Surface Microcracks and Relief Caused by Lamella Sliding during High Temperature Tension of Titanium Alloy with Lamella Structure

张力的样品的破裂附近的侧面的表面被在氧化物电影搬迁前后扫描电子显微镜学(SEM ) 检验。在表面形态学和微观结构之间的关系被建立。微裂缝被表面氧化物的易碎物破裂引起的结果表演由于高山拍摄哈薄片沿着高山滑动哈薄片边界。并且滑动排列高山哈薄片相对优先的样品表面带给微快克形成而且殖民地的加薪不仅。A 滑倒模型，描绘在表面形态学和微观结构之间的关系，向前被带分析观察。

Nano-refinement of the face-centered cubic Zr(Fe,Cr)_(2)secondary phase particles in Zircaloy-4 alloy via localized-shearing/bending-driven fracture under high-temperature compression

Nanoparticles are extensively introduced to improve the mechanical,physical,and chemical properties of alloys.In the present study,the underlying nano-refinement mechanisms of face-centered cubic Zr(Fe,Cr)_(2)secondary phase particles(SPPs)that precipitated in Zircaloy-4 alloy under high-temperature compression were investigated in detail by utilizing high-resolution transmission electron microscopy(HRTEM)and conventional TEM techniques.The frequently observed Zr(Fe,Cr)_(2)SPPs were incoherent with the matrix and exhibited brittle fracture behaviors without measurable plasticity.HRTEM observations revealed two mechanisms underlying the nano-refinement of incoherent micro-sized SPPs via localized shear fracture on{11¯2}SPP and nanoprecipitate-assisted bending fracture,respectively.The latter was,for the first time,found to occur when the movements of large SPPs were blocked by nanometer-sized SPP during alloy deformation.Accordingly,two force models were proposed to visualize their potential nano-refinement processes.The knowledge attained from this study sheds new light on the deformation behaviors of Zr(Fe,Cr)_(2)SPPs and their associated size refinement mechanisms under high-temperature compression,and is expected to greatly benefit the process optimization of zirconium alloys to achieve precipitate nano-refinement.

Deformation twinning in octahe dron-base d face-centere d cubic metallic structures:Localized shear-force dipoles drive atomic displacements

Twinning is found to impart favorable mechanical,physical and chemical properties to nanostructured materials.Deformation twinning prevails in face-centered cubic(FCC)nanocrystalline materials upon loading.In FCC structures,the<112>{111}deformation twinning is traditionally believed to nucleate and grow through layer-by-layer emission of 1/6<112>Shockley partial dislocations on consecutive{111}planes.We report that deformation twinning is able to occur in crystalline(Fe,Nb)_(23)Zr_(6)nanoparticles(NPs)that have a large Mn 23 Th 6-type FCC structure with a Zr-octahedron as a motif.Based on direct atomic-scale observations,we discover a new zero-net-strain path for the<112>{111}deformation twin-ning in FCC structures.To form a[¯1¯12]/(111)twin,for example,short(¯1¯11)planes within two adjacent(111)plane layers in the repeated three-layer sequence of(111)planes are shear deformed continuously by a shear-force dipole along the[11¯2]direction like a domino effect,whereas the other(111)plane in the repeated sequence remains intact.In addition,a loading criterion for deformation twinning of a FCC NP under uniaxial compression is proposed based on our observations.Our work here not only extends the fundamental understanding on deformation twinning in FCC structures,but also opens up studies of deformation behaviors in a class of Mn 23 Th 6-type FCC materials.

Atomic scale investigation of FCC→HCP reverse phase transformation in face-centered cubic zirconium

Mechanism of FCC→HCP reverse phase transformation in face-centered cubic zirconium(FCC-Zr)along with a concomitant 70.5°rotation ofα-Zr matrix were investigated in zircaloy-4(Zr-4)cladding tube by using transmission electron microscopy(TEM).Results showed that the interaction among a secondary phase particle(SPP)and three FCC-Zr grains resulted in the formation of cross stacking faults in SPP and exerted a drag force on minor axis of the adjacent FCC-Zr phase.Moreover,when the shear stress along[112]_(FCC-Zr)direction was large enough to initiate the emission of 1/6[112]Shockley partial dislocation on every other(111)_(FCC-Zr)close-packed plane,the stacking sequence would change from ABC ABCA to AB ABABA viz.(0001)planes of the daughter HCP phase.Thus,FCC→HCP reverse phase transformation in FCC-Zr was presented.

TC11钛合金中α″相和α′相的组织演变和显微硬度

研究了TC11钛合金中α"相和α'相的显微组织转变和显微硬度。金相显微组织观察和X射线衍射分析的结果表明:随着固溶温度的提高α"相逐渐向α'相的晶体结构转变,α相、α"相和α'相的显微组织演变规律为:α+α",α+α"+α',α+α',α'。显微硬度测试的结果表明:在935~995℃固溶后显微硬度随着温度的提高先增大后减少,在985℃固溶后显微硬度达到峰值。综合分析显微组织影响合金显微硬度的机理:在935~985℃固溶后α'片层的厚度和间距变化的幅度小,β转变组织长大缓慢,在β转变组织中先后析出α"和α'相,随着固溶温度的提高α'片层的含量随之提高产生了相变强度效果,使其显微硬度提高;在985~995℃固溶后α'片层的厚度和间距明显增大,β转变组织变粗大,α"相消失,α'相的含量降低,相变强化的效果减弱,使β转变组织的显微硬度降低。

The influence of microtexture on the formation mechanism of nodules in Zircaloy-4 alloy tube

Corrosion re sistance of Zircaloy-4 alloy tube in superheated steam at 673 K/10.3 MPa is anisotropic.A part of the surface undergoes uniform corrosion while the other suffers nodular corrosion.Narrow and wide nodules are observed after an exposure period of 3 and 30 days,respectively.A new matrix transformation method is established in order to study the formation mechanism of nodules in the cross-section(CS) of Zircaloy-4 alloy tube using the EBSD technique,while the CS perpendicular to axial direction(AD).The results reveal that the microtexture is a key factor behind the two types of corrosion.Furthermore,the oxide layers grow anisotropically over the corroded surface.A thick oxide layer forms over the nodular corrosion region on the grains with c-axis oriented in the range of 40° around tangential direction(TD),whereas a thin oxide layer over the uniform corrosion region is detected on the grains with c-axis oriented in the range of 68° around TD.In short,the anisotropic growth of oxide layer was caused by the change of microtexture of the Zr-4 alloy tube,and this anisotropic growth of oxide layer contributed to the nodules formation.

{332}<113> Twinning transfer behavior and its effect on the twin shape in a beta-type Ti-23.1Nb-2.0Zr-1.0O alloy

The interaction between twins and grain boundaries(GB) has an important influence on the deformation and fracture behavior of materials. In the present work, {332}<113> twinning transfer(TT) behavior and its effect on the twin shape in a deformed β-type Ti-23.1 Nb-2.0 Zr-1.0 O Ti alloy were investigated experimentally and with molecular dynamics simulation. The crystallographic alignment factor of the two twinning systems in the neighboring grains and the misorientation angle of the grain pairs were found to influence the occurrence of TT. This further determines the twin shape: twins present a ruler shape when TT occurs but are in a lenticular shape otherwise. Such different twin shapes are attributed to the local stress states related to TT occurring or not. Both ruler-shaped paired twinning and lenticular twinning would provide effective mechanisms to release or reduce the stress concentration in front of the twin tips in different grain pairs.

Intermediate state of hexagonal close-packed structure to face-centered cubic structure transformation: Direct evidence for basal-type face-centered cubic phase via partial dislocation in zirconium

1.Introduction Zirconium(Zr)and its alloys show great applications in nuclear and chemical industry thanks to their appropriate mechanical properties,low thermal neutron absorption cross-section and excellent corrosion resistance[1–3].Zr displays three different crystal structures on the temperature-pressure phase diagram:the hexagonal close-packed structure(HCP,α-Zr),the body centered cubic structure(BCC,β-Zr)and the simple hexagonal structure(ω-Zr).

A new type face-centered cubic zirconium phase in pure zirconium

So far,only two orientation relationships(OR)between hexagonal close-packed(HCP)(αphase)and facecentered cubic(FCC)structures in zirconium and titanium alloys have been reported.Here a new type FCC phase(named γ phase)with OR:<11■0>_(α)‖<100>_(γ) and{0001}_(α)‖{002}_(γ) was observed for the first time in annealed pure zirconium by means of transmission electron microscopy(TEM)technique.The α→γ phase transformation can be accomplished via expansion along[1■00]direction and slip of Shockley partial dislocation with 1/3[1■00]on(0001)basal planes.