不同弹性畸变程度下Ni75Al14Mo11合金沉淀过程的多尺度模拟

基于微观相场模型和第一性原理方法模拟了Ni75Al14Mo11合金在不同弹性畸变能常数下的相变过程。当弹性畸变能从无到有时,沉淀相形貌由椭圆状变为块状,分布由不规则随机排列变为沿弹性"软"方向规则排列,具有一定方向性;弹性畸变能对短程DO22有序相的析出有抑制作用,并且对沉淀粗化过程的影响要大于对析出过程的影响;弹性畸变能对沉淀相的有序化及原子簇聚的影响并不是随着其增加而简单的起抑制或促进作用,而是与其取值范围有关。在相同的外界条件下,Ni、Al元素形成Ni3Al要比Ni、Mo元素形成Ni3Mo容易,导致Ni75Al14Mo11合金在1073 K时效下较易析出Ni3Al。     

Microscopic phase-field simulation for precipitation behavior of Ni-Al-Cr alloy during two-step aging

Based on the microscopic phase-field model, the pre-aging temperature effects on the precipitation mechanism and microstructure evolution during two-step aging for Ni75A19Cr16 alloy were simulated. The results show that the early precipitation mechanism of Ll2 phase is the mixed mechanism of spinodal decomposition and non-classical nucleation growth, whereas the early precipitation mechanism of DOzz phase is spinodal decomposition when the pre-aging temperature is 873 K. The early precipitation mechanism of LIz phase is non-classical nucleation growth, whereas the early precipitation mechanism of DOzz phase is spinodal decomposition when the pre-aging temperature is 973 K. Under the effects of elastic strain energy, the cubic particles exhibit directional alignment along [ 100] and [010] directions during the late precipitation, which is more obvious at lower pre-temperature. DOzz phases appear earlier than Llz phases under these two kinds of precipitation processes; and the nucleation incubation time becomes long with the increase of pre-temperature.     

Ni-Al合金中沉淀相Ni3Al相互关系的微观相场模拟

基于微观相场动力学模型和微观弹性理论,研究了Ni-Al合金中沉淀相Ni_3Al(γ')形貌演化、体积分数以及铝浓度对其相互关系的影响.结果表明,对于所有浓度的合金,沉淀后期,γ'相均沿着[001]和[010]方向规则排列,但是彼此之间存在着不同的相互关系.对于低铝浓度合金,γ'相之间彼此互相独立.对于中铝浓度的合金,γ'相之间主要存在着4种相互关系:L-状,双透镜状,三重组结构和四重组结构.对于高铝浓度的合金,γ'相之间主要呈现双透镜状关系.     

低Al含量Ni-Cr-Al合金有序化及相边界演化的数值模拟

基于三元微观相场模型,模拟研究了873K时低Al含量三元合金Ni-Cr-Al有序化及相边界演化过程。研究发现,合金Ni-11Cr-7Al(原了百分数,下同)沉淀机制为非经典形核长大,沉淀过程中L12有序相伴随着DO22有序相的形核长大,同时,部分DO22有序相向L12有序相转化。由于Cr原子替代Al原子位置,在L12有序相内两种原子占位几率接近,形成Ni3(CrxAl1-x)结构的L12有序相,并且与DO22有序相共存。     

时效温度对Ni-Al-V合金筏化影响的微观相场模拟

基于微观相场动力学模型,以Ni<,75>Al<,25-x>V<,x>合金为对象,研究时效温度变化对沉淀相竞争生长机制及筏状组织形成的影响.结果表明:相的生长和粗化存在各向异性和竞争机制;当具有生长各相异性的DO<,22>相数量较少、尺寸较大时,易形成单一方向排布的组织,从而促使具有生长各向同性的L12相也沿着特定的方向生长,最终形成具有高度择向生长的"筏状"组织,且随着时效温度的降低,沉淀相提前析出;若L12相先析出,时效温度越低,DO<,22>相越多,组织筏化越不明显;若DO<,22>先析出,时效温度越低,DO<,22>相越少,组织筏状越显著.     

Microscopic phase-field simulation of atomic site occupation in ordering process of NiAl9Fe6 alloy

The process of γ（fcc）→γ（fcc）＋γ＇（L12） phase transformation was simulated by using microscopic phase-field method for the low supersaturation NiAl9Fe6 alloy. It is found that in the γ＇ phase, the ordering degree of Al atoms is obviously higher than that of Fe atoms, and the ordering of Al atoms precedes their clustering, while the case of Fe atoms is opposite. The a site is mainly occupied by Ni atoms, while the β site is occupied in common by Al, Fe and Ni atoms. At order-disorder interphase boundary, the ordering degree of Al atoms is higher than that of Fe atoms, and at the β site, the Fe atomic site occupation probabilities vary from high to low during ordering; the Al atomic site occupation probabilities are similar to those of Fe atoms, but their values are much higher than those of Fe atoms; Ni atoms are opposite to both of them. Meanwhile, during the ordering transformation, γ＇ phase is always a complex Ni3（AlFeNi） single-phase, and it is precipitated by the non-classical nucleation and growth style. Finally, in the alloy system, the volume of γ＇ ordered phase is less than that of γ phase, and the volume ratio of order to disorder is about 77%.     

MICROSCOPIC PHASE-FIELD SIMULATION COUPLED WITH ELASTIC STRAIN ENERGY FOR γ′(Ni3Al) PRICIPITATION IN Ni-Al ALLOY

基于微观相场动力学模型和微观弹性能理论,对Ni-Al合金中沉淀相Ni3Al(γ′)形貌演化、早期沉淀机制和后期粗化过程进行了原子层面的计算机模拟.结果表明:沉淀过程中γ′相形貌由早期随机分布的圆形或不规则状逐渐向方形转变,其排列的取向性也越来越明显,最后形成周边圆滑的长方块状颗粒,沿[10]和[01]弹性"软"方向规则排列.弹性应变能作用下的粗化过程遵循优先选择的原则,位于弹性"软"方向上的颗粒不断长大和粗化,位于弹性"软"方向外的颗粒逐渐消失,沉淀后期在基体中形成高度择优取向的微观组织.低浓度Ni-Al合金中γ′相的早期沉淀机制为非经典形核长大机制,其演化序列为:过饱和固溶体→非化学计量比有序相→化学计量比平衡γ′相→长大.     

Ni75MnxAl25-x合金早期沉淀相的微观相场模拟

采用三元微观相场动力学模型研究Ni75MnxAl25-x合金早期沉淀相的形成过程。对合金微观组织演化图像、有序相体积分数曲线、序参数曲线及占位几率的分析表明:该合金首先析出L10结构,随后L10结构向L12结构转变,L12结构在L10结构的内部析出。随着Al浓度的增大,等成分有序化阶段缩短;且L10结构体积分数增大,发生结构转变的时间提前。Al和Mn原子在(001)和(002)面几乎同时有序排列,但是一定时间后(002)面原子开始贫化,发生结构转变,Al原子主要占据β位,Mn原子主要占据αⅡ位。合金最终析出单一的L12伪二元结构。     

Computer simulation of γ''and θ phase precipitation of Ni-Al-V alloy using microscopic phase-field method

The precipitation processes of γ'and θ phases in Ni75 Al6.5 V18.5 alloy were simulated at different temperatures and the precipitation sequence of two phases and morphological evolution were investigated.The simulation demonstrates that the two phases precipitate simultaneously at high temperature and γ'phase precipitates earlier than θ phase at 1 000 K and 1 120 K.With the temperature decreasing,the velocity of precipitation quickens,the quantity of θ phase increases and the size reduces;but the volume fraction increases,the quantity of phase increases and the size reduces as well.The two phases nucleate and grow independently at high temperature and the θ phase precipitates from the boundaries of γ'phase at 1 000 K and 1 120 K.We also find that there are many kinds of domain boundaries between the same and different phases.The results of average deviation of composition and average absolute long range order parameter show that the ordering and compositional clustering of γ'phase happen simultaneously at high temperature,the congruent ordering occurs prior to spinodal decomposition at 1 000 K and 1 120 K and the ordering advances and quickens as the temperature decreases.Ordering and compositional clustering of θphase occur simultaneously at each temperature and are quickened with temperature decreasing.     

低铝含量Ni75AlxV25-x合金早期沉淀过程的原子尺度计算机模拟

采用微观相场模型, 基于离散格点形式的微观扩散方程和非平衡自由能函数, 编制了三元Ni75AlxV25-x合金的原子层面计算机模拟程序.模拟发现: 低铝含量Ni75AlxV25-x合金的θ相先于γ′相析出, 其沉淀机制为等成分有序化 失稳分解; γ′相在θ相的相界处非经典形核, 二者均先形成非化学计量比有序相, 之后向化学计量比有序相转变.     

Ni75Al5.5V19.5合金沉淀行为的微观相场模拟

利用微观相场方法模拟了Ni75Al5.5V19.5合金两种有序相D022和L12随温度变化时的不同沉淀过程.发现过冷度在相变驱动力中处于主导地位.高温下D022相首先析出,之后L1 2相在D022相和无序相的界面以及D022相形成的界面处析出,L1 2相长大时同时向无序基体和D022相推移;低温下L1 2相先析出,D022相在L1 2相的界面处形核长大,同时L1 2相通过失稳分解由非化学计量相向平衡相转变,其尺寸减小.该合金最终两相体积分数同时达到平衡并基本相等.随温度降低,L1 2相由高温时的非经典形核与失稳分解的混合机制向低温时的失稳分解转变;D022相的沉淀机制由非经典形核与失稳分解的混合机制向低温时的非经典形核转变.     

Ni-Al-Cr合金分级时效的微观相场模拟

基于三元体系的微观相场动力学模型,从原子层次上模拟了Ni-11at%Al-7at%Cr合金在873 K预时效,1023 K再时效的组织演化过程,结合原子图像,计算了有序相内序参数分布和体积分数随时间的变化,并与1023 K下的单级时效工艺进行了对比.研究结果表明:两种工艺条件下. 均析出单一的LI2结构有序相,分级时效的沉淀机制为非经典形核长大与失稳分解的混合机制;单级时效的沉淀机制为失稳分解机制:分级时效获得的沉淀相呈45°方向倾斜排列的弥散颗粒状,单级时效获得的沉淀相呈45°方向倾斜的条纹状;分级时效工艺下孕育期缩短,达到平衡时,二者的体积分数相等.     

时效工艺对Ni75Al15Ti10合金沉淀过程的微观相场模拟

本文通过微观相场动力学模型模拟了Ni₇₅Al₁₅Ti₁₀合金的沉淀过程。首先通过原子演化图发现,沉淀过程分为两步,起初为L1₀相向L1₂相的转变,随后为化学计量比L1₂相的形成。随后研究了单级时效温度对微结构,原子占位以及原子扩散的影响,结果表明：随着温度升高无规则形状的γ′相变为规则立方体状并且择优取向显著;同时Al原子从γ′相界面向内部扩散,Ti原子正好相反。但是温度越高,原子占位以及有序化程度越低。为了提高γ′相的原子占位,我们进一步比较了双级时效对γ′相的影响。发现双级时效不仅能获得规则排列稳定的γ′相,同时还可以提高Al与Ti原子在其正位处的原子占位并抑制反位缺陷的产生。我们的实验结果在一定程度上为制备具有优异力学性能的Ni-Al-Ti合金提供了理论依据。     

应变能对Ni75Al15V10合金预析出相影响的微观相场研究

采用微观相场方法,以Ni75Al15V10合金为例研究了应变能对预析出相的影响。研究发现：合金沉淀早期的应变能影响预析出相L10的析出。无应变能作用时,体系中没有预析出相L10相出现;应变能越大,L10预析出相的孕育期越短,析出量增加,稳定存在时间越长,且体系所析出的L10相的结构特征越明显。应变能较小时,无序基体有些区域先析出L10相,随后所析出的L10相转变为L12相,而在有些区域却直接析出L12相;当应变能较大时,基体大范围先析出L10相,随后部分L10预析出相溶解,只有未溶解部分最终能转变为L12相。     

微观相场法研究应变能对Ni68.2Al22.7V9.1合金中两相沉淀及原子占位的影响

采用微观相场方法,以 Ni68.2Al22.7V9.1 合金为例研究了应变能对两相沉淀及原子占位的影响。研究结果显示:沉淀过程中应变能明显使 L12沉淀相增加,对DO22相的沉淀有一定的抑制作用;由于 DO22相减少,V原子在L12相中各个位置的占位几率增大,而且应变能越大占位几率越高;应变能对Al原子在L12相中的α1位的占位几率影响不大,只有小幅度的降低,但明显降低了Al原子在α2位和β位的占位几率;各种情况下V原子在 L12相β位的占位几率始终高于α位。     

四近邻对势对Ni75Al5V20合金沉淀机制影响的 微观相场模拟

利用微观相场动力学模型,研究了4近邻对势对Ni75Al5V20合金沉淀机制的影响.结果表明,不改变4近邻对势,DO22相和Ll2相沉淀机制均为失稳分解与非经典形核混合型机制.随Ni-Al4近邻对势V4Ni-Al向负值方向绝对值增大,Ll2相沉淀机制转变为失稳分解.随Ni-V4近邻对势V4Ni-V增大,DO22相沉淀机制转变为失稳分解,Ll2相转变为非经典形核机制,Ll2相中的Al浓度平衡值增大.随Al-V 4近邻对势V4Al-V向负值方向绝对值增大,对沉淀机制的影响趋势与V4Al-V增大类似;随V4Al-V向正值方向增大,与V4Al-V减小的影响类似.     

Simulation of interphase boundary of Ni75AlxV25-x alloys using microscopic phase-field method

The evolution of ordered interphase boundary （IPB） of Ni75AlxV25-x alloys was simulated using the microscopic phase-field method. Based on the atomic occupation probability figure on 2D and order parameters, it was found that the IPB formed by different directions of θ phase has great effect on the precipitation of γ′ phase. The γ′ phase precipitated at the IPB that is formed by [100]θ direction where the （001）θ plane is opposite, and then grows up and the shape is strap at fmal. The IPB structure between γ′phase and θ phase is the same. There is no γ′ phase precipitate at the IPB where the （002）θ and （001）θ planes are opposite, the ordered IPB is dissolved into disordered area. There is γ′ phase precipitation at the IPB formed by the [001]θ and [100]θ directions, and the IPB structure is different between γ′ phase and the different directions of θ phase. The IPB where （001）γ′, and （100）θ plane opposite does not migrate during the γ′ phase growth, and γ′ phase grows along [100]θ direction.     

多元合金耦合热力学数据非等温凝固的相场模拟

研究一种多元合金的非等温相场模型,定量地模拟工业多元合金的真实凝固过程,结合热力学和扩散迁移率的数据来预测整个系统中的相平衡、溶质扩散系数、比热容和放出的潜热。结果表明：这些参数不是常数,它们的值与成分和温度有关。没有这些参数,定量模拟多元合金的凝固几乎是不可能。在这个模型中,界面区域假设是由有同样化学势的固相和液相混合而成的,但组成不同。这个模型中同样考虑反溶质截流。一并将模型应用到工业Al?Cu?Mg合金的各向枝晶自由长大的凝固过程。