Strength,Toughness And Impact Abrasive Wear Resistance Of Particles Reinforced Iron Matrix Composites

In mining machinery,building materials and environmental protection and other industries,many workpieces are subjected to abrasive wear under impact,such as the driving teeth of roadheader,hammer and crushing teeth of crusher,etc..Impact abrasive wear is a very severe wear condition,which greatly shortens the service life of the machine and causes great economic loss.The research and development of iron composites with more excellent impact abrasive wear resistance is conducive to energy saving,reducing mechanical loss and maintenance costs,promoting the upgrading of domestic advanced machinery and equipment.In this thesis,Fe45 as the matrix,millimeter ZTA_p（zirconia toughened alumina ceramic particle）as reinforcement phase,polyvinyl alcohol（PVA）as binder,ZTA_p/Fe45 composites with different particle sizes（0.1 mm,0.5 mm,1.0 mm,2.0 mm,2.5 mm）,shape（spherical and irregular）,volume fraction（10%,20%,30%,40%）and bonding state of interface between ZTA_pand Fe45 matrix（modified and unmodified）were sintered by powder metallurgy.The effects of ZTA_psize,shape,volume fraction and interfacial bonding state on the strength,toughness and fracture mechanisms of the composites were studied systematically.The influence mechanisms of ZTA_psize,interface and impact energy on impact abrasive wear resistance and wear mechanisms of ZTA_p/Fe45 composites were studied by impact abrasive wear test.The effect laws of the strength and toughness of different ceramic particles（ZTA_p,Al₂O₃,Zr O₂）on the impact abrasive wear resistance and wear mechanisms of the composites were studied.The phase transformation of Zr O₂was analyzed to reveal the mechanism of the phase transformation toughening of ZTA_pin the wear process.The following main conclusions are drawn:（1）Fe45 matrix material and ZTA_p/Fe45 composites were prepared by powder metallurgy method,and the technological parameters were optimized.After modification,ZTA_pmetallurgical bonding with Fe45 occurs,the interface porosity decreases,the bonding strength increases,and the hardness and elastic modulus of the interface are between Fe45 matrix and ZTA_p,which forms a good transition effect.With the increase of ZTA_psize,the density and hardness of the composites increase,and micron ZTA_pagglomeration occurs,reducing the density and hardness of the composites.（2）After adding ZTA_p,the tensile strength and bending strength of the composites decrease,and the bending strength and elastic modulus of the composites decrease with the increase of the volume fraction of ZTA_p.ZTA_psize has little effect on the strength of the composites.The strength and elastic modulus of the interfacial modified composites are improved,and the improvement effect is better when the volume fraction of ZTA_pis higher than 20%.The bending strength formula of ZTA_p/Fe45composites were proposed by data fitting.Typical brittle fracture is formed in Fe45matrix after bending fracture,and the fracture mechanisms are cleavage fracture and intergranular fracture.The crack propagation crosses the grain and grain boundary and terminates at Zr O₂in ZTA_p,indicating that Zr O₂plays a certain role in inhibiting the crack propagation.（3）The impact toughness of the ZTA_p/Fe45 composites decreases with the increase of ZTA_pvolume fraction.The impact toughness of the ZTA_p/Fe45 composites with spherical ZTA_pis lower than that of the ZTA_p/Fe45 composites with angular ZTA_p.The impact toughness of the composites increases with the increase of ZTA_psize.After interfacial modification,the impact toughness of the composites decreases.The fracture mechanism of Fe45 matrix is cleavage fracture.The failure ways of ZTA_p/Fe45composites during impact fracture are particle fracture and particle debonding and pulling out.The fracture mechanism of ZTA_pare intercrystalline and transgranular fracture.The failure ways of ZTA_pare closely related to ZTA_psize,shape and interface strength.（4）The impact abrasive wear resistance and wear mechanism of ZTA_p/Fe45composites are closely related to the ratio of abrasive particle size to ZTA_psize（d_a/d_z）.When the value of d_a/d_zis 0.5～1,ZTA_pplay an obvious role of shadow protection,resisting the cutting of Si O₂abrasive and impact load on friction pair effectively.When the value of d_a/d_zis 1～2,the shadow protection effect of ZTA_pdecreases with the increase of d_a/d_z.When d_a/d_z≤0.4,the impact load on the ZTA_pincreases with the decrease of d_a/d_z,which accelerates the fracture of ZTA_p.When d_a/d_z≥2,ZTA_pproduce wear loss easily under micro-plough action of Si O₂abrasive.The wear resistance of ZTA_p/Fe45 composites modified by interface is improved significantly with the increase of impact energy.In the process of impact abrasive wear,the shedding of ZTA_pis improved obviously.There is an obvious transition layer between ZTA_pand Fe45matrix,which can slow down the impact wear effect of Si O₂abrasive on ZTA_p.Impact abrasive wear mechanisms of Fe45 matrix are mainly micro-cutting or micro-plowing,and fatigue flaking-off caused by repeated impact plastic deformation,while the wear mechanism of ZTA_pis micro-step peeling off.（5）The impact abrasive wear resistance of the three composites decrease with the increase of impact energy and the impact abrasive wear resistance of ZTA_p/Fe45composite is better than Al₂O₃/Fe45 and Zr O₂/Fe45 composite.In the process of impact abrasive wear,ZTA_pprotrude obviously from the surface of the matrix,playing a good impact wear resistance in the composites.Brittle fracture and spalling of Al₂O₃particles occur,which accelerates the wear process of the composites.Zr O₂particles have high toughness,but low hardness,and can be easily removed from Fe45 matrix in the process of cutting wear of Si O₂abrasive.The impact abrasive wear resistance of the three composites are positively correlated with the product value of fracture toughness and hardness(H·K_IC)of the ceramic particles.During the impact wear process,the phase transition from t-Zr O₂to m-Zr O₂occurs in ZTA_pand Zr O₂particles.With the increase of impact energy,the amount of phase transition increases.When the impact energy is higher than 2J,the amount of phase transition tends to be stable.Under the same impact energy,the amount of t→m phase transition in Zr O₂particles is much lower than that in ZTA_p.The toughness of ZTA_pis enhanced by t→m phase transformation,and the impact abrasive wear resistance of ZTA_p/Fe45 composites is improved.The above research results have reference value and practical significance for the design,research and development of particle reinforced iron matrix composites used in impact abrasive wear condition.