The Study On Pretreatment Of Diamond Coated Cemented Carbide Substrate Based On The Coupling Of Spray Cooling And Laser Etching

Deposition of high quality diamond coating on the surface of cemented carbide tools can significantly improve the cutting performance of the tools,but the poor adhesion of the coating with the substrate has been restricting the application of diamond coated tools in the field of precision machining.The key factor weakening the adhesion properties is the graphitization effect of cobalt binding phase.The two-step method is commonly used as a pretreatment method for cemented carbide substrate.However,here come some problems such as low efficiency in the first step,uncontrollable results and large amount of chemical liquid waste.In recent years,lots of researches on the substrate pretreatment conducted with laser direct writing technology have been reported,and the common principle is to coarsen the substrate surface or directly form specific texture on it in order to increase the mechanical locking force between the coating and the substrate.Direct laser action on the target will result in slags,cracks and other defects due to the existence of the heat affected zone.Therefore,cooling method should be taken to limit the influence of the heat affected zone.In order to improve the quality of CVD diamond coating and strengthen the adhesion,in the mean time explore the new substrate pretreatment method,this thesis proposes a laser pretreatment method assisted by spray cooling.(1)Based on the growth mechanism of diamond on the surface of cemented carbide,the main problems of diamond deposition are analyzed.The pretreatment methods and principles of cemented carbide substrate in recent five years are reviewed,and the mechanism of laser pretreatment on cemented carbide substrate and its effect on the quality of diamond coating are discussed;(2)Based on the discrete phase model,the numerical simulation of spray cooling heat transfer was carried out.The effects of different atomization pressure,nozzle diameters,nozzle inclination angles and heights on spray and cooling characteristics are studied.(3)The response surface regression analysis is performed to study the influence of pretreatment parameters on the substrate and the interaction among those factors.A pretreatment quality factor Q_i is defined to evaluate the pretreatment effect quantitatively;(4)The prediction model of the outputs is built based on response surface regression,and the steepest ascent method is used to optimize the pretreatment process.The reliability of the prediction model and the applicability of the pretreatment quality factor Q_i are both verified by experiments.Figure[71]Table[27]Reference[186]...