Fabrication And Erosion Wear Behaviors Of ZTAP-WCP Reinforced Ni Matrix Composites

Because of their properties of high strength,high hardness,corrosion resistance,and high toughness,Ceramic particles reinforced metal matrix composites have attracted more attention.Adapting to and meeting the requirements of high-tech wear-resistant materials,the research and development of high-toughness and high wear-resistant composite materials is an important subject for saving resources and energy.Based on the principles of composite materials design and the strengthening mechanism of metal-matrix composites,composites of ZTAp-WCp/Ni55 had been fabricated with powder metallurgy.The effects of ZTA particle size(F12,F14,F20),WC particle composition(3%,5%,10%),and the structure of the composite material on the mechanical properties of the composite material such as density,hardness,and fracture toughness were thoroughly studied.The effects and mechanisms of hybrid particles on the erosion and wear properties of composites are further studied.Conclusions are as follows:(1)The composition,structure and process of hybrid particle reinforced metal matrix composites had been designed with strengthening mechanism of solid solution,particle dispersion and bearing strengthening.At the same time,the secondary granulation process of mixing strengthening phase with ball milling was designed.The secondary granulation process,which uses solid paraffin as a binder and absolute ethanol as a dispersant,and adds different ceramic particles to the matrix powder in batches through mechanical stirring,effectively avoids the"segregation"and"Reunion".The composite materials obtained by sintering processes such as grading loading pressure and"three-stage insulation"shrink uniformly,and ZTA,WC are evenly and independently distributed in the matrix,without bridging and obvious defects.The average relative density of the composite is 96.5%,and the matrix hardness is between HRC50-60.(2)The effect of ZTA particle size and WC content on the density and hardness of composites is mainly due to their effect on the relative density.When the ZTA content is constant,the bulk density and relative density of the composite material decrease with the decrease of its particle size.The smaller the ZTA particle size,the larger the contact area and the higher the probability of defects,which affects the density of the composite.With the increase of WCp content,the hardness of the matrix of the composite material increases first and then decreases.When the WCp volume content is 10%,the relative density of the composite material decreases significantly,which is also the main reason for the decrease of the macro hardness of matrix.The relative density of the composite material has a significant positive correlation with its matrix hardness,and the correlation coefficient is 0.6747.(3)ZTAp-WCp/Ni55 composites are mainly composed of?-Ni(Cr,Fe),Al₂O₃,Zr O₂,WC,W₂C,M₂₃C₆and some silicides.The interface between ZTAp and Ni55,without element diffusion,is well mechanical bonding.The interface between WCp and Ni55 matrix is a metallurgical bonding with element diffusion and the generation of a clear"core-rim"Structure.The core is undissolved WC,and the rim is the diffusion region between W and matrix after WC decomposition.A solid solution was formed in the diffusion region with W and Ni,Cr,Fe in matrix.The proportion of W and Cr in M₂₃C₆in the rim is related to its relative distance to undissolved WC particles.Through thermodynamic calculations,W₅Si₃and other silicides were formed,making Si element enriched in the diffusion region.The thickness of WC and Ni55matrix transition layer is related to sintering temperature and holding time.The existence of the"core-rim"structure makes the micro hardness a gradient change from the WC core to the matrix.(4)The addition of ZTAp and WCp did not significantly improve the toughness of the composite.Excessive volume fraction of the second phase particles cleaves the integrity of the composite matrix.With the increase of particles,the number of interfaces inside the composite material increases,and most of them are discontinuous brittle materials.Although the analysis shows that precipitates can prevent cracking by deflecting or terminating cracks,it is insignificant compared to cracking caused by macroscopic interface defects.The matrix of the composite material,ZTAp and WCp all show fracture along the mixture of intergranular and transgranular.The impact energy and relative density have a significant positive correlation with a correlation coefficient of 0.8434.The relative density of the composite material is the key factor affecting the impact properties of composite materials.(5)The addition of reinforcing particles significantly improves the erosion resistance of the composite material.The impact angle determines the way in which the Si C particles in the slurry act on the composite surface.At 30°,the Si C particles in the slurry act on both the tangential and normal directions of the material surface.The erosion wear mechanism is mainly micro ploughing and fatigue spalling,and the wear surface is mainly represented by the furrow of the substrate.And spalling pits of reinforced particles.At 90°,the erosion wear mechanism is mainly the fatigue spalling caused by the continuous impact of normal load,and the wear morphology of the material surface is mainly formed by fatigue fracture pits.The addition of acidic corrosive media exacerbates the wear process of composite materials.During erosion and wear,wear and corrosion affect each other and promote each other,resulting in the erosion wear rate under acidic conditions is much greater than neutral conditions.(6)Dynamic observation of the morphological changes of the composite material during the erosion process had been taken.Erosion wear first occurred at the combination of reinforced particles and the matrix,impact pits,plastic stress concentration areas around the furrow,and micro-cracks.Under the multiple effects of corrosion,abrasion and their interaction,those areas became the most severe erosion wear districts.The"core-rim"structure formed by the WC particles due to the diffusion reaction,that is,the good interface between the WC particles and the matrix,makes the WC particles improve the erosion and wear resistance of the composite from both mechanical and chemical aspects.The matrix provides strong support for ZTA particles,provides a basis for ZTA particles to play a reinforcing role,and exhibits good and stable anti-erosion wear performance.After mixing WC particles with ZTA particles,the density,hardness,corrosion resistance and erosion and abrasion resistance of the composite are improved by solid solution strengthening,dispersion strengthening and particle bearing strengthening.