系统研究了Al含量对铸态和挤压态Mg-2.5Sn-2Ca-x Al (x=2、4、9,质量分数,%)合金微观组织和力学性能的影响。结果表明,随着Al含量的升高,合金的强度有所降低,延伸率增加。Mg-2.5Sn-2Ca-2Al、Mg-2.5Sn-2Ca-4Al和Mg-2.5Sn-2Ca-9Al合金的...系统研究了Al含量对铸态和挤压态Mg-2.5Sn-2Ca-x Al (x=2、4、9,质量分数,%)合金微观组织和力学性能的影响。结果表明,随着Al含量的升高,合金的强度有所降低,延伸率增加。Mg-2.5Sn-2Ca-2Al、Mg-2.5Sn-2Ca-4Al和Mg-2.5Sn-2Ca-9Al合金的屈服强度分别约为370、325和290 MPa,延伸率分别约为6.2%、11.0%和12.0%。第四组元Al元素的加入改变了Mg-Sn-Ca合金中纳米尺寸第二相的类型和含量。Mg-2.5Sn-2Ca-2Al和Mg-2.5Sn-2Ca-9Al合金中分别形成高密度的G.P.区和Mg17Al12第二相,Mg-2.5Sn-2Ca-4Al合金中未见明显的纳米相析出。高密度的G.P.区阻碍再结晶晶粒长大的效率较Mg17Al12纳米相更为显著,因此Mg-2.5Sn-2Ca-2Al合金的再结晶晶粒更为细小(约0.5μm)。同时TEM观察表明,Mg-2.5Sn-2Ca-2Al合金的晶粒内部还存在较高密度的位错,且这些位错一般与G.P.区伴生,因而合金内部还保留有较高密度的亚晶片层组织(片层厚度0.2~1.0μm)。大量G.P.区以及残余位错的存在会成为新产生位错运动的障碍,这些均会对Mg-2.5Sn-2Ca-2Al合金高的屈服强度做出贡献,但同时也会损伤合金材料的塑性。在Mg-2.5Sn-2Ca-9Al合金中,由于高含量Al元素的存在以及Mg17Al12纳米相阻碍位错运动能力相对较弱,导致残余位错密度更低,所以Mg-2.5Sn-2Ca-9Al合金表现出了更大的晶粒尺寸、较低的屈服强度以及更高的塑性。展开更多
本论文使用球差校正的高角环形暗场扫描透射电镜(Aberration-Corrected High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy,HAADF-STEM)结合选区电子衍射(Selected Area Electron Diffraction,SAED)技术系统表...本论文使用球差校正的高角环形暗场扫描透射电镜(Aberration-Corrected High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy,HAADF-STEM)结合选区电子衍射(Selected Area Electron Diffraction,SAED)技术系统表征了Mg-19.6 wt.%Gd合金300℃等温时效100 h后的时效析出行为。研究结果表明,Mg-19.6 Gd合金时效后期析出的平衡相为β-Mg5Gd。β-Mg5Gd相为fcc结构(空间群:■;晶格参数:a=22.34?),呈透镜状。β-Mg5Gd相具有一个■的惯习面,它们沿■3个方向均匀分布。β-Mg5Gd相在β1-Mg3Gd中形核,并由内而外生长取代β1相。β相与β1,以及与α-Mg基体都是完全共格的,其与β1相、基体的取向关系为[110]β//[110]β1//[0001]α;■。展开更多
Microstructures of a duplex-phase Zr-2.5Nb alloy treated by pulsed laser were characterized by electron backscatter diffraction （EBSD） and electron channeling contrast （ECC） imaging techniques. Major attention has...Microstructures of a duplex-phase Zr-2.5Nb alloy treated by pulsed laser were characterized by electron backscatter diffraction （EBSD） and electron channeling contrast （ECC） imaging techniques. Major attention has been paid to non-equilibrium hybrid microstructure consisting of both prior a and β phases, and a plates transformed from new β phases to probe α→β transformation characteristics in the alloy. The origin of the hybrid microstructure is attributed to the specific thermodynamic conditions induced by the pulsed laser treatment. ECC observation shows that newly formed [3 phases during laser heating prefer to nucleate and grow at the expense of edges of prior α grains rather than their interiors. EBSD analyses further reveal that orientations of the new β phases are not determined by the prior a grains according to the Burgers relationship but maintain those of the prior β phases in an epitaxial growth way.展开更多
In this work,the role of Zn content in modifying the microstructure and mechanical properties of the Mg-1.2Ca-xZn(x=0.6,2.0 wt.%,named as XZ10-0 and ZX21-0,respectively)based alloys was studied,and it is found that th...In this work,the role of Zn content in modifying the microstructure and mechanical properties of the Mg-1.2Ca-xZn(x=0.6,2.0 wt.%,named as XZ10-0 and ZX21-0,respectively)based alloys was studied,and it is found that the yield strength(YS)of the present Mg-(Zn)-Ca based alloys increases monotonically with increasing the Zn concentration,from~339 MPa in low-Zn content XZ10-0 sample to~406 MPa in high-Zn content ZX21-0 sample.Microstructure characterization shows that the enhanced YS can be attributed to the grain refinement,fine and dispersed nano-phases,a large number of lamellae structures,and the decrease of recrystallization fraction.TEM results show that the formation mechanism for the ultra-fine grains in present Mg-(Zn)-Ca based alloys can be attributed to the co-segregation of Ca and Zn elements at the grain boundary,as well as the dynamic nanoprecipitations.When the Zn content is high,the nano-phases in ZX21-0 sample belong to the Ca;Mg;Zn;ternary phases,which exert much higher thermal stability than the nano-sized Mg2 Ca binary phases formed in the low-Zn content XZ10-0 sample.The finer size and higher number density of the nano-Mg Zn Ca phases lead to the much finer grain size and sub-grain lamellae thickness in ZX21-0 sample,which thus results in the higher YS of~406 MPa.展开更多
A duplex-phase Zr-2.5Nb alloy was treated by pulsed laser, followed by careful microstructural characterization using field emission gun scanning electron microscope and attached electron backscatter diffraction. Bene...A duplex-phase Zr-2.5Nb alloy was treated by pulsed laser, followed by careful microstructural characterization using field emission gun scanning electron microscope and attached electron backscatter diffraction. Beneath the modification zones with common uniform α-plate structures(UPS), a layer of unreported bimodal α-plate structures(BPS) featured by coarse(submicron)plates forming multiple cores surrounded by dense fine(nanoscale) plates was found. Presence of such BPS is attributed to non-equilibrium thermodynamic conditions induced by the pulsed laser treatments. Limited diffusion of Nb due to the short pulse during laser heating allows β phases with distinctly different Nb contents to be presented: Nb-enriched prior β films and Nb-depleted β phases, transforming into the fine and the coarse plates during cooling, respectively. Orientation analyses show that both types of plates in the BPS are aroused essentially from a single β orientation, suggesting epitaxial growth of the Nb-depletedβ phases from the preexisting β films.展开更多
文摘系统研究了Al含量对铸态和挤压态Mg-2.5Sn-2Ca-x Al (x=2、4、9,质量分数,%)合金微观组织和力学性能的影响。结果表明,随着Al含量的升高,合金的强度有所降低,延伸率增加。Mg-2.5Sn-2Ca-2Al、Mg-2.5Sn-2Ca-4Al和Mg-2.5Sn-2Ca-9Al合金的屈服强度分别约为370、325和290 MPa,延伸率分别约为6.2%、11.0%和12.0%。第四组元Al元素的加入改变了Mg-Sn-Ca合金中纳米尺寸第二相的类型和含量。Mg-2.5Sn-2Ca-2Al和Mg-2.5Sn-2Ca-9Al合金中分别形成高密度的G.P.区和Mg17Al12第二相,Mg-2.5Sn-2Ca-4Al合金中未见明显的纳米相析出。高密度的G.P.区阻碍再结晶晶粒长大的效率较Mg17Al12纳米相更为显著,因此Mg-2.5Sn-2Ca-2Al合金的再结晶晶粒更为细小(约0.5μm)。同时TEM观察表明,Mg-2.5Sn-2Ca-2Al合金的晶粒内部还存在较高密度的位错,且这些位错一般与G.P.区伴生,因而合金内部还保留有较高密度的亚晶片层组织(片层厚度0.2~1.0μm)。大量G.P.区以及残余位错的存在会成为新产生位错运动的障碍,这些均会对Mg-2.5Sn-2Ca-2Al合金高的屈服强度做出贡献,但同时也会损伤合金材料的塑性。在Mg-2.5Sn-2Ca-9Al合金中,由于高含量Al元素的存在以及Mg17Al12纳米相阻碍位错运动能力相对较弱,导致残余位错密度更低,所以Mg-2.5Sn-2Ca-9Al合金表现出了更大的晶粒尺寸、较低的屈服强度以及更高的塑性。
文摘本论文使用球差校正的高角环形暗场扫描透射电镜(Aberration-Corrected High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy,HAADF-STEM)结合选区电子衍射(Selected Area Electron Diffraction,SAED)技术系统表征了Mg-19.6 wt.%Gd合金300℃等温时效100 h后的时效析出行为。研究结果表明,Mg-19.6 Gd合金时效后期析出的平衡相为β-Mg5Gd。β-Mg5Gd相为fcc结构(空间群:■;晶格参数:a=22.34?),呈透镜状。β-Mg5Gd相具有一个■的惯习面,它们沿■3个方向均匀分布。β-Mg5Gd相在β1-Mg3Gd中形核,并由内而外生长取代β1相。β相与β1,以及与α-Mg基体都是完全共格的,其与β1相、基体的取向关系为[110]β//[110]β1//[0001]α;■。
基金supported by the National Natural Science Foundation of China(Grant No.51401040)China Postdoctoral Science Foundation(Grant No.2015M572446)+1 种基金Postdoctoral Science Foundation of Chongqing(Grant No.Xm2015003)Scientific and Technological ResearchProgram of Chongqing Municipal Education Commission(Grant No.KJ1500901)
文摘Microstructures of a duplex-phase Zr-2.5Nb alloy treated by pulsed laser were characterized by electron backscatter diffraction （EBSD） and electron channeling contrast （ECC） imaging techniques. Major attention has been paid to non-equilibrium hybrid microstructure consisting of both prior a and β phases, and a plates transformed from new β phases to probe α→β transformation characteristics in the alloy. The origin of the hybrid microstructure is attributed to the specific thermodynamic conditions induced by the pulsed laser treatment. ECC observation shows that newly formed [3 phases during laser heating prefer to nucleate and grow at the expense of edges of prior α grains rather than their interiors. EBSD analyses further reveal that orientations of the new β phases are not determined by the prior a grains according to the Burgers relationship but maintain those of the prior β phases in an epitaxial growth way.
基金supported by the National Natural Science Foundation of China(Grant Nos.51701211,and 51971053)the Project of Promoting Talents in Liaoning Province(Grant No.XLYC1808038)+2 种基金the financial assistance from Young Elite Scientists Sponsorship Program by CAST(Grant Nos.2019-2021QNRC001,and 2019-2021QNRC002)the Fundamental Research Funds for the Central Universities(Grant No.N2002011)the Joint Research Fund LiaoningShenyang National Laboratory for Materials Science(Grant No.2019JH3/30100040)。
文摘In this work,the role of Zn content in modifying the microstructure and mechanical properties of the Mg-1.2Ca-xZn(x=0.6,2.0 wt.%,named as XZ10-0 and ZX21-0,respectively)based alloys was studied,and it is found that the yield strength(YS)of the present Mg-(Zn)-Ca based alloys increases monotonically with increasing the Zn concentration,from~339 MPa in low-Zn content XZ10-0 sample to~406 MPa in high-Zn content ZX21-0 sample.Microstructure characterization shows that the enhanced YS can be attributed to the grain refinement,fine and dispersed nano-phases,a large number of lamellae structures,and the decrease of recrystallization fraction.TEM results show that the formation mechanism for the ultra-fine grains in present Mg-(Zn)-Ca based alloys can be attributed to the co-segregation of Ca and Zn elements at the grain boundary,as well as the dynamic nanoprecipitations.When the Zn content is high,the nano-phases in ZX21-0 sample belong to the Ca;Mg;Zn;ternary phases,which exert much higher thermal stability than the nano-sized Mg2 Ca binary phases formed in the low-Zn content XZ10-0 sample.The finer size and higher number density of the nano-Mg Zn Ca phases lead to the much finer grain size and sub-grain lamellae thickness in ZX21-0 sample,which thus results in the higher YS of~406 MPa.
基金supported by the National Natural Science Foundation of China(Grant Nos.51401040&51401039)the Scientific and Technological Research Program of Chongqing Municipal Education Commission(Grant No.KJ1500901)+1 种基金the Natural Science Foundation of Hebei Province of China(Grant No.E2015203250)the Young Teachers Program of Yanshan University(Grant No.14LGA005)
文摘A duplex-phase Zr-2.5Nb alloy was treated by pulsed laser, followed by careful microstructural characterization using field emission gun scanning electron microscope and attached electron backscatter diffraction. Beneath the modification zones with common uniform α-plate structures(UPS), a layer of unreported bimodal α-plate structures(BPS) featured by coarse(submicron)plates forming multiple cores surrounded by dense fine(nanoscale) plates was found. Presence of such BPS is attributed to non-equilibrium thermodynamic conditions induced by the pulsed laser treatments. Limited diffusion of Nb due to the short pulse during laser heating allows β phases with distinctly different Nb contents to be presented: Nb-enriched prior β films and Nb-depleted β phases, transforming into the fine and the coarse plates during cooling, respectively. Orientation analyses show that both types of plates in the BPS are aroused essentially from a single β orientation, suggesting epitaxial growth of the Nb-depletedβ phases from the preexisting β films.
