微观相场法反演L12结构的原子间相互作用势

基于微观相场理论,根据Khachaturyan的占位几率和能量关系方程,推导出L12结构的第一近邻原子间相互作用势与长程序参数关系的反演方程-4W1·η/kBT=1n(1-η)[1-c(1+3·η)]/(1+3·η)[1-c(1-η)],根据该方程,只需输入根据相图中L12结构相变点的温度和原子浓度,就可以计算出不同温度和原子浓度下的L12结构的第1近邻原子间相互作用势,计算结果与第1性原理及其他方法计算的值接近;同时在计算过程中发现了L12结构的第1近邻原子间相互作用势在析出L12相的相图范围内随温度和原子浓度变化.     

Ni-Al-Cr原子间近邻作用势及沉淀过程的相场法模拟

基于微观相场理论研究了不同原子间近邻作用势(W)对Ni-Al-Cr合金析出过程和微观结构的影响。根据原子间近邻作用势与长程序参数方程的L1₀、L1₂和D0₂₂相的原子间近邻作用势公式,计算出Ni-Al-Cr合金的L1₀、L1₂和D0₂₂相的不同原子间近邻作用势。结果表明:随着温度的增长/减小,原子间近邻作用势近似呈线性增长/减小;随着溶质原子浓度的增长以及长程序参数的增大,原子间近邻作用势均呈上升趋势;Ni-Al、Ni-Cr、Cr-Al原子间近邻作用势的变化对L1₀、L1₂和D0₂₂析出相的沉淀形貌和体积分数的影响也各不相同:Ni-Al的第二近邻作用势的变化对于沉淀形貌和体积分数几乎无影响,而Ni-Cr第四近邻作用势的变化对沉淀形貌和体积分数的影响非常大。同时发现与其他方法相比,所得不同原子间近邻作用势结果近似,且沉淀形貌与实验结果吻合。     

基于微观相场DO22原子间相互作用势的计算模型

基于微观相场原理, 根据Khachaturyan占位几率和能量关系方程,推导出DO22相第一近邻原子间相互作用势的计算模型,其输入参数为相变点的温度和原子浓度。针对Ni3V-DO22相的反演计算表明：随温度和浓度增大,第一近邻原子间相互作用势w1增大。将计算所得随温度和浓度变化着的原子间相互作用势代入微观相场方程中,表明该方法得到的原子演化结构的温度和浓度相关性更加明显。     

Ni-Cr-Al合金中D022相和L12相沉淀过程微观相场模拟

基于微观相场动力学模型和微观弹性理论,对Ni75Cr19Al6.0合金的沉淀过程进行了研究.结果表明,合金沉淀初期,DD22相以失稳分解机制从无序基体中析出,L12相以非经典形核长大机制析出,两相均呈现不规则形状且随机分布.共格沉淀相和母相之间的点阵错配度引起的弹性场对沉淀过程产生明显影响,D022相和L12相在沉淀后期表现出强烈的各向异性特征,其形貌均转变为长方块状,沿弹性"软"方向([100]和[001])规则分布,沉淀后期在基体中形成高度择优取向的微观组织.粗化过程中,D022相和L12相的平均半径的立方与时效时间整体上并不满足线性关系,弹性约束系统中的长大规律发生变化.     

微观相场法反演Ni0.75AlxV0.25-x合金的原子间相互作用势

采用微观相场法,利用Khachaturyan所给原子间相互作用势与长程序参数关系方程,计算出Ni_(0.75)Al_xV_(0.25-x)合金L1_0、L1_2和DO_(22)相第一近邻原子间相互作用势,并用计算的原子间相互作用势模拟了Ni_(0.75)Al_xV_(0.25-x)合金沉淀过程以及最终形貌。计算结果表明,L1_0、L1_2和DO_(22)相第一近邻原子间相互作用势随温度增大而增大,随浓度增大而增大,且计算得到的随温度和浓度变化的原子间相互作用势与之前的实验值符合较好。计算的原子间相互作用势的模拟结果能依次得到预析出相L1_0、稳定相L1_2和第二相DO_(22),且合金沉淀形貌与实验结果吻合。相场法反演原子间相互作用势,拓宽了相场法在合金设计中的应用范围。     

相场法模拟扩散场相互作用对沉淀相形貌及成分的影响

在把网格引入的各向异性的影响降低到合理范围的基础上,采用相场法研究了在无弹性场作用时,沉淀颗粒间的扩散场相互作用对沉淀相形貌及成分的影响.模拟结果表明:由于扩散场的相互作用,在沉淀相生长及粗化过程中,沉淀颗粒形貌可出现圆形→方形→圆形→菱形→圆形的多种变化,且沉淀内部呈现成分不均匀性.随着沉淀相体积分数的增大,沉淀颗粒间的扩散场相互作用加强,对沉淀相形貌及其成分的影响也更加显著.     

合金沉淀过程相场法模拟研究进展

通过简单介绍研究合金的一些方法,综述了相场法的界面模型、动力学模型、常用的求解方法以及目前国内外运用微观相场法模拟合金沉淀过程的研究进展,提出了微观相场模型在模拟合金沉淀机制中的一些成功及不足之处,以及今后的研究方向.     

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.     

微观相场法研究Ni-Al-Fe合金原子间作用势的变化规律

基于微观相场理论,利用Khachaturyan所给原子间作用势与长程序参数关系方程得出L12结构第一近邻原子间作用势推演公式,反演出Ni-Al-Fe合金L12结构第一近邻原子间作用势。反演结果表明,Ni-Al和Ni-Fe第一近邻原子间作用势(即WNi-Al和WNi-Fe)随温度升高而增大。随Al原子浓度增大,WNi-Al增大而WNi-Fe减小,反之亦然。且原子间作用势随温度升高呈线性增大;原子间作用势随原子浓度变化近似呈线性变化。将反演作用势反代入到微观相场方程中得到的原子演化图的晶粒更细,同时其有序结构的有序度会更高。     

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.     

相场法研究Ni-Al间作用势对Ni75Al14Cr11合金L10预析出相的影响

采用微观相场法研究了Ni_(75)Al_(14)Cr_(11)合金第1个近邻到第4个近邻Ni-Al原子间相互作用势对L1_0预析出相沉淀过程的影响。结果表明,当第3近邻Ni-Al原子间相互作用势增大或第4种近邻Ni-Al原子间相互作用势减少时,L1_0预析出相和L1_2平衡相均提前沉淀,且L1_0预析出相体积分数减少而L1_2相的最终体积分数几乎不变;当第3近邻Ni-Al原子间相互作用势减少或第4近邻Ni-Al原子间相互作用势的增大时,L1_0预析出相和L1_2最终相都会推迟沉淀,且L1_0预析出相和L1_2相体积分数均增大;与上述2种情况相比,改变第1近邻Ni-Al原子间相互作用势对L1_0预析出相沉淀过程的影响较小,而改变第2近邻Ni-Al原子间相互作用势对沉淀过程几乎没有影响。进一步研究表明,Ni-Al原子间相互作用势改变不影响合金的沉淀机制,将影响L1_0预析出相、L1_2平衡相的析出时间、速度和2种相的体积分数,沉淀形貌等,从而影响Ni_(75)Al_(14)Cr_(11)高温合金的结构和性能,对合金优化设计有指导意义。     

GMR effects in the process of decomposition of Co10Cu90 ribbons

The progress spinodal decomposition in aged Co₁₀Cu₉₀ ribbons is closely correlated with giant magnetoresistance (GMR). In the phase decomposition, the MR ratio due to spin dependent scattering increases with the increase in the interface area in the constant wavelength regime. A maximum MR ratio of 8.1% in 15 kOe is obtained in the Co₁₀Cu₉₀ ribbon aged at 673 K for 166 h. By further aging, the MR ratio in high fields decreases with the increase of the wavelength, while the susceptibility of the MR ratio in low fields becomes larger due to the coarsening of ferromagnetic particles.     

Microscopic phase-field simulation coupled with elastic strain energy for precipitation process of Ni-Cr-Al alloys with low Al content

The precipitation process of Ni-Cr-Al alloy with low Al content was studied at atomic scale based on the microscopicphase-field kinetic model coupled with elastic strain energy.The aim is to investigate the effect of elastic strain energy onprecipitation mechanism and morphological evolution of the alloy.The simulation results show that in the early stage of precipitation,D022 phase and L12 phase present irregular shape,and they randomly distribute in the matrix.With the progress of aging,L12 phaseand D022 phase change into the quadrate shape and their orientations become more obvious.In the later stage,L12 phase and D022phase present quadrate shape with round corner and align along the[100]and[010]directions,and highly preferential selectedmicrostructure is formed.The mechanism of early precipitation of L12 phase in Ni-17%Cr-7.5%Al(mole fraction)alloy is the mixedstyle of non-classical nucleation growth and spinodal decomposition and the D022 phase is the spinodal decomposition.Themechanisms of early precipitation of L12 phase and D022 phase in Ni-12.5%Cr-7.5%Al alloy are both the non-classical nucleationand growth.The coarsening process follows the rule of preferential selected coarsening.     

Phase-field study for the splitting mechanism of coherent misfitting precipitates in anisotropic elastic media

Through a phase-field study upon the splitting behavior and morphological evolution of coherent precipitates, we show that an interface instability driven by elastic anisotropy and a diffusion field can generate elastically induced splitting during diffusional phase transition. Particle splitting is triggered by interface grooving which advances by penetrating grooves into the interior of the particle. The sequential evolution of shapes during the splitting process is in good agreement with previous experiments.     

Recrystallization of the cold-deformed discontinuous precipitation microstructure in Al-Zn (-Cu) alloys

Recrystallization of cold-rolled discontinuous precipitation microstructure which has fine laminar structure in an Al-40% Zn (atom fraction) binary alloy is investigated by optical microscopy, SEM and TEM. It is found that there are two kinds of recrystallization mechanisms: continuous coarsening (CC) and discontinuous coarsening (DC). The latter can be divided into coarsening mainly driven by stored deformation energy at colony boundaries and slip bands and the one mainly driven by boundary energy in the area with little deformation. It is shown that the addition of Cu can retard the nucleation of coarsening cells and their growth. X-Ray diffraction analysis indicated the metastable phase CuZn4 transformed into equilibrium phase Al4Cu3Zn during the heating process.     

Modeling of whole process of ageing precipitation and strengthening in Al-Cu-Mg-Ag alloys with high Cu-to-Mg mass ratio

A physically based numerical model to predict the microstructure evolution and yield strength of high Cu-to-Mg mass ratio Al-Cu-Mg-Ag alloys during the whole ageing process was developed.A thermodynamically-based precipitation model,employing the classical nucleation and growth theories,was adapted to deal with the precipitation kinetics (evolution of radius and volume fraction of precipitates for Ω phase) of aged Al-Cu-Mg-Ag alloys.The model gives an estimation of the precipitation kinetics (evolution of radius and density of precipitates for both θ' and Ω phases) of the alloy.The strengthening model based on Orowan mechanism was deduced.The microstructural development and strength predictions of the model are generally in good agreement with the experimental data.     

Phase-field study for the pre-precipitation process of L12-Ni3Al phase in Ni–Al–V alloy

The microscopic phase-field dynamic model is employed to study the pre-precipitation process of Ni–Al–V alloy. Our computer simulation results show that there exists pre-precipitated phase with L1₀ structure before L1₂ phase formed, temperature and elastic strain energy play significant effect on the pre-precipitated phase with L1₀ structure. The elastic strain energy can induce the formation of L1₀ pre-precipitated phase. Under the same temperature, the greater the elastic strain energy is, the easier L1₀ pre-precipitated phase will form; under the same elastic strain energy, with the temperature increasing, the incubation period and existent time of L1₀ pre-precipitate phase are prolonged, the number of L1₀ precipitated phase also increases, and the formation of the L1₂ phase are delayed.     

镁合金等离子体微弧氧化过程负电压调控的研究

研究了AZ31镁合金在不同电压条件下的成膜效果,着重研究了在固定正电压而改变负电压的情况下的成膜厚度、致密度、耐腐蚀性能等差别,讨论了负电压在成膜过程中的作用,并且比较了在不同的溶液体系中负电压对于成膜性能以及二次放电现象的影响.结果表明：较低的负电压能在一定程度上促进氧化膜的生长,使致密的氧化层变厚,提高膜的性能.而高负电压会加速成膜速度并导致较为剧烈的二次放电现象,使膜的致密性降低,从而降低膜的性能.