Study On Coating Titanium On Surface Of Tungsten Carbide Particles

Coating nickel and cobalt on the surface of tungsten carbide can promote the wettability between tungsten carbide and metal effectively.However,decarburizing reactions are always taken place in laser cladding process,so the high-temperature oxidation resistance of tungsten carbide need to be improved.Coating metal on tungsten carbide's surface maybe is an effective method to improve it's high-temperature oxidation resistance and restrain the decarburizing reactions,but there are few reports about the correctness of this assumption.This paper is aimed to explore the preparation technology and laser cladding application of coating titanium on the surface of tungsten carbide particles and try to verity the correctness of the assumption that titanium coatings can protect the inner tungsten carbide effectively.Therefore,this paper's research has an important theoretical significance and practical valve in heightening tungsten carbide's proterities and expanding its application areas.Firstly,adopting hydrogen reduction technology based on traditional halide decomposition method,and choosing spherical casting tungsten carbide particles as matrix,crude titanium powder,titanium hydride and ammonia chloride as feed reactants to coat titanium layer on the surface of tungsten carbide particle through common horizontal type tubular furnace.The results show that:(1)Based on thermodynamics calculation,it is proved that coating titanium layer on the surface of tungsten carbide is available when the temperature is over 700?.The best process parameters in coating titanium layer on the tungsten carbide are:900? for 2h,m(WC):m(crude titanium powder):m(NH4Cl):m(TiH2)=1:0.4:0.84:0.4.(2)A multi-layer structure(W2C-W-TiC-Ti)is formed at the interface between tungsten carbide and titanium layer after the preparation process,and the forming mechanism is that:Ti layer reacts with WC to form TiC while WC transforms into W2C due to decarbonization process,and then W2C reacts with Ti layer to form W continually.W atoms will aggregate in TiC/W2C interface layer,because W atom has higher diffusion activation energy in TiC.(3)The coating layer can protect tungsten carbide from the oxidation process,so tungsten carbide have a better stability in an air environment when the temperature reaches 1000?.Secondly,adopting original casting WC as reference sample to study whether the coating layer has a protective effect on inner WC particles.Research indicates that:(1)The original casting WC suffered serious burning in the cladding process,and two main types of burning loss are solution-diffusion and recrystallization.(2)Under the protection of Ti,TiC and W layers,the WC particle has a better stability in laser cladding process.