Particle-Reinforced Iron-Based Composites Study On Microstructure And Properties Of In-Situ Carbide

Particle-reinforced iron-based composite is a new type of steel wear-resistant material developed to solve the problem of poor matching between toughness and wear resistance of traditional single wear-resistant steel materials.It not only has the good plasticity and toughness of steel materials,but also the high strength,high hardness and high wear resistance of hard particles,which achieves"the combination of rigidity and flexibility"very well and is widely interested in high-wear fields such as mining,metallurgy,and machinery.Currently,the use of composite grinding rollers and lining plates made of particle-reinforced iron-based composite has solved the problem of easy peeling and short service life of traditional wear-resistant materials under strong impact and high-stress wear conditions.However,composites have not yet been applied to small and medium-sized wear-resistant parts such as shield or roadheader cutter heads and shovel teeth.In addition,with the rapid increase in major projects such as road and bridge paving,and tunnel boring in China,wear-resistant equipment is developing rapidly towards large-size and high-efficiency operation.The service conditions of the equipment have also become more demanding,which also poses a higher challenge to the performance of wear-resistant structural parts.In the wear resistant materials industry,the design and development of new advanced wear-resistant iron-based composites are urgently needed.The widespread promotion of wear-resistant iron-based composites will completely change the industrial structure and status quo of traditional wear-resistant materials,which is also an inevitable trend in the upgrade and replacement of wear-resistant steel materials in the wear-resistant field.At the same time,it is also of great significance to promote the national"dual carbon"strategy goal.This article combines the powder metallurgy with traditional gravity casting to use high-temperature melt to induce in-situ reaction of self-exothermic active powder,and obtain iron-based composites reinforced with one or more carbide particles,such as TiC,WC,TiWC₂ and M₇C₃,in BTMCr26 wear-resistant cast iron.By developing multi-system self-exothermic active powder materials,the thermodynamic and kinetic reaction principles are clarified,the influence of factors such as the composition,content,and melt temperature of the active powder on the induction of in-situ reaction of the preform is studied,and the changes in system heat capacity during the exothermic process are calculated.The formation and evolution laws of self-generated phases in the composite reaction during casting and infiltration processes are studied.The metallurgical reaction mechanism of multiple phase-mixed interfaces between the reinforcing particles and the matrix are elucidated.The effects of different component self-exothermic active powders on the types,morphology,quantity,distribution,and size of self-generated reinforcing phases are revealed.The relationship model between active powders,preform configuration,preparation process,composite structure,and performance is constructed.Finally,to realize the stable preparation of iron-based composites with good microstructure and excellent properties at low cost.Through the analysis of three self-exothermic active powder systems,Ti-C,Ti-W-C,and Ti-Cr-C,it was found that the differences in active powder composition have a significant impact on the microstructure,phase composition,hardness,and wear resistance of composites.For Ti-C active powder,the effect of Ticontent on the interface structure,size and proportion of reinforcing particles,hardness,and wear behavior of composites was studied.The results showed that the TiC particles generated in situ in the microstructure did not have an obvious orientation relationship,and the particle size increased with increase Ticontent,but remained at the submicron level.The multi-phase mixed interface in the composite was well bonded,and there was a 20-30μm transition layer between the matrix and the composite region.At the microscopic scale,the existence of high-density dislocations between the reinforced particle and the matrix was found.When the Ticontent of the active powder was 50%,composites with an optimal microstructure were finally obtained with a high percentage of TiC-reinforced particles of more than 70%.Compared with the matrix,the microhardness of the composite was increased by more than 1 times,the sliding wear resistance was increased by nearly 3 times,and the three-body abrasive wear resistance was increased by more than 1.5 times.For Ti-W-C active powder,as the W/Tiratio increased in the powder,the phase transformation reaction temperature gradually increased,and the range of the starting and ending temperatures of the phase transformation also increased.When the W/Tiratio increased from 2:8 to 4:6,the maximum heat flow density of the powder exothermic peak decreased from 13 MW/mg to 1.5 MW/mg,and the heat released per unit temperature of the powder also decreased from 27.04 J/g to 2.81 J/g.The experimental results showed that the composite prepared with the active powder of W/Tiratio of 4:6 had the best microstructure and properties.Due to the presence of TiC,WC,and other complex phase-reinforced particles,the microhardness of the composite increased from about 750 HV of the matrix wear-resistant cast iron material to more than 1600HV.Under abrasive wear conditions,the wear resistance of the composite was also improved more than 2 times after continuous wear for 120 min compared to the matrix.In addition,through changes in the shape and sintering temperature of the preforms,as well as the casting temperature of the melt,it was found that there was no significant impact on the final structure and wear resistance of the composite.In contrast,the TiC particle sizes obtained in the composite after in situ reaction of Ti-Cr-C reactive powders were mainly concentrated in the range of 0.5-1.5μm.The overall Rockwell hardness of the composite exceeded 62 HRC,and it had an increase of more than 10 HRC compared to the matrix.At the same time,the wear resistance of the composite in the three-body abrasive wear process also increased by 2-3 times compared to the matrix wear-resistant cast iron.During abrasive wear,the experimental steels all undergo two stages of severe wear and stable wear.These larger-sized plate-like or block-like M₇C₃-type carbides in the matrix wear-resistant cast iron are relatively brittle and easily crack during the wear process.These cracked carbides are mostly shed as a whole in lamellar form,which to further exacerbate the wear failure of the surrounding materials.Meanwhile,the abrasive leaves large and deep furrows on the relatively soft surface of the matrix,causing obvious plastic deformation behavior near the furrows.In contrast,the hardness of the composite is significantly increased and much greater than that of the abrasive due to the high concentration of small reinforcing particles in its microstructure.Therefore,only shallow and small abrasion marks can be observed on the surface of the composite after wear.The main wear failure mechanism of the composite material is the combined effect of micro-plowing and micro-cutting by the abrasive on the material.Overall,understanding the wear mechanisms of materials can better insight into their failure behavior of materials and provide guidance for material design and improved wear resistance.