The Preparation And Mechnism Of Ultrafine W-base Powder By Two Step Reduction Method

The strength and hardness of WC-Co alloys would increase with decreasing the grain size of WC.The mechanical properties will increase manifold as the grain size of WC is decreased to ultrafine scale.At present,the fabrication of nano cemented carbides have become a hot pot.The key technologies involved in the study of high quality ultrafine/nano cemented carbide powder and inhibiting the grain growth in the sintering process.This subject aims at some common problems about ultrafine/nano powder is easily agglomerated during preparation.Using the waste hard alloy YG8 and APT as raw materials,the ultrafine/nano W-base powder was prepared by two step reduction method.The effects of the ultrafine/nano powder on the particle size and phases,milling time,reaction time and temperature,carbon content,doping elements and content,were analyzed systematically.This project has developed a preparation technique for ultra/nanosized powder with the features of highproduction efficiency,short process,low production cost,fine stability,high controllable degree.Take the as the waste hard alloy YG8 as raw materials the starting material,the optimum process of preparing nanometer violet tungsten powder was obtained.Firstly,the carbonization reaction process of WO2.72/Co WO4 and C was theoretically analyzed and predicted.The suitable of temperature range was determined based on theoretical calculations and DSC experiment results.By optimizing the powder milling and carbonization reaction parameters,the most appropriate processing for preparing nano WC-Co composite powder was obtained.The WO2.72/Co WO4 powder performed reduction carbonization with anhydrous alcohol as carbon source.The pure WC-Co powder was obtained at a temperature of 1073 K for 3h.The nano-sized powder has good dispersibility,uniform particle size,and the average particle size is about 120 nm.Compared with WO3/Co WO4 direct reduction carbonization,the preparation of p u r e c o m p o s i t e p o w d e r i s s h o r t e r t i m e a n d th e p o w d e r q u a l i t y i s b e t t e r.At the same time,carbonation model was also given by TEM.The effects of the ultrafine powder on the particle size and phases of hydrogen reduction,different oxides tungsten,reduction temperature and doping elements and content,were analyzed comprehensively by a serials of experiments.The most optimun process of preparing ultrafine tungsten powder was obtained.The results show that the special morphology of purple tungsten was beneficial to reduce thechemical deposition of hydrogen reduction,and to obtain high quality ultrafine tungsten powder.The violet tungsten of doping vanadium was very sensitive to the temperature.The grain could be significantly inhibited by the addition of yttrium.The additions of vanadium and yttrium changed the energy state of some crystal planes of tungsten grains,and promoted the preferential growth of grains.The tungsten powder presented the morphological characteristics of polyhedral.Using ethanol as the carbon source,the violet tungsten of doping the vanadium and yttrium element,respectively,was carbonized and reduced.The pure WC powder was obtained at the temperature of1073 K for 1.5h.The average particle size was about 200 nm without the absence-carbon phase.Therefore,the carbonization temperature and the holding time can be effectively reduced using the ethanol as the carbon source by two step reduction method.