The Discontinuous Gradient Structure Study Of ZTA_P/steel Matrix Composites Under Thermal Shock Condition

In recent years,internal and foreign scholars have carried out various researches on the thermal shock stability of ceramic particle reinforced metal matrix composites,due to the huge thermodynamic performance difference between ceramic particles and matrix in composite materials,it is more likely to generate thermal stress in the thermal shock environment and affect the structural stability of the composite material.Therefore,through the non-continuous gradient structure design,the gradient structure designed with transitional effect and the discontinuous structure of honeycomb arrangement reduce the stress concentration at the macroscopic interface,inhibit the crack extension and improve the thermal stability of the composite.In this paper,ZTA_P/steel-based discontinuous gradient structure specimens with uniform particle distribution and good interface were successfully prepared by powder metallurgy+extrusion casting method.ABAQUS finite element software was used to simulate discontinuous gradient composites and discontinuous single components.The thermal stress field of composite materials was used to investigate the influence of different composite structures on the thermal stress.At the same time,pre-compression experiments,thermal shock tested and residual stress tests were used to investigate the effects of different structures on the thermal fatigue properties of composites and the crack propagation.Explore.The research focuses on the thermal shock resistance of ZTA_P/steel-based discontinuous gradient composites and the relationship between thermal shock resistance and thermal fatigue,which provides a theoretical basis for the new structural design of composites.The result of finite element simulation shows that the difference in thermodynamic properties between ZTA ceramic particle reinforcement and 45 steel matrix increases with the increase of ZTA volume fraction.During the rapid cooling process,the ceramic particle reinforcement and 45 steel matrix are produced large thermal stress,single component discontinuous composites with the increase of ZTA volume fraction,the thermal stress inside the composite increases gradually,and the stress concentration is the macroscopic interface;the maximum thermal stress of the discontinuous gradient composite is less than that of the single structure of the same ZTA volume fraction.The results of thermal fatigue test shows that in the pre-compression experiment,the higher the ZTA volume fraction,the less the cyclic loading-unloading stress-strain can be withstood by the reinforcement,and the maximum stress is gradually reduced.The gradient structure reinforcement and the single component reinforcement of the same ZTA volume fraction has better resistance to pre-strain and can withstand larger loads;from the surface fracture morphology after the pre-compression experiment,the outer ring structure of the gradient structure reinforcement wraps the interior The high ZTA volume fraction component produces a large number of microcracks and deforms in the low ZTA volume fraction region with good toughness,and effectively protects the brittle phase inside the reinforcement.In the thermal shock experiment,as the volume fraction of ZTA increases,the initiation and propagation of cracks change from the inside of the reinforcement to the macroscopic interface.After 100times thermal shocks,the expansion width of the crack increases with the increase of the volume fraction of ZTA.And the 70volZTA volume fraction enhances the partial shedding of the surface,and the gradient structure composite has a small crack width,there is no shedding;the internal crack of the reinforcement first sprouts at the microscopic interface between the ceramic particles and the matrixes,gradually penetrates the ceramic particles or extends a certain distance along the microscopic interface.When the ceramic particles are close to each other and also cause source cracks,The two source cracks are connected through a 45 steel matrix to form a main crack to achieve crack propagation.The change of residual stress before and after thermal shock was tested,which was the same as the trend of simulation and experiment.Therefore,in order to improve the thermal stability of ZTA_P/steel-based composites,the discontinuous gradient structure design can effectively reduce the thermal stress at the macro interface and improve the thermal shock stability of the composite.