Study On The Mechanical Properties Improvement And Toughness Mechanism Of Barium Titanate Ceramic Coatings With Carbon Nanotubes And Graphene Nanoplatelets

In numerous piezoelectric ceramic materials,barium titanate?BaTiO₃?is a kind of lead-free ceramics with excellent dielectric and piezoelectric properties.But in consideration of obvious ceramics brittleness,lack of synergy deformation with metal substrate easily causes the failure of coatings.It limits its application in many occasions.Toughness of the ceramic is at the core of the ceramic subject in recent years.In this paper,by using the method of surface modification and ultrasonic dispersion,carbon nanotubes?CNTs?and graphene nanoplatelets?GNPs?were evenly dispersed into BaTiO₃ powders respectively.BaTiO₃/CNTs composite ceramic coatings and BaTiO₃/GNPs composite ceramic coatings were prepared using plasma spraying technology on 45^#steel substrate.By means of many testings and analysis methods,the coating composition,structure,mechanical performance were shown and analyzed.Micro-indentation method was introduced to characterize elastic modulus and fracture toughness of the coatings.Finally,comparative analysis of influence of different toughening materials and different contents on coating toughness and toughening mechanism were explored to realize the actual research and application of the piezoelectric ceramic coatings in structural health monitoring.The final results indicated that:?1?BaTiO₃/CNTs composite powders and BaTiO₃/GNPs composite powders were prepared successfully using the combination method of ultrasonic dispersion and surface modification.By discussing three different dispersion mechanism of cationic CTAB and anionic SDS and nonionic Triton X-100,it was found that SDS distributed in composite powders made CNTs stable adsorption on surface of BaTiO₃ because of the chemical bonding between-SO₄^2-on the CNTs surface and-OH attached on BaTiO₃ surface.?2?BaTiO₃/CNTs composite coatings with four different CNTs additions were used to prepare by plasma spraying technique.With the increase of CNTs amount,cracks throughout the coatings and micro-cracks reduced gradually,but the pores obviously increased.The toughening effect of CNTs was increased with the content increasing.It revealed the toughening mechanism includes CNTs bridging,CNTs pulled-out and crack deflection.When CNTs content was 3.0 wt.%,the elastic modulus of composite coatings continued to increase gently,while fracture toughness tends to be stable.It illustrated that CNTs was added too more to exert their toughening effect obviously.?3?BaTiO₃/GNPs composite coatings with four different GNPs additions were used to prepare by plasma spraying technique.Almost no existence of big cracks throughout the composite coatings was observed.However,there was no obvious improvement on porosity,and GNPs amount was more,micro-cracks were more.When GNPs content increased to 0.1 wt.%,elastic modulus and fracture toughness of the composite coatings increased obviously,and GNPs bridging and crack deflection were mainly observed as GNPs toughening mechanism.From the above conclusion,the appropriate amount of CNTs and GNPs can play a good role to the toughening effect of BaTiO₃ piezoelectric ceramic coatings prepared by plasma spraying.Aimed at solving brittle failure problemsfor piezoelectric coating in the monitoring of gear in the process of service,it has very broad prospects for development,but further studies are needed.