,the effects of various surface treatments on the friction and wear behavior of AISI 4140 steel have been evaluated.Sample surfaces of AISI 4140 steel were treated by quenching,carburizing,boronizing and plasma transferred arc （PTA） modification.The microstructural characteristics of surface treated steel samples were examined by optical microscopy and scanning electron microscopy （SEM）.The mechanical properties of the samples including the surface roughness,microhardness,and abrasive and adhesive wear characteristics were also evaluated.Wear tests were applied by using a block-on-disc configuration under dry sliding conditions.The wear behavior and friction characteristics of the samples were determined as a function of sliding distance.Each sample group was compared with the other sample groups,and it was observed that the carburized samples demonstrated the lowest weight losses;however,PTA-treated samples demonstrated the lowest coefficient of friction in comparison to the other sample groups at the same sliding distance.展开更多
The effects of rod falling and moving, external flow field, boiling film and radiation were investigated on fluid flow and heat transfer of AISI 4140 steel horizontal rod during direct quenching by mathematical modeli...The effects of rod falling and moving, external flow field, boiling film and radiation were investigated on fluid flow and heat transfer of AISI 4140 steel horizontal rod during direct quenching by mathematical modeling. The flow field and heat transfer in quenching tank were simulated by computational fluid dynamics （CFD） method considering falling and moving of rods during process. Therefore, modeling of flow field was done by a fixed-mesh method for general moving objects equations, and then, energy equation was solved with a numerical approach so that effeet of boiling film heat flux was considered as a source term in energy equation for solid-liquid boundary. Simulated results were verified by comparing with published and experimental data and there was a good agreement between them. Also, the effects of external forced flow and film boiling were investigated on heat flux output, temperature distribution and heat transfer coefficient of rod. Also simulated results determined optimum quenching time for this process.展开更多
Inconel 718 with thickness ranged from 0. 1 - 1.7 mm was chosen as interlayer to promote weldability in friction welding of TiAl intermetallics and structural steel such as AIS14140, in which the welded joint presents...Inconel 718 with thickness ranged from 0. 1 - 1.7 mm was chosen as interlayer to promote weldability in friction welding of TiAl intermetallics and structural steel such as AIS14140, in which the welded joint presents single fin showing less welding deformation on TiAl side. The correlations between tensile strength and the interlayer thickness were analyzed and fitted to a model. It indicates an optimum interlayer thickness ranged from 0.9 - 1.1 mm where the tensile strength reaches as high as 360 MPa. Otherwise, while the interlayer thickness decreases to 0. 1 mm, brittle compounds of TiC, Al2Ti4C2 and MTC3 are formed in the welded zone so that the tensile strength decays. Thicker interlayer should be also avoided as double joints may occur at TiAl -lnconel 718 and lnconel 718 -AISI 4140, respectively, which lowers the tensile strength to some extent.展开更多
基金The authors acknowledge financial support from the National Natural Science Foundation of China(Grant Nos.51771114,51371117).
文摘The distinctive distribution of acoustic emission(AE)characteristic parameters generated during tensile testing of low-temperature tempered AISI 4140 steel was investigated.Two clusters of acoustic emission signals were distinguished using power-law distribution fitting and k-means clustering methods.These clusters were identified as resulting from dislocation motion during yielding and dislocation entanglement during uniform plastic deformation.The conclusion is further confirmed by transmission electron microscopy images at different strains.In particular,the unique"arch-shaped"distribution of the acoustic emission energy during yielding implies a change in unusual dislocation motion modes.The effect of carbide precipitation was qualitatively discussed as not considering the primary cause of the formation of this arch-shaped distribution.The evolution of dislocation motion modes during yielding of low-temperature tempered martensite was elucidated by comparing the significant difference in cumulative energy values during yielding of annealed and low-temperature tempered specimens.Dislocations emit from Frank–Read or grain boundary sources and slip along short free paths,contributing to the initial increase in AE signals energy.Subsequently,the primary source of acoustic emission energy“arch-shaped”peak during yielding was generated by the avalanche behavior of accumulated dislocations,leading to the accelerated dislocation motion.
基金supported by the Eskisehir Osmangazi University Research Council (No. 200315015)
文摘In this study,the effects of various surface treatments on the friction and wear behavior of AISI 4140 steel have been evaluated.Sample surfaces of AISI 4140 steel were treated by quenching,carburizing,boronizing and plasma transferred arc （PTA） modification.The microstructural characteristics of surface treated steel samples were examined by optical microscopy and scanning electron microscopy （SEM）.The mechanical properties of the samples including the surface roughness,microhardness,and abrasive and adhesive wear characteristics were also evaluated.Wear tests were applied by using a block-on-disc configuration under dry sliding conditions.The wear behavior and friction characteristics of the samples were determined as a function of sliding distance.Each sample group was compared with the other sample groups,and it was observed that the carburized samples demonstrated the lowest weight losses;however,PTA-treated samples demonstrated the lowest coefficient of friction in comparison to the other sample groups at the same sliding distance.
文摘The effects of rod falling and moving, external flow field, boiling film and radiation were investigated on fluid flow and heat transfer of AISI 4140 steel horizontal rod during direct quenching by mathematical modeling. The flow field and heat transfer in quenching tank were simulated by computational fluid dynamics （CFD） method considering falling and moving of rods during process. Therefore, modeling of flow field was done by a fixed-mesh method for general moving objects equations, and then, energy equation was solved with a numerical approach so that effeet of boiling film heat flux was considered as a source term in energy equation for solid-liquid boundary. Simulated results were verified by comparing with published and experimental data and there was a good agreement between them. Also, the effects of external forced flow and film boiling were investigated on heat flux output, temperature distribution and heat transfer coefficient of rod. Also simulated results determined optimum quenching time for this process.
文摘Inconel 718 with thickness ranged from 0. 1 - 1.7 mm was chosen as interlayer to promote weldability in friction welding of TiAl intermetallics and structural steel such as AIS14140, in which the welded joint presents single fin showing less welding deformation on TiAl side. The correlations between tensile strength and the interlayer thickness were analyzed and fitted to a model. It indicates an optimum interlayer thickness ranged from 0.9 - 1.1 mm where the tensile strength reaches as high as 360 MPa. Otherwise, while the interlayer thickness decreases to 0. 1 mm, brittle compounds of TiC, Al2Ti4C2 and MTC3 are formed in the welded zone so that the tensile strength decays. Thicker interlayer should be also avoided as double joints may occur at TiAl -lnconel 718 and lnconel 718 -AISI 4140, respectively, which lowers the tensile strength to some extent.
