【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， 2016， 硕士

【摘要】 陶瓷颗粒增强铁基复合材料具有高强度、高耐磨性及良好的高温性能,因此在高温、高速和磨损等工作环境中表现出巨大的应用前景。目前对颗粒增强金属基复合材料力学行为的研究还主要停留在细观力学的层面上,但颗粒增强金属基复合材料的微观结构,尤其是增强相与基体相界面处的微观结构,对复合材料的宏观物理和力学性能有着重要影响。因此,从原子尺度建立科学、合理的力学模型为复合材料的设计提供理论基础和依据是目前的重点研究方向。课题组在实验研究中发现,增强粒子尺寸对SiCp/Fe复合材料的强度影响并不是单调变化,而是出现峰值;而不同类型强化颗粒混合增强复合材料的强度优于单一类型增强时的强度。解释这两个实验结果是对材料学基础研究的一个挑战,充分利用好两个新的强化方法是颗粒增强复合材料性能提高的重要发展方向。本工作采用分子动力学模型,研究体积分数为15%,SiC颗粒尺寸和SiC、TiN和TiC颗粒单一增强和混合类型对其增强的铁基复合材料力学性能的影响规律,计算复合材料的应力-应变曲线,探索在原子尺度的强化机理和载荷传递的微观机制。结果表明,SiCp/Fe复合材料的弹性模量随着粒子尺寸的增加先增加后降低,粒径为4.4nm的SiCp/Fe的弹性模量比粒径为2.6和13.2nm的分别高出9.2%和13.1%。在SiCp/Fe复合材料应力-应变曲线的初始阶段,受力随颗粒尺寸的增大而增大到达最高点,随后应力开始下降,从原子结构图上分析对应材料在(011)面产生1/2[111]的位错,当位错与粒子开始相互作用后,粒子间位错滑移面贯通导致复合材料应力出现最低点(即屈服应力),而SiC颗粒尺寸的增大导致屈服过程对应的应力下降量越大,对强化效果减弱越强,这两个矛盾因素的平衡将导致屈服强度对增强粒子尺寸的最佳点,对应粒径为3.3nm的SiCp/Fe复合材料屈服应力最大。这一结果对以上第一实验现象提供了一个机理解释,也证明了本模拟建模的合理性。对比SiC、TiN和TiC颗粒增强的铁基复合材料的应力-应变曲线,SiC的强化效果最好,TiC其次,TiN最差,说明颗粒弹性模量越高其强化效果越好,这与实验结果吻合的很好。对比SiC、TiN和TiC两两等比例混合增强的铁基复合材料的应力-应变曲线,(TiC+TiN)粒子混合的强化效果可优于对应的两种单一类型,(SiC+TiN)混合强化效果处于对应的两种单一类型之间,而(SiC+TiC)混合强化效果则明显地低于对应的单一类型。进一步分析(TiN+TiC)p/Fe复合材料发现,在受力的初始阶段,TiCp/Fe复合材料高于(TiN+TiC)p/Fe和TiNp/Fe;当粒子间位错滑移面贯通时,(TiN+TiC)p/Fe的应力下降幅度最小;在变形量达到13.5%后,(TiC+TiN)p/Fe的应力值要高于TiNp/Fe和TiCp/Fe,表现出可贵的混合强化效果,这与以上第二实验结果相符合。模拟表明TiN增强的失效形式是粒子断裂,但TiC增强的失效形式是铁基体屈服,因此,可以初步确定,混合类型粒子增强是不同类型的粒子周围的微观应力场巨大差别,当不同粒子的应力场相互进行叠加时,将抵消部分局部裂纹形成的驱动力,导致复合材料强度的提高。更多还原

【Abstract】 Ceramic particle reinforced iron matrix composites(PRIMCs)have high strength,high wear resistance and excellent elevated temperature performance,therefore they have great prospects in high-temperature,high-speed,and wearing fields.At present,most of the models to investigate mechanical behaviour of the PRIMCs are at mesoscale.As the microstructure of the PRIMC is crucial to the mechanical behaviour,especially the interface between the matrix and particles,it is important to establish a scientific and reasonable mechanical model at atomic scale in order to provide a theoretical basis for the PRMMC design.Our experimental results showed that with decreasing particle size,the tensile strength of SiCp/Fe composite has not increased monotonically rather has an optimum value.With the mixed-type particles as reinforcement,the tensile strength of PRIMC is better than that of the composite reinforced with its corresponding single-type particle.To explain both experimental observations is a challenge of fundamental research in material science.Moreover,the two new strengthening mechanisms could provide a new way to improve mechanical property of the PRIMC.In this work,molecular dynamic(MD)model is used to study the effects of SiC particle size and mixed type(SiC,TiN and TiC)on mechanical behaviour of the PRIMCs with the 15 vol.%reinforcement.Then the stress-strain curves of the PRIMCs can be obtained and the strengthening mechanism and the load transfer mechanism at atomic scale will be explored.The results show that the elastic modulus of SiCp/Fe composites with increasing particle size first increases and then decreases.The elastic modulus of 4.4nm SiCp/Fe composite is 9.2%and 13.1%higher than the 2.6nm and 13.2nm SiCp/Fe,respectively.In the initial stage of the stress-strain curve of SiCp/Fe composite,the stress of the composite increases,reaches the highest stress and then decreases.During stress decreasing from peak stress,it corresponds to the 1/2[111]dislocation nucleation on the(011)plane from the particle/matrix interface,the dislocation movement and the dislocation slip plane conjunction between the particles,which occurs at the lowest stress in the first stress drop,that is the yield stress.In the initial stage of the stress-strain curve,with increasing particle size the peak stress of the composite increases and the stress drop is larger.The balance of these two contradictory factors will lead to the maximum yield strength with an optimum particle size,that is the particle size of 3.3nm.These results provide a mechanism to explain the first experimental observation above and also prove the rationality of this MD modelling.Compare the stress-strain curves of SiCp/Fe,TiNp/Fe and TiCp/Fe composites,the SiC particle has the best strengthening effect,the TiC has the second and then the TiN has the worst.It indicates the higher elasticity modulus the better strengthening effect of the particles is,in a good agreement with the experimental observation.Compare the stress-strain curves of the(SiC+TiC)p/Fe,(SiC+TiN)p/Fe and(TiN+TiC)p/Fe,the hybrid(TiC+TiN)particle has a better strengthening effect can than the TiC and TiN particle,the strengthening effect of hybrid(SiC+TiN)particle is better than that of the TiN but worse than that of the SiC,and the strengthening effect of hybrid(SiC+TiC)particle is worse than that of the SiC and TiC.Further analysis focuses on the(TiN+TiC)p/Fe composites and it is found that in the initial stage of the stress-strain curve,the stress of TiCp/Fe is higher than(TiN+TiC)p/Fe and TiNp/Fe;the stress drop from the peak stress of the(TiN+TiC)p/Fe is the smallest.After the strain is higher than 13.5%,the stress of the(TiC+TiN)p/Fe is higher than that of the TiNp/Fe and TiCp/Fe,which exhibits the valuable hybrid strengthening effect.These results provide a mechanism to explain the second experimental observation above.The results show that the failure mode in the TiNp/Fe composite is the particle fracture,but the failure mode in the TiCp/Fe composite is the yielding of iron matrix.Therefore,it could be regarded that the hybrid strengthening effect of the mixed type particle is from a huge difference of stress field around different types of particles at micro-scale,and when the stress field is superimposed with each other,part of the driving force of the local crack formation will be offset,which leads to an increase in the strength of the PRIMCs.更多还原