含TiCr2 Laves相过共析钛铬合金的制备

通过非自耗磁控电弧炉熔铸和 70 0℃ ,2 0h高温退火处理 ,制备出了含铬量为 18%～ 30 % (质量分数 )的含TiCr2 Laves相过共析钛铬合金 ,并研究了合金的组织变化规律。结果表明 ,稳定化系数为 2 .5 7～ 4 .6 2的过共析钛铬合金经过熔炼后 ,在随炉冷却条件下得到的是单相 β Ti组织 ;铸态合金在 70 0℃保温退火时 ,金属间化合物TiCr2 不仅沿晶界生成并形成连续分布 ,还在基体内部弥散析出 ;在随后的空冷过程中合金内局部发生 β Ti→α Ti TiCr2 共析分解。合金含铬量越高 ,在高温退火时析出的TiCr2 量越多 ,尺寸越粗大 ,合金的硬度也越高。电弧熔炼 70 0℃ ,2 0h高温退火是一种制备含Laves相过共析钛铬合金的可行工艺     

High temperature oxidation behaviors of Ti-Cr alloys with Laves phase TiCr2

1　ＩＮＴＲＯＤＵＣＴＩＯＮＷｉｔｈａｈｉｇｈｍｅｌｔｉｎｇｔｅｍｐｅｒａｔｕｒｅ ,ｃｈｒｏｍｉｕｍｉｓｔｈｅｓｏｌｅｒｅｆｒａｃｔｏｒｙｍｅｔａｌｅｌｅｍｅｎｔｗｉｔｈｇｏｏｄｈｉｇｈｔｅｍ ｐｅｒａｔｕｒｅｏｘｉｄａｔｉｏｎｒｅｓｉｓｔａｎｃｅ[1] ,ｓｏ     

Laves相TiCr2基金属间化合物的研究进展

Laves相铬化物以其熔点高、适当的密度和良好的高温强度成为重要的潜在高温结构材料。对Laves相TiCr2金属间化合物的研究进展进行了综述,重点对TiCr2的性质及其基础研究、热力学性能以及TiCr2的合金化研究现状进行了论述。     

Defect structures in ZrCo2 Laves phase

Point defect structures in the C15 ZrCo₂ alloys were studied by bulk density and X-ray lattice parameter measurements. It was found that, for the ZrCo₂ alloys quenched from 1000°C, the lattice parameter increases linearly as the Zr content increases up to 33.3 at.% Zr. The lattice parameter of the Laves phase remains constant for the alloys with Zr content higher than 33.3 at.%, indicating that the solubility range of Zr in ZrCo₂ on the Zr-rich side is essentially zero. The constitutional defects were found to be of the anti-site type. Thermal vacancies exhibiting a maximum at the stoichiometric composition were observed in the ZrCo₂ Laves phase alloys after quenching from 1250 and 1000°C, with higher thermal vacancies obtained from 1250°C. The defect structures in the ZrCo₂ phase may be correlated to the relative magnitude of formation enthalpies for anti-site and quadruple defects in this compound. Thermal vacancy concentration at a level of 1% in ZrCo₂ does not affect fracture toughness at room temperature.     

Effect of lattice anharmonicity in the structural phase transformation of Laves phase HfV2 alloy: A first-principles investigation

First-principles theory was developed to study the structural phase transformations in the Laves phase HfV₂ alloy. We explored the energy landscape and established the role of lattice anharmonicity underlying the structural phase transitions. Our approach is based on a phenomenological Landau theory for the structural phase transition and a mean-field approximation for the free energy. First-principles calculations were utilized to obtain the distortion energy as a function of relevant deformations, and to deduce parameters for constructing the free energy. Our result for the phase transition temperature of HfV₂ is in good agreement with experiment. We find that the high-temperature cubic C15 phase is stabilized by the effect of lattice anharmonicity. The theory also predicts an anomalous increase in shear modulus with increasing temperature for systems where the anharmonicity is pronounced.     

CuZnSnSi合金钎料相变过程的热分析动力学

CuZnSnSi合金钎料在钎焊钢工件中具有良好的综合性能.为进一步探究其合金性能,借助差示扫描分析(DSC)和热重分析(TG)技术,分别采用微分非等温法和积分非等温法分析了CuZnSnSi合金钎料相变过程的热分析动力学.结果表明,CuZnSnSi合金的相变温度范围为1150.5~1221.5 K,吸热峰温度为1174.46 K,在相变过程中没有化学反应,但出现升温段的吸热峰温度滞后于降温段的放热峰,说明了合金钎料在结晶过程需要一定的过冷度;非等温分析法计算得到合金钎料相变表观活化能为615.72 kJ/mol;由Arrhenius公式得出合金钎料相变速率常数k的变化规律为1.71×1027exp(-6.16×10⁵/RT).     

Evaluation of the maximum transformation rate for analyzing solid-state phase transformation kinetics

An evaluation of the maximum in the transformation rate of a solid-state transformation is given for isothermal and isochronal transformations, on the basis of a general, flexible, analytical transformation model incorporating different combinations of nucleation, growth and impingement modes. For isothermal phase transformations, the position of the peak maximum is determined by the growth exponent and the impingement mode whereas, for isochronal phase transformations, only the impingement mode influences the position of the peak maximum. A straightforward method has been developed for determining the mode of impingement and the separate activation energies for nucleation and growth. The results obtained by application of the proposed transformation-rate maximum analysis to model systems are in good agreement with the values assigned to the kinetic parameters of the model systems. The proposed recipes have also been applied successfully to experimental data on the crystallization of an initially amorphous Mg–Cu–Y alloy.     

Point defects in binary Laves phase alloys

Point defects in the binary C15 NbCr₂ and NbCo₂, and C14 NbFe₂ systems on both sides of stoichiometry were studied by bulk density and X-ray lattice parameter measurements. It was found that the vacancy concentrations in these systems after quenching from 1000°C are essentially zero. The constitutional defects on both sides of stoichiometry for these systems were found to be of the anti-site type in comparison with model predictions. Thermal vacancies exhibiting a maximum at the stoichiometric composition were observed in NbCr₂ Laves phase alloys after quenching from 1400°C. However, there are essentially no thermal vacancies in NbFe₂ alloys after quenching from 1300°C. Anti-site hardening was found on both sides of stoichiometry for all the three Laves phase systems studied. Neither the anti-site defects nor the thermal vacancies affect the fracture toughness of the Laves phases significantly.     

The native point defects in C14 Mg2Ca Laves phase: A first-principles study

The native point defects in C14 Mg₂Ca Laves phase are studied from the first-principles density functional theory calculations within GGA approximation. The defect formation energies indicate that anti-site defects are energetically favored over vacancies. Under Mg-rich and even general Ca-rich condition, defect Mg_Ca of Mg anti-site on Ca sublattice is favorable owing to the lowest formation energy. The Ca_Mg2 defect of Ca anti-site on Mg2 sublattice is also likely dominant only under extreme Ca-rich environment. The present results could explain reasonably the asymmetric off-stoichiometry of Mg₂Ca. The effective point defect concentrations of Mg₂Ca as a function of composition and temperature at experimental range are also calculated from a canonical statistical model, and the derived results show a linear relationship between the logarithm of defect concentration and T⁻¹. Geometrical factor is further studied, and it is found that atomic size possesses an obvious influence on the structure of point defect in Mg₂Ca. The electronic feature is further studied to reveal underlying mechanism for formation of point defects.     

颗粒各向异性生长对固态相变动力学的影响(英文)

基于对颗粒各向异性生长引起阻碍效应的几何概率分析,研究生长各向异性效应对固态相变动力学的影响。结果表明:阻碍效应导致生长速率降低,进而导致Avrami指数的规律变化。根据先前的解析模型,推导动力学参数Avrami指数和总有效激活能的解析表达。各向异性效应对相变的影响不仅取决于非阻碍因子?,还取决于阻碍级数k。各向异性效应直接作用在颗粒生长维度上,却不影响转变过程的总有效激活能。考虑到各向异性生长所引起的阻碍效应与转变分数的演化,发现各向异性效应在相变过程中期最为剧烈。     

合金化对ZrMn2基Laves相贮氢合金相组成的影响

研究了Ni、V、Cr、Co、Fe、Cu和Ti等合金化元素取代ZrMn2 基Laves相贮氢合金的B侧或A侧对合金相组成的影响。结果表明 ,采用不同的元素对A侧或B侧进行部分取代 ,将引起ZrMn2 基合金相组成的变化。采用Ni取代Mn后 ,ZrMn2 合金的主相结构转变为C15型Laves相 ,表明Ni为C15相稳定元素。对Zr Mn Ni三元合金 ,V为C14相稳定元素 ,而Co、Fe、Cu则为C15相稳定元素。取代量较少时 ,Cr为C15相稳定元素 ,取代量增加时 ,C15相稳定作用减弱。Ti元素为C14相稳定元素 ,Ti对Zr的部分取代将导致合金主相结构转变为C14型Laves相。合金化元素对ZrMn2 合金的相组成的影响与元素的电子浓度和原子尺寸不同有关     

Zr-Nb-Cu合金连续升温相转变动力学研究

采用热膨胀法对Zr-1Nb-0.01Cu合金在不同升温速率下α_(Zr)→α_(Zr)+β_(Zr)相转变动力学进行了研究。结果表明,α_(Zr)→α_(Zr)+β_(Zr)相转变起始温度与升温速率之间的关系为:Tα→α+β=744.4+9.4ln(R H),升温速率对合金相转变温度的影响要小于E110合金;结合JMA方程计算得到α_(Zr)→α_(Zr)+β_(Zr)相转变的激活能为149.1 kJ/mol,低于Zr-4和M5合金的相转变激活能。根据合金相转变动力学曲线,给出了合金连续升温过程α_(Zr)→α_(Zr)+β_(Zr)相转变的CHT连续升温相转变图。     

17-4PH不锈钢连续冷却转变及相变动力学

通过热模拟试验、X射线衍射、扫描电镜(SEM)、透射电镜(TEM)等方法研究了17-4PH不锈钢连续冷却转变行为、奥氏体稳定化以及马氏体相变动力学。研究发现,在0.05~5 ℃/s冷却速度范围内,17-4PH不锈钢只发生马氏体转变,Ms和Mf分别为116 ℃和35 ℃;在0.05~0.3 ℃/s冷速范围内出现奥氏体稳定化现象,当冷速≥0.5 ℃/s时奥氏体稳定化现象消失。在0.05~5 ℃/s冷速范围内,试验钢中都有少量的NbC析出;而在冷速≤0.08 ℃/s时,试验钢中可析出一定数量弥散的纳米ε-Cu颗粒。此外,根据试验数据构建了预测17-4PH不锈钢马氏体相变动力学的K-M方程。     

Hydrogen diffusion studies in Zr-based Laves phase AB2 alloys

The diffusion of hydrogen in the tetrahedral interstitials of bulk spherical Laves phase ZrMn_0.85Cr_0.1V_0.05Fe_0.5Ni_0.5 and ZrMn_0.85Cr_0.1V_0.05Fe_0.5Ni_0.5 + 1 wt% B alloys has been studied in the α-phase (solid-solution) region over the temperature range 450–650 °C, for hydrogen pressures up to 100 mbar using Sieverts-type apparatus. The diffusion constants have been determined from the gas–solid reaction, where the gas pressure dependence on time has been measured at fixed temperature. The results have been discussed on the basis of Fick's law of diffusion. The dependence of diffusion constant on alloy composition and initial pressure has been evaluated. Activation energy has been obtained from the temperature dependence of diffusion using Arrhenius relation.     

Point defect structures of YAl2 and ZrCo2 Laves phase compounds by first-principles calculations

In Laves phase alloys with prominent size mismatch between constituent atoms and/or large negative enthalpy of formation, the existence of vacancies as the dominant point defect type is often suggested. However, there are not enough experimental data to prove or disprove these arguments. Employing first-principles calculations, we study the point defect structures of YAl₂ and ZrCo₂ C15 Laves phases, as both compounds exhibit large size mismatch between constituent atoms, and large negative enthalpy of formation. We find that one must go beyond the simple geometrical or enthalpy arguments in determining the point defect structures of these alloys. In both compounds, the point defect structure is found to be dominated by the anti-site defects on the larger atom-rich side of the stoichiometry.     

1000MPa级冷轧双相钢奥氏体的等温相变动力学

在DIL 805A膨胀仪上测定了Nb微合金化1000 MPa级冷轧双相钢连续加热及两相区保温过程中的热膨胀曲线,根据杠杆定律计算的奥氏体体积分数与定量金相测量值符合较好.740、770和800℃保温100 s的过程中,奥氏体的等温相变动力学曲线明显分为两个阶段,两个阶段可分别由JMAK方程描述.第Ⅰ阶段时间指数较大,奥氏体体积分数增长较快,奥氏体长大由C的扩散控制;第Ⅱ阶段时间指数降低,奥氏体体积分数的增长明显变慢,奥氏体长大转变为由Mn的扩散控制.在较低的保温温度下,奥氏体长大可以更快的由C扩散控制转变为由Mn扩散控制.     

Microstructural formation in Ti alloys: In-situ characterization of phase transformation kinetics

The prediction of microstructure during processing needs to characterize the phase transformation occurring during the thermal treatments and their kinetics. In-situ high-energy synchrotron x-ray diffraction experiments performed during temperature variations allow the characterization of the phase evolution. For some transformation conditions, the continuous recording of diffraction diagrams evidences clearly intermediate phases. The quantitative analysis of the diffraction diagrams gives the transformation kinetics of each phase as well as their cell parameters. Transformation kinetics obtained by this method are compared to results obtained by electrical resistivity.