In-situ Fatigue Crack Propagation Of Steel Matrix Composites ?Fe-TiB₂? Based On Eutectic Solidification Process

Nowadays,lightening of automotive structures is the inevitable tendency,but this has mainly been achieved by gauge reduction which can significantly reduce the stiffness and it has a limit.Therefore,developing new steel matrix composite?SMC?with lower density and higher stiffness to reduce further the weight of automotive parts has received extensive attentions in recent years.TiB₂-reinforced SMC fabricated by eutectic solidification has overcome the shortcomings of the SMC produced by external force such as powder metallurgy,this process is simple,cost effective and can be applied to large-scale industrial production.At the same time,the SMC prepared by eutectic solidification have strong interfacial strength,which is expected to improve the toughness and fatigue crack growth resistance of the composites.In this paper,the fatigue crack growth resistance and growth behavior of two steel matrix composites?Fe-TiB₂?with different TiB₂ content?vol:9%and 13%?was studied by in-situ SEM.The results show that,benefiting from the high interfacial strength between TiB₂ and matrix,when the crack tip approaches the strengthening phase TiB₂ gradually,the growth rate will decrease obviously.Simultaneously,branches and zigzag propagation paths will be generated,which can effectively improve the fatigue crack growth resistance of SMC?Fe-TiB₂?.In addition,in the fatigue crack growth test,the crack growth rate of Fe-TiB₂?vol:13%?is obviously higher than that of Fe-TiB₂?vol:9%?.The main reasons for this phenomenon are the following three points:1)there are many large TiB₂ particles in Fe-TiB₂?vol:13%?,and it's easier to produce fracture and defects during hot rolling which can introduce many micro cracks.2)there are many clusters of primary particles in Fe-TiB₂?vol:13%?,making the brittle fracture of primary particles is prone to occur when the crack tip approaches to these particles.3)micro cracks are easier to initiate at the front of the crack tip in Fe-TiB₂?vol:13%?.