\left\{ {10\bar 12} \right\} twinning behavior in magnesium single crystal

In order to investigate $\left\{ {10\bar 12} \right\}$ tensile twinning behavior, the magnesium single crystal was deformed by compressing along the $\left[ {2\bar 1 \bar 10} \right]$ direction at room temperature, as $\left\{ {10\bar 12} \right\}$ tensile twinning easily takes place when the compression direction is perpendicular to the c-axis. Numerous $\left\{ {10\bar 12} \right\}$ primary tensile twins were activated during deformation, and the Schmid factor (SF) criterion was applied to the six $\left\{ {10\bar 12} \right\}$ twin variants. The analysis shows that the majority of the $\left\{ {10\bar 12} \right\}$ primary twins belong to high SF variants, and high SF twin boundaries provided nucleation sites for low SF variants. The $\left\{ {10\bar 12} \right\}$ secondary tensile twins were formed inside the high SF of wide $\left\{ {10\bar 12} \right\}$ primary twin bands, and the basal plane of the $\left\{ {10\bar 12} \right\}$ secondary twin was tilted about 60° with respect to the original parent matrix. In the case of the $\left\{ {10\bar 12} \right\}$ secondary tensile twin, relatively low SF variants were activated while counterparts with higher SF variants were absent.     

Detailed Structures and Formation Mechanisms of Well-Known Al_(10)RE_2Mn_7 Phase in Die-Cast Mg-4Al-4RE-0.3Mn Alloy

The detailed structures and the corresponding formation mechanisms of the well-known Al_(10)RE_2Mn_7 phase in the conventional die-cast Mg–4Al–4RE–0.3Mn alloy were thoroughly investigated using transmission electron microscopy(TEM). The results indicate that the Al_(10)RE_2Mn_7 phase ordinarily contains both normal (111) twins and orientation twins.Both detailed TEM observations and density functional theory calculations indicate that the Al_(10)RE_2Mn_7 phase is transferred from the Al_8REMn_4 phase following an orientation relationship as [010]_(Al_8REMn_4)//[101]_(Al_(10)RE_2Mn_7) and (101)_(Al_8REMn_4)//(110)_(Al_(10)RE_2Mn_7). Moreover, forming orientation twins in the Al_(10)RE_2Mn_7 phase is attributed to the blurry regions at incoherent twin boundaries in the Al_8REMn_4 phase. Finally, these formed orientation twins result in the (111) twins in the Al_(10)RE_2Mn_7 phase.     

Relationships between deformation mechanisms and initial textures in polycrystalline magnesium alloys AZ31

1　INTRODUCTIONMagnesiumisthelightestmetallicstructuralma terialwithhighspecificstrengthandisusedinauto motive ,electronicsandaerospacefield[1,2 ] .Howev er ,magnesiumoftenshowspoorformabilityatroomtemperatureduetoitshexagonalstructurewithlessindependentslipsystems ,whichlimitsitsuse .Dif ferentslipsystemshavebeendetectedinmagnesiumsuchasbasalslipof { 0 0 0 1}〈112 0〉 ,prismslipof{ 10 10 }〈112 0〉[3,4 ] andpyramidslip (includingthea typeof {hkil}〈112 0〉andthea +ctypeof {hkil}〈112 3〉[…     

The Effect of Texture on the Corrosion Behavior of AZ31?Mg Alloy

Magnesium (Mg) grains show anisotropic corrosion behavior, which implies that the single-phase, hot-rolled Mg alloy AZ31 sheet, if highly textured, will have different corrosion performance depending on its crystallographic orientation of the grains. Its rolling surface, dominated by (0001) basal crystallographic planes, is more corrosion resistant than its cross-section surface, which is mainly composed of $ \{ 10\overline{1} 0\} $ and $ \{ 11\overline{2} 0\} $ prismatic crystallographic planes. Furthermore, grain refinement by hot rolling is beneficial to the overall corrosion resistance of AZ31 because of the dissolution of AlMn(Fe) intermetallic precipitates in the alloy. Surface compressive deformation machining can lead to refined grains and an expected preferred grain orientation, thus improving the corrosion resistance of AZ31 alloy.     

A Quantitative Study on the Effect of Heat Treatment on the Microstructure and Orientation of Titanium Hydride in Electrochemically Hydrogenated Pure Titanium

The electrochemical hydrogen charging of pure titanium and its alloys has been investigated previously, while how a subsequent annealing treatment affects 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 diffraction. The results show that δ-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 dense δ-hydride with a thickness of approximately 42 μm, the orientation relationship between α-matrix and δ-hydride follows only the orientation relationship of OR2, {0001}_α//{1$\overline{1}$1}_δ, $\langle 1\overline{2}10\rangle_{\alpha }$//$\langle 110\rangle_{\delta }$ and an interface plane $\{ 10\overline{1}3\}_{\alpha }$//$\{ 1\overline{1}0\}_{\delta }$. Besides OR2, a part of hydrides show an orientation relationship of OR1 with the matrix after annealing, {0001}_α//{001}_δ, $\langle 1\overline{2}10\rangle_{\alpha }$//$\langle 110\rangle_{\delta }$ and an interface plane of $\{ 10\overline{1}0\}_{\alpha }$//$\{ 1\overline{1}0\}_{\delta }$. It is further found that the relative frequency of OR1and OR2 is closely related to annealing duration. Under an argon atmosphere at 450 °C, 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.     

Effect of Zn and Y Additions on Grain Boundary Movement of Mg Binary Alloys During Static Recrystallization

Texture evolution in rolled Mg–1 wt% Zn and Mg–1 wt% Y binary alloys was analyzed by quasi-in situ electron backscatter diffraction (EBSD) during static recrystallization. Mg–1 wt% Zn and Mg–1 wt% Y alloys exhibited strong basal texture at the initial recrystallization state. After grain growth annealing, the basal texture component {0001} < $11\overline{2}0$ > was increased in Mg–1 wt% Zn alloy and that of Mg–1 wt% Y alloy was decreased to be a random texture. Zn and Y atoms segregated strongly to the recrystallized grain boundaries in Mg–1 wt% Zn alloy and Mg–1 wt% Y alloy, respectively. Thus, Zn and Y elements facilitated the grain boundary movements along contrary directions during grain growth. In Mg–1 wt% Zn alloy, due to the Zn element segregation on grain boundaries, the grains consisted of a strong texture grew more easily because the grain boundary migration tended to move from the orientation close to normal direction to the orientation near to transverse direction or rolling direction. Therefore, after grain growth, the volume fraction of texture component {0001} < $11\overline{2}0$ > was increased by consuming the neighboring grains, leading to a stronger basal texture. On the contrary, in the Mg–1 wt% Y alloy, the Y element segregation caused the opposite direction of grain boundary migration, resulting in a random texture.     

Mechanical Properties and Deformation Mechanisms of Mg-Gd-Y-Zr Alloy at Cryogenic and Elevated Temperatures

In this study, mechanical properties and deformation mechanisms of Mg-Gd-Y-Zr alloy at temperatures ranging from 77 K to 523 K have been investigated. The effects of temperature on the mechanical properties, deformation mechanism, and fracture mechanism are discussed. The results show that the strengths of alloy decrease gradually while the elongations increase progressively with increasing temperature. The maximum ultimate tensile strength of the alloy as high as 442 MPa is obtained at 77 K. As the temperature increases from 77 K to 523 K, the ultimate tensile strength of the alloy decreases from 442 MPa to 254 MPa and the elongations increase from 6.3% to 28.9% gradually. The study verifies that the deformation at 77 K is predominated by basal slip and \({{\left\{ {10\bar{1}2} \right\}} \mathord{\left/ {\vphantom {{\left\{ {10\bar{1}2} \right\}} {\left\langle {10\bar{1}1} \right\rangle }}} \right. \kern-0pt} {\left\langle {10\bar{1}1} \right\rangle }}\) deformation twinning system. At 223 K, lots of twins emerge primarily at grain boundaries. At 373 K, all dislocations are proved to be 〈a〉 dislocations. At 523 K, although basal slip is still the dominant deformation mechanism, non-basal slip systems also become activate.     

High-Temperature Structural Stabilities of Ni-Based SingleCrystal Superalloys Ni–Co–Cr–Mo–W–Al–Ti–Ta with Varying Co Contents

It has been recently pointed out that the compositions of industrial alloys are originated from cluster-plus-glueatom structure units in solid solutions. Specifically for Ni-based superalloys, after properly grouping the alloying elements into Al, Ni-like(■), r-forming Cr-like(■) and c-forming Cr-like(■), the optimal formula for single-crystal superalloys is established [Al–Ni_(12)](Al_1■~_(0:5) ■_(1:5)). The Co substitutions for Ni at the shell sites are conducted on the basis of the first-generation single-crystal superalloy AM3, formulated as [Al–■_(12)Co_x](Al_1Ti_(0.25)Ta_(0.25)Cr_1W_(0.25)Mo_(0.25)), with x = 1.5, 1.75, 2 and 2.5(the corresponding weight percents of Co are 9.43, 11.0, 12.57 and 15.71, respectively). The900 ℃ long-term aging follows the Lifshitz–Slyozov–Wagner theory(LSW theory), and the Co content does not have noticeable influence on the coarsening rate of c0. The microstructure and creep behavior of the four(001) single-crystal alloys are investigated. The creep rupture lifetime is reduced as Co increases. The alloy with the lowest Co(9.43 Co) shows the longest lifetime of about 350 h at 1050 ℃/120 MPa, and all the samples show N-type rafting after creep tests.     

Formation of Face-Centered Cubic Phase in Ti35 Alloy Under In Situ Heating Transmission Electron Microscopy

A thermally induced hexagonal close-packed (HCP) to face-centered cubic (FCC) phase transition was investigated in an α-type Ti35 alloy with twinned structure by in situ heating transmission electron microscopy (TEM) and ab initio calculations. TEM observations indicated that the HCP to FCC phase transition occurred both within matrix/twin and at the twin boundaries in the thinner region of the TEM film, and the FCC-Ti precipitated as plates within the matrix/twin, while as equiaxed cells at twin boundaries. The crystallographic orientation relationship between HCP-Ti and FCC-Ti can be described as: $\left\{ {111} \right\}_{{{\text{FCC}}}} //\left\{ {0002} \right\}_{{{\text{HCP}}}} \;{\text{and}}\; < 110 >\,_{{{\text{FCC}}}} //\, <1\overline{2} 10>\,_{{{\text{HCP}}}}$. The HCP to FCC phase transition was accomplished by forming an intermediate state with a BB stacking sequence through the slip of partial dislocations. The formation of such FCC-Ti may be related to the thermal stress and temperature. Ab initio calculations showed that the formation of FCC-Ti may also be related to the contamination of interstitial atoms such as oxygen.     

Molecular Dynamics Simulations of the Orientation Effect on the Initial Plastic Deformation of Magnesium Single Crystals

Molecular dynamics simulation is employed to study the tension and compression deformation behaviors of magnesium single crystals with different orientations.The angle between the loading axis and the basal a direction ranges from 0° to 90°.The simulation results show that the initial defects usually nucleate at free surfaces,but the initial plastic deformation and the subsequent microstructural evolutions are various due to different loading directions.The tension simulations exhibit the deformation mechanisms of twinning,slip,crystallographic reorientation and basal/prismatic transformation.The twinning,crystallographic reorientation and basal/prismatic transformation can only appear in the crystal model loaded along or near the a-axis or c-axis.For the compression simulations,the basal,prismatic and pyramidal slips are responsible for the initial plasticity,and no twinning is observed.Moreover,the plastic deformation models affect the yield strengths for the samples with different orientations.The maximum yield stresses for the samples loaded along the c-axis or a-axis are much higher than those loaded in other directions.     

Modeling the Dynamic Recrystallization of Mg–11Gd–4Y–2Zn–0.4Zr Alloy Considering Non-uniform Deformation and LPSO Kinking During Hot Compression

Hot compression tests of Mg–11 Gd–4 Y–2 Zn–0.4 Zr alloy(GWZK114) were conducted at a deformation temperature range of 300–500 °C and a strain rate range of 0.01–10.0 s-1. Based on systematic microstructure observation, it is confirmed that long period stacking ordered(LPSO) phase displays essential and evolving roles on the dynamic recrystallization(DRX)behavior. The results indicate that the plastic deformation is mainly coordinated by simultaneous exist of LPSO kinking of lamella 14 H-LPSO phase and DRX at 350–450 °C, and DRX at 500 °C. Further, it is found that the LPSO kinking induced during 350–450 °C can delay the DRX. A phenomenological DRX model of GWZK114 alloy is established to be XDRX = 1. exp[-0.5((ε-ε_c)/ε~*)~(0.91)]. Non-uniform distribution of plastic strain during compression was considered via finite element method and it ensures a good prediction of DRX fraction under a large plastic strain. Meanwhile, an enhanced DRX model, taking its formulation as XDRX = {1. exp[-0.5((ε-ε_c)/ε~*)~(0.91)]}( T/(226.8)-1)n, n = 3.82ε~(0.083), is proposed for the first time to capture the hindering effect of 14 H-LPSO kinking on DRX behavior. The predicted results of this enhanced DRX model agree well with the experimental cases, where 14 H-LPSO kinking is dominated or partially involved(300–450 °C). Besides,a size model of DRX grains is also established and can depict the evolution of DRX grain size for all the investigated compression conditions with accounting for temperature rising at high strain rates(5 s-1 and 10 s-1).     

Deformation Mechanisms of Alpha-Uranium Single Crystals

The operative deformation elements in α-uranium single crystals under compression at room temperature have been determined as a function of the compression directions. The deformation mechanisms noted may be arranged with respect to their frequency of occurrence and ease of operation in the following order: 1—(010)-[100] slip, 2—{130} twinning, 3—{~172} twinning, and 4—under special conditions of stress application, kinking, cross-slip, {~176} twinning, and {011} slip. The composition planes of the {172} and {176} systems were found to be irrational. Cross-slip was shown to be associated with the major (010) slip system, coupled with localized interaction of slip on the (001) planes. The mechanism of kinking was found to be similar to that observed in other metals in that it occurred chiefly when the compression direction was nearly parallel to the principal slip direction [100] and was associated with a lattice rotation about an axis contained in the slip plane and normal to the slip direction: the [001] in the uranium lattice. The resolved critical shear stress for slip on the (010)-[100] system was found to be 0.34 kg per mm². In a single test it was shown that under compression in suitable directions twinning on the {130} also occurs at 600°C     

黄芪总甙的抗炎作用及其作用机制探索

目的 探索黄芪总甙(AST) 的抗炎作用及其作用机制。方法 采用大鼠角叉菜胶气囊炎症模型, 测定渗出液量、中性白细胞游出数、蛋白质、PGE₂、IL-8、NO、PLA₂含量以及$\mathop{{O}}_{2}^{{\mathop{}_{\ ·}^{-}}}$的生成量。结果 AST40、80 mg·kg^-1 可使角叉菜胶诱导大鼠气囊炎症的渗出液量、中性白细胞游出数、蛋白质含量显著减少, 降低渗出液及中性白细胞中PLA₂活性,减少渗出液中IL-8 含量及中性白细胞$\mathop{{O}}_{2}^{{\mathop{}_{\ ·}^{-}}}$的生成。AST 也可明显减少渗出液中PGE₂、NO 的含量。结论 AST 的抗炎作用机理与其降低血管通透性和抑制白细胞游出、降低PLA₂活性、减少IL-8、PGE₂、NO 等炎症介质的产生与抑制氧自由基生成有关。     

Quasi-Ternary System Ag2Se-CdSe-Ga2Se3

Phase equilibria in the quasi-ternary system Ag₂Se-CdSe-Ga₂Se₃ were investigated by differential thermal and x-ray phase analysis methods. Phase diagrams of nine vertical sections were constructed. The boundaries of seven single-phase fields were determined which are solid solution ranges of system components and intermediate phases. We constructed the isothermal section at 820 K and the liquidus surface projection, and have determined the position in the system of six invariant processes with the participation of liquid: $ {\text{L}}_{{{\text{U}}_{1} }} + {\upzeta} {\leftrightarrows} {\upbeta} + {\upeta} $ L U 1 + ζ ? β + η (1145 K), $ {\text{L}}_{{{\text{U}}_{ 2} }} + \upzeta \leftrightarrows \upgamma + \upeta $ L U 2 + ζ ? γ + η (1138 K), $ \text{L}_{{U_{3} }} + \upeta \leftrightarrows \updelta + \upgamma $ L U 3 + η ? δ + γ (1113 K), $ {\text{L}}_{{{\text{E}}_{ 1} }} \leftrightarrows \upbeta + \updelta + \upeta $ L E 1 ? β + δ + η (1083 K), $ {\text{L}}_{{{\text{E}}_{ 2} }} \leftrightarrows \upalpha + \upbeta + \upvarepsilon $ L E 2 ? α + β + ε (969 K), $ {\text{L}}_{{{\text{E}}_{ 3} }} \leftrightarrows \upbeta + {\updelta} + \upvarepsilon $ L E 3 ? β + δ + ε (963 K). Two invariant processes in the sub-solidus part, $ \upbeta + \updelta \leftrightarrows \upeta + \uplambda $ β + δ ? η + λ and $ \upbeta + \updelta \leftrightarrows \upvarepsilon + \uplambda $ β + δ ? ε + λ at 968 and 938 K, respectively, were investigated as well.     

Crystallographic analysis of the martensitic transformation in medium-carbon steel with packet martensite

Based on X-ray diffraction studies of the martensite texture in a single martensite packet, exact orientation relationships between the orientations of martensite crystallites and the original austenite single crystal in medium-carbon steel 37KhN3A have been determined to be as follows: (011)_α||(1; 0.990; 1.009)_γ to an accuracy of \( \pm 0.15^\circ ,{\left[ {01\overline 1 } \right]_\alpha }||{\left[ {1;1.163; - 2.133} \right]_\gamma }\) to an accuracy of ±0.15°. It has been shown that the orientation relationships proved to be almost the same as in the Fe–31% Ni alloy with a twinned martensite with close lattice parameters. Therefore, the conclusion has been drawn that the mechanism of the lattice deformation upon the martensitic transformation is the same in both alloys. It is described as follows. The lattice deformation occurs by shear on the (111) plane in the \({\left[ {11\overline 2 } \right]_{_\gamma }}\) direction and is accompanied by an additional change in the dimensions in the mutually perpendicular directions \({\left[ {11\overline 2 } \right]_{_\gamma }},\left[ {111} \right],\;and{\left[ {1\overline 1 0} \right]_{_\gamma }}\). The invariantlattice deformation is implemented by slip in martensite on the planes of the (112)_α type in the direction \({\left[ {\overline 1 \overline 1 1} \right]_\alpha }\). One of the 24 crystallographically equivalent variants of the transformation mechanism has been considered. Apart from this type of deformation, an additional deformation of martensite is possible that does not change its orientation. It has been shown that the orientation of the martensite crystallite calculated via the phenomenological theory of the martensitic transformations (PTMT) differs by approximately 1° from the experimentally determined orientation. This refers to both the lath and twinned martensite. In the twinned martensite, the invariant plane obtained in the PTMT calculations and the habit plane coincide. In lath martensite of 37KhN3A steel, the invariant plane of the martensite crystal obtained in PTMT calculations deviates by ~25° from the orientation of the surface of the martensite plate (habit plane), which is close to the (111)_γ plane. An explanation of this phenomenon is given.     

High-Temperature Deformation Behavior of MnS in 1215MS Steel

The effect of manganese sulfide (MnS) inclusions on the machinability of free-cutting steel is based on their morphology, size and distribution. Furthermore, the plasticity of MnS is high during the hot working caused different characterization of MnS. In this study, the deformation behavior of MnS in 1215MS steel after a thermomechanical process was investigated at 1323 K. The microstructures of MnS inclusions were characterized by optical microscopy, scanning electron microscopy, energy-dispersive spectrometry, and electron backscattering diffraction (EBSD). As the thickness reduction of the inclusions increased from 10 to 70%, their average aspect ratio increased from 1.20 to 2.39. In addition, the deformability of MnS inclusions was lower than that of the matrix. The possible slip systems of A, B, C, and D plane traces were \(\left( {\bar{1}0\bar{1}} \right)\left[ {\bar{1}01} \right],\left( {10\bar{1}} \right)\left[ {101} \right],\left( {011} \right)\left[ {01\bar{1}} \right]\), and \(\left( {110} \right)\left[ {1\bar{1}0} \right]\). Furthermore, the EBSD measurements suggested that slip planes in MnS inclusions occur on {110} planes.     

钛单晶纳米柱拉压不对称性的分子动力学模拟

本文基于分子动力学模拟,通过研究钛单晶纳米柱在拉伸和压缩下的力学响应特征及晶体结构演化行为,揭示其塑性变形机制。结果表明沿[0001]晶向拉伸条件下主要塑性变形机制为伴生的{101 ?2}孪晶和基面层错;而沿[0001]晶向压缩条件下,基面位错作为优先形核的缺陷参与到塑性变形过程,随后锥面位错出现并协调了轴向和横向变形,压缩条件下无孪晶产生。拉伸模拟过程中观察到一种有别于传统孪生的晶体再取向现象,其孪晶与基体间呈现基面/柱面对应关系。     

Investigation of the structural defects in GaN thin films grown by organometallic vapor phase epitaxy

GaN thin films were prepared on {0001} planes of sapphire substrates by organometallic vapor phase epitaxy (OMVPE) techniques. The crystall orgaphic relation between the film and the substrate as well as the structural features of the defects in the film were investigated by transmission electron microscopy (TEM). Epitaxial relationship was observed in the GaN/sapphire heterostructure preparedin this investigation; (0001) GaN//(0001) sapphire; sapphire. Dislocations of Burgers vector were observed in the film; the propagation behavior of the dislocations exhibits a slip system is operative in the film. Inversion domain boundary (IDB) facets lying parallel to and planes were observed; the type of anti-site bonds (Ga-Ga, N-N) is altemate along these IDB planes, keeping the simple stoichiometry of the compound.     

动态压缩条件下高纯钛微观组织特征研究

利用光学显微镜(OM)、背散射电子衍射(EBSD)技术及透射电子显微镜(TEM)对高纯钛低-中应变动态压缩变形的微观组织特征进行了研究。结果表明：随着应变量(ε)的增加,晶粒内部通过孪晶与孪晶,孪晶与位错以及位错与位错之间的交互作用逐步细化原始晶粒;变形初期,形变孪生以{11-22}孪晶为主,当ε达到0.2后,{10-12}孪晶转变为主要形变孪生类型,孪生改变了原始晶粒的取向,进一步促进晶粒内部的位错滑移。高纯钛动态压缩变形经历了由位错滑移到形变孪生,再到位错滑移主导的过程,但位错滑移和孪生始终共同作用协调动态压缩变形。     

Microstructural Evolution and Biodegradation Response of Mg-2Zn-0.SNd Alloy During Tensile and Compressive Deformation

The effect of deformation behavior on the in vitro corrosion rate of Mg-2Zn-0.5Nd alloy was investigated experimentally after uniaxial tensile and compressive stress.The microstructure and texture were characterized using electron backscattered diffraction and X-ray diffraction,while potentiodynamic polarization and immersion tests were used to investigate the cor-rosion response after deformation.The result reveals that applied compressive stress has more dominant effect on the corro-sion rate of Mg-2Zn-0.5Nd alloy as compared to tensile stress.Both tensile and compressive strains introduce dislocation slip and deformation twins in the alloy,thereby accelerating the corrosion rate due to the increased stress corrosion related to dislocation slips and deformation twins.The { 10(1)2} tension twinning and prismatic slip were the major contributors to tensile deformation while basal slip,and { 10(1)2} tension twin were obtainable during compressive deformation.The twinning activity after deformation increases with the plastic strain and this correlates with the degradation rate.