【作者】 刘新；

【导师】 朱亚新；

【作者基本信息】 华中科技大学 ， 固体力学， 2023， 硕士

【摘要】 作为一种多主元新型合金材料,高熵合金(High entropy alloys,HEAs)展现出高强度、高硬度、耐低温等优异性能,成为当前世界瞩目的先进金属材料,具有极大的工程应用潜力。HEAs的主要塑性变形机制是位错运动,广义层错能是影响位错运动特性的重要因素。由于HEAs具有局部化学无序的特点,传统计算金属广义层错能的方法不再适用,采用传统Peierls-Nabarro(P-N)模型研究位错运动特性的方法也不再适用,导致缺乏描述HEAs位错运动演化的定量模型和介观尺度模拟算法。鉴于此,本文开展了以下研究:(1)提出了一种局域层错能(Localized Stacking Fault Energy,LSFE)计算的新方法。该方法可以考虑HEAs局部化学无序的结构特点,并实现HEAs广义层错能高通量计算。结果显示,HEAs滑移面上的广义层错能呈非均匀分布形式,且LSFEs的非均匀性取决于滑移面划分尺寸的大小。结合统计方法,对两种面心立方(FCC)HEAs和两种体心立方(BCC)HEAs局域层错能的定量概率分布进行了研究,得到了描述LSFEs的最佳概率密度函数;基于机器学习的方法,建立了LSFEs与局部化学特征的关联,并基于LSFE的大小对局部化学特征进行归类,用以解释LSFE在滑移面上非均匀分布的现象,并指导HEAs组分优化设计。(2)基于高通量SVPN模型和新提出的局部广义层错能面构建方法,研究了FCC高熵合金Co Cr Fe Mn Ni的局部位错滑移阻力Peierls应力。研究结果表明:FCC HEAs滑移面内位错局部Peierls应力的非均匀性非常显著,可解释HEAs中位错滑移时非均匀的运动特性,局部区域存在非常高的Peierls应力,可以解释位错运动时的“自钉扎”效应。结合统计分析,得到了滑移面内局部Peierls应力的定量统计模型。统计结果显示:Co Cr Fe Mn Ni滑移面内的局部Peierls应力服从“Exponentiated Weibull”分布。(3)发展了基于定量统计模型的HEAs位错动力学算法,该算法可以充分考虑HEAs滑移面上Peierls应力的非均匀分布特征,进而模拟位错的非均匀运动。基于发展的位错动力学算法,研究了HEAs内Frank-Read(F-R)位错源增殖及位错环的运动过程。结果表明:该位错动力学算法可以很好的捕捉HEAs中位错线粗糙的结构和非均匀的运动特点;局部Peierls应力的非均匀性一方面会增大F-R位错源的临界形核应力,抑制F-R位错源的增殖,另一方面会降低位错环的运动速度,阻碍位错环的扩张和收缩运动,为揭示HEAs中局部化学无序导致的强化机理提供了重要的依据。更多还原

【Abstract】 As a new type of multi-principal element alloys,high entropy alloys(HEAs)exhibit excellent properties such as high strength,high hardness,low-temperature resistance,etc.,and have become the remarkable advanced metal material with great engineering application potential worldwide.The microscopic plastic deformation mechanism of HEAs is based on the motion of dislocations,and the generalized stacking fault energy(GSFE)is an important factor affecting the motion of dislocations.The traditional method of calculating the GSFE and the traditional Peierls-Nabarro(P-N)method to study dislocation motion characteristics is no longer applicable,due to the local chemical disorder of HEAs.Up to now,the algorithms that depict the dislocation motion and evolution in HEAs is lacking,leading to the shortage of quantitative simulation of HEAs at the mesoscopic scale.Based on the above background,this dissertation performed the following work:(1)A new method for calculating the Localized Stacking Fault Energy(LSFE)is proposed.The proposed method can consider the structural characteristics of local chemical disorder in HEAs and realize the high-throughput calculation of GSFE in HEAs.The results show that the GSFEs in HEAs exist in the form of nonuniform distribution on the slip plane,and the inhomogeneity of LSFEs depends on the partition size.The quantitative probability distribution functions of the LSFEs of two face-centered cubic(FCC)HEAs and two bodycentered cubic(BCC)HEAs are investigated by combining statistical methods.The correlation between LSFE and local chemical features is established via machine learning methods,and the local chemical features are categorized based on the value of LSFE,which is used to explain the phenomenon of undulating fluctuation of LSFE in the whole slip plane and to guide the design of HEAs.(2)Based on the high-throughput SVPN method and the proposed local GSFEs surface(γ surface)construction method,the local dislocation slip resistance(i.e.,Peierls stress)of the FCC HEAs Co Cr Fe Mn Ni is investigated.The results show that the inhomogeneity of the local Peierls stress of dislocations within the slip plane is significant,which can be used to explain the non-uniform motion characteristics of dislocations in HEAs.Some pretty high Peierls stresses exist in the local regions,which can be used to the self-pinning effect of dislocation.In addition,the quantitative statistical model of the local Peierls stress within the slip plane is obtained by combining the statistical analysis,the statistical results show that the local Peierls stress in the slip plane of CoCrFeMnNi obey the "Exponentiated Weibull" distribution.(3)The dislocation dynamics(DD)algorithm based on quantitative statistical model is developed for HEAs,which can fully consider the characteristics of inhomogeneously distributed Peierls stress on the slip plane of HEAs,and then simulate the non-uniform motion of dislocations.Based on the developed DD algorithm,the multiplication of FrankRead(F-R)sources within HEAs and the slip process of dislocation loops are investigated.The results show that the proposed DD algorithm can simulate the rugged morphology and non-uniform slip process of dislocation lines in HEAs.On the one hand,the inhomogeneity of local Peierls stress increases the critical nucleation stress of F-R dislocation sources,and hence inhibits the multiplication of the F-R dislocation source.On the other hand,it decreases the slip velocity and hinders the expansion and shrinkage motion of dislocation loops.The results provide an important basis for revealing the strengthening mechanism caused by local chemical disorder in HEAs.更多还原