Creep Behavior Of Tungsten Carbide During Sinter Forging Under Alternating Load

As a hard material,WC ceramics have been widely used in industrial fields,but the poor toughness limits its further application.Obtaining the high-density and ultrafine grains is a way to improve toughness.However,the current sintering processes are difficult to achieve complete densification of WC ceramics and keep ultra-fine grain structure.Sintering forging has been proved to be a technology that can realize rapid densification and maintain fine grain of ceramics at low temperature,but ceramics are required to have good high-temperature plasticity,while WC ceramics are difficult to produce plastic deformation and cannot be obtained by sintering forging.Alternating load has been proved to effectively promote the plastic deformation of ceramics in the preparation of ceramics.If alternating load is introduced into sintering forging,it is expected to prepare WC ceramics with high density and ultra-fine grain.In view of the fact that sintering forging is a high-temperature creep process of porous materials,this paper explores the creep behavior and mechanical properties of porous WC ceramics under alternating load,so as to provide a theoretical basis for the preparation of high-density and ultrafine WC ceramics.The main contents are as follows:（1）The pore evolution of porous WC ceramics during high temperature creep under alternating load was studied.It is found that both alternating load and static load can reduce the porosity of the sample,but the porosity of alternating load is much lower,and the pore size and distribution are more uniform.This may be that alternating load effectively promotes the shear deformation under the state of high porosity and accelerates the reduction and discharge of pores;It is found that the porosity decreases with the increase of temperature,time and alternating load amplitude.When the temperature is 1500℃and the time is 120 min,the porosity is less than 2%;When the porosity is 20%-36%,the densification mechanism is plastic deformation;When the porosity is 5%-10%,the densification mechanism is pipe diffusion.（2）The deformation behavior of porous WC ceramics during high temperature creep under alternating load was studied.It is found that alternating load can promote the deformation of materials,which may be caused by more stacking faults and dislocations under alternating load;It is found that increasing the temperature,time and amplitude can effectively promote the plastic deformation of WC ceramics.When the frequency is 2Hz,the amplitude is 155±93 MPa,the temperature is 1500℃and the time is 30 min,the strain is1.232.The volume strain increases with the increase of shear strain.The higher the shear strain is,the smaller the pore volume is;Under the condition of high porosity,the creep mechanism of porous WC ceramics is grain boundary slip.（3）The grain growth behavior of porous WC ceramics during high temperature creep under alternating load was studied.At the same temperature,the grain size of alternating load samples is smaller and the grain size distribution area is narrower;The grain size increases with the increase of temperature and time;When the frequency is 2 Hz,the amplitude is 186±62 MPa,the temperature is 1500℃and the time is 30 min,the grain size is 264 nm;The grain growth index n=3 and the grain growth activation energy E=213k J·mol^-1are calculated.The corresponding grain growth mechanism is volume diffusion.（4）The hardness and fracture toughness of WC ceramics after high temperature creep were measured.It is found that the hardness and fracture toughness of the samples under alternating load are higher than those under static load,because the alternating load can reduce the porosity of WC ceramics and the grain size is smaller.In addition,there are more defects such as stacking faults and dislocations;It is found that the hardness of WC ceramics increases with the increase of amplitude,and the increase of hardness is due to the decrease of porosity;The fracture toughness of WC ceramics increases with the increase of amplitude.The increase of fracture toughness is due to the more tortuous crack propagation path and the characteristics of increasing crack propagation energy such as bridging;When the frequency is 1 Hz and the amplitude is 186±62 MPa,the hardness and fracture toughness of WC ceramics are 29.49 GPa and 7.18 MPa·m^1/2.