Formation Mechanism And Properties Study On Tac Coating Produced On Iron In Situ

Tantalum carbide(TaC)coatings were produced in this study on gray cast iron samples by a combination of casting and heat treatment.This was mainly studied the in situ reaction process and organization evolution law of tantalum plate and gray cast iron substrate.This analyzed the thermodynamic conditions of in situ reaction based on the gibbs free energy function method.The diffusion coefficients and activation energy of the in-situ reaction process wlere calculated by classical diffusion dynamics theory.At the same time wear coefficient,wear volume,and specific wear rate of TaC dense ceramic layer were characterized by the method of friction and wear.And combined with the wear morphology,discussed the wear mechanism of TaC dense ceramic layer surface.Experimental results show that:(1)In the Ta-Fe-C system,the stability of carbide followed by the strong to weak are Ta2C,TaC and Fe3C.Ta2C,TaC and a small number of Fe3C can exist stably at the reaction temperature(1115,1 135,1155?),respectively.(2)TaC ceramic layer is compact and uniform.Holding time for 5 min,as the increase of treatment temperature,the size of TaC particle increase,the volume fraction of TaC compound layer decrease.When the temperature is 1155?,as the extension of treatment time,the thickness of TaC ceramic layer increase significantly,TaC particles also grow up and scatter.(3)Within the scope of the 1115-1155?,the diffusion coefficient of the TaC ceramic layer increases with treatment temperature increase.And the activation energy Q is 388.68kJ/mol.The variation of TaC layer thickness with time and temperature can be expressed as follows:(?) The diffusion of carbon atom is given priority to interstitial diffusion,created conditions for in-situ reaction.The diffusion of Ta atoms is given priority to vacancy diffusion.TaC grain belongs to heap structure,the diffusion rate of Ta atomic is very low in the TaC dense ceramic layer.(4)The highest hardness value of TaC dense ceramic layer near the interface of tantalum plate,where is one of the most dense area,can be up to 21.56 GPa.The hardness of TaC ceramic layer is about 5 times of the gray cast iron substrate.In the pin-plate sliding friction experiment,with the increase of load,the friction coefficient of TaC dense ceramic layer decrease,the abrasion loss increase,and specific wear rate increase,at room temperature.With the increase of test temperature,the friction coefficient of TaC dense ceramic layer presents the little change,decrease,and the increasing trend.The abrasion loss is as temperatures rise,first after falling.At room temperature,the wear mechanism of TaC dense ceramic layer is mainly abrasive wear and mild adhesive wear.Under the environment of high temperature,the wear forms of the TaC dense ceramic layer are mainly adhesion wear,accompanied by a certain oxidation wear and abrasive wear.