| With the development of social economy,the demand has become increasingly urgent for high-performance cemented carbide products in the manufacturing industry.However,such internal defects as uneven particle size and density distribution can result in such problems as chipping,cracking,and fracture failure in the application,which seriously affects the service life and the safety of cemented carbide.Therefore,How to improve such internal defects as uneven particle size and density distribution of cemented carbide and improve product performance is a key topic in the field of cemented carbide.Compression is one of the essential processes in the production process of cemented carbide,which has a certain impact on the uniformity of particle size and density distribution of cemented carbide.Therefore,this paper proposes a longitudinal ultrasonic-assisted compression process and carries out a study on the effect of ultrasonic vibration on the compact density,mechanical properties of cemented carbide,and micro-mechanism.The main research contents are as follows:Comparative analysis is conducted on the effects of different pressing forces,the heightdiameter ratio,pre-pressing ultrasonic time,and ultrasonic amplitudes on the density,surface quality,and cemented carbide mechanical properties of coarse-grained and fine-grained billets pressed by conventional and ultrasonic pressing methods.The results show that compared with conventional pressing,powder particles undergo intense collisions under ultrasonic vibration,which enhances the particle flowability.For coarse-grained cemented carbide,when the pressing force is between 80 and 100 MPa,the greater the density,the greater the pressure.For fine-grained cemented carbide,the density change is more significant relative to coarse-grained cemented carbide when the pressing force is between 20 and 40 MPa.Decreasing heightdiameter ratio,increasing the pre-pressing ultrasonic time,and increasing the ultrasonic amplitude significantly improves the density of the billet.Under ultrasonic vibration,the surface quality of the billet is improved,and the elastic aftereffect of both coarse-grained and fine-grained cemented carbide is improved.After sintering,the porosity of the cemented carbide is reduced,the grain size distribution is more uniform,and the number of large grains decreases.The fracture toughness of coarse-grained cemented carbide increases by 5.83% ～16.10%,and the bending strength decreases slightly,however,the hardness and density does not change.The fracture toughness of fine-grained hard alloy increases by 0.42%～18.1%,and the bending strength increases by 1.8%-5.3%.Weibull statistical analysis is used to compare the dispersion of bending strength in coarse-grained and fine-grained cemented carbide pressed by the two pressing methods.The results show that ultrasonic pressing can effectively reduce the dispersion of bending strength in the cemented carbide.The micro-mechanism of ultrasonic vibration-assisted compaction is explored.Based on experimental conditions and conclusions of ultrasonic vibration-assisted compaction of coarsegrained cemented carbide,the pressing process of WC-Co cemented carbide is simulated with the help of ABAQUS and Python.The simulation results show that the ultrasonic vibration amplitude has a significant influence on the billet density,which gradually increases with the increase of ultrasonic amplitude.In the initial stage of compaction,particles undergo intense movement under the action of ultrasonic vibration,which flowability is significantly improved.The "arch effect" between particles is destroyed,therefore,small particles rapidly fill the pores between large particles to increase the density of the billet in a short time.The residual stress inside the billet is reduced after the compaction.The billet density curves are within a reasonable error range by the experiment and simulation.The particle size distribution is uniform and the size instability is improved. |
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