Preparation And Properties Of In-situ Synthesized Micro/Nanoscale Carbide Reinforced Copper Matrix Composites

The copper matrix composite material combine the excellent electrical and thermal conductivity of copper and the high mechanical wear of the reinforcement phase.Especially when the micro/nanoscale granular reinforcement phase distributes in the copper matrix homogeneously,the composite material will have higher hardness and wear resistance.Based on this,considering the high hardness and high wear resistance of NbC,WC and Mo₂C,combined with the advantages of forming a good bonding interface of the reinforcement phase with the matrix and controllable distribution of uniform size.In this thesis,we fabricated the in-situ mirco/nanoscale Me-C（Me=Nb,W,Mo）carbide reinforced copper matrix composites via long-term（60h,84h,96h,120h）ball milling and hot-pressing.XRD,SEM,TEM,hardness testing,electrical conductivity testing Materials microstructure and properties were characterized using XRD,SEM,TEM,hardness,electrical conductivity and wear resistance measurement techniques,and the materials structure-property relationship with the ball milling time was investigated.The main research contents are as follows:1.Cu-Nb-C micron powders were long-term milled and hot-pressed in order to obtain copper matrix reinforced by in-situ mirco/nanoscale niobium carbide.The result show composites show an outstanding mechanical performance,in which the hardness can reach180Hv with 120h ball milling time.The 120h ball milling hot-pressed sintered sample possesses a smaller friction coefficient and displays a wear rate(2.6×10^-5mm³N^-1m^-1)two orders of magnitude lower than the 60h ball milling hot-pressed sintered sample(123.5×10^-5mm³N^-1m^-1).Such property enhancement is attributed to the hardness improvement and the solid lubricating effects induced by nanoscale niobium carbides/oxides as well as iron oxides.2.Cu-W-C micron powders were long-term milled and hot-pressed in order to obtain copper matrix reinforced by in-situ mirco/nanoscale tungsten carbide.The result show longer-term ball milling found the refinement and homogenization of nano-Cu and nano-W in milled powders,which enlarged W and C contact probability and promoted WC formation accordingly.At 120 h milling,the sintered material was composed of WC micro areas and Cu-rich composite areas where the nanosized and ultrafine WC coexisted.This better microstructure increased hardness by 42%only with a small reduction in electrical properties compared to the case of 60h milling.The 96h ball milling hot-pressed sample with network shape microstructure of tungsten carbide possesses a smallest wear rate,and the 60h ball milling hot-pressed sample with stick shape microstructure of tungsten carbide possesses a smallest corrosion current density.3.Cu-Mo-C micron powders were long-term milled and hot-pressed in order to obtain copper matrix reinforced by in-situ mirco/nanoscale molybdenum carbide.During milling,Moreacted with C forming a little MoC.As the milling time increased from 60 to 120 h,flaky powder particles were replaced by finer granular particles composed of Cu and Monanocrystals.For 84h-and 120h-milled powders,Mocombined with C besides MoC+Moforming P63/mmc hexagonal-structured Mo₂C without residual Moduring sintering,instead of primitive hexagonal Mo₂C in the case of un-milled powders.Both types of Mo₂C occurred in the sintered sample of 60h-milled powders.In-situ formed Mo₂C especially with nanoscale sizes in the 120h ball milling hot-pressed sintered sample with good electrical property was responsible for the hardness improvement by 63.6%than the un-milled case.