Investigation On Mechanical Properties And Damage Mechanisms Of TiB₂/Fe Composite Fabricated By Eutectic Solidification

Particle-rinforced metal matrix composites（PRMMCs）have broad application prospects in the aerospace,space and automotive industries because of their high specific strength,specifice modulus and superior wear resistance.There are more than dozens of processes of processes to prepare PRMMCs,but few of them can obtain good strength,toughness and interfacial bonding at the same time.It is an important research direction to obtain superior mechanical properties of PRMMCs by adopting the best preparation technology and reasonably controlling many characteristics of reinforced phase,such as content,aize and distribution.In addition,with the complexity and diversification of structural components subjected to loads in practical engineering applications,it is necessary to understand the damage evolution o f PRMMCs from multiple scales and reveal their intrinsic damage mechanisms with mechanical and materialistic implications.To this end,a Ti B₂ particle-reinforced iron matrix composites was prepared by eutectic solidification process as the research object in this paper,and a series of studies on the macroscopic mechanical properties and fine-scale damage mechanisms were carried out.The effects of different particle volume fractions and heat treatment processes on the microscopic deformation mechanisms and damage evolution patterns of this composit under static and cyclic loading were investigated and compared by means of advanced in-situ techniques and multi-cale characterization.The research ideas and methods for obtaining superior mechanical properties of PRMMCs under reasonable particle characteristics and rolling processes are further revealed,and will be helpful in future applications in the manufacture of key components for various equipment in service.Based on this idea,the work carried out and completed in this paper is as flollows.（1）The mechanical properties and damage mechanism of Ti B₂/Fe composites were investigated under static loading.The Ti B₂/Fe composites with 9%and 13%wolume fraction were prepared by eutectic solidification process,and the microstructure of the composites and their mechanical properties were analyzed.The tensile fracture behaviors of Ti B₂/Fe composites in four states were obtained based on an advanced in-situ tensile experimental system.The effects of Ti B₂/Fe particle characteristics on fracture damage mechanism and strength and toughness of the coposite were analyzed in detail,and the relationship between the tensile damage behavior and the macroscopic mechanical properties of the composites was established.（2）The fracture properties and damage mechanisms of Ti B₂/Fe composites under static loading were investigated.Based on the advanced electron-driven mechanical system,the fracture toughness values of Ti B₂/Fe composites in four states were measured under three-point bending load.Combined with the in-situ scanning electron microscopy technique,the interaction forms between the particle characteristics and the crack tips under different particle volume fractions and heat treatment processes were observed,thus revealing the fracture damage mechanism of the four states Ti B₂/Fe composites and summarizing the influence of Ti B₂ particle characteristics on the macroscopic fracture mechanism and fracture resistance performance of this composite.（3）The fatigue crack initiation mechanism of Ti B₂/Fe composites under cyclic loading was investigated.Based on the in-situ fatigue experimental system,the low-cycl fatigue crack initiation and small crack growth behavior of Ti B₂/Fe composites in four states were obtained.The fatigue crack initiation mechanism under different particle characteristics and the effect of crack initiation position on the main crack evolution were studied in comparion.Thus,the effects of particle volume fraction and heat treatment process on the low-cycle fatigue crack initiation behavior and damage mechanism of Ti B₂/Fe composites were revealed.（4）The fatigue crack growth behavior and damage mechanism of Ti B₂/Fe composites under cyclic loading were investigated.Based on the in-situ fatigue experimental system,the fatigue crack growth behaviors of Ti B₂/Fe composites in four states were obtained.The interaction between Ti B₂ particle and fatigue crack tips was observed in-situ,thus revealing the fatigue crack growth mechanism of Ti B₂/Fe composites in the four states.The rates of different growth stages were compared,and it was found that the Ti B₂ particle characteristics have an important influence on the fatigue crack growth rate and crack growth resistance.