Mechanism Of WC Nano-powders Prepared By Hydrogen-free Carbonation Under The Catalysis Of Platinum And Application In Preparing Ultrafine Grained Binderless Tungsten Carbide

Binderless tungsten carbide has higher wear resistance,higher hardness,higher corrosion resistance,higher oxidation resistance and polishing performance than WC-Co cemented carbide,which has a wide application prospect in the fields of precision optical mold and special wear resistant materials.To prepare WC nano-powders with excellent performance is the key factor to manufacture binderless tungsten carbide with excellent performance.In this paper,WC nano-powders was prepared by hydrogen-free carbonation under the catalysis of platinum.Ultrafine-grained binderless tungsten carbide was prepared by hot-press sintering using the prepared WC nano-powders as raw materials.This paper study on the production process,performance and mechanism of WC nano-powders and binderless tungsten carbide.Its major contents are as follows:1.The phase transformation during the process of hydrogen-free carbonation under the catalysis of platinum was studied.The influence of the amount of platinum on the phase and morphology of WC nano-powders,and the effect of carbonization temperatures on the phase and morphology of WC nano-powders was investigated.The results show that the process of AMT to WC in the process of hydrogen-free carbonation is:AMT?WO3?WO2.72 WO2?W?W2C?WC.A small amount of platinum is helpful to reduce the carbonization temperature and improves the morphology and performance of WC powders.But excessive platinum will consume carbon in the precursor and cause the product to lack carbon.And as the carbonization temperature increases,the particle size of WC powders increase and the dispersibility become worse.The optimal process of the hydrogen-free carbonation under the catalysis of platinum is the platinum catalyst addition 0.01 wt%,the carbonization temperature of 1050?,the carbonization time of 100 min.Under the optimal process,the fine and dispersive WC powders with the average particle size of 89.5 nm is obtained.2.Ultrafine-grained binderless tungsten carbide was prepared by hot-press sintering using the WC nano-powders prepared by hydrogen-free carbonation as raw material.The effects of sintering process parameters on the microstructure and mechanical properties of binderless tungsten carbide were studied.The results show that with the increase of sintering temperature and holding time,the average grain size and the relative density of samples increased.The mechanical properties of samples are closely related to the density and grain size.If the sintering temperature is excessively high,grain size of the sample would grow up abnormally,lead to the W2C appears in the sample,and decrease the mechanical properties of the sample.The optimal hot-press sintering process parameter of binderless tungsten carbide is the sintering temperature of 1700?,the pressure of 40 MPa,the holding time of 60 min.Under the optimal process,the mean grain size of the binderless tungsten carbide was 263.6 nm,the hardness is 2887 kg·mm-2 and the fracture toughness is 7.1 MPa·mm1/2.