Study On Super High Temperature Atomizing Process And Mechanism For Spherical Tungsten Carbide Powder

Thermal Spraying is one of the key technologies in surface engineering industry and is a hot area of research and development which attracts attention around the world.Currently tungsten carbide for thermal spray was fabricated by casting method, leading to angular powder morphology, lower flowability and lower hardness. Those powders can not meet the requirement of advanced thermal spray materials. It is a key study for thermal spray industry to develop spherical tungsten carbide powder with good flowability and excellent wear resistance.To realize high flowability and high wear resistance of tungsten carbide hard facing material and its industrialization , the idea of fabrication spherical tungsten carbide by gas atomization at super high temperature in inert gas was put forwarded , high temperature melting and atomizing equipment were designed and fabricated, the influence of starting materials, atomizing gas and its pressure, over heat degree of melt and cylinder flow dimension of melt on fabricating process of tungsten carbide were discussed in detail. Fabricating theory and super high temperature atomizing mechanism for spherical tungsten carbide were also discussed in detail. Mathematical model was also built up. The research result was well industrialized. Following conclusions were reached.1) A breakthrough on atomizing temperature limit, typically 1700℃, was realized. Theory for super high temperature melting and gas atomizing was studied systematically. An equipment for super high temperature melting and gas atomizing was designed and fabricated, so continuous atomizing of melt over 3000℃was made possible both for industrial and experimental uses.2) Spherical tungsten carbide was fabricated at 2700℃by super high temperature inert gas atomization process. Optimized atomizing conditions, such as high purity argon atomizing, atomizing at 2875℃and 1.2 MPa, 10mm for the diameter and 200mm for the length of melt cylinder, particle size of starting materials ranging from 15 to 20 micro meters and particle size for precuse ranging from 75 to 175 micro meters were determined by systematically research on the influence of atomizing parameters on fabricating processes.3) Spherical tungsten carbide with fine micro structure, hardness equal to 3200HV, flowability equal to 6.5s/50g, and excellent wear resistance were made by super high temperature melting and inert gas atomizing starting both from carbon black, tungsten powder and tungsten carbide and from angular tungsten powder. In field application it was found that service life of components using spherical powder was increased by several times than those using angular powders. 4) It was found super high temperature gas atomizing process was an unstable one. The unstable phenomenon for melt column was calculated and analyzed by linear unstable theory and linear unstable model for super high temperature atomizing was built up to explain related rules.5) Super high temperature melt spheroidizing model was built up based on characteristics of melt flow and melt spheroidization. Relationship between mass flow rate and melt parameters and relationship between spheroidization index S and over heat degree T were deduced.6) Industrialization of the research was realized with excellent field application and a breakthrough was made on fabrication of spherical tungsten carbide and gas atomization at high temperature ranging from 2000℃to 3000℃,in which few progress were made in past 50 Years.