First-Principles Studies on Twinnability of Magnesium Alloys: Effects of Yttrium and Lithium on $$\left( {10\bar{1}1} \right)\left[ {\bar{1}012} \right]$$ Compression Twinning Deformation Processes

We investigate the energetics involved in the \(\left( {10\bar{1}2} \right)\left[ {\bar{1}011} \right]\) tension and \(\left( {10\bar{1}1} \right)\left[ {\bar{1}012} \right]\) compression twinning deformation processes in magnesium via first-principles studies. Through identification of structural changes associated with each deformation process, we study the energetics of each deformation process and the local instability in the twin boundary region. We observe that the energy barrier in the \(\left( {10\bar{1}1} \right)\left[ {\bar{1}012} \right]\) compression twinning deformation pathway is higher than that in the \(\left( {10\bar{1}2} \right)\left[ {\bar{1}011} \right]\) tension twinning deformation pathway, even though the \(\left( {10\bar{1}1} \right)\) compression twin boundary is more stable than the \(\left( {10\bar{1}2} \right)\) tension twin boundary. We extend our study to examine the effects of Y and Li as alloying elements on each twinning deformation process. Our calculations predict that the addition of Y causes a reduction in the probability of fracture by an order of magnitude when the twinning deformation occurs and weakening of the resistivity to twinning deformation. However, the effect of Li addition on the twinning deformations is weaker than that of Y addition.     

Atomistic simulation of tension deformation behavior in magnesium single crystal

The deformation behavior in magnesium single crystal under c-axis tension is investigated in a temperature range between 250 K and 570 K by molecular dynamics simulations. At a low temperature, twinning and shear bands are found to be the main deformation mechanisms. In particular, the {1012} tension twins with the reorientation angle of about 90° are observed in the simulations. The mechanisms of {1012} twinning are illustrated by the simulated motion of atoms. Moreover, grain nucleation and growth are found to be accompanied with the {1012} twinning. At temperatures above 450 K, the twin frequency decreases with increasing temperature. The {1012} extension twin almost disappears at the temperature of 570 K. The non-basal slip plays an important role on the tensile deformation in magnesium single crystal at high temperatures.     

Effect of nitrogen and stacking-fault energy on twinning in [ \bar 1 11] single crystals of austenitic stainless steels

The dependence of critical shear stresses for twinning τ _cr ^tw on the stacking-fault energy γ₀, the nitrogen concentration C _N (wt %), and the test temperature has been studied for [ $ \bar 1 $ 11] single crystals of austenitic stainless steels upon tensile deformation. It is shown that τ _cr ^tw ～ γ₀/b ₁ in nitrogen-free steels, while it exhibits a nonmonotonic dependence on the nitrogen concentration C _N in nitrogen-alloyed steels. An increase in τ _cr ^tw at C _N = 0.3 wt % and its decrease at C _N ≥ 0.5–0.7 wt % are determined by the competition of two contributions to τ _cr ^tw , namely, a decrease in γ₀ and a solid-solution hardening with increasing nitrogen concentration.     

Sulfidation properties of an Fe-26.4Cr-8Al-6Mn alloy at 973 and 1073 K in H2S-H2 atmospheres,10^{ - 4} \leqslant {\text{P}}_{{\text{S}}_{\text{2}} } \leqslant 10^2 {\text{Pa}}

The sulfidation behavior of an Fe-26.4Cr-8Al-6Mn (at.%) alloy in H₂S-H₂ atmospheres, \(10^{ - 4} \leqslant {\text{P}}_{{\text{S}}_{\text{2}} } \leqslant 10^2 {\text{Pa}}\) .     

Atomistic simulation of the structural evolution in magnesium single crystal under c-axis tension

Molecular dynamics simulation is applied to investigate the microstructure evolution of magnesium single crystals under c-axis extension at different temperatures. At low temperatures, both {10 ˉ 12} and {10 ˉ 11} twins are observed. At elevated temperatures, {10 ˉ 11} twining decreases quickly with increasing temperature, while the amount of {10 ˉ 12} twins increases. The {10 ˉ 12} twin is found to be the main deformation mechanism under the c-axis tension in the magnesium single crystal. Meanwhile, shear ...     

DD6单晶合金筏化过程中元素定向迁移行为

对[001]取向DD6单晶合金进行1000°C、300MPa条件下的拉伸蠕变实验,以研究合金的筏化现象以及元素的定向迁移行为,SEM对合金显微组织的观察表明,γ′相在温度和应力的作用下发生了筏化,且筏化方向与应力轴垂直,同时平行于应力轴的基体通道变宽,垂直方向的基体通道逐渐消失。TEM对合金的成分统计分析表明,合金中Al、Re、W元素发生了定向迁移,其中Al向与应力轴平行的基体通道扩散,而Re、W向与应力轴垂直的基体通道扩散,并主要富集于相互垂直的基体通道的交叉区域。     

The cyclic oxidation behavior of the single crystal TMS‐82+ superalloy in humidified air

The cyclic oxidation behavior of a single crystal Ni‐based superalloy TMS‐82+ was studied at 800 and 900 °C for 200 h in water vapor (air plus 15% H₂O). Regardless of the exposure temperature, time‐dependence of the growth rate of the scale for the superalloy was fitted by a subparabolic relationship. The oxidation rate was enhanced with increase in exposure temperature, which was evidenced by a higher mass gain and thicker scale. The oxides on the specimen at 800 °C consisted of (Ni,Co)O, CrTaO₄, AlTaO₄, Cr₂O₃, and θ‐Al₂O₃, whereas for the specimen exposed at 900 °C, spinels of NiCr₂O₄ and (Ni,Co)Al₂O₄ as well as α‐Al₂O₃ were observed. An innermost dense α‐Al₂O₃ layer was responsible for a stable growth rate of the scale after the initial rapid oxidation.     

连续柱状晶组织Cu-12%Al合金在3.5%NaCl和10%HCl溶液中的腐蚀行为

采用静态浸泡腐蚀实验、电化学分析方法等研究连续定向凝固方法制备的具有连续柱状晶组织的Cu-12%Al(质量分数,下同)合金在3.5%NaCl(质量分数)溶液和10%HCl(体积分数)溶液中的耐腐蚀性能及腐蚀机理。结果表明:Cu-12%Al合金在3.5%NaCl溶液中的耐腐蚀性能可达到耐蚀级。虽然在40℃以下的10%HCl溶液中该合金的耐腐蚀性能可达到耐蚀级,但在40℃以上的10%HCl溶液中的耐腐蚀性能欠佳。连续柱状晶组织Cu-12%Al合金的耐腐蚀性能优于Al含量为5%~11%的传统铝青铜和QBe2合金的耐腐蚀性能,但劣于QBe2.15合金的耐腐蚀性能。在3.5%NaCl溶液和10%HCl中连续柱状晶组织Cu-12%Al合金的自腐蚀电位分别为-271 mV(vs SCE)和-333 mV(vs SCE)。腐蚀发生后试样表面的Al元素含量明显下降,腐蚀机制为脱铝腐蚀。     

Oxidation behavior of the single crystal Ni-based superalloy at 900 °C in air and water vapor

The oxidation behavior of a single crystal Ni-based superalloy TMS-82+ was studied in cyclic air and water vapor (air plus 15% H₂O) at 900 °C for 200 h. Oxidation kinetics was evaluated by mass gain measurements and the oxide scale was analysed by XRD, SEM and EDS, including the quantitative elemental concentration profiles by EPMA. Water vapor accelerated the growth rate of the oxides of NiO, Cr₂O₃ and spinel of NiCr₂O₄ due to the incursion of H, resulting in a higher mass gain and a thicker oxide scale with larger oxide grains of (Ni,Co)O.     

Antiferromagnetic transition in ternary rare-earth metal silicide Er5Ir4Si10 single crystal

In the present paper the electric field dependence of the permittivity of (Ba, Sr)TiO₃ ceramics is reported. Single phase Ba_1−xSr_xTiO₃ (x = 0.20 and 0.30) ceramics were obtained by powders synthesized by a modified Pechini method. The dc-tunability at room temperature is higher for the ceramic with lower strontium content as this composition is ferroelectric at room temperature, whereas the composition corresponding to the higher strontium content is paraelectric. The data are well described by the Johnson's approximation for the ferroelectric state and by an additional “extrinsic” contribution due to the polar clusters in the case of the paraelectric state (Ba, Sr)TiO₃ ceramic.     

Peculiarities of component interaction in {Gd, Er}-V-Sn Ternary systems at 870 K and crystal structure of RV6Sn6 stannides

The phase equilibria in the Gd-V-Sn and Er-V-Sn ternary systems were studied at 870 K by means of X-ray and metallographic analyses in the whole concentration range. Both Gd-V-Sn and Er-V-Sn systems are characterized by formation of one ternary compound at investigated temperature, with stoichiometry RV₆Sn₆ (SmMn₆Sn₆-type, space group P6/mmm, a = 0.55322(3) nm, c = 0.91949(7) nm for Gd, a = 0.55191(2) nm, c = 0.91869(8) nm for Er). Solubility of the third component in the binary compounds was not observed. Compounds with the SmMn₆Sn₆-type were also found with Dy, Ho, Tm, and Lu, while YV₆Sn₆ compound crystallizes in HfFe₆Ge₆ structure type. All investigated compounds are the first ternary stannides with rare earth elements and vanadium.