Tensile tests of TWIP steels of two compositions are performed in the strain rate range of 10^-5-10^3 s^-1. Results indicate that steel 1^# does not exhibit TWIP effect but deformation-induced martensitic transformati...Tensile tests of TWIP steels of two compositions are performed in the strain rate range of 10^-5-10^3 s^-1. Results indicate that steel 1^# does not exhibit TWIP effect but deformation-induced martensitic transformation appears only. There exists TWIP effect in steel 3^# . Tensile properties at room temperature are sensitive to strain rate in the studied strain rate ranges. Analysis on the relationship between strain-hardening exponent and strain rates shows that strain induced martensitic transformation and formation of twins during deformation have significant in- fluence on their strain-hardening behavior.展开更多
The recent studies on nanotwinned(NT)and hierarchical nanotwinned(HNT)face-centered cubic(FCC)metals are presented in this review.The HNT structures have been supposed as a kind of novel structure to bring about highe...The recent studies on nanotwinned(NT)and hierarchical nanotwinned(HNT)face-centered cubic(FCC)metals are presented in this review.The HNT structures have been supposed as a kind of novel structure to bring about higher strength/ductility than NT counterparts in crystalline materials.We primarily focus on the recent developments of the experimental,atomistic and theoretical studies on the NT and HNT structures in the metallic materials.Some advanced bottom-up and top-down techniques for the fabrication of NT and HNT structures are introduced.The deformation induced HNT structures are available by virtue of severe plastic deformation(SPD)based techniques while the synthesis of growth HNT structures is so far almost unavailable.In addition,some representative molecular dynamics(MD)studies on the NT and HNT FCC metals unveil that the nanoscale effects such as twin spacing,grain size and plastic anisotropy greatly alter the performance of NT and HNT metals.The HNT structures may initiate unique phenomena in comparison with the NT ones.Furthermore,based on the phenomena and mechanisms revealed by experimental and MD simulation observations,a series of theoretical models have been proposed.They are effective to describe the mechanical behaviors of NT and HNT metals within the applicable scope.So far the development of manufacturing technologies of HNT structures,as well as the studies on the effects of HNT structures on the properties of metals are still in its infancy.Further exploration is required to promote the design of advanced materials.展开更多
The mechanical properties of the TWIP steel subjected to impact loading at various strain rates were analyzed by the split Hopkinson pressure bar. Meanwhile the microstructure of the TWIP steel fore-and-aft dynamic de...The mechanical properties of the TWIP steel subjected to impact loading at various strain rates were analyzed by the split Hopkinson pressure bar. Meanwhile the microstructure of the TWIP steel fore-and-aft dynamic deformation was oberseved and analyzed by optical microscope （OM）, X-ray diffraction （XRD）, and transmission electron microscope （TEM）. The results show that when the TWIP steel was deformed under dynamic condition, the stress, microhardness and work hardening rate increase with the increase of strain and strain rate; there is decline of work hardening rate for adiabatic temperature rising softening. There are many pin-like deformation twins in the microstructure of the TWIP steel subjected to impact loading, and the grain size after deformation is bigger than that before; the interaction of twins with dislocation and twins with twins, especially emergence of multiple deformation twins are the main strengthening mechanisms of the TWIP steel. The nucleation mechanism of deformation twins will be ＂rebound mechanism＂;the incomplete deformation twins can be observed when the strain rate is low; when strain rate increases, deformation twins unite together;and deformation twins become denser because the nucleation rate increases with increasing the strain rate.展开更多
Although the development of titanium alloys with working temperatures above 600?C faces enormous difficulties and challenges,the related research has not stopped.In the present work,detailed analyses on microstructure...Although the development of titanium alloys with working temperatures above 600?C faces enormous difficulties and challenges,the related research has not stopped.In the present work,detailed analyses on microstructure evolution and hot deformation behavior of a new temperature resistant 650?C titanium alloy Ti65 were investigated from micrometer scale to nanometer scale.The results revealed that lamellarαgrains gradually fragmentized and spheroidized during theα+βphase region compression and the orientation of the c-axis ofαgrains gradually aligned to radial directions,forming two high Schmid factors(SFs)value texture eventually with the increase of strain to 0.7.Moreover,there were some strengthening characters in theα+βphase region such as lenticularαsand nano silicide(TiZr)6 Si3.In theβphase region,fine equiaxed dynamic recrystallized(DRX)βgrains were formed.Besides,the variant selection ofαm′artensite followed Burgers orientation relationship during the compression process.The main deformation mechanisms of theα+βphase region were dislocation slip and orientation dependent spheroidization.Whereas,the deformation process in theβphase region was controlled byβgrain DRX.Interestingly,many nano scale FCC twins were generated at the interface ofαl′ath during deforming in theβphase region,which was firstly observed in Ti65 alloy.展开更多
基金Item Sponsored by National Natural Science Foundation of China (50671061)
文摘Tensile tests of TWIP steels of two compositions are performed in the strain rate range of 10^-5-10^3 s^-1. Results indicate that steel 1^# does not exhibit TWIP effect but deformation-induced martensitic transformation appears only. There exists TWIP effect in steel 3^# . Tensile properties at room temperature are sensitive to strain rate in the studied strain rate ranges. Analysis on the relationship between strain-hardening exponent and strain rates shows that strain induced martensitic transformation and formation of twins during deformation have significant in- fluence on their strain-hardening behavior.
基金J.L.acknowledges the supports from the National Key R&D Program of China(Project No.2017YFA0204403)Research Grants Council of the Hong Kong Special Administrative Region(Grant No.CityU-11247516)+3 种基金the Hong Kong Collaborative Research Fund(CRF)Scheme(C4028-14G)Guangdong Science and Technology Department(Ref:2014B050504003)SZSTI(Ref:ZDSYS201602291653165)X.H.is grateful for the support from the Research Grants Council of the Hong Kong Special Administrative Region(Grant No.CityU-11204414).
文摘The recent studies on nanotwinned(NT)and hierarchical nanotwinned(HNT)face-centered cubic(FCC)metals are presented in this review.The HNT structures have been supposed as a kind of novel structure to bring about higher strength/ductility than NT counterparts in crystalline materials.We primarily focus on the recent developments of the experimental,atomistic and theoretical studies on the NT and HNT structures in the metallic materials.Some advanced bottom-up and top-down techniques for the fabrication of NT and HNT structures are introduced.The deformation induced HNT structures are available by virtue of severe plastic deformation(SPD)based techniques while the synthesis of growth HNT structures is so far almost unavailable.In addition,some representative molecular dynamics(MD)studies on the NT and HNT FCC metals unveil that the nanoscale effects such as twin spacing,grain size and plastic anisotropy greatly alter the performance of NT and HNT metals.The HNT structures may initiate unique phenomena in comparison with the NT ones.Furthermore,based on the phenomena and mechanisms revealed by experimental and MD simulation observations,a series of theoretical models have been proposed.They are effective to describe the mechanical behaviors of NT and HNT metals within the applicable scope.So far the development of manufacturing technologies of HNT structures,as well as the studies on the effects of HNT structures on the properties of metals are still in its infancy.Further exploration is required to promote the design of advanced materials.
基金Item Sponsored by Scientific Research Plan of Shanxi Province of China(20090321072)
文摘The mechanical properties of the TWIP steel subjected to impact loading at various strain rates were analyzed by the split Hopkinson pressure bar. Meanwhile the microstructure of the TWIP steel fore-and-aft dynamic deformation was oberseved and analyzed by optical microscope （OM）, X-ray diffraction （XRD）, and transmission electron microscope （TEM）. The results show that when the TWIP steel was deformed under dynamic condition, the stress, microhardness and work hardening rate increase with the increase of strain and strain rate; there is decline of work hardening rate for adiabatic temperature rising softening. There are many pin-like deformation twins in the microstructure of the TWIP steel subjected to impact loading, and the grain size after deformation is bigger than that before; the interaction of twins with dislocation and twins with twins, especially emergence of multiple deformation twins are the main strengthening mechanisms of the TWIP steel. The nucleation mechanism of deformation twins will be ＂rebound mechanism＂;the incomplete deformation twins can be observed when the strain rate is low; when strain rate increases, deformation twins unite together;and deformation twins become denser because the nucleation rate increases with increasing the strain rate.
基金the Major State Research Development Program of China(No.2016YFB0701305)the National Natural Science Foundation of China(No.51801156)the Natural Science Basic Research Plan in Shaanxi Province of China(Nos.2018JQ5035 and 2019JM-584)for the financial support.
文摘Although the development of titanium alloys with working temperatures above 600?C faces enormous difficulties and challenges,the related research has not stopped.In the present work,detailed analyses on microstructure evolution and hot deformation behavior of a new temperature resistant 650?C titanium alloy Ti65 were investigated from micrometer scale to nanometer scale.The results revealed that lamellarαgrains gradually fragmentized and spheroidized during theα+βphase region compression and the orientation of the c-axis ofαgrains gradually aligned to radial directions,forming two high Schmid factors(SFs)value texture eventually with the increase of strain to 0.7.Moreover,there were some strengthening characters in theα+βphase region such as lenticularαsand nano silicide(TiZr)6 Si3.In theβphase region,fine equiaxed dynamic recrystallized(DRX)βgrains were formed.Besides,the variant selection ofαm′artensite followed Burgers orientation relationship during the compression process.The main deformation mechanisms of theα+βphase region were dislocation slip and orientation dependent spheroidization.Whereas,the deformation process in theβphase region was controlled byβgrain DRX.Interestingly,many nano scale FCC twins were generated at the interface ofαl′ath during deforming in theβphase region,which was firstly observed in Ti65 alloy.
