Effects Of Particle Size And Mixture Of Particle Types On Stress-strain Curve Of Particle Reinforced Iron Matrix Composite Using Molecular Dynamic Simulation

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.