【作者】 王璐；

【导师】 宗亚平； 金剑锋；

【作者基本信息】 东北大学 ， 材料学， 2021， 博士

【摘要】 石墨烯作为一种新型二维碳材料,具有优秀的力学、物理和化学等特性,在新型复合材料研发方面具有独特的优势。通过充分发挥石墨烯的特性,可以开发出具有不同结构和功能特性的金属基复合材料,在航空航天、军工、交通运输以及能量储存等领域具有潜在的广阔应用前景。近年来的国内外大量应用研究表明,石墨烯增强材料的器件对力学性能提出了越来越高的需求。目前,石墨烯增强金属基复合材料的研究是材料领域的热点之一,通过模拟开展复合材料结构演化和微观机理的研究,可为复合材料的结构设计和性能调控提供理论指导。但大多数研究主要集中在功能性方面,关于力学性能的研究相对较少。为此,本研究以石墨烯纳米片增强铁基复合材料(Gr/Fe复合材料)为例,采用分子动力学(MD)模拟方法深度解析复合材料中界面强度、石墨烯片分布特性及尺寸对Gr/Fe复合材料综合力学性能影响的规律,以期对颗粒增强复合体显微组织设计新领域有奠基作用。通过对石墨烯/铁界面的模拟研究发现,当石墨烯与铁基体形成化学结合(强)界面时,石墨烯/铁{110}、{111}、{112}和{100}界面的相互作用能为-7.92J/m2、-6.81J/m2、-7.68J/m2 和-7.31J/m2,Fe-C原子键长主要在1.80～2.00?和2.30～2.50?两个区间内不连续分布,Fe-C原子以化学键结合,界面区出现渗碳体结构(如Fe3C、Fe7C3),不同界面呈现出不同的周期性原子结构特征;而当石墨烯与铁基体形成吸附(弱)界面时,对应的相互作用能为-1.48J/m2、-1.09J/m2、-1.26J/m2和-1.20J/m2,Fe-C原子键长在2.20～3.00?范围内连续分布,Fe-C原子以范德华力结合,无特定成键类型,各界面原子结构均未观察规律性的特征。通过模拟研究界面强度、石墨烯片分布取向特性对Gr/Fe复合材料综合力学性能的影响发现,形成强界面时,(110)、(112)和(111)Gr/Fe的屈服应力分别为505 MPa、991MPa和968MPa;而形成弱界面时,相应Gr/Fe的屈服应力分别为520 MPa、827MPa和830MPa。同时,铁基体内不同分布的石墨烯片与位错的作用机制不同,且作用机制受界面强度的影响显著。以平行铁基体(110)、(112)和(111)晶面的石墨烯片两两混合为例,研究了石墨烯片混合分布对Gr/Fe复合材料性能的影响。当形成强界面时,Gr/Fe均未表现出混合强化效果;当形成弱界面时,Gr/Fe呈现出一定的混合强化效果,其中((111)+(110))Gr/Fe的屈服应力较(111)和(110)Gr/Fe分别提升了1.66%和106.25%。由此表明,混合颗粒(石墨烯片)增强复合材料的性能不是简单的混合定律所能描述的,且仅有部分的混合才能表现出可贵的混合效果。以石墨烯片尺寸为80A、56A和46A为例,研究石墨烯片尺寸对Gr/Fe复合材料力学性能影响。当石墨烯片平行铁基体(110)晶面时,石墨烯片尺寸对强和弱界面的(110)Gr/Fe力学性能均无明显影响。当石墨烯片平行铁基体(111)晶面时,石墨烯片尺寸对(111)Gr/Fe的力学性能有影响且强和弱界面呈现相同的规律,随着石墨烯片尺寸的减小,Gr/Fe的屈服应力显著增加:强界面的Gr/Fe的屈服应力依次为991 MPa、1390MPa和2429MPa;弱界面的Gr/Fe的屈服应力分别为830MPa、1316MPa和2082MPa。当石墨烯片平行铁基体(112)晶面时,石墨烯片尺寸对(112)Gr/Fe的力学性能有影响且强和弱界面呈现出不同的规律:石墨烯与铁基体形成强界面时,随着石墨烯片尺寸的减小,Gr/Fe的屈服应力逐渐增加,依次为1044MPa、1171MPa和1184 MPa;而形成弱界面时,Gr/Fe的屈服应力呈现先下降后上升的规律,依次为860 MPa、729 MPa和897 MPa。因此可见,颗粒增强复合材料的力学性能无法通过简单的通用公式得到,复合体显微组织的设计必须通过基体和增强体本构模型具体模拟来实现。以石墨烯片平行铁基体(11 2)晶面的Gr/Fe复合材料为例,研究了不同尺寸的石墨烯片混合对Gr/Fe性能的影响。当形成强界面时,尺寸为(56 A+46 A)的石墨烯片混合的Gr/Fe的屈服应力为1184 MPa,较石墨烯片尺寸为56 A的Gr/Fe提升了1.11%,与石墨烯片尺寸为46 A的Gr/Fe一致,其力学性能表现出一定的混合强化效果;当石墨烯片与铁基体形成弱界面时,尺寸为(56 ?+46?)的石墨烯片混合的Gr/Fe的屈服应力为761 MPa,较石墨烯片尺寸为56 A的Gr/Fe提升了 4.39%,较石墨烯片尺寸为46 ?的Gr/Fe下降了 15.16%,其力学性能基本符合混合定律。由此可见,混合尺寸强化的机理可能是单个强化粒子的应力场相互叠加形成材料中高应力梯度平均场所致,而弱界面无法保存高梯度平均应力场。更多还原

【Abstract】 Graphene,a new type of two-dimensional carbon material,with excellent mechanical,physical and chemical properties,is potentially used in new-generation composites.By combining these unique properties,graphene reinforced metal matrix composites are prosperous in the applications of future aerospace,military,transportation,and energy industries.Recently,much attention has been paid to improving mechanical property of the devices made by graphene reinforced materials.Nowadays,graphene reinforced metal matrix composites have been attached great interests in new-material developments.Studying microstructural evolution and revealing the mechanisms through simulations can provide theoretical guidance for structural design and property optimization in these composites.However,most of studies are mainly focused on functional properties of the composites,and relatively few of them are on mechanical properties.Therefore,taking graphene nanosheet reinforced iron matrix composites(Gr/Fe composites)as an example material,this work investigates the effects of interface strength,distribution and size of graphene nanosheet on mechanical properties of the Gr/Fe composites through molecular dynamics(MD)simulations,which expects to further support the development of particulate compound materials from microstructural design.Through MD simulations of interfacial characteristic between graphene and iron matrix,it is found that when graphene and iron matrix form a chemical(strong-bonded)interface,the interactive energy of the graphene/iron {110},{111},{112} and {100} interface is-7.92 J/m2,-6.81J/m2,-7.68J/m2 and-7.31J/m2,respectively.The length distribution of the Fe-C bonding is discontinuous and divided into two parts of 1.80～2.00? and 2.30～2.50?,which proves that the carbides(e.g.,Fe3C and Fe7C3)are formed in the interface.Meanwhile,the characteristics of atomic structures in different-oriented interfaces are also different.When graphene and iron matrix form a physical adsorption(weak-bonded)interface,the interactive energy is-1.48J/m2,-1.09J/m2,-1.26J/m2 and-1.20J/m2,respectively.The lengths of the Fe-C bonding are distributed in 2.20～3.00? without carbide formation,and less characteristics of atomic structures are observed,compared with the strong-bonded ones.Through MD simulations about the effects of interfacial strength and distribution of graphene nanosheet on mechanical properties of Gr/Fe composites,the results show that when graphene and iron matrix form a strong-bonded interface,the yield stress is 505 MPa,991 MPa and 968 MPa on(110)、(112)and(111)Gr/Fe composites,respectively.The yield stress becomes 520 MPa,827 MPa and 830 MPa,respectively,when graphene and iron matrix form a weak-bonded interface.Meanwhile,the different-distributed graphene nanosheets interact differently with the edge dislocation and the related mechanisms are also affected by interfacial strength.The hybrid effect of graphene-distributed mixture on mechanical properties of the Gr/Fe composites is further studied.When graphene and iron matrix form a strong-bonded interface,there is no hybrid strengthening effect on the Gr/Fe composites.However,when graphene and iron matrix form a weak-bonded interface,the hybrid strengthening occurs on the((111)+(110))Gr/Fe composite,where the yield stress increases by 1.66%and 106.25%,compared with that of(111)and(110)Gr/Fe one,respectively.These results indicate that mechanical properties of hybrid particles reinforced composite cannot be easily described by the rule of mixture of the monolithic ones,and only a few of the composites can exhibit the valuable hybrid strengthening effect.Through MD simulations on the size effect of graphene nanosheets(80?,56?,46?),it is found that the graphene size has no significant inffluence on mechanical properties of(110)Gr/Fe composites with both strong-and weak-bonded interfaces.However,the graphene size shows the similar effects on mechanical properties of(111)Gr/Fe composites:the stress of the 80 A,56 A and 46 A sized graphene nanosheet reinforced composites with the strongbonded interface is 991 MPa,1390 MPa and 2429 MPa,respectively;while it becomes 830 MPa,1316 MPa and 2082 MPa for the weak-bonded composites.In contrast,the graphene size has different effects on(112)Gr/Fe composites:when the graphene and iron matrix form a strong-bonded interface,the yield stress increases with the size decrease,which is 1044 MPa,1171 MPa and 1184 MPa,respectively;when graphene and iron matrix form a weak-bonded interface,the yield stress firstly decreases and then increases with the size decrease,which is 860 MPa,729 MPa and 897 MPa,respectively.Therefore,the results indicate that mechanical properties of particle reinforced composite cannot be easily described by a general formula,and microstructure design of the composite can only be realized through specific simulations considering both particle and matrix constitutive relations.Taking the(112)Gr/Fe composite as an example,the hybrid effect of graphene size mixture on mechanical properties of the composite is studied.When graphene and iron matrix form a strong-bonded interface,the(56?+46?)mixture-sized Gr/Fe composite has a hybrid strengthening effect with the yield stress of 1184 MPa,which is 1.11%higher than that of the 56 A one and the same as that of the 46 A one.However,when graphene and iron matrix form a weak-bonded interface,the yield stress of(56?+46?)mixture-sized Gr/Fe composite becomes 761 MPa,which is 5.39%higher than that of the 56? one and 15.16%lower than that of the 46 A one,satisfied with the rule of mixture.Therefore,hybrid strengthening of particle size mixture may be derived by the superimposition of the stress fields from each monolithic reinforcement to form a mean field of high stress gradient in particulate reinforced composites,while the weak-bonded interfaces cannot hold such stress field in the composites.更多还原