Discrete Element Simulation On Deformation Process And Controllable Preparation Of ZrCu-based Metallic Glass/Carbon Nanotube Composites

Metallic glass(MG)/carbon nanotube(CNTs)composites have broad applicationprospects in the field of photoelectric and mechanical materials.The preparation of CNTs composites with uniform dispersion,good interfacial bonding and orientation is the key to achieve good properties.The orientation distribution of CNTs has been a difficult and hot topic in this field.In this paper,ZrCu-based MG was used as matrix material to prepare composite materials with CNTs.The process of uniaxial compression of MG and superplastic deformation of composites were simulated by discrete element method.The preparation and superplastic deformation behavior of composites were studied by mechanical alloying,hot pressing and electroforming.This paper mainly carries out the following research:(1)The simulation model of ZrCu-based MG under uniaxial compression was established by discrete element method.The micro-parameters of ZrCu-based MG were calibrated.The effects of taper angle and extrusion ratio on the orientation of CNTs in composites were studied.The results show that the parallel bond model is suitable for simulating the mechanical properties of ZrCu-based MG at room temperature,and the linear contact bond model is suitable for simulating the superplastic deformation behavior of ZrCu-based MG within supercooled liquid region.In the process of deformation,CNTs in composites will be subjected to shear and tensile forces during deformation,resulting in orientation distribution.The orientation of carbon nanotubes is directly affected by the central cone angle of the extrusion die and the extrusion ratio.When the extrusion ratio is 9 and the center cone angle of the die is 100°,the orientation of carbon nanotubes is the best.(2)The(Zr₄₇Cu₄₄Al₉)₉₈Nb₂ metallic glass powders were prepared by mechanical alloying method.The effects of ball milling conditions on the microstructure and morphology of the alloy powder were studied,and the thermal stability of MG was also studied.The results show that(Zr₄₇Cu₄₄Al₉)₉₈Nb₂metallic glass powder were successfully prepared by intermittent ball milling at 360 r/min,12:1 ball-to-material ratio and 70 h under argon protection.The supercooled liquid region is 50.1K.Using Kissinger method,the apparent glass transition activation energy(E_g),apparent crystallization activation energy(E_x)and apparent crystallization peak activation energy(E_p)of the metallic glass powder were calculated to be 345.297 k J/mol,409.068 k J/mol and 333.757 k J/mol,respectively,indicating that the present MG has excellent glass forming ability,wide supercooled liquid region and good thermal stability.(3)The(Zr₄₇Cu₄₄Al₉)₉₈Nb₂ MG/CNTs composites were prepared by freeze-drying method and hot-pressing sintering method.The effects of sintering temperature,pressure and CNTs content on the microstructure and density of the composites were investigated.The electrical properties of composites with different carbon nanotube contents were tested using Hall tester.The results show that the higher the sintering temperature in supercooled liquid region of(Zr₄₇Cu₄₄Al₉)₉₈Nb₂ MG is,the higher the densification of the bulk sample after sintering is and the amorphous structure remains.The higher the applied pressure is,the higher the density of the sintered sample is.When the content of CNTs in the composite exceeds 0.5wt%by weight,the density is significantly reduced.When the CNTs content is 0.3wt%,the carrier concentration is up to 4.38×10²¹/cm³,which is two orders of magnitude higher than the matrix.(4)According to the simulation results and the previous test results,the electroforming technology was used to conduct diameter reduction extrusion on the composite.When the pulse voltage is 4V,the current is 100A,and the loading pressure is 120MPa,the composite material with 0.3wt%CNTs is subjected to radial extrusion.The matrix still remains amorphous and CNTs present obvious orientation.