The angular deviations and influential factors of Burgers orientation relationship(BOR)in Ti-6Al-4V and Ti-6.5Al-2Zr-1Mo-1V alloys were investigated by optical microscope(OM),scanning electron microscope(SEM),electron...The angular deviations and influential factors of Burgers orientation relationship(BOR)in Ti-6Al-4V and Ti-6.5Al-2Zr-1Mo-1V alloys were investigated by optical microscope(OM),scanning electron microscope(SEM),electron backscattered diffraction(EBSD)and high-angle annular dark-field scanning transmission electron microscope(HAADF-STEM).A spherical center angle model was introduced to calculate the angular deviations from the ideal BOR between α and β phases.The results indicate thatαand β phases in α colonies of both alloys do not follow the perfect BOR during β→α phase transformation,with angular deviation values less than 3°.Through detailed microstructure characterization,the broad face of α/β interfaces viewed along two different electron incident directions shows the atomic-scale terrace-ledge structure,and many dislocations are observed within α and β phases and near α/β interfaces.Further studies reveal that the angular deviations mainly originate from lattice distortions caused by dislocations in α and β phases and lattice mismatches at α/β interfaces.展开更多
Titanium aluminide(TiAl)alloys,known for their light weight and high specific strength,hold promising potential for aerospace applications.Recent studies have focused on improving their properties through composite st...Titanium aluminide(TiAl)alloys,known for their light weight and high specific strength,hold promising potential for aerospace applications.Recent studies have focused on improving their properties through composite strengthening.An in situ synthesized Ti_(5)Si_(3)-reinforced TiAl composite with excellent performance was successfully fabricated via a dual-wire electron beam-directed energy deposition(EB-DED)process.The microstructure of the as-deposited Ti_(5)Si_(3)/TiAl composite consisted of primary Ti_(5)Si_(3)rods,eutectic Ti_(5)Si_(3)needles,and lamellar TiAl+Ti_(3)Al structures.The phase transformation during the EB-DED process was L→Ti_(5)Si_(3)+L→Ti_(5)Si_(3)+(α+Ti_(5)Si_(3))Eutectic→Ti_(5)Si_(3)+(Ti3Al+TiAl)Eutectoid.The expanded Blackburn orientation relationships among the ternary phases emerged from the eutectic reaction of L→α+Ti_(5)Si_(3)with an undercooling exceeding 136°C and the subsequent eutectoid reaction with ordering transformation and were expressed as<1120>TisAl//<10I0>Ti_(5)Si_(3)//<110]Ti_(3)Al and{0001}TiзA//{0001}Ti_(5)Si_(3)//{111}TiAl.The Ti_(5)Si_(3)phase had a greater hardness than did the lamellar structures and enhanced the mechanical properties of the matrix.The compressive yield strengths at room temperature and 750°C were 1221±51 and 1034±34 MPa,respectively,whereas the tensile yield strength was 347.4±12.7 MPa at 950°C,surpassing those of other TiAl alloys.The calculated strength with different strengthening mechanisms was 1056.4 MPa,and the greatest improvement in strength was attributed to the decreased interlamellar spacing.This work provides critical insight into the design of TiAl composites with superior mechanical properties and aids in understanding the microstructural evolution of as-deposited Ti_(5)Si_(3)/TiAl composites.展开更多
The crystallographic features of pearlite were investigated by experiments and edge-to-edge matching principle. Two new orientation relationships between ferrite and cementite were determinated by selected area electr...The crystallographic features of pearlite were investigated by experiments and edge-to-edge matching principle. Two new orientation relationships between ferrite and cementite were determinated by selected area electron diffraction and then explained by our modified edge-to-edge matching method. The consistence of the experimental results with theoretical prediction confirms the practicability of the modified edge-to-edge matching model.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
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
Martensite is one of the most important structures determining the ability to tailor the performance of steel and several other engineering materials.In previous studies,the face-centered cubic(FCC)to hexag-onal close...Martensite is one of the most important structures determining the ability to tailor the performance of steel and several other engineering materials.In previous studies,the face-centered cubic(FCC)to hexag-onal close-packed(HCP)(or body-centered cubic(BCC))martensitic transformation and the FCC to body-centered tetragonal(BCT)(or BCC)martensitic transformation during deformation and quenching were widely investigated;these transformations usually improve the plasticity and strength of steel,respec-tively.In this work,detailed transmission electron microscopy(TEM)observations and electron diffraction pattern analyses of the BCT and BCC twins are performed along the[110],[131],and[¯153]zone axes.The transformation of BCT twins into BCC twins along the[131]zone axis is also analyzed through in situ heating during the TEM observations.The high-resolution TEM observations of mutually perpendicular BCT variants are consistent with the atomic arrangement obtained for the quenching pathway during the martensitic transformation.In addition,different orientation relationships between austenite and marten-site are explained in terms of the atomic migration occurring during the deformation pathway and the quenching pathway of the martensitic transformation.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
In situ observation of electron backscattering diffraction technique was used to evaluate the orientation relationships between austenite and α′-martensite（α′-M） for high manganese transformation-induced plastic...In situ observation of electron backscattering diffraction technique was used to evaluate the orientation relationships between austenite and α′-martensite（α′-M） for high manganese transformation-induced plasticity steel.It was noted that different from the thermal martensite,which well obeyed K-S relationship with austenite,the orientation relationship between deformation-induced α′-M with austenite changed during deformation,namely K-S and N-W relations coexisted.No clear differences existed between α′-M variants with two kinds of relationships in terms of martensitic orientation,shape and the misorientation between α′-M variants.And this phenomenon happened in almost all austenitic grains with different orientations investigated in this study.An atom displacement mechanism through conjugate complex slips of partial dislocations in the distorted fcc lattice was applied in this article to interpret the coexistence of K-S and N-W relationships.展开更多
The origin of the misorientations after fcc(face-centered cubic)to hcp(hexagonal close-packed)transformation in pure cobalt was elucidated by utilizing the electron backscatter diffraction(EBSD)technique and transform...The origin of the misorientations after fcc(face-centered cubic)to hcp(hexagonal close-packed)transformation in pure cobalt was elucidated by utilizing the electron backscatter diffraction(EBSD)technique and transformation crystallographic models.It is found the Shoji−Nishiyama orientation relationship during fcc→hcp transformation leads to four hcp variants,characterized by a common misorientation angle of 70.5°with respect to the<1120>direction,which is the predominant misorientation observed.Other statistically significant misorientation angles between hcp grains,including 32°,36°,38°,60°,71°and 86°−91°,are also identified.These newly observed misorientation angles are linked to the microstructure of the fcc matrix at elevated temperatures,with twin structures in the fcc matrix being the primary cause.Furthermore,a novel method is proposed for estimating the fraction of twins in the fcc grains based on misorientation angles between hcp variants,which is found to be consistent with experimental observations.In-situ EBSD observations validate the possible origin of fcc twins from the hcp→fcc transformation.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
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
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
The orientation relationships（ORs）between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied s...The orientation relationships（ORs）between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction（SAED）as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_（bcc）.A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.展开更多
To obtain high-quality aviation forgings of titanium alloys, b forging is an essential processing step which must be considered throughout a production process. In this work, the effect of b forging on the crystal ori...To obtain high-quality aviation forgings of titanium alloys, b forging is an essential processing step which must be considered throughout a production process. In this work, the effect of b forging on the crystal orientation and morphology of lamellar a was experimentally investigated in a two-phase titanium alloy. Strong dynamic recovery during b working resulted in the formation of low-angle grain boundary(LAGBb) inside b grains. The lamellar a can penetrate through the LAGBb, leading to similar intra a LAGBs on subgrain boundaries. Deformation banding occurs at high strain rates, and both diffusive and sharp boundaries of deformation bands can be observed.A continuous change of the b orientation in diffusive boundaries results in the formation of fine and disordered a lamellae without intra-lamellar boundary to hold the Burgers orientation relationship(OR). On sharp boundaries, it is prone to producing continuous grain boundary a(aGB) with a highly similar orientation along the boundaries. Meanwhile, there may exist several lower-angle boundaries within the grain boundary a for a smoother orientation change on the b grain boundary.展开更多
Strain-induced martensites in high manganese TRIP/TWIP steels were investigated in the presence of thermal martensites and under the influence of austenitic grain orientation by X-ray diffraction （XRD）, scanning ele...Strain-induced martensites in high manganese TRIP/TWIP steels were investigated in the presence of thermal martensites and under the influence of austenitic grain orientation by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electron backscattered diffraction （EBSD）. Before deformation, the morphology of α＇- M depended mainly on the number of variants and growing period. Regardless of martensite morphologies and deformation, the Kurdjumov-Sachs （K-S） orientation relationships always maintained. The 6 α＇-M variants formed from a plate of ε-M were of 3 pairs of twins with a common axis 〈110〉α＇ parallel to the normal of {112}γ habit plane to minimize transformation strain. When α＇-M could be formed only by deformation, it nucleated at the intersection of ε-M variants and grew mainly in thick ε-M plates. Thick ε plates promoted significantly the α＇-M and weakened the influence of grain orientations. During tension, the transformation in 〈100〉-oriented grains was observed to be slower than that in 〈121〉-oriented grains. Deformation twins promoted ε-M formation slightly and had no apparent effect on α＇-M. Deformation increased the number of ε-M variants, but reduced that of α＇-M variants.展开更多
The present studies are aimed at understanding the effect of cooling rate and prior strain on the evolution of morphology,orientation relationship (OR) and variant selection in pipeline steel with 0.09wt% niobium.In i...The present studies are aimed at understanding the effect of cooling rate and prior strain on the evolution of morphology,orientation relationship (OR) and variant selection in pipeline steel with 0.09wt% niobium.In identical prior austenite grain,all products include granular bainite(GB) by coherent transformation,keep orientation relationship (OR) with parent austenite.Fast cooling and large deformation below T nr both can raise drive force of coherent transformation and weaken variants selection,and it can generate higher frequency of high angle boundaries (HABs) (≥15degree).Moreover,large deformation by few passes below T nr can accelerate nucleation of ferrite grains at the austenite boundary by incoherent transformation.These fine grains haven’t OR with prior austenite grain in any side of boundary,and exhibit significant misorientations between themselves.展开更多
Directionally solidified dual-phase Al_(2)O_(3)/Y_(3)Al_(5)O_(12)(YAG)eutectic ceramics(DSECs)typically exhibit strong anisotropy.To improve their properties,various single-phase sapphire seeds,including r-axis[1-102]...Directionally solidified dual-phase Al_(2)O_(3)/Y_(3)Al_(5)O_(12)(YAG)eutectic ceramics(DSECs)typically exhibit strong anisotropy.To improve their properties,various single-phase sapphire seeds,including r-axis[1-102],m-axis[10-10],c-axis[0001],and a-axis[11-20],were used as seeds to induce the orientation of the Al_(2)O_(3)/YAG DSECs.The results showed that Al_(2)O_(3) in the eutectics could be governed by the sapphire seeds.The YAG in each induced eutectic had a specific growth direction endowed by Al_(2)O_(3) in the asinduced eutectics or the sapphire seed.Herein,we calculated the planar lattice misfits and interfacial strain energies of four crystallographic orientation relationships based on the constructed lattice models.It was elucidated the constraint of the sapphire seed caused YAG to grow following the rule of mini-mizing the interfacial strain energy.This revealed the reason why Al_(2)O_(3)/YAG DSECs orientation can be successfully induced.These results may provide a novel method for the design of high-performance eu-tectic ceramic materials.展开更多
The electrochemical hydrogen charging of pure titanium and its alloys has been investigated previously,while how a subsequent annealing treatment aff ects the type of hydride and its orientation relationship with matr...The electrochemical hydrogen charging of pure titanium and its alloys has been investigated previously,while how a subsequent annealing treatment aff ects the type of hydride and its orientation relationship with matrix is not clear.In the present study,a quantitative study on the microstructure and orientation of titanium hydrides during electrochemical hydrogen charging and subsequent annealing treatment was carried out using scanning electron microscopy,transmission electron microscopy and electron backscatter diff raction.The results show thatδ-hydride is the main in both the electrochemically hydrogenated sample and the subsequent annealing treated sample.After electrochemical hydrogen charging for 48 h,the surface is mainly composed of denseδ-hydride with a thickness of approximately 42μm,the orientation relationship betweenα-matrix andδ-hydride follows only the orientation relationship of OR2,{0001}_(α)//{111}_(δ),<1210>_(α)//<110>_(δ) and an interface plane{1013}_(a)//{110}_(δ).Besides OR2,a part of hydrides show an orientation relationship of OR1 with the matrix after annealing,{0001}a//{001}_(δ),<1210>_(a)//{110}_(δ) and an interface plane of {1010}_(δ)//{110}_(δ).It is further found that the relative frequency of OR1and OR2 is closely related to annealing duration.Under an argon atmosphere at 450℃,the frequencies of OR1 and OR2 are nearly balance with an annealing time of 12 h,while OR1 becomes to be the predominant one with a relative frequency of 96.5%after annealing for 96 h.The mechanism for the evolution of orientation relationship of hydrides with annealing time was discussed.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51971009,12002013,51831006)the Natural Science Foundation of Zhejiang Province,China(No.LZ23E010004).
文摘The angular deviations and influential factors of Burgers orientation relationship(BOR)in Ti-6Al-4V and Ti-6.5Al-2Zr-1Mo-1V alloys were investigated by optical microscope(OM),scanning electron microscope(SEM),electron backscattered diffraction(EBSD)and high-angle annular dark-field scanning transmission electron microscope(HAADF-STEM).A spherical center angle model was introduced to calculate the angular deviations from the ideal BOR between α and β phases.The results indicate thatαand β phases in α colonies of both alloys do not follow the perfect BOR during β→α phase transformation,with angular deviation values less than 3°.Through detailed microstructure characterization,the broad face of α/β interfaces viewed along two different electron incident directions shows the atomic-scale terrace-ledge structure,and many dislocations are observed within α and β phases and near α/β interfaces.Further studies reveal that the angular deviations mainly originate from lattice distortions caused by dislocations in α and β phases and lattice mismatches at α/β interfaces.
基金financially supported by the National Natural Science Foundation of China(No.52301050)the Young Elite Scientists Sponsorship Program by the China Association for Science and Technology(No.2022QNRC001)the China Postdoctoral Science Foundation(No.2023M741701).
文摘Titanium aluminide(TiAl)alloys,known for their light weight and high specific strength,hold promising potential for aerospace applications.Recent studies have focused on improving their properties through composite strengthening.An in situ synthesized Ti_(5)Si_(3)-reinforced TiAl composite with excellent performance was successfully fabricated via a dual-wire electron beam-directed energy deposition(EB-DED)process.The microstructure of the as-deposited Ti_(5)Si_(3)/TiAl composite consisted of primary Ti_(5)Si_(3)rods,eutectic Ti_(5)Si_(3)needles,and lamellar TiAl+Ti_(3)Al structures.The phase transformation during the EB-DED process was L→Ti_(5)Si_(3)+L→Ti_(5)Si_(3)+(α+Ti_(5)Si_(3))Eutectic→Ti_(5)Si_(3)+(Ti3Al+TiAl)Eutectoid.The expanded Blackburn orientation relationships among the ternary phases emerged from the eutectic reaction of L→α+Ti_(5)Si_(3)with an undercooling exceeding 136°C and the subsequent eutectoid reaction with ordering transformation and were expressed as<1120>TisAl//<10I0>Ti_(5)Si_(3)//<110]Ti_(3)Al and{0001}TiзA//{0001}Ti_(5)Si_(3)//{111}TiAl.The Ti_(5)Si_(3)phase had a greater hardness than did the lamellar structures and enhanced the mechanical properties of the matrix.The compressive yield strengths at room temperature and 750°C were 1221±51 and 1034±34 MPa,respectively,whereas the tensile yield strength was 347.4±12.7 MPa at 950°C,surpassing those of other TiAl alloys.The calculated strength with different strengthening mechanisms was 1056.4 MPa,and the greatest improvement in strength was attributed to the decreased interlamellar spacing.This work provides critical insight into the design of TiAl composites with superior mechanical properties and aids in understanding the microstructural evolution of as-deposited Ti_(5)Si_(3)/TiAl composites.
基金supported by the National Natural Science Foundation of China (Grant Nos.51001069 and 51031001)
文摘The crystallographic features of pearlite were investigated by experiments and edge-to-edge matching principle. Two new orientation relationships between ferrite and cementite were determinated by selected area electron diffraction and then explained by our modified edge-to-edge matching method. The consistence of the experimental results with theoretical prediction confirms the practicability of the modified edge-to-edge matching model.
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 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.
基金supported by the National Natural Science Foundation of China(Grant Nos.51931005 and 51901235).
文摘Martensite is one of the most important structures determining the ability to tailor the performance of steel and several other engineering materials.In previous studies,the face-centered cubic(FCC)to hexag-onal close-packed(HCP)(or body-centered cubic(BCC))martensitic transformation and the FCC to body-centered tetragonal(BCT)(or BCC)martensitic transformation during deformation and quenching were widely investigated;these transformations usually improve the plasticity and strength of steel,respec-tively.In this work,detailed transmission electron microscopy(TEM)observations and electron diffraction pattern analyses of the BCT and BCC twins are performed along the[110],[131],and[¯153]zone axes.The transformation of BCT twins into BCC twins along the[131]zone axis is also analyzed through in situ heating during the TEM observations.The high-resolution TEM observations of mutually perpendicular BCT variants are consistent with the atomic arrangement obtained for the quenching pathway during the martensitic transformation.In addition,different orientation relationships between austenite and marten-site are explained in terms of the atomic migration occurring during the deformation pathway and the quenching pathway of the martensitic transformation.
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.
基金financially supported by the National Natural Science Foundation of China(No.51271028)
文摘In situ observation of electron backscattering diffraction technique was used to evaluate the orientation relationships between austenite and α′-martensite（α′-M） for high manganese transformation-induced plasticity steel.It was noted that different from the thermal martensite,which well obeyed K-S relationship with austenite,the orientation relationship between deformation-induced α′-M with austenite changed during deformation,namely K-S and N-W relations coexisted.No clear differences existed between α′-M variants with two kinds of relationships in terms of martensitic orientation,shape and the misorientation between α′-M variants.And this phenomenon happened in almost all austenitic grains with different orientations investigated in this study.An atom displacement mechanism through conjugate complex slips of partial dislocations in the distorted fcc lattice was applied in this article to interpret the coexistence of K-S and N-W relationships.
基金supported by the National Key R&D Program of China(No.2022YFB3504403).
文摘The origin of the misorientations after fcc(face-centered cubic)to hcp(hexagonal close-packed)transformation in pure cobalt was elucidated by utilizing the electron backscatter diffraction(EBSD)technique and transformation crystallographic models.It is found the Shoji−Nishiyama orientation relationship during fcc→hcp transformation leads to four hcp variants,characterized by a common misorientation angle of 70.5°with respect to the<1120>direction,which is the predominant misorientation observed.Other statistically significant misorientation angles between hcp grains,including 32°,36°,38°,60°,71°and 86°−91°,are also identified.These newly observed misorientation angles are linked to the microstructure of the fcc matrix at elevated temperatures,with twin structures in the fcc matrix being the primary cause.Furthermore,a novel method is proposed for estimating the fraction of twins in the fcc grains based on misorientation angles between hcp variants,which is found to be consistent with experimental observations.In-situ EBSD observations validate the possible origin of fcc twins from the hcp→fcc transformation.
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financially supported by the National Natural Science Foundation of China (Nos. 51301106 and 51471110)
文摘The orientation relationships（ORs）between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction（SAED）as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_（bcc）.A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.
基金the support of the National Natural Science Foundation of China(No.51575449)
文摘To obtain high-quality aviation forgings of titanium alloys, b forging is an essential processing step which must be considered throughout a production process. In this work, the effect of b forging on the crystal orientation and morphology of lamellar a was experimentally investigated in a two-phase titanium alloy. Strong dynamic recovery during b working resulted in the formation of low-angle grain boundary(LAGBb) inside b grains. The lamellar a can penetrate through the LAGBb, leading to similar intra a LAGBs on subgrain boundaries. Deformation banding occurs at high strain rates, and both diffusive and sharp boundaries of deformation bands can be observed.A continuous change of the b orientation in diffusive boundaries results in the formation of fine and disordered a lamellae without intra-lamellar boundary to hold the Burgers orientation relationship(OR). On sharp boundaries, it is prone to producing continuous grain boundary a(aGB) with a highly similar orientation along the boundaries. Meanwhile, there may exist several lower-angle boundaries within the grain boundary a for a smoother orientation change on the b grain boundary.
基金funded by the National Natural Science Foundation of China (No. 50771019)Specialized Research Fund for the Doctoral Program of Higher Education (No. 20090006110013)
文摘Strain-induced martensites in high manganese TRIP/TWIP steels were investigated in the presence of thermal martensites and under the influence of austenitic grain orientation by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electron backscattered diffraction （EBSD）. Before deformation, the morphology of α＇- M depended mainly on the number of variants and growing period. Regardless of martensite morphologies and deformation, the Kurdjumov-Sachs （K-S） orientation relationships always maintained. The 6 α＇-M variants formed from a plate of ε-M were of 3 pairs of twins with a common axis 〈110〉α＇ parallel to the normal of {112}γ habit plane to minimize transformation strain. When α＇-M could be formed only by deformation, it nucleated at the intersection of ε-M variants and grew mainly in thick ε-M plates. Thick ε plates promoted significantly the α＇-M and weakened the influence of grain orientations. During tension, the transformation in 〈100〉-oriented grains was observed to be slower than that in 〈121〉-oriented grains. Deformation twins promoted ε-M formation slightly and had no apparent effect on α＇-M. Deformation increased the number of ε-M variants, but reduced that of α＇-M variants.
文摘The present studies are aimed at understanding the effect of cooling rate and prior strain on the evolution of morphology,orientation relationship (OR) and variant selection in pipeline steel with 0.09wt% niobium.In identical prior austenite grain,all products include granular bainite(GB) by coherent transformation,keep orientation relationship (OR) with parent austenite.Fast cooling and large deformation below T nr both can raise drive force of coherent transformation and weaken variants selection,and it can generate higher frequency of high angle boundaries (HABs) (≥15degree).Moreover,large deformation by few passes below T nr can accelerate nucleation of ferrite grains at the austenite boundary by incoherent transformation.These fine grains haven’t OR with prior austenite grain in any side of boundary,and exhibit significant misorientations between themselves.
基金financially supported by the National Natural Science Foundation of China(Nos.52171046,51804252,52234010,and 51922068).
文摘Directionally solidified dual-phase Al_(2)O_(3)/Y_(3)Al_(5)O_(12)(YAG)eutectic ceramics(DSECs)typically exhibit strong anisotropy.To improve their properties,various single-phase sapphire seeds,including r-axis[1-102],m-axis[10-10],c-axis[0001],and a-axis[11-20],were used as seeds to induce the orientation of the Al_(2)O_(3)/YAG DSECs.The results showed that Al_(2)O_(3) in the eutectics could be governed by the sapphire seeds.The YAG in each induced eutectic had a specific growth direction endowed by Al_(2)O_(3) in the asinduced eutectics or the sapphire seed.Herein,we calculated the planar lattice misfits and interfacial strain energies of four crystallographic orientation relationships based on the constructed lattice models.It was elucidated the constraint of the sapphire seed caused YAG to grow following the rule of mini-mizing the interfacial strain energy.This revealed the reason why Al_(2)O_(3)/YAG DSECs orientation can be successfully induced.These results may provide a novel method for the design of high-performance eu-tectic ceramic materials.
基金financially supported by the National Natural Science Foundation of China(Nos.52071039 and 51871032)the Natural Science Foundation of Jiangsu Province(No.BK20202010)。
文摘The electrochemical hydrogen charging of pure titanium and its alloys has been investigated previously,while how a subsequent annealing treatment aff ects the type of hydride and its orientation relationship with matrix is not clear.In the present study,a quantitative study on the microstructure and orientation of titanium hydrides during electrochemical hydrogen charging and subsequent annealing treatment was carried out using scanning electron microscopy,transmission electron microscopy and electron backscatter diff raction.The results show thatδ-hydride is the main in both the electrochemically hydrogenated sample and the subsequent annealing treated sample.After electrochemical hydrogen charging for 48 h,the surface is mainly composed of denseδ-hydride with a thickness of approximately 42μm,the orientation relationship betweenα-matrix andδ-hydride follows only the orientation relationship of OR2,{0001}_(α)//{111}_(δ),<1210>_(α)//<110>_(δ) and an interface plane{1013}_(a)//{110}_(δ).Besides OR2,a part of hydrides show an orientation relationship of OR1 with the matrix after annealing,{0001}a//{001}_(δ),<1210>_(a)//{110}_(δ) and an interface plane of {1010}_(δ)//{110}_(δ).It is further found that the relative frequency of OR1and OR2 is closely related to annealing duration.Under an argon atmosphere at 450℃,the frequencies of OR1 and OR2 are nearly balance with an annealing time of 12 h,while OR1 becomes to be the predominant one with a relative frequency of 96.5%after annealing for 96 h.The mechanism for the evolution of orientation relationship of hydrides with annealing time was discussed.
