Pb-Au合金热力学性质的分子动力学模拟

使用分子动力学方法模拟Pb40Au60、Pb80Au20和Pb90Au103种合金的热力学性质,计算合金的过剩自由能、结合能和形成能等能量方程。结果显示:合金的形成能和过剩自由能均为正值,因此Pb-Au合金为正偏差体系。从微观和宏观角度分析原子间的相互作用,并且使用形成能定量描述合金与理想熔体的偏离程度。     

Cu3Au中脱合金层产生内应力的分子动力学模拟

Cu3Au在腐蚀或应力腐蚀时表层Cu原子择优溶解形成脱合金疏松层,对具有疏松层的三维晶体（约148000个原子）,用镶嵌原子方法（EAM）势进行了分子动力学模拟,结果表明,一旦出现疏松层就会产生一个拉应力,它使单端固定,单边存在疏松层的晶体发生弯曲,其挠度（或拉应力）随疏松层增厚以及空位浓度升高而升高。     

AuNiCu合金摩擦磨损的分子动力学模拟

通过分子动力学模拟的方法,研究了Au-7.5Ni-xCu合金的摩擦磨损性能。首先采用粗糙体-平面接触模型和Atomsk软件构造合金模型;再由lammps软件计算出合金的摩擦力、摩擦系数判断出合金的摩擦学特性;最后通过Ovito软件对摩擦磨损过程进行可视化分析,包括摩擦磨损过程中组织结构和位错的演变,磨损表面原子的堆积情况等。结果表明,合金摩擦系数随着Cu含量的增加而呈现上升趋势,磨损后基体表明呈“U”形堆积,当Cu含量为10%时,基体抗变形能力最强;磨损过程中观察到晶粒的分裂和合并现象,合金基体内部位错密度明显增加。     

Ni-Al合金凝固过程的分子动力学模拟

利用分子动力学研究Ni3Al和NiAl合金在不同冷速下的凝固过程,分析冷却过程中不同温度下的偶分布函数、能量和体积的变化.研究表明:冷却速率为4×1013 K/s时,Ni3Al形成非晶结构;冷却速率为4×1011 K/s时,Ni3Al在1 100 K左右结构开始发生变化,最终形成晶体结构.冷却速率为4×1013 K/s时,NiAl形成非晶;冷却速率为4×1011 K/s时,NiAl在810 K形成部分的晶体结构.     

原位合成TiB和TiC增强钛基复合材料热力学

根据热力学理论编程计算了钛与Ｂ４Ｃ反应的反应生成焓ΔＨ与Ｇｉｂｂｓ自由能ΔＧ以及反应式（ｘ＋５）Ｔｉ＋Ｂ４Ｃ＝ｘＴｉ＋４ＴｉＢ＋ＴｉＣ的绝热温度。计算结果表明：钛与Ｂ４Ｃ反应释放出大量热,反应能自发维持,而过量钛与Ｂ４Ｃ反应更易生成ＴｉＢ和ＴｉＣ增强体。由于钛作为稀释剂吸收热量,随着过剩钛含量的增加,反应的绝热温度逐渐下降,过剩钛完全熔解的初始温度逐渐升高。     

Fe-Cu合金基体损伤的分子动力学模拟研究

采用分子动力学模拟了压力容器模型材料Fe-0.05Cu和Fe-0.3Cu合金的级联碰撞过程.研究了辐照导致的缺陷构型及其特征能量、Cu的空位迁移机理、Cu含量对初始损伤的影响、辐照温度对间隙原子团簇和空位团簇的影响等.结果表明,Cu对级联碰撞产生的缺陷数量、湮灭和复合没有明显影响,但可降低空位迁移能.辐照温度对团簇有明显影响.     

Cu64Zr36合金非晶剪切带形成的分子动力学模拟

用分子动力学(MD)模拟方法研究在轴向压缩下,冷却速率、应变率、环境温度、裂缝对Cu64Zr36二元非晶合金力学性能的影响。在模拟中,采用EAM势函数表述原子间的相互作用。计算结果表明:非晶的弹性模量和抗压强度都比晶体试样大一倍多,而当应变≥15%时两种试样的流动应力几乎相等;冷却速率缓慢得到的非晶试样由于原子发生重组变疏松,产生剪切带,而冷却速率较快得到的试样则没有发生重组;试样的弹性模量、抗压强度和流动应力对应变率变化很不敏感;随着环境温度的升高,流动应力、抗压强度和弹性模量降低;有初始裂纹的试样剪切带集中,从裂纹尖端开始,与加载方向呈45o方向扩展。     

低Al含量Ti-Al合金相变行为的分子动力学模拟

利用分子动力学模拟研究了Ti-5Al和Ti-10Al两种合金的β→α相变过程。比较分析了不同Al含量下相变过程的体系内能、径向分布函数、不同晶体结构相对含量的变化以及晶体结构的演化。结果表明:Ti-10Al较Ti-5Al更快发生α相形核析出,体现出实际相变过程中Al作为α相稳定元素的作用;β→α的结构转变通过{110}β面原子层间的相互滑移发生,并伴随一定畸变,新相与母相间晶体学关系符合{0001}α//{110}β;新相中易形成层错、孪晶等晶体缺陷,以消除部分相变过程中畸变引起的应力。     

单晶γ-TiAl合金纳米切削过程的分子动力学模拟

采用分子动力学方法研究单晶γ-TiAl合金纳米切削过程,通过对单晶γ-TiAl合金的建模、计算和分析,讨论了不同切削深度和切削速度对切削过程的影响,结果发现:在切削过程中,随着切削深度的增大,切屑体积逐渐增大,切屑中原子排列越来越紧密,位错密度也会随之增大;但随着切削速度的增大,位错密度反而会随之降低。在一定的切削深度和切削速度范围内,切削过程中刀具前方都会产生\"V\"型位错环,工件的温度和势能也都会相应的增大。特别是,当切削速度为400 m/s时,刀具前方的切削表面上未出现原子错排。     

Molecular Dynamics Simulation of Thermodynamic Properties for Pb-Au Alloys

The molecular dynamics method was used to simulate thermodynamic properties of three binary alloys: Pb40Au60, Pb80Au20 and Pb90Au10. The energy functions, including excess free energy, cohesive energy and formation energy, were calculated. Formation energy and excess free energy are all negative values, so Pb-Au alloys belong to negative system. The atomic interactions were analyzed in macroscopic and microcosmic views. The calculated formation energy can describe the deviation degree between the actual alloy and the ideal melt quantitatively     

NaF-AlF_3系熔盐结构的分子动力学计算

使用Born Mayer Huggins(BMH)型势函数 ,用分子动力学 (MD)方法模拟计算了 (NaF) x(AlF3) 1-x(x=0 .8,0 .75 ,0 .6 7,0 .5 )熔盐体系在 132 3K时的结构 ,得到了径向分布函数、F Al F键角分布等结构信息 ,其中各熔体的F Al F键角分布呈现相似的特征 ,在 80°～ 90°之间和 16 0°～ 170°之间出现峰值。统计了由平衡构像所得到的熔体中Al F的配位情况 ,结果证实在所得势函数作用下 ,熔体中主要基团形式是AlF3-6八面体 ,其中桥氟在结构形成中起很大作用 ,NaAlF4 熔体中的铝氟八面体通过氟桥连接成较大的集团或空间网络     

Tensile properties of nanocrystalline tantalum from molecular dynamics simulations

The tensile behaviors of nanocrystalline tantalum are studied using molecular dynamics simulations. The results show that the elastic modulus increases linearly with density. The flow stress decreases with decreased grain size, but increases with increased strain rate or decreased temperature. A strain rate sensitivity of ∼0.14 is derived from the simulations with a resultant activation volume of ∼1b³ associated with plastic deformation. Grain rotation, grain boundary sliding or migration, dislocation motion and intergranular activities are observed in the deformation process. Twinning is regarded to be a secondary mechanism. Stress-induced phase transitions from body-centered cubic to face-centered cubic (fcc) and hexagonal close-packed (hcp) structures take place locally, and the hcp structure is a derivative of the fcc structure. The higher the strain rate, the further delayed the phase transition. Such phase transitions are found to occur only at relatively low-temperatures and are reversible with respect to stress.     

Thermodynamic calculation of high zinc-containing Al-Zn-Mg-Cu alloy

Phase fraction and solidification path of high Zn-containing Al-Zn-Mg-Cu series aluminum alloy were calculated by calculation of phase diagram (CALPHAD) method. Microstructure and phases of Al-9.2Zn-1.7Mg-2.3Cu alloy were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The calculation results show that η(MgZn₂) phase is influenced by Zn and Mg. Mass fractions of η(MgZn₂) in Al-xZn-1.7Mg-2.3Cu are 10.0%, 9.8% and 9.2% for x=9.6, 9.4, 8.8 (mass fraction, %), respectively. The intervals of Mg composition were achieved for θ(Al₂Cu)+η(MgZn₂), S(Al₂CuMg)+η(MgZn₂) and θ(Al₂Cu)+S(Al₂CuMg)+η(MgZn₂) phase regions. Al₃Zr, α(Al), Al₁₃Fe₄, η(MgZn₂), α-AlFeSi, Al₇Cu₂Fe, θ(Al₂Cu), Al₅Cu₂Mg₈Si₆ precipitate in sequence by no-equilibrium calculation. The SEM and XRD analyses reveal that α(Al), η(MgZn₂), Mg(Al,Cu,Zn)₂, θ(Al₂Cu) and Al₇Cu₂Fe phases are discovered in Al-9.2Zn-1.7Mg-2.3Cu alloy. The thermodynamic calculation can be used to predict the major phases present in experiment.     

Reactive molecular dynamics study of the oxidation behavior of iron-based alloy in supercritical water

A theoretical study of the oxidation behavior of iron-based alloy in the supercritical water (SCW) has been carried out based on ReaxFF force-field molecular dynamics simulation. An atomic model has been proposed to simulate the initial chemisorption reactions and atoms diffusion behavior across the oxide layer. Simulation results imply that Cr addition has an important effect on the oxidation behavior of iron-based alloy. In the initial stage of oxidation, H₂O prefers to adsorb on the Cr atom, and some species in the form of Cr(OH)₄ are observed on the FeCr alloy surface. Once an initial oxide layer is formed, further oxidation is controlled by the migration of vacancy. The O vacancies are formed at the oxide/FeCr alloy interface and migrate toward the steam, whereas Fe vacancies are formed at the oxide/steam interface and migrate toward the FeCr alloy. Attributed to the stronger binding energy of O–Cr bond than O–Fe bond, the Cr diffusivity in the oxide is less than Fe atoms. Thus, double oxide layers, including the inner Fe–Cr–O layer and outer Fe–O layer, are formed on the FeCr alloy, which is in good agreement with previous experimental observation.     

The circumferential tensile properties of zirconium alloy fuel claddings under a simulated high burn-up environment

To study the circumferential tensile properties of fuel claddings under a simulated high burn-up environment, ring tensile tests were carried out at both room temperature and 350 °C for Zr-Nb based fuel claddings such as Zr-Nb based HANA-6 (Zr-1.10Nb-0.05Cu), HANA-4 (Zr-1.50Nb-0.40Sn-0.20Fe-0.10Cr) and Zircaloy-4 (Zr-1.26Sn-0.23Fe-0.12Cr) cladding after they had been differently charged with hydrogen up to 2,850 ppm. The results showed that the HANA-6 cladding maintained more than a 20% circumferential elongation at room temperature without a decrease in its maximum strength when it was charged with hydrogen up to about 1,500 ppm, although the maximum circumferential strength and elongation of the Zircaloy-4 cladding decreased with increasing hydrogen content above 500 ppm. The circumferential elongation of the above claddings decreased as the hydrogen content increased at both room temperature and 350 °C but the strength increased a little with the hydrogen content at 350 °C. The maximum circumferential strength of the HANA-4 cladding also increased with the hydrogen content up to a level of 1,109 ppm, even at room temperature. It seemed that the Nb in the matrix contributed to better circumferential elongation and resistance to hydrogen embrittlement in the Zr-Nb based HANA-4 and HANA-6 claddings than was present in the Zircaloy-4 cladding.     

Ag-Cu-Ti活性钎料热力学分析

在陶瓷与金属的活性钎焊连接技术中,Ag—Cu—Ti合金是研究和应用最多的钎料之一。合金组元Ti的活度是影响钎料／陶瓷界面反应的关键因素,对钎料与陶瓷的润湿性和连接能力起着重要的作用。作者借助热力学对Ag—Cu—Ti活性钎料进行了热力学分析,重点分析了Ti的热力学活度及其与组分浓度之间的关系,计算了各组分之间的相互作用参数。分析和计算结果表明,Ti的活度随着Cu含量的增加而减小,随着Ag含量的增加而增大;Ag与Ti之间存在较大的排斥作用,两者的相互作用参数为32．83kJ／mol;而Cu与Ti之间存在强烈的吸引作用,其相互作用参数为-16．14kJ／mol;Ag—Cu—Ti合金中添加某些与Cu的结合力大、与Ti的结合力小、且与合金组元不形成高熔点化合物或脆性相的合金元素,有利于提高合金中的Ti活度。