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Investigation of Migration and Transformation of Self-Interstitial Atoms in 3C-SiC via DFT Calculations 用DFT计算研究3C-SiC中自间隙原子的迁移和转变
Pub Date : 2021-01-26 DOI: 10.2139/ssrn.3770989
Shangquan Zhao, G. Ran, Fei Gao, S. Ma
First-principles calculations were carried out to investigate the stable and potential metastable structure of self-interstitial atoms (SIAs) in 3C-SiC. The most stable C and Si interstitials we obtained are Ci-C and Sii-Si split interstitials, respectively. In addition, a serious of metastable structures Ci-C (x = 0.63 ~ 0.81), Ci-C , Ci-Si , Sii-Si and Sii-Si have been observed. The migration and transformation of these SIAs were systematically studied. The minimum migration barrier for the full space rotation of C and Si interstitial are 0.49 eV and 0.73 eV, respectively. For the long-distance migration of SIAs, the minimum migration energy for C and Si interstitials is 0.71 eV and 0.73 eV, the corresponding migration paths are Ci-C(2 ‾5‾ 2) ↔ Ci-Si(1 1 6) ↔ Ci-C(‾5‾ 2 2), and Sii-Si ↔ SiTC ↔ Sii-Si .
采用第一性原理计算研究了3C-SiC中自间隙原子(SIAs)的稳定和潜在亚稳结构。我们得到的最稳定的C -C和Si间隙分别是Ci-C和Si -Si分裂间隙。此外,还观察到一系列亚稳结构Ci-C (x = 0.63 ~ 0.81)、Ci-C、Ci-Si、si - si和si - si。系统地研究了这些SIAs的迁移和转化。C和Si间隙全空间旋转的最小迁移势垒分别为0.49 eV和0.73 eV。对于sia的长距离迁移,C和Si的最小迁移能量分别为0.71 eV和0.73 eV,相应的迁移路径为Ci-C(2 - 5 - 2)↔Ci-Si(1 1 6)↔Ci-C(5 - 2), Sii-Si↔Sii-Si。
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引用次数: 0
Novel Ti–20zr–49.7pd High Temperature Shape Memory Alloy with Facilitated Detwinning and Precipitation Strengthening 新型Ti-20zr-49.7pd高温形状记忆合金,易孪晶和析出强化
Pub Date : 2021-01-01 DOI: 10.2139/ssrn.3947687
H. Tobe, Shunsuke Kojima, E. Sato
It is desirable to develop high temperature shape memory alloys with a martensitic transformation start temperature (Ms) above 100°C and a recoverable strain of about 4‐6% in the shape memory effect. The latter property is achieved with low variant reorientation stress due to easy detwinning of martensite and high plastic deformation stress due to precipitation strengthening. We have previously demonstrated the facilitation of detwinning for Ti–Zr–Ni–Pd quaternary alloy systems through controlling the crystal structure of martensite, and proposed that Ti–(15‐20)Zr–49.7Pd (at.%) and surrounding Ni‐containing compositions are candidates. In this study, aging temperature was optimized for a Ti–20Zr–49.7Pd alloy, and an excellent shape memory effect with Ms above 130°C, low reorientation stress around 200 MPa, high plastic deformation stress around 1800 MPa, and large recovery strain of 4.5% was achieved. On the other hand, short‐range ordering of solute atoms occurs just above the reverse transformation temperature and decreases Ms.
在形状记忆效应中,希望开发出马氏体相变起始温度(Ms)高于100℃、可恢复应变约为4‐6%的高温形状记忆合金。后一种性能是在马氏体易失孪的低变取向应力和析出强化的高塑性变形应力下实现的。我们之前已经证明了通过控制马氏体的晶体结构可以促进Ti - zr - Ni - pd四元合金体系的双晶化,并提出Ti -(15‐20)Zr-49.7Pd (at.%)和周围的含Ni成分是候选成分。本研究对Ti-20Zr-49.7Pd合金进行时效温度优化,获得了优异的形状记忆效果,Ms在130℃以上,重定向应力在200 MPa左右,塑性变形应力在1800 MPa左右,恢复应变高达4.5%。另一方面,溶质原子的短程有序发生在刚好高于反转变温度的地方,并降低了Ms。
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引用次数: 1
Interpreting Dynamic Hardness: Separating Roles of Speed, Strain Rate and Shock 解释动态硬度:分离速度、应变率和冲击的作用
Pub Date : 2021-01-01 DOI: 10.2139/ssrn.3931597
Y. Mao, B. Barnett, K. Prasad, A. Vivek, G. Daehn
Mechanical hardness is classically defined as force divided by indented area. Hardness (dynamic) is alternately sometimes defined based on indentation energy absorbed normalized by displaced volume. This elementary study compares static and dynamic hardness using standard definitions. Hardness is often observed to increase with strain rate and this is commonly interpreted as strain-rate hardening by mechanisms such as dislocation drag. This analysis considers the simplest situation – ballistic indentation of an elastic-perfectly plastic material without rate dependence. Results from both Coupled Eulerian-Lagrangian (CEL) and Smoothed Particle Hydrodynamics (SPH) show a linear correlation between indenter impact speed and dynamic hardness. Extrapolating to an impact speed of 0 m/s converges to static hardness. Neither approach demonstrates indenter size dependence. High impact speeds also can introduce shock. It is suggested that speed and shock hardening effects can account for the increase in dynamic hardness with increased indenter speed without strain-rate-hardening.
机械硬度通常定义为力除以压痕面积。硬度(动态)有时是根据被位移体积归一化的吸收压痕能量来定义的。这项初步研究使用标准定义比较静态和动态硬度。硬度通常随应变速率的增加而增加,这通常被解释为由位错阻力等机制引起的应变速率硬化。这种分析考虑了最简单的情况-弹塑性材料的无速率依赖的弹道压痕。欧拉-拉格朗日耦合力学(CEL)和光滑颗粒流体力学(SPH)结果表明,压头冲击速度与动态硬度呈线性相关。外推到0米/秒的冲击速度收敛到静态硬度。这两种方法都不能证明压头大小的依赖性。高冲击速度也会带来冲击。速度和冲击硬化效应可以解释动态硬度随压头速度的增加而增加而没有应变率硬化的原因。
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引用次数: 0
Unveiling Solidification Mode Transition and Crystallographic Characteristics in Laser 3D-Printed Al 2O 3-ZrO 2 Eutectic Ceramics 揭示激光3d打印al2o3 - zro - 2共晶陶瓷的凝固模式转变和晶体学特征
Pub Date : 2021-01-01 DOI: 10.2139/ssrn.3939456
Z. Fan, Yu Yin, Qiyang Tan, Xuliang Li, P. Niu, Rui-di Li, Tiechui Yuan, Mingxing Zhang, Han Huang
The crystallographic texture distribution in 3D-printed Al2O3-ZrO2 eutectics was found completely different from those prepared by directional solidification. The as-fabricated specimen was mainly composed of randomly oriented eutectic colonies, as a result of the initial uncoupled growth at molten pool boundaries. Specifically, the free-grown Al2O3 faceted particulates in the uncoupled region acted as effective nucleation sites that triggered coupled eutectic renucleation and growth. Except for some misoriented ZrO2 precipitates in Al2O3 matrix, well-defined multiple crystallographic orientation relationships existed between eutectic phases in the colony, e.g. {0001}Al2O3 ∥ {100}ZrO2 and {1120}Al2O3∥ {100}ZrO2. The lattice matching change was attributed to the varied solidification conditions along the solid/liquid interface, as predicted by Jackson-Hunt model.
3d打印的Al2O3-ZrO2共晶的晶体织构分布与定向凝固制备的完全不同。由于熔池边界处初始的非耦合生长,制备试样主要由随机取向的共晶菌落组成。具体来说,在非耦合区自由生长的Al2O3面状颗粒作为有效的成核位点,触发了耦合共晶再核和生长。除Al2O3基体中有少量错取向的ZrO2析出外,群体中共晶相之间存在明确的多取向关系,如{0001}Al2O3∥{100}ZrO2和{1120}Al2O3∥{100}ZrO2。根据Jackson-Hunt模型的预测,晶格匹配的变化归因于沿固/液界面的凝固条件的变化。
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引用次数: 1
Role of a Shear Planar Mesodefect in Nucleation of Crack at Grains Junction Due to Athermal Grain Boundary Sliding 剪切平面细观缺陷在晶界非热滑动晶界裂纹成核中的作用
Pub Date : 2021-01-01 DOI: 10.2139/ssrn.3885130
V. Perevezentsev, S. Kirikov, J. Svirina
We consider the conditions for microcrack nucleation in a grain junction due to athermal sliding along the grain boundary, containing a strain-induced shear-type planar mesodefect. The dependences of critical external stress of microcrack nucleation on the mesodefect length, its strength and the threshold stress of athermal sliding are obtained. It is shown that the presence of the mesodefect at the grain boundary can lead to a significant decrease of the crack nucleation stress in comparison with the case of pure grain boundary sliding. It is concluded that the induced athermal grain boundary sliding, carried out by the motion of the glissile components of dislocations, accumulating at the grain boundaries during intragranular plastic deformation, can be considered as one of the possible mechanisms for microcracks nucleation in materials with fragmented structure.
我们考虑了由于沿晶界的非热滑动而导致的晶界微裂纹形核的条件,其中包含应变诱导的剪切型平面介孔缺陷。得到了微裂纹形核临界外应力与中缺陷长度、中缺陷强度和非热滑动阈值应力的关系。结果表明,与纯晶界滑动相比,晶界中缺陷的存在使裂纹形核应力显著降低。结果表明,在晶内塑性变形过程中,由位错的滑块运动引起的晶界非热滑动可以被认为是碎片化结构材料微裂纹成核的可能机制之一。
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引用次数: 0
In Situ Growth of a Novel Nanoscaled Rock Salt Titanium Zirconium Nitride Phase in a Silicon Nitride Matrix 新型纳米岩盐氮化钛锆相在氮化硅基体中的原位生长
Pub Date : 2021-01-01 DOI: 10.2139/ssrn.3920960
M. Bechelany, Abhijeet Lale, Maxime Balestrat, C. Gervais, S. Malo, R. Nishihora, S. Bernard
The first demonstration of a nanoscaled titanium zirconium nitride (TiZrN2) single-phase isolated during the formation of precursor-derived silicon nitride (Si3N4) matrix nanocomposites is highlighted in the present paper. We employed polymethylsilazane (PMSZ) as a Si3N4 precursor, which was chemically modified with Zr[N(CH2CH3)2]4 and Ti[N(CH3)2]4, ammonolyzed and pyrolyzed under ammonia (1000 °C) then annealed in flowing nitrogen (1500 °C). The TiZrN2 phase grew in the temperature range 1000-1500 °C and was isolated - because of its confinement into a Si3N4matrix - as a nanoscaled rock salt structure after annealing at 1500 °C as shown by X-ray diffraction. HRTEM investigations confirmed the unique nanostructural feature of the nanocomposites made of TiZrN2 nanocrystals with a size as low as 9 nm distributed in a- and b-Si3N4 phases.
本文首次展示了在前驱体衍生的氮化硅(Si3N4)基纳米复合材料形成过程中分离出的纳米级氮化钛锆(TiZrN2)单相。以聚甲基硅氮烷(PMSZ)为Si3N4前驱体,用Zr[N(CH2CH3)2]4和Ti[N(CH3)2]4进行化学改性,在氨水(1000℃)下进行氨解和热解,然后在流动氮(1500℃)中进行退火。x射线衍射显示,TiZrN2相在1000 ~ 1500℃的温度范围内生长,并在1500℃退火后被隔离为纳米级岩盐结构,因为它被限制在si3n4基体中。HRTEM研究证实了由尺寸低至9 nm的TiZrN2纳米晶体组成的纳米复合材料的独特纳米结构特征,这些纳米晶体分布在a-和b-Si3N4相中。
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引用次数: 0
Near-White Light and Near-Infrared Luminescence in Perovskite Ga:LaCrO 3 钙钛矿Ga:LaCrO 3的近白光和近红外发光
Pub Date : 2021-01-01 DOI: 10.2139/ssrn.3918915
T. Rajalekshmi, V. Mishra, Tejendra Dixit, M. Miryala, M. S. Ramachandra Rao, K. Sethupathi
We report the realization of near-white light emission (near-WLE) and the selective tuning to the near-infrared (NIR) luminescence from Ga substituted lanthanum chromite perovskite with electron-beam excitation. The Ga3+ acts as an electron donor in the LaCrO3 system and the emission intensity increases with Ga substitution. The near-WLE in CL, arises from the combination of 4T1(F)→4A2 (blue), 4T1(P)→4A2 (green) and 4T2→4A2 (red) spin allowed transitions and 2E→4A2 spin forbidden transitions from the Cr3+ ion. The spin allowed transitions from the Cr3+ ions are not common, however can be accomplished by adjusting the Cr3+/Ga3+ ion concentration in the host lattice. The NIR emission originates from the selective 2E→4A2 transition, which dominates with the increasing concentration of Ga3+ ions. The Density Functional Theory (DFT) calculations point out the presence of extra electronic states with Ga substitution, which validates the observation of NIR emission in Ga substituted samples.
本文报道了用电子束激发的方法,实现了镓取代镧铬铁矿钙钛矿的近白光发射和近红外(NIR)选择性调谐。在LaCrO3体系中,Ga3+作为电子给体,随着Ga的取代,发射强度增加。CL中的近wle是由Cr3+离子的4T1(F)→4A2(蓝色)、4T1(P)→4A2(绿色)和4T2→4A2(红色)自旋允许跃迁和2E→4A2自旋禁止跃迁共同引起的。自旋允许的Cr3+离子跃迁并不常见,但可以通过调节主晶格中的Cr3+/Ga3+离子浓度来实现。近红外发射源于选择性的2E→4A2跃迁,随着Ga3+离子浓度的增加,这种跃迁占主导地位。密度泛函理论(DFT)计算指出了Ga取代的额外电子态的存在,验证了Ga取代样品近红外发射的观察结果。
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引用次数: 2
A Comparison of in- and ex-situ Shear Bands in Metallic Glass by Transmission Electron Microscopy 金属玻璃原位剪切带与非原位剪切带的透射电镜比较
Pub Date : 2021-01-01 DOI: 10.2139/ssrn.3880065
H. Rösner, C. Kübel, S. Ostendorp, G. Wilde
Plastic deformation of metallic glasses performed at temperatures well below the glass transition proceeds via the formation of shear bands. In this contribution shear bands originating from in situ tensile tests of Al88Y7Fe5 melt-spun ribbons conducted in a transmission electron microscope are compared with ones which had formed ex situ during cold rolling. The observed contrasts for shear bands generated in situ at the edges of thin electron-transparent foils are shown to be related to a meniscus-like foil thickness reduction. In comparison with ex situ samples, alternating contrast changes due to volume changes are missing and the shear band width is a factor of 15 larger. The meniscus-like shear band profile is accounted for by the thin foil allowing volume increase due to shear deformation to annihilate via the free surfaces of the thin foil and the sheared zones to widen.
金属玻璃的塑性变形在远低于玻璃化转变的温度下通过剪切带的形成进行。通过透射电镜对Al88Y7Fe5熔体纺带原位拉伸试验中产生的剪切带与冷轧过程中形成的剪切带进行了比较。观察到的剪切带在薄电子透明箔边缘产生的对比显示与半月板状箔厚度减少有关。与非原位样品相比,由于体积变化而产生的交替对比度变化缺失,剪切带宽度增大了15倍。半月板状剪切带轮廓是由薄箔引起的,由于剪切变形通过薄箔的自由表面湮灭而使体积增加,剪切区扩大。
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引用次数: 0
In-situ Observation of Migration of {10¯12} α Twinning in an Mg-5Gd-3.5Ga (at.%) As-Cast Alloy Mg-5Gd-3.5Ga (at.%)铸态合金{10¯12}α孪晶迁移的原位观察
Pub Date : 2021-01-01 DOI: 10.2139/ssrn.3880066
Kaixuan Li, Yuanlin Zhuang, Ligong Zhao, Dongshan Zhao, He Zheng, Shuangfeng Jia, Ying Zhang, Peili Zhao, J. Gui, Jianbo Wang
We have achieved direct observation of the interaction between {10¯12}α twinning and long period stacking ordered (LPSO) structures in an Mg-5Gd-3.5Ga (at.%) as-cast alloy through in-situ compression experiments of submicron-sized pillars, and found that thick LPSO plates effectively retard the twinning propagation in the direction of perpendicular to the LPSO basal plane. In addition, although twinning can easily pass through low-density stacking faults (SFs), the step of twin boundaries on both sides of SFs on the atomic scale also exhibits resistance of SFs to twins. Dense LPSO structures hinder the occurrence of plastic deformation caused by twinning deformation. In this study, an in-situ technique was used to further discuss the strengthening mechanism of LPSO structures.
通过亚微米柱的原位压缩实验,直接观察了Mg-5Gd-3.5Ga (at.%)铸态合金中{10¯12}α孪晶与长周期有序堆积(LPSO)结构之间的相互作用,发现厚的LPSO板有效地延缓了与LPSO基面垂直方向的孪晶扩展。此外,虽然孪晶可以很容易地通过低密度层错,但在原子尺度上,层错两侧的孪晶边界步进也表现出对孪晶的抗性。致密的LPSO结构阻碍了孪生变形引起的塑性变形的发生。在本研究中,采用原位技术进一步探讨了LPSO结构的强化机理。
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引用次数: 0
Large Energy Storage Density and Electrocaloric Strength of Pb 0.97La 0.02(Zr 0.46-xSn 0.54Ti x)O 3 Antiferroelectric Thick Film Ceramics Pb 0.97La 0.02(Zr 0.46-xSn 0.54Ti x) o3反铁电厚膜陶瓷的大储能密度和电强度
Pub Date : 2021-01-01 DOI: 10.2139/ssrn.3910607
Shibin Wang, Pengfei Zhao, Xiaodong Jian, Yingbang Yao, T. Tao, B. Liang, Shengguo Lu
Pb0.97La0.02(Zr0.46-xSn0.54Tix)O3 (PLZST, x=0.04, 0.06, 0.08, 0.15, and 0.18) antiferroelectric thick film ceramics were fabricated via a tape-casting approach. The energy storage performance and electrocaloric effect were investigated in terms of the measurements on the hysteresis loops and Maxwell relation. The maximum value of energy storage density of 5.2 J/cm3 and efficiency of 78.2 % were procured at 600 kV/cm in Pb0.97La0.02(Zr0.42-xSn0.54Ti0.04)O3 thick film ceramics at room temperature. In addition, the ECE was indirectly calculated using the Maxwell relation and the P-E loops as a function of temperature and electric field, a reversible adiabatic temperature change of ΔT=2.47 °C was presented in Pb0.97La0.02(Zr0.42-xSn0.54Ti0.04)O3 thick film ceramics at 500 kV/cm, corresponding to the calculated electrocaloric strength of 0.48 K(MV/m)-1. These results indicate that the PLZST thick film ceramics are promising for practical applications in high-power energy storage capacitors and solid-state refrigeration devices.
采用带铸法制备了Pb0.97La0.02(Zr0.46-xSn0.54Tix)O3 (PLZST, x=0.04, 0.06, 0.08, 0.15, 0.18)反铁电厚膜陶瓷。通过对磁滞回线和麦克斯韦关系的测量,研究了储能性能和热效应。在室温下,Pb0.97La0.02(Zr0.42-xSn0.54Ti0.04)O3厚膜陶瓷在600 kV/cm下的储能密度最大值为5.2 J/cm3,效率为78.2%。此外,利用麦克斯韦关系和P-E回路作为温度和电场的函数间接计算了ECE, Pb0.97La0.02(Zr0.42-xSn0.54Ti0.04)O3厚膜陶瓷在500 kV/cm下的可逆绝热温度变化ΔT=2.47℃,对应于计算的电热强度为0.48 K(MV/m)-1。这些结果表明,PLZST厚膜陶瓷在大功率储能电容器和固态制冷装置中具有广阔的应用前景。
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引用次数: 0
期刊
AMI: Scripta Materialia
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