Comparision And Combination Of Solid Carburization And Interstitial Carburization For The Preparation Of Tungsten Carbide Coating On Tungsten Surface

Tungsten and its alloys have a wide range of applications in aerospace,military,mining and other fields.However,in some practical applications,the performance or lifetime of tungsten alloys is limited by low surface hardness and low wear resistance,and the preparation of ceramic layers on tungsten surfaces by carburization is a feasible way to solve this problem.In this paper,tungsten carbide hard coatings were prepared on tungsten surfaces by solid carburization and interstitial carburization at the same carbon potential and temperature,and the intrinsic differences and causes of the two carburization methods in preparing tungsten carb ide coatings on tungsten surfaces were clarified by comparing the microstructure and properties of the two coatings.In addition,this work combines the principles of interstitial carburization method and solid carburization method,and proposes iron coating mediated carburization method,which is applied to the preparation of WC coatings.The role of iron coating is elucidated by comparing the organization and hardness of WC coatings on tungsten surfaces prepared by the new method and conventional solid carburization,and their sensitivity to process parameters.The results indicated that:(1)The coatings prepared by solid carburization consisted of fine equiaxed WC grains,while the coatings prepared by interstitial carburization at the same carbon potential and temperature consisted of larger columnar WC grains and a very small amount of W2C dispersed at the coatingsubstrate interface.The growth rate coefficient and nanohardness of the coatings prepared by solid carburization were 0.31 μm·h-1/2 and 18 GPa;while the growth rate coefficient and nanohardness of the coatings prepared by interstitial carburization were 5.97 μm·h-1/2 and 30 GPa.(2)The main reason for the differences in microstructure,phase transition paths and growth rates of coatings prepared by solid carburization and interstitial carburization is the influence of Fe elements,which are inevitably present in coatings prepared by interstitial carburization.Interstitial carbon atoms do not require surface adsorption to enter the tungsten substrate,and therefore interstitial carburization is more efficient for carbon absorption.(3)Iron coating mediated carburization is a combination of the principle of interstitial carburization and solid carburization technology.The tungsten carbide ceramic coating prepared by iron coating mediated carburization is dense and uniform in thickness.The ceramic coating has an obvious WC grain size gradient and a hardness of 2800 HV0.05.The electroplated iron coating can play a catalytic and buffering role in the carburizing process.Compared with conventional solid carburization,iron coating mediated carburization can obtain dense ceramic coating in a larger temperature and carbon potential range,and the growth rate of the ceramic coating is higher at the same temperature and carbon potential,thus further optimizing the organization and properties of the coating;compared with interstitial carburization,it solves the problem that interstitial carbonization cannot be applied to complex surfaces,and makes the principle of interstitial carburization promising for application.