原子间相互作用势对δ''相在过渡区沉淀影响的计算机研究

基于离散格点形式的微扩散方程(Langevin方程)和非平衡自由能函数,编制了引入原子间相互作用能变化的Al3Li(δ')相沉淀原子层面计算机模拟程序.该程序包容亚稳区到失稳区的全部温度、成分范围,孕育期至粗化的全过程,可以处理与时间相关的过程问题.开展了不同原子间相互作用势下原子图像、序参数的计算机模拟,进而探讨了最近邻原子相互作用能(W1)对Al3Li相沉淀的影响机制.探明过渡区合金,随W1的增大,A13Li相沉淀的孕育期缩短,形核率增加,合金有序化速度和原子簇聚速度加快,在所研究的时间范围内达到的长程序参数和成分偏离序参数最大值增大.W1的增大促进Al3Li相以失稳分解形式析出.     

L12 +D022体系含共格应变的组织演化和粗化行为模拟

利用微观相场方法研究了Ni₇₅Al_xV_25-x合金有序沉淀相含共格应变作用的粗化行为．通过对组织演化图像、结构函数的标度行为及平均半径的分析，得出如下结论：L1₂和D0₂₂相的形状转变以及两相间的空间排列关系是由与组态相关的各向异性弹性应变能引起．两相的最终组织形貌呈长方块状，沉淀颗粒在粗化阶段均达到了动力学标度．由于不同相之间的弹性交互作用，Lifshitz Slyozov Wagner（LSW）理论并不适用于该沉淀体系的粗化行为．中间浓度时，两相的沉淀和粗化过程同时发生；高浓度时，先析出相的长大和粗化分为较明显的两个阶段，而后析出相的长大和粗化仍同时进行．     

Ni75Al10V15合金早期沉淀过程的原子尺度计算机模拟

基于二元合金沉淀动力学相场方程的微观离散格点形式建立三元体系模型,在倒易空间中求解方程.用此模型对实际三元Ni75Al10V15合金的早期沉淀过程进行了模拟,计算γ′有序相的成分序参数和长程序参数.结果表明:Ni75Al10V15合金中γ′相的沉淀机制为非经典形核长大,先形成非化学计量比有序相,然后才形成化学计量比有序相,其中非化学计量比有序相并非热力学意义上的亚稳相;DO22结构的非化学计量比θ有序相在γ′相界处形成,其成分和有序化程度较低,且距离相界越远,有序程度越低,θ有序畴存在两种类型:水平分布和垂直分布,和它所依附的γ′相界面取向有关;该模型无须预先设定新相结构和沉淀类型,可在原子水平模拟三元体系的两个有序相析出、成分簇聚等过程.     

L12+D022体系含共格应变的组织演化和粗化行为模拟

利用微观相场方法研究了Ni75AlxV25-x合金有序沉淀相含共格应变作用的粗化行为.通过对组织演化图像、结构函数的标度行为及平均半径的分析,得出如下结论:L12和D022相的形状转变以及两相间的空间排列关系是由与组态相关的各向异性弹性应变能引起.两相的最终组织形貌呈长方块状,沉淀颗粒在粗化阶段均达到了动力学标度.由于不同相之间的弹性交互作用,Lifshitz Slyozov Wagner(LSW)理论并不适用于该沉淀体系的粗化行为.中间浓度时,两相的沉淀和粗化过程同时发生;高浓度时,先析出相的长大和粗化分为较明显的两个阶段,而后析出相的长大和粗化仍同时进行.     

核反应堆压力容器模拟钢中富Cu纳米团簇析出早期阶段的研究

采用调质处理后热时效模拟方法,用原子探针层析成像技术研究了核反应堆压力容器模拟钢中富铜纳米团簇的析出过程.模拟钢经880℃加热水淬,660℃高温回火调质处理,并经400℃时效处理1000 h后基体中析出了富铜纳米团簇.使用MSEM(maximum separation envelope method)方法重点研究了富铜纳米团簇在析出早期阶段成分变化规律.结果表明,富铜纳米团簇容易在镍含量较高的位置形核,并随着富铜纳米团簇中铜原子聚集程度的增加,纳米团簇中心处铜含量逐渐增加,镍含量逐渐减少;在纳米团簇与α--Fe基体界面处,镍和锰含量逐渐增加,形成了富镍和富锰包裹富铜纳米团簇的结构.结合实验结果讨论了压力容器钢中合金元素镍及杂质元素磷会增加中子辐照脆化敏感性的原因.     

Ni基高温合金中有序化和电子结构的计算

为了研究镍基合金的强化机理,给合金设计提供理论基础.在紧束缚框架下应用Recursion方法,计算了镍基合金Ni-X(X=Ti、Al、Nb、Ta)的电子结构,给出了合金原子局域态密度及它们之间的相互作用能.研究结果表明,合金原子Ti、Al、Nb、Ta的相互作用能均为正值,具有强烈的有序化倾向.有序化形成第二相粒子后阻碍位错运动,提高合金强度.     

预拉伸对7050铝合金腐蚀性能的影响

通过硬度、电导率、Tafel极化曲线、慢应变速率拉伸测试及光学显微镜、透射电镜组织观察,研究预拉伸变形量对7050铝合金板材强度和腐蚀性能的影响.研究结果表明:预拉伸引入大量位错,在时效过程中促进η平衡相的形核;随着预拉伸变形量的增大,晶内η相增多、粗化,合金的强度降低,电导率升高;随着预拉伸变形量增大,合金内的位错密度增大,空位浓度降低,晶界析出相间距先增大后减小,抗腐蚀性能先增大后减小;无沉淀析出带(PFZ)先变宽后消失,抗腐蚀性能先减小后增大;综合晶界析出相的分布和PFZ宽度的共同影响,随着预拉伸变形量的增大,板材的抗腐蚀性能先逐渐减小后迅速降低.     

工艺参数对低铝钛GH600合金显微组织及析出相的影响

利用Gleeble3800热模拟实验机,对低铝钛GH600合金进行热压缩实验;利用金相显微镜研究工艺参数对显微组织演变规律的影响;利用透射电镜及能谱观察分析析出相、位错等微观结构。结果表明:提高变形量可以得到细晶组织,改善合金的使用性能,并且在大变形量下,动态再结晶容易进行,软化效果得到提高,在一定程度上改善合金的加工性能。当变形温度升高时,再结晶比例得到很大的提高,合金动态再结晶体积分数增大,位错密度降低,使加工容易进行。但当变形温度过高时,再结晶组织会出现粗化现象。低铝钛GH600合金的优选热加工工艺参数为:温度1 100~1 150℃,变形量60%。在这种工艺条件下,合金中的再结晶程度最高,再结晶晶粒没有出现粗化现象,并且析出相的成分、尺寸也为理想状态。     

镍基单晶高温合金定向粗化机制有限元分析

采用有限元计算了[001]取向时,镍基单晶合金中γ基体和γ′沉淀相在施加外力前后弹性应变能密度的分布,并依据元素的扩散性质对定向粗化过程做了相应分析.结果表明,外应力改变了基体通道中的应变能密度的分布,γ′沉淀颗粒的定向粗化与基体通道中的应变能密度分布密切相关,其定向粗化在应变能密度高的基体通道扩展,且应变能密度变化越大,元素扩散速率越快,γ′颗粒定向粗化的速率也越快.     

工艺参数对低铝钛GH600合金显微组织及析出相的影响

利用Gleeble3800热模拟实验机,对低铝钛GH600合金进行热压缩实验;利用金相显微镜研究工艺参数对显微组织演变规律的影响;利用透射电镜及能谱观察分析析出相、位错等微观结构。结果表明:提高变形量可以得到细晶组织,改善合金的使用性能,并且在大变形量下,动态再结晶容易进行,软化效果得到提高,在一定程度上改善合金的加工性能。当变形温度升高时,再结晶比例得到很大的提高,合金动态再结晶体积分数增大,位错密度降低,使加工容易进行。但当变形温度过高时,再结晶组织会出现粗化现象。低铝钛GH600合金的优选热加工工艺参数为:温度1 100~1 150℃,变形量60%。在这种工艺条件下,合金中的再结晶程度最高,再结晶晶粒没有出现粗化现象,并且析出相的成分、尺寸也为理想状态。     

Atomic-scale computer simulation for early precipitation process of Ni75Al10V15 alloy

The kinetic model for a ternary system is introduced based on the microscopic diffusion form of the phase-field equations for a binary alloy. The equation is solved in the reciprocal space. This model is used to investigate the early precipitation process of Ni75-Al10V15 by simulating the atomic pictures of the two ordered phases and calculating the order parameters of γ′(Ni3Al) phase. Simulation results show that the γ′ ordered phases precipitate from the disordered matrix by a non-classical nucleation mechanism, and the nonstoichiometric γ′ ordered phase appears first and then transforms into the stoichiometric one. Clusters of V atoms appear at the γ′ phase boundaries followed by the formation of the nonstoichiometric θ ordered phase. The farther the location from γ′ phase boundary is, the lower the order degree of θ phase is. There exist two kinds of DO22 ordered domains: a horizontal one and a vertical one, related to their adjacent γ′ phase boundaries. The model could describe the atomic ordering and composition clustering simultaneously, and any a priori assumption about the new phase structure and precipitation mechanism etc. is unnecessary.     

Atomic-scale computer simulation for ternary alloy Ni-Cr-Al during early precipitation process

The aging behaviors of Ni-Cr-Al ternary alloy are studied at temperature 873 K based on the mean-field theory, and the early precipitation process is simulated at atomic-scale with microscopic phase-field model. The precipitation mechanism of the low supersaturated alloy Ni-12.2at.%Cr-7.8at.%Al is non-classical nucleation and growth, the L12 structure (Ni3Al) and D022 structure (Ni3Cr) phases precipitate simultaneously, a part of D022 phase transmits to L12 structure phase, and other part retains its previous structure. For high supersaturated alloy, congruent ordering appears first, then followed by spinodal decomposition, the nonstoicheometric ordered phases are produced in this process, which occurs before clustering. The precipitation mechanism of Ni-8at.%Cr-18at.%Al alloy is similar to Ni-10at.%Cr-12at.%Al alloy, but the ordering process of the former is ahead of the latter.     

NiAl晶体中点缺陷的模拟

利用嵌入原子法（ＥＡＭ）势函数,通过分子静态弛豫方法ＮｉＡｌ合金中各种点缺陷的形成能进行了模拟计算。结果表明,从点缺陷的形成能来看,在ＮｉＡｌ晶格中很难形成Ｎｉ反位置缺陷,而Ａｌ原子亚点阵位置总是被占据。当合金富Ｎｉ时,Ｎｉ占据Ａｌ位置形成Ａｌ的反位置缺陷;当合金富Ａｌ时,形成Ｎｉ空位。点缺陷周围原子的位移情况及双空位形成能与空位之间间距的关系的研究表明,随着两个空位之间距离的增大,其交互作用逐渐     

Atomic-scale computer simulation for early precipitation process of Ni75AlxV25-x alloy with intermediate Al composition

The microscopic phase-field approach is applied to model the early precipitation process of Ni75AlxV25-x alloy. Without any prior assumptions, this model can be used to simulate the temporal evolution of arbitrary morphologies and microstructures on atomic scale. By simulating the atomic pictures, and calculating the order parameters and volume fraction of the θ (Ni3V) and γ'(Ni3Al) ordered phases, we study Ni75AlxV25-x alloys with Al composition of 0.05, 0. 053 and 0. 055 (atom fraction). Our calculated results show that,for these alloys, θ and γ' phases precipitate at the same time; with the increase of Al content, the amount of γ' phase increases and that of θ phase decreases; the precipitation characteristic of γ' phase transforms from Non-Classical Nucleation and Growth (NCNG) to Congruent Ordering Spinodal Decomposition (CO SD) gradually; otherwise, the precipitation characteristic of θ phase transforms from Congruent Ordering Spinodal Decomposition (CO SD) to Non-Classical Nucleation and Growth (NCNG) mechanism gradually. Both θ and γ' phases have undergone the transition process of mixture precipitation mechanism characterized by both NCNG and CO SD mechanisms. No incontinuous transition of precipitation mechanism has been found.     

Core-shell structure nanoprecipitates in Fe-xCu-3.0Mn-1.5Ni-1.5Al alloys: A phase field study

The core-shell structure precipitatates of Fe-xCu-3.0Mn-1.5Ni-1.5Al alloys under internal and external strain was investigated by using a multicomponent continuous phase field model based on Gibbs free energy of sub regular solution. Results show that the early cluster nuclei are not pure Cu, and Mn/Ni/Al also gather in the same position of Cu rich nuclei, resulting in four core-shell structures in precipitation. In the absence of external strain, the morphology of precipitates is mainly determined by interfacial energy, intrinsic elastic anisotropy and lattice distortion between new phase and parent phase. Intrinsic elastic strain energy can inhibit precipitation, while has no obvious effect on particle morphology. In coarsening, the elastic energy decreases due to the combination of particles. The loading direction and magnitude of the applied elastic strain field can control the morphology of precipitates. The external strain and the interaction between Mn, Ni and Al promote the joining and merging of adjacent core-shell particles. This work has guiding significance for the design of Fe-xCu-3.0Mn-1.5Ni-1.5Al alloys and other core-shell precipitates materials.     

Solute atom migration in GH4169 superalloy under electrostatic fields

Electric field treatment (EFT) was applied on GH4169 alloy during aging at 500–800℃ to investigate the microstructure and property variation of the alloy under the action of EFT. The results demonstrate that the short-distance diffusion of Al, Ti, and Nb atoms can be accelerated by EFT, which results in the coarsening of γ′ and γ″ phases. Meanwhile, lattice distortion can be caused by the segregation of Fe and Cr atoms, owing to the vacancy flows migrating toward the charged surfaces of the alloy. Therefore, the alloy is hardened by the application of EFT, even if the strength of the alloy is partly reduced, which is caused by precipitation coarsening.     

Computer simulation for the precipitation process of Ni75Al7.5V17.5 alloy

The precipitation mechanism of Ni75Al7.5V17.5 alloy above the L12 instability line, between the L12 and D022 instability lines and below the D022 instability line are studied using microscopic phase-field kinetic equation. This paper is aimed at investigating the effect of temperature on precipitation mechanism and morphological evolution of the alloy. Our simulations demonstrate that the precipitation is a mixed mechanism of non-classical nucleation growth and spinodal decomposition above the L12 instability line. It needs certain thermal fluctuations for nucleation and the number of θ phases is small at this temperature. The precipitation mechanism of γ'phase is congruent ordering followed by spinodal decomposition, and θ phase is a mixed mechanism of non-classical nucleation growth and spinodal decomposition between the L12 and D022 instability lines. The mechanism below the D022 instability line is similar to that between the L12 and D022 instability lines. With the decrease of the temperature, ordering and phase separation becomes fast, the dimension of γ'phase becomes small, the shape transforms from equiaxed to block, the dimension of θ phase becomes large and the shape transforms from strip to circle.     

A phase field study for influence of elastic energy on L1<Subscript>0</Subscript>→L1<Subscript>2</Subscript> transient ordering in Ni<Subscript>75</Subscript>Al<Subscript>17</Subscript>Zn<Subscript>8</Subscript>

The influence of the elastic energy on L1₀→L1₂ transient ordering transformation was investigated by microscopic phase field method. It is found that there are three stages experienced in atomic ordering: solute clustering+L10 short range ordering → L1₀ long range ordering → L1₂ long range ordering. Before the formation of the high ordered L1₂ phase, it has firstly taken place the transformation from matrix to L1₀ phase, and then held the L1₀→L1₂ secondary transformation. Elastic energy is proved to take little effect on the stage of short range ordering, but as the elastic energy is multiplied, it obviously shortened the course of the solute clustering, and speeded up the proceeding of the L1₀ long range ordering transition. Accordingly, the increased elastic energy also strengthens the single crystalline directionality of L1₀ phase projecting on 2D plane and makes the ordered degree of Al and Zn atoms enhanced. With the temperature elevation, Al’s and Zn’s ordered degree decreased in L10 phase.     

镍钼矿浮选尾矿工艺矿物学及再选试验研究

镍钼矿浮选尾矿中Ni、Mo的品位分别为0.42%、0.62%,仍然具有开发利用价值.通过工艺矿物学分析,解释了镍钼矿浮选尾矿中镍、钼均主要以硫化矿形式存在,钼矿物与脉石矿嵌布关系密切,镍矿物与黄铁矿共生关系密切.通过再选闭路试验,浮选得到了Ni、Mo品位分别为1.44%、1.89%的再选精矿,Ni、Mo回收率分别为46.39%、41.24%,增加了镍钼矿综合回收利用.     

Ni-Mo合金电沉积规律研究

应用恒电位沉积法和循环伏安法(CV)研究碱性柠檬酸盐溶液中Ni-Mo合金共沉积规律.恒电位沉积结果表明:MoO42-的加入可以降低Ni的沉积过电位,随电位负移Ni-Mo合金的沉积电流效率逐渐低于镀Ni溶液中Ni的沉积效率.循环伏安测试结果表明:随着Ni 2+的含量增加,Ni沉积的第一个还原峰电位和Ni-Mo合金的沉积峰电位均正移;随MoO42-的含量增加,Ni-Mo合金沉积峰电位负移.