Although the non-basal precipitates, those not parallel to the basal plane, are more effective to block basal slip in Mg-Al alloys, the crystallographic orientation relationship(OR) between these precipitates and the ...Although the non-basal precipitates, those not parallel to the basal plane, are more effective to block basal slip in Mg-Al alloys, the crystallographic orientation relationship(OR) between these precipitates and the α-Mg matrix has not been well established. In this work, the crystallography of the non-basal Mg_(17)Al_(12) precipitates in AZ80 alloy was systematically investigated by transmission electron microscopy(TEM). By tilting to a suitable electron beam direction, different kinds of non-basal precipitates were recognized in TEM, and the following four new ORs between the non-basal Mg_(17)Al_(12) precipitates and the matrix were revealed: ■, and ■.Furthermore, these ORs and their habit planes were explained using the edge-to-edge matching model. The findings in this work can provide some guidelines for designing the microstructure of Mg-Al alloys to enhance their precipitation hardening potential.展开更多
The morphology and distribution of VC precipitates in HSLA steel as well as the orientation relationship between VC precipitate and α-Fe were studied by transmission electron microscopy (TEM). The chemical composit...The morphology and distribution of VC precipitates in HSLA steel as well as the orientation relationship between VC precipitate and α-Fe were studied by transmission electron microscopy (TEM). The chemical composition of the VC precipitate was analyzed qualitatively by using analytical electron microscopy (AEM) equipped with an energy dispersive spectrum (EDS) system. The VC precipitate is needle-like in shape with a size of about 10 nm in length and is homogeneously dispersed in the α-Fe matrix. The smaller lattice misfit along the 〈100〉 lattice direction of α-Fe matrix leads to VC precipitate forming with its long axes nearly parallel to the 〈100〉 lattice direction of α-Fe matrix. It is confirmed that the orientation relationship between VC precipitate and α- Fe is the "N-W" orientation relation by selected area electron diffraction (SAED) patterns.展开更多
A Mn18Cr2 steel containing TiN precipitates was fabricated by vacuum induction melting.The morphology of TiN precipitates and the interface orientation relationship between TiN and γ-Fe were characterized by means of...A Mn18Cr2 steel containing TiN precipitates was fabricated by vacuum induction melting.The morphology of TiN precipitates and the interface orientation relationship between TiN and γ-Fe were characterized by means of SEM,TEM and SAED,and the formation mechanism of TiN precipitates in Mn18Cr2 steel was clarified.Results show that the TiN precipitates are more likely to exhibit a cubic-shaped morphology and form both within the grain and at the grain boundary of γ-Fe.The interface orientation relationship between TiN and γ-Fe is determined as follows:(100)_(TiN)//■_(γ-Fe),■_(TiN)//■_(γ-Fe).Because of the smallest interfacialmisfit,the secondary close-packed lane {100} of TiN preferentially combines with the close-packed plane {111} of γ-Fe during the precipitation in order to minimize the interface energy.After nucleation,the TiN precipitates exhibit cubic appearance due to the fact that the TiN has a FCC structure with rock salt type structure.This study provides reference for the material design of the austenitic high-manganese steels with excellent yield strength.展开更多
Electron Back Scattering Diffraction (EBSD) technique in a SEM was used to obtain local orientationalinformation on new grains and their surrounding deformed matrices at the early stages of recrystallization in pureA1...Electron Back Scattering Diffraction (EBSD) technique in a SEM was used to obtain local orientationalinformation on new grains and their surrounding deformed matrices at the early stages of recrystallization in pureA1-1 .3%Mn alloy. Results show that special orientation relationships including twin-relationship often exist betweennew grains, between new grains and deformed grains or between deformed grains. The occurrence of such specialorientation relationships is attributed to the special deformation behavior in the samples with large initial grain size.The formation of recrystallization twins is discussed in a different way to those of traditional ones.展开更多
Eutectic orientation relationships(EORs) in an undercooled Ni-38 wt.%Si alloy were analyzed by electron backscatter diffraction. A total of seven EORs were identified, and three of them were found at the under-cooling...Eutectic orientation relationships(EORs) in an undercooled Ni-38 wt.%Si alloy were analyzed by electron backscatter diffraction. A total of seven EORs were identified, and three of them were found at the under-cooling degree ?T≈31 K. It is found that their orientations of the primary NiSi phase are same but the misorientation between the neighboring NiSi2 grains can be either 50° or 60°. The multiple EORs were ascribed to a possible change in the growth direction of the primary phase, the change of the primary phase from the NiSi phase to the NiSi2 phase, and the transition from coupled to uncoupled eutectic growth. The current work shows that epitaxial growth of the second eutectic phase on the primary eutectic phase can obey either a single EOR or multiple EORs, which is a unique phenomenon.展开更多
The orientation relationships,carbon partitioning and strengthening mechanism of a novel ultrahigh strength steel were analyzed in depth during the complex process of heat treatment.The experimental results reveal tha...The orientation relationships,carbon partitioning and strengthening mechanism of a novel ultrahigh strength steel were analyzed in depth during the complex process of heat treatment.The experimental results reveal that the(011)α//()γ,[100]α//[011]γ orientation relationships can be drawn between martensite and retained austenite.The position and angle of martensite and retained austenite are shown more clearly from the stereographic projections.Moreover,the calculated results show that the carbon content near the austenite interface is the highest in the shorter carbon allocation time.With the further increase of time,its carbon content gradually decreases.Furthermore,a model of the relationship between yield strength and strengthening mechanism was established.It was proved that the main strengthening components contributing to the yield strength include Orowan strengthening,grain-size strengthening and dislocation hardening.The main strengthening mechanism of steel in this experiment is dislocation strengthening.展开更多
High entropy alloys are the focus of current research.An accurate description of their phase-transformation path,however,is a challenge when their phase constituent and transformation process are complex.In this study...High entropy alloys are the focus of current research.An accurate description of their phase-transformation path,however,is a challenge when their phase constituent and transformation process are complex.In this study,a FeCoNiSn x eutectic high entropy alloy(EHEA)system was investigated and a novel FeCoNiSn EHEA composed of BCC+HCP phases was reported.The transition from the hypoeutectic to the fully eutectic and then to the hypereutectic microstructure with the Sn addition was characterized by the electron backscatter diffraction(EBSD)technology,and the phase-transformation path was clari-fied by crystallographic orientation relationships.The studies reveal that the primary phase of FeCoNiSn x(x=0.2,0.4)is FCC structure,and a further Sn addition induces an obvious phase-transformation from FCC to BCC in both the primary phase and eutectic lamellar,which satisfies the Kurdjumov-Sachs(K-S)or Nishiyama-Wasserman(N-W)variant orientation relationship.The mechanical results confirm that the phase structure and microstructure transition caused by Sn addition do significantly improve the strength and hardness of FeCoNiSn x EHEAs,but have serious adverse effects on plasticity.This study would be of significance to understanding the phase-transformation process in HEAs and preparing the HEAs with aimed mechanical properties.展开更多
基金financially supported by the National Natural Science Foundation of China (Project No.51871036,52071040 and 51421001)the open funding of International Joint Laboratory for Light Alloys (MOE),Chongqing University。
文摘Although the non-basal precipitates, those not parallel to the basal plane, are more effective to block basal slip in Mg-Al alloys, the crystallographic orientation relationship(OR) between these precipitates and the α-Mg matrix has not been well established. In this work, the crystallography of the non-basal Mg_(17)Al_(12) precipitates in AZ80 alloy was systematically investigated by transmission electron microscopy(TEM). By tilting to a suitable electron beam direction, different kinds of non-basal precipitates were recognized in TEM, and the following four new ORs between the non-basal Mg_(17)Al_(12) precipitates and the matrix were revealed: ■, and ■.Furthermore, these ORs and their habit planes were explained using the edge-to-edge matching model. The findings in this work can provide some guidelines for designing the microstructure of Mg-Al alloys to enhance their precipitation hardening potential.
基金This work was financially supported by the National Natural Science Foundation of China (No.59971008).
文摘The morphology and distribution of VC precipitates in HSLA steel as well as the orientation relationship between VC precipitate and α-Fe were studied by transmission electron microscopy (TEM). The chemical composition of the VC precipitate was analyzed qualitatively by using analytical electron microscopy (AEM) equipped with an energy dispersive spectrum (EDS) system. The VC precipitate is needle-like in shape with a size of about 10 nm in length and is homogeneously dispersed in the α-Fe matrix. The smaller lattice misfit along the 〈100〉 lattice direction of α-Fe matrix leads to VC precipitate forming with its long axes nearly parallel to the 〈100〉 lattice direction of α-Fe matrix. It is confirmed that the orientation relationship between VC precipitate and α- Fe is the "N-W" orientation relation by selected area electron diffraction (SAED) patterns.
基金the financial support from the National Natural Science Foundation of China(Grant No.U1604251)the Major Scientific and Technological Project of Luoyang,China(Grant No.2001017A)。
文摘A Mn18Cr2 steel containing TiN precipitates was fabricated by vacuum induction melting.The morphology of TiN precipitates and the interface orientation relationship between TiN and γ-Fe were characterized by means of SEM,TEM and SAED,and the formation mechanism of TiN precipitates in Mn18Cr2 steel was clarified.Results show that the TiN precipitates are more likely to exhibit a cubic-shaped morphology and form both within the grain and at the grain boundary of γ-Fe.The interface orientation relationship between TiN and γ-Fe is determined as follows:(100)_(TiN)//■_(γ-Fe),■_(TiN)//■_(γ-Fe).Because of the smallest interfacialmisfit,the secondary close-packed lane {100} of TiN preferentially combines with the close-packed plane {111} of γ-Fe during the precipitation in order to minimize the interface energy.After nucleation,the TiN precipitates exhibit cubic appearance due to the fact that the TiN has a FCC structure with rock salt type structure.This study provides reference for the material design of the austenitic high-manganese steels with excellent yield strength.
文摘Electron Back Scattering Diffraction (EBSD) technique in a SEM was used to obtain local orientationalinformation on new grains and their surrounding deformed matrices at the early stages of recrystallization in pureA1-1 .3%Mn alloy. Results show that special orientation relationships including twin-relationship often exist betweennew grains, between new grains and deformed grains or between deformed grains. The occurrence of such specialorientation relationships is attributed to the special deformation behavior in the samples with large initial grain size.The formation of recrystallization twins is discussed in a different way to those of traditional ones.
基金Project(2018-JC007)supported by the Science Fund for Distinguished Young Scholars from Shaanxi Province,ChinaProject(3102017HQZZ008)supported by the Fundamental Research Funds for the Central Universit ies,China。
文摘Eutectic orientation relationships(EORs) in an undercooled Ni-38 wt.%Si alloy were analyzed by electron backscatter diffraction. A total of seven EORs were identified, and three of them were found at the under-cooling degree ?T≈31 K. It is found that their orientations of the primary NiSi phase are same but the misorientation between the neighboring NiSi2 grains can be either 50° or 60°. The multiple EORs were ascribed to a possible change in the growth direction of the primary phase, the change of the primary phase from the NiSi phase to the NiSi2 phase, and the transition from coupled to uncoupled eutectic growth. The current work shows that epitaxial growth of the second eutectic phase on the primary eutectic phase can obey either a single EOR or multiple EORs, which is a unique phenomenon.
基金Funded by the Key Research and Development(R&D)Projects of Shanxi Province(No.201803D121028)the Research Project Supported by Shanxi Scholarship Council of China(No.2021-122)+1 种基金the Fundamental Research Program of Shanxi Province(No.20210302123014)the Shanxi Province Science Foundation for Youths(No.201901D211266)。
文摘The orientation relationships,carbon partitioning and strengthening mechanism of a novel ultrahigh strength steel were analyzed in depth during the complex process of heat treatment.The experimental results reveal that the(011)α//()γ,[100]α//[011]γ orientation relationships can be drawn between martensite and retained austenite.The position and angle of martensite and retained austenite are shown more clearly from the stereographic projections.Moreover,the calculated results show that the carbon content near the austenite interface is the highest in the shorter carbon allocation time.With the further increase of time,its carbon content gradually decreases.Furthermore,a model of the relationship between yield strength and strengthening mechanism was established.It was proved that the main strengthening components contributing to the yield strength include Orowan strengthening,grain-size strengthening and dislocation hardening.The main strengthening mechanism of steel in this experiment is dislocation strengthening.
基金the Natural Science Foundation of China(No.51975474)the Fundamental Research Funds for the Central Universities(No.3102019JC001)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(No.CX201907).
文摘High entropy alloys are the focus of current research.An accurate description of their phase-transformation path,however,is a challenge when their phase constituent and transformation process are complex.In this study,a FeCoNiSn x eutectic high entropy alloy(EHEA)system was investigated and a novel FeCoNiSn EHEA composed of BCC+HCP phases was reported.The transition from the hypoeutectic to the fully eutectic and then to the hypereutectic microstructure with the Sn addition was characterized by the electron backscatter diffraction(EBSD)technology,and the phase-transformation path was clari-fied by crystallographic orientation relationships.The studies reveal that the primary phase of FeCoNiSn x(x=0.2,0.4)is FCC structure,and a further Sn addition induces an obvious phase-transformation from FCC to BCC in both the primary phase and eutectic lamellar,which satisfies the Kurdjumov-Sachs(K-S)or Nishiyama-Wasserman(N-W)variant orientation relationship.The mechanical results confirm that the phase structure and microstructure transition caused by Sn addition do significantly improve the strength and hardness of FeCoNiSn x EHEAs,but have serious adverse effects on plasticity.This study would be of significance to understanding the phase-transformation process in HEAs and preparing the HEAs with aimed mechanical properties.