Study On The Preparation Of CNTs/Cu-Ti Composites By Spray Pyrolysis And Their Interface Problems

Carbon nanotubes?CNTs?are known for their high tensile strength?11-63 GPa?and elastic modulus?270-950 GPa?,excellent thermal and electrical properties.It is considered to have broad application prospects to as an idedal reinforcement phase in high performance metal matrix composites.The performance of the CNTs is not fully utilized due to the strong van der Weals forces of CNTs and poor wettability between the CNTs and metal matrix.Therefore,how to effectively disperse CNTs uniformly in a metal matrix and achieve a good interface with the matrix is the two main challenges.In this study,CNTs/Cu-Ti alloy composites with good mechanical properties were prepared by powder metallurgy combined with spray pyrolysis?SP?.Firstly,the CNTs dispersion was mixed with CuAc aqueous solution,and the nano-sized CNTs/Cu₂O composite powder with uniform dispersion was prepared by ultrasonic spray pyrolysis.Then,the gas atomized Cu-Ti alloy powder and the nano-sized CNTs/Cu₂O were mixed by low-energy ball milling,and then the CNTs/Cu-Ti alloy composite powder was obtained by reduction.Finally,CNTs/Cu-Ti composites were prepared by hot pressing?HP?and plasma activated sintering?SPS?.The results show that the mass fraction of CNTs in the mixed solution is 30%,the spray rate is 150 ml/h,and the spray pyrolysis temperature is 773 K.The nano-sized Cu₂O particles are fine?less than 50 nm?and uniformly coated on the surface of CNTs.CNTs have good dispersibility,and CNTs and Cu₂O particles achieve a close interface bond by chemical bonding.After the CNTs/Cu₂O composite powder and the Cu-Ti alloy powder were mixed by ball milling at 150 rpm for 4 h,the composite powder was reduced in a tube furnace at 573 K,H₂ atmosphere for 4 h.The CNTs are uniformly dispersed in the Cu-Ti alloy matrix,and the reduced nano-sized Cu particles and the CNTs maintain a tight bonding state,which improves the interface bonding between the CNTs and the Cu-Ti matrix.CNTs/Cu-Ti alloy composites with excellent mechanical properties were prepared by HP and SPS.X-ray diffraction?XRD?,Raman spectroscopy?RM?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and tensile testing were used to research the relationship between the interfacial structure evolution and mechanical properties of CNTs/Cu-Ti alloy composites.The results show that the CNTs/Cu-Ti composites with mass fractions of 0.0%,0.2%,0.4%,0.6%and 0.8%were obtained after HP for 30 min at 1123 K.The best mechanical properties were obtained with 0.4wt.%CNTs/Cu-Ti composites and a simultaneous improvement in strength and ductility is achieved compared to the Cu-Ti alloy matrix.CNTs/Cu-Ti alloy composites with a mass fraction of 0.3%were sintered by SPS and held at 1073K,50 Mpa for 10 min,20 min,30min respectively.Three typical transition interfaces appeared?10 min:Ti₈C₅,20 min:Ti₈C₅+TiC,30 min:TiC?.When the holding time is 10 min,a weak interfacial reaction occurs on the surface of CNTs,which produces two transition interfaces of Ti₈C₅ nanoparticles and Ti₈C₅ nano-transition layer,which realizes strong interfacial bonding between CNTs and Cu-Ti matrix and completely preserves the structure of CNTs.In addition,when the holding time is 20 min,the transition of the Ti₈C₅ interface transition phase to the TiC interface transition phase occurs,in which the?219?plane of Ti₈C₅ and the?111?plane of TiC have a parallel orientation relationship[?219?_Ti8C5//?111?_TiC].The CNTs/Cu-Ti alloy composites with a mass fraction of 0.3%obtained by SPS sintering at 1073 K for 10 min were measured by mechanical tensile test to have a yield strength of 368 MPa and a tensile strength of 512 MPa.Compared with the Cu-Ti alloy matrix without the CNTs reinforcement phase,the yield strength is increased by 59%and the tensile strength is increased by 51%.The yield strength and tensile strength are increased by 27%and25%,respectively in contrast with 0.3wt.%CNTs/Cu composites.The good dispersion of CNTs and the strong interfacial bonding with the matrix significantly improve the mechanical properties of the CNTs/Cu-Ti composites.This provides a new bright spot for achieving good interface integration through interface evolution and control interface reaction,and improving load transfer efficiency from metal matrix to reinforcement phase.