Microstructure And Mechanical Properties Of Micro-nano Structure TaC Compact Ceramic Layer Performed By In-situ

Micro-nano structure TaC compact ceramic material was prepared by the combined technology of "casting and heat treatment" in this research.Its reaction temperature,microstructure and phase composition were studied by the testing technologies of DSC,XRD,SEM and EDS.And the mechanism of in-situ reaction was discussed through thermodynamic and kinetic.The critical load,hardness,elastic modulus and fracture toughness of micro-nano structure TaC compact ceramic material were measured by the methods of nano-indentation and micro-indentation.The dense ceramic surface crack propagation mechanism was discussed through combining the indentation morphology.The binding ability of dense ceramic layer and gray cast iron was discussed by the automatic scratch apparatus,then the critical load LC was determined.Through the observation of the scratch morphology,the elastic-plastic deformation mechanism and failure mechanism was analyzed.Experimental results show that:(1)Through analyzing the feasibility of in-situ reaction,micro-nano structure TaC compact ceramic material can be prepared by the raw materials of tantalum plate and gray cast iron with the condition of casting composite under 1430 ? and heat treatment under 1165 ?.The dense ceramic layer and matric combined well,and there was no interface effect.The reaction interface was clean and it embodied the advantages of in-situ reaction.(2)TaC ceramic layer was compact,uniform and not formed particles dispersed.Its crystal particle size was micro-nano level and about between 100-200 nm.As the extension of heat preservation time,the thickness of TaC ceramic layer increased.TaC ceramic layer diffused and became less compact,its particles would be tend to scattered and formed the wave structure.The diffusion mechanism of in-situ reaction was mainly the interstitial diffusion of C atom and the vacancy diffusion of Fe,Ta atom.(3)The critical load was between 400-450 mN and the fracture toughness was 2.227 MPa·m1/2 of micro-nano structure TaC compact ceramic layer measured by nano-indentation.And the critical load was between 500-1000 mN and the fracture toughness was 2.942 MPa·m1/2 of micro-nano structure TaC compact ceramic layer measured by micro-indentation.The toughness of micro-nano structure TaC compact ceramic material was analyzed though the fracture toughness and the crack propagation resistance curve.By observing the indentation crack morphology,the cracks had a tortuous path,and showed the characteristic of the typical intergranular fracture.And there were three phenomenon:crack deflection,grain bridge behavior and the tend to grain uproot.(4)The binding ability of micro-nano structure TaC compact ceramic layer was evaluated comprehensively by the friction scratch method,the acoustic emission method and the scratch microstructure.The critical load was determined to 48.7 N.The main failure form of ceramic layer and gray cast iron was the rupture and spalling of the ceramic layer.