Investigation On The Microstructure Evolution And Structural Design Of TaC Reinforced Iron Matrix Composite Layer

Iron and steel are one of the most widely used materials in industry and construction.They often fail due to limited strength and wear resistance.Preparation of ceramic-reinforced steel-based composites is a feasible approach for increasing their strength and wear resistance.At present,the structure of ceramic-reinforced steel matrix composites includes uniform distribution,lamellar distribution,network distribution and bundle distribution of ceramics.The bundled structure can remarkably increase the strength without sacrificing the toughness.The preparation methods of bundle distribution mainly include powder metallurgy,cast infiltration,special casting methods and solid diffusion methods.The composite material prepared by the solid diffusion method has a good compatibility between the matrix and the reinforcement,and its advantages are strong interfaces,no pollution,simple preparation process and so on.For composite materials prepared by this method,the microstructure and properties of the ceramic composite layer are the most important.However,so far,the evolution of the microstructure of the composite layer in the bundle-shaped composite material prepared by the solid-state diffusion method is not clear,and thus the controllable preparation has not been achieved.On the other hand,how to further improve the composite mechanical properties of the composite layer by designing the microstructure within the composite layer needs to be studied.Therefore,the influence of factors such as the volume fraction,size and distribution of reinforcing phase on strength and toughness of the composite layer is studied,which is of great significance for the development of this material.In this paper,solid-state diffusion combined with in-situ reaction method is used to prepare the reinforced composite layer of bundle structure.On the one hand,XRD,SEM,EDS and other detection techniques were used to analyze the phase composition and microstructure of the reinforced composite layer prepared under different heat treatment conditions.Combined with thermodynamic and kinetic analysis,the formation process of TaC reinforced composite layer was elucidated.The controllable preparation of TaC reinforced composite layer was realized,and the elastic modulus and hardness of TaC reinforced composite layer were measured by nanoindentation method.On the other hand,the influence of particle volume fraction,particle size and distribution morphology on the mechanical properties of TaC reinforced composite layer was studied by finite element method.The main conclusions are as follows:(1)It is found that the heat treatment temperature and time are the key factors which,control the microstructure of TaC reinforced composite layer material.Under the conditions of short heat treatment time and low temperature,the thickness of the TaC reinforced composite layer is only dozens of micrometers.Under the condition of long time and high temperature,the thickness of TaC reinforced composite layer can reach millimeter level.With the change of heat treatment process,the volume fraction,size and agglomeration degree of the microstructure in the reinforced composite layer will change.(2)In the range of 1105-1125?,the TaC reinforced composite layer prepared by solid-state diffusion in-situ reaction method was measured.Finally,it was found that the growth of TaC reinforced composite layer obeys the parabolic relation(d2=Kt).The growth rate constants of TaC reinforced composite layer were:K_1105?=2.63× 10^-9cm²/s,K1115?=8.84×10^-9cm²/s,and K1125?=1.16×10^-8cm²/s,respectively.Diffusion activation energy Q=663.29 kJ/mol.The relationship between the thickness of TaC reinforced composite layer and the heat treatment time and temperature was calculated,and the controllable preparation of the composite layer was realized.(3)In the TaC reinforced composites layer,as the volume fraction of the reinforcing particles gradually increases,the elastic modulus and tensile strength of the TaC reinforced composite layer also gradually increase,but the fracture toughness gradually decreases.As The size of the reinforcing particles gradually increases,the elastic modulus and fracture toughness value of the reinforced composite layer do not change much,but its tensile strength gradually decreases.It is also found that the fracture toughness without agglomeration was the highest,followed by minor agglomeration,and the fracture toughness with severe agglomeration was the lowest.In all three distributions,the highest tensile strength was achieved without agglomeration.Therefore,in order to improve the hardness and modulus of the TaC reinforced composite layer,it is necessary to increase the volume fraction of the particles,reduce the particle size,and avoid the agglomeration of the reinforcing particles.