Controllable Preparation And Sintering Behavior Of Iron-Coated Composite Powder

Powder metallurgy is a low-cost process for preparing titanium carbide and titanium parts.During the preparation of titanium carbide and titanium materials by powder metallurgy process,some problems including high sintering temperature and hard to densification are not ignorable.Introduction of suitable sintering aids can effectively reduce the sintering temperature of the material and promote its densification process.Iron is an ideal sintering aid for low cost powder metallurgy.It has been widely used in sintering and densification of titanium carbide and titanium.The conventional way for adding iron sintering aid is powder mixing method.However,due to the density difference between iron and the base material,some problems such as uneven dispersion are easy to occur during the mixing process.It will seriously affect the uniformity of the microstructure of the sintered product,which restricts the application of materials.In order to solve this problem,titanium carbide and titanium powders are used as substrates in this paper.The Fe-coated TiC composite powder with core-shell structure and the Fe-coated Ti composite powder were prepared by the process of fluidized bed chemical vapor deposition.It improves the microscopic uniformity of the composite material effectively and improves the sintering performance of the material.The following results were obtained:Proper gas-phase precursor is the key and foundation for preparing iron-coated composite powder by fluidized bed chemical vapor deposition.The thermodynamic process of gasification and decomposition of FeCl3 was systematically studied.The vapor pressure of FeCl3 changed significantly with temperature,and the gasification temperature should be controlled within 327?.In the FeCl3-H2 system,in order to control the formation of impurity FeCl2 and improve the reaction conversion rate,The mole ratio of H2 should be increased to above FeCl3:H2=1:50,and the decomposition temperature should be controlled above 560?.As an excellent iron precursor,FeCl3 could be used to prepare TiC-Fe composite powder.But in the process of Ti-Fe coating,FeC13 would corrode the Ti powder.Using ferrocene as the iron precursor avoided the corrosion of the Ti powder effectively during the deposition process.FeC13 was used as Fe precursor.The deposition process dynamics rule of Fe and defluidization mechanism were deeply studied.Due to the sintering and agglomeration of micron-scale self-nucleating Fe particles and the directional growth of Fe particles on TiC surface,the defluidization phenomenon during the fluidization process occured easily after the formation of giant TiC-Fe agglomerates.The optimized gasification temperature of the deposition process was 275?,and the reaction temperature was 600?.The coating layer was uniform and dense and a good interfacial bonding condition was observed.After hot-pressed sintering,the density of the TiC-14Fe material was about 2.36%higher than the material prepared by mixing powder.The coated Ti-Fe composite powder with controllable Fe content was prepared by using ferrocene as the precursor.The preferred gasification temperature during deposition was 160? and the reaction temperature was 500?.During the sintering process,the coated Ti-Fe composite powder could form equiaxed crystals of ?-Ti with better isotropy.It could withstand and transfer external loads evenly in all directions.The C deposited during the coating process would react with Ti and TiC was generated.It could greatly improve the compressive strength and yield strength of the composites.But the plasticity of titanium matrix composites reduced.