Discrete Element Simulation and Experimental Study on W-Cu Homogeneous Composites Processed by High-Pressure Torsion

Abstract:

The discrete element simulation of high-pressure torsion (HPT) deformation of W-Cu homogeneous powder material was carried out by PFC-3D software. The force chain and displacement distribution of particles during compression and torsion deformation were analyzed, and their effects on porosity, coordination number, and equivalent stress in different regions were discussed. The simulation results indicate that the particle displacement exhibits a gradient distribution along both the compression direction and radial direction, with the maximum displacement located at the sample edge and on the upper surface. During the compression stage, particle rearrangement reduces the porosity rapidly, while shear deformation further promotes secondary particle rearrangement and rotation, which leads to a gradual decrease in porosity. The relative density and coordination number at the sample edge are higher than at the center, indicating that shear deformation under large torsional radius is beneficial for powder densification. Under the conditions of 400 ℃ and 1.5 GPa, HPT deformation is applied to the cold-pressed W-30Cu powder compacts with different turns. The experimental results show that with the increase in torsional radius and HPT turns, the degree of particle breakage, microstructure refinement, and homogeneity are improved significantly. Under the combined effect of high hydrostatic pressure and shear force, the pores are elongated and enclosed, which results in increased relative density from (95.44±0.87)% (after 10 turns) to (96.03±0.54)% (after 20 turns). The crystallite size of tungsten significantly reduces to 20.8 nm and the dislocation density rapidly increases to 2.35×10¹⁴ m^-2 after 15 turns; the grain refinement and dislocation accumulation achieve the dynamic equilibrium. After 20 turns, due to the combined effects of powder densification, microstructure refinement, and dislocation accumulation, the microhardness at the samples edge reaches (334.8±4.2) HV, which represents an increment of approximately 78.7% compared to the sample center after 10 turns.