AuCu_3-亚格子系统的合金基因Gibbs能配分函数和平衡全息网络相图(英文)

以AuCu3-亚格子系统为例,介绍3项发现:第一,迄今阻碍金属材料科学进步的第三大障碍是研究者们习惯用平衡均匀转变的思维方式认识温度极其缓慢变化的合金相变实验现象,然后以实验现象的错误认识为选择信息,建立Gibbs能函数和所谓的"平衡相图";第二,AuCu3-型亚格子系统的平衡全息网络相图可用来描述与成分和温度有关的合金基因排列结构和各种热力学性质的系统相关性;第三,每个合金的平衡转变都是均匀的单相转变,不是非均匀的双相转变,存在一条没有有序相和无序相共存区的单相相界线,相界线顶点成分和温度远偏离AuCu3化合物临界点的计量成分和温度。     

Au_3Cu-亚格子系统的合金基因Gibbs能配分函数和平衡全息网络相图(英文)

以Au3Cu-亚格子系统为例,介绍了3项发现:第一,至今阻碍金属材料科学进步的第四大障碍是研究者们尚未认识到一个真正的合金相Gibbs能函数应由合金基因序列和它们自己的Gibbs能级序列构建的Gibbs能配分函数导出。第二,建立合金基因Gibbs能配分函数的六条规则,特别证明了计算合金组态熵的简并因子中结构单元占居Gibbs能级的概率应按照组元占居格点的概率方式简并;第三,以前研究者从未预料到的主要特征:具有一条没有有序相和无序相共存区的单相相界线;相界线顶点成分和温度远偏离Au3Cu化合物临界点的成分和温度;在0 K时,Gibbs能随成分变化曲线上的最低点成分远偏离Au3Cu化合物的成分;Au3Cu-型长程有序合金的理论极限成分范围由第一跳变有序度决定。     

Au3Cu-亚格子系统的合金基因Gibbs能配分函数和平衡全息网络相图（英文）

以Au3Cu-亚格子系统为例,介绍了3项发现:第一,至今阻碍金属材料科学进步的第四大障碍是研究者们尚未认识到一个真正的合金相Gibbs能函数应由合金基因序列和它们自己的Gibbs能级序列构建的Gibbs能配分函数导出。第二,建立合金基因Gibbs能配分函数的六条规则,特别证明了计算合金组态熵的简并因子中结构单元占居Gibbs能级的概率应按照组元占居格点的概率方式简并;第三,以前研究者从未预料到的主要特征:具有一条没有有序相和无序相共存区的单相相界线;相界线顶点成分和温度远偏离Au3Cu化合物临界点的成分和温度;在0 K时,Gibbs能随成分变化曲线上的最低点成分远偏离Au3Cu化合物的成分;Au3Cu-型长程有序合金的理论极限成分范围由第一跳变有序度决定。     

合金基因、全息网络相图和全息合金定位设计与研发系统

以系统科学哲学为指导,以Au-Cu合金系为实例,介绍了以下内容:合金基因、合金基因全息信息传输的Gibbs能函数以及AuCuI(Cu4Au8AA)化合物无序化的平衡和亚平衡传输方式,Au3Cu、AuCu和AuCu3亚格子系统的平衡全息网络相图(HNP);描述组元—成分—结构—性能—温度之间的关系;预测设计合金信息的蓝图:Au-Cu合金系的平衡和亚平衡HNP图。实现"网络化、信息化和智能化设计与研发先进合金"的路径规程是"基本组元合金系统—合金基因序列—亚格子合金系统的平衡HNP图—合金系的平衡和亚平衡HNP图—合金基因工程—合金系统全息知识与数据库"。实施此路径规程的基地称之为"全息合金定位设计与研发系统(HAPDS)"。     

14K彩色金合金的时效机理研究

研究了14K彩色金合金在时效过程中微观组织和结构的变化.在700 ℃×2h固溶处理后得到面心立方单相组织α0相,400℃不同时间时效使α0相发生分解.随时效时间及合金成分的不同,α0相发生分解的方式也不同,在2h时效时,借助淬火产生的大量空位,Cu原子发生迁移,最终生成具有调幅组织的α'0相,随着时效时间的延长,α’0相逐渐转变为AuCuⅠ有序相,出现时效硬化效果,最终随着合金中Cu含量的增加,α'0相完全转变为AuCu Ⅰ有序相.     

贵金属齿科铸造合金时效后结构和性能研究

通过对Au—Ag—Cu—Pt高含金量齿科铸造合金的研究，分析此合金的时效硬化行为，为其临床实际应用提供理论基础。试样经800℃，30min固溶处理后在350℃，500℃进行等温时效，通过金相组织观察、显微硬度测试、X射线衍射（XRD）和扫描电子显微（SEM）分析，研究了此齿科合金时效后的显微结构与性能。结果表明，该合金是典型的时效硬化型合金。长时间时效使面心立方基体α0相发生分解，最终转变为面心立方富银α2无序相和富Cu的面心正方AuCuⅠ有序相。两相以片状存在。晶界周围的片层厚，晶内的片层很薄，两者的分解方式不同。350℃短时间时效析出的AuCuⅠ有序相与基体保持共格，使基体中产生应力场，有效地提高了合金的硬度。     

Al-Y包晶合金非平衡凝固过程及组织特征

包晶凝固过程中小平面-小平面两相复相生长方式是凝固领域研究的一个热点。以初生相和包晶相都是严格计量比金属间化合物的Al-Y包晶合金作为研究对象,利用DSC热分析技术,严格控制冷却速度,获得不同凝固条件的非平衡凝固试样,研究了两相为小平面相的Al-Y包晶合金的凝固行为。发现小平面-小平面包晶系合金包晶凝固过程中,非平衡凝固特性及宏观偏析特点比非小平面包晶系更加明显。凝固特征温度与平衡相图偏差明显,包晶反应温度和包晶相直接凝固温度都远高于平衡相图给定的值,相对于相图是在“过热”条件下发生的,而固溶体型包晶合金一般是在“过冷”条件下发生的。包晶转变过程非常微弱,致使初生相残留量远高于平衡相图。即使对于过包晶成分的合金,其凝固组织中仍存在大量的共晶凝固组织,最终得到的凝固组织与平衡相图存在显著差异。     

Al对AuCu合金性能的影响

低Cu含量的AuCu和AuAgCu合金是传统的首饰和货币用合金,这类合金的铸造和加工性能良好。22KAuCu和AuAgCu合金相比,颜色以AuAgCu合金为佳。本实验研究了在22KAuCu合金中加少量Al对其加工性能和颜色的影响。对新合金初步进行了硬度、抗拉强度、延伸率、耐磨、耐人工汗腐蚀实验及光谱反射曲线的测量。结果表明,Al的加入降低了AuCu合金的强度,产生轻微的褪色。这种AuCuAl合金与AuAgCu合金相比,硬度、强度和延性都有明显提高,耐磨、耐蚀性完全相同,颜色也相近。     

基于热力学计算设计WC-10%Co-Cr3C2-VC超细硬质合金烧结温度

集成热力学计算和关键实验研究烧结温度对WC-10%Co-Cr₃C₂-VC超细硬质合金结构和性能的影响,基于平衡相图及固态黏结相完全消失温度设计合金成分和烧结工艺。结果表明：采用相图计算设计碳含量及烧结温度,合金微观结构中未出现有害相并且合金致密度都在99%以上,说明基于多组元硬质合金热力学数据库进行相图计算设计合金是可靠的;其次,同种合金成分下,烧结温度高于固态黏结相完全消失温度60℃时,合金的力学性能及可靠性最优,说明合理的调整烧结温度可减少合金中微型缺陷。     

湿化学法一步合成高有序L10-AuCu纳米粒子

利用湿化学法成功一步合成出高品质L1₀-AuCu纳米粒子。研究了合成工艺对AuCu纳米粒子的形貌、成分和有序度的影响。研究表明：随着温度的升高,AuCu纳米粒子结构将发生有序转变。当温度高于320℃时,AuCu纳米粒子开始转变为L1₀结构。AuCu纳米粒子中前驱体的添加比例也会影响其形貌和有序度。当金和铜的摩尔比x由小增大时,AuCu纳米粒子的分散度变差,L1₀结构的特征峰强度呈现出先增强后减弱的趋势。在合成温度为340℃,金铜摩尔比x为1.11时,成功获得了粒径小、有序度高、分散性好的AuCu纳米粒子。该制备方法工艺简单,可控性强,为直接合成高品质AuCu有序化纳米粒子提供了新思路。     

Thermal conductivity of Ni3V–Ni3Al pseudo-binary alloys

The effect of changes in the composition and microstructure of the Ni₃V–Ni₃Al pseudo-binary alloys on their thermal conductivity has been investigated. For Ni₃V and Ni₃Al-based single-phase alloys, the thermal conductivity shows a maximum value at the stoichiometric compositions, and it decreases as the V (or Al) content of the Ni₃Al (or Ni₃V) alloy increases, following the Nordheim rule. For Ni₃V–Ni₃Al two-phase alloys, the thermal conductivity of the constituent Ni₃Al phase exhibits a smaller value than that of the Ni₃V phase. Eventually, the thermal conductivity of the two-phase alloys decreases as the Al content increases because of the increase in the volume fraction of the Ni₃Al phase with low conductivity. As the temperature increases from 293 K to 1073 K, the conductivity increases for all of the alloys but not for stoichiometric Ni₃V. However, the dependence of the thermal conductivity on the alloy composition between 293 K and 1073 K is similar. Hence, it is confirmed that the thermal conductivity of the Ni₃V–Ni₃Al pseudo-binary alloys is controlled by the composition and volume fraction of the constituent phase.     

Order-disorder transformations in the heusler alloy Cd2AgAu

A sequence of order-disorder phase transformations was studied in the alloy Cd-Ag-Au at or near the Heusler alloy stoichiometry Cd₂AgAu. Total energy calculations based on an LMTO-ASA Hamiltonian were performed for a series of bcc compounds, from which equilibrium formation enthalpies were computed. A set of effective cluster interactions were fit to these results and then used as input to ternary cluster variation method calculations. The predictions for the B2 to Heusler alloy transition agreed well with experiment, as did the low-temperature portion of an isoplethal section of the ternary phase diagram. Predictions of sublattice occupations indicated a preference of Ag for the Cd sublattice in the phase with B2 symmetry.     

Order-disorder transformations in the heusler alloy Cd2AgAu

A sequence of order-disorder phase transformations was studied in the alloy Cd-Ag-Au at or near the Heusler alloy stoichiometry Cd₂AgAu. Total energy calculations based on an LMTO-ASA Hamiltonian were performed for a series of bcc compounds, from which equilibrium formation enthalpies were computed. A set of effective cluster interactions were fit to these results and then used as input to ternary cluster variation method calculations. The predictions for the B2 to Heusler alloy transition agreed well with experiment, as did the low-temperature portion of an isoplethal section of the ternary phase diagram. Predictions of sublattice occupations indicated a preference of Ag for the Cd sublattice in the phase with B2 symmetry.     

Isothermal Sections in the Mg-Corner of Mg-Er-Sn Ternary System at 300, 400 and 500 °C

The phase equilibria in the magnesium (Mg) rich corner of the Mg-Er-Sn ternary system at 300, 400 and 500 °C have been determined through key alloy method by means of x-ray diffraction and scanning electron microscopy with assistance of energy dispersive spectroscopy. The results show that in the composition range of our studied, each isothermal section consists of five single-phase regions, seven two-phase regions, and three three-phase regions, four compounds, i.e. Mg₂Sn, ErMgSn, Er₅Sn₃ and Er₅Mg₂₄ are found in equilibrium with the Mg solid solution. The homogeneity ranges of Mg solid solution as well as the solid solubilities of the intermediate phases at different temperatures are reported.     

Simultaneous phase separation and ferromagnetic transition in NdIn3−xCox

The crystal structures and magnetic properties of 3d transition metal Co dilute NdIn_3−xCo_x alloys have been studied by means of X-ray diffraction and magnetic measurements. Co doping into NdIn₃ causes the phase separation from cubic AuCu₃-type to hexagonal CaIn₂-type structure associated with a magnetic transition from paramagnetic to ferromagnetic. Rietveld's structural refinement confirms that two nonequivalent crystal positions (2b and 4f) exist in one unit cell for the hexagonal phase, which are occupied by 2Nd and 4(In,Co), respectively. The ferromagnetism of NdIn_3−xCo_x is suggested to be caused by the spin-spin interactions between Co and Co atoms. The increase of magnetic moment in NdIn_3−xCo_x might be due to the partial substitution of non-magnetic element In by 3d transition metal Co in the host material and thus a net moment is produced.     

Structure,magnetic and magnetocaloric properties of nonstoichiometric TbCo<Subscript>2</Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> compounds

The structure and magnetic and magnetocaloric properties of new nonstoichiometric TbCo₂Ni _x compounds (0 ≤ x ≤ 0.4) have been studied. The alloys with х ≤ 0.1 have been shown to be single-phase with the MgCu₂-type structure; in alloys with х > 0.1, an additional phase with a PuNi₃-type structure has been formed. It has been found that the concentration dependences of the Curie temperature and magnetic moment of the 3d-metal sublattice have a maximum at x = 0.025. The magnetocaloric effect magnitude for the TbCo2Nix compounds has been estimated using the results of magnetic and heat-capacity measurements.     

First-principles study of site occupancy of dilute 3d, 4d and 5d transition metal solutes in L10 TiAl

Using a statistical-mechanical Wagner–Schottky model parametrized by first-principles density-functional (DFT-GGA) calculations on 32-atom supercells, we predict the lattice site occupancy of 3d (Ti–Cu), 4d (Zr–Ag) and 5d (Hf–Au) transition-metal elements in L1₀ TiAl intermetallic compound as a function of both alloy composition and temperature. The effects of local atomic relaxations, anisotropic lattice distortions, as well as magnetism on point defect energetics are fully taken into account. Our calculations show that, at all alloy compositions and temperatures, Zr and Hf consistently show a preference for the Ti sublattice, while Co, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt and Au consistently show a preference for the Al sublattice. In contrast, the site preference of V, Cr, Mn, Fe, Ni, Cu, Nb, Mo, Tc, Ta and W strongly depend on both alloy stoichiometry and temperature. Our calculated results compare favorably with the existing theoretical and experimental studies in the literature.     

The steady-State corrosion kinetics of two-phase binary alloys forming the most-stable oxide

The steady-state kinetics in the high-temperature oxidation of binary A-B alloys containing a mixture of the conjugated solid solutions of B in A (alpha phase) and A in B (beta phase) with exclusive formation of the most-stable oxide BO_v have been examined, assuming that the external scale grows on top of a subsurface layer of alpha phase. The results obtained are compared with the corresponding behavior of alloys which are single phase in the whole range of composition. Under identical values of all the parameters involved the concentration of B at the alloy-scale interface is smaller for two-phase than for single-phase alloys under the same concentration of B in the alloy as a result of the restricted flux of B through the alpha-phase layer. As a consequence of this, the two-phase alloys corrode more slowly than single-phase alloys and this difference increases as the solubility of B in the alpha phase decreases. Finally, the simultaneous formation of BO_v both externally and as internal oxide is more likely for two-phase than for single-phase materials.     

The effect of microstructure on the shape recovery of a Fe–Mn–Si–Cr–Ni stainless steel shape memory alloy

In this work the effect of varying the microstructure on the shape memory properties of a Fe-15Mn-7Si-9Cr-5Ni (wt.%) stainless steel shape memory alloy was evaluated using a simple bend test. The best shape recovery was obtained for a single-phase austenite microstructure and for a two-phase microstructure composed of an austenite matrix and Fe₅Ni₃Si₂ type intermetallic grain boundary phase. The maximum shape recovery was achieved at the reversion temperature of 600 °C and when the pre-stain was less than 2%.     

Thermodynamics and nonstoichiometry in the D03 compound Ni3Sb

The thermodynamic activity of antimony was determined for nickel–antimony alloys in the composition range between 20 and 52 at% Sb by means of a Knudsen Effusion Mass Spectrometric (KEMS) method. The experimental data in the homogeneity range of the hexagonal γ-NiSb phase (B8-type) were compared with the literature data obtained by a different method. For the activity values in the nonstoichiometric compound Ni₃Sb (D0₃-type), a statistical-thermodynamic model was applied which uses the energies of formation of the six different types of point defects, obtained from ab initio calculations, as parameters. According to these formation energies, the most prominent point defects in nonstoichiometric Ni₃Sb are nickel vacancies. It was found that the inclusion of a full volume relaxation in the ab initio calculations improves the fit of the theoretical curve considerably.