Research On The Graphite Forming Mechanism And Correlation Between Morphology Parameters And Processing In Laser Cladding Of Grey Cast Iron

Laser cladding technology has unique advantages in surface modification and repair of components and parts.In recent years,it has received extensive attention in the field of surface treatment of materials.The current research on laser cladding with gray cast iron mainly focuses on the physical properties of the cladding layer,microstructure and morphology,cladding materials and equipment,etc.But there are few studies of the behavior mechanism of graphite phase and the process influence on graphite morphology.Therefore,take deep study of the graphite phase has a significant impact on the development of cast iron cladding technology.The research work in this dissertation aims at graphite morphology in the melting zone.In order to clarify the behavior mechanism of graphite phase,the thermal mechanism of laser cladding and the thermal response characteristics of graphite phase were studied profoundly based on the experiment and finite element method.Finally,extract the controllable parameters of graphite morphology and study the process influence on graphite morphology parameters.The main research contents are as follows.Based on the analysis of thermal mechanism of laser cladding,a double track lap cladding model of gray cast iron is established.The temperature field in different cladding regions and the characteristic of weld pool are analyzed,so as to provide a theoretical basis for the analysis of the driving condition of graphite behavior mechanism.In order to explore thermal stress response characteristics of different graphite under different temperature load and compare the thermal values in different cladding zone,a graphite phase model is established based on the cladding model,so as to forecast the defect inductivity of graphite phase.In order to explore the appropriate cladding power,a double track lap cladding experiment of gray cast iron with Fe314 alloy powder is established,and the formability of the cladding layer under different power is analyzed.In order to find the target range of graphite phase analysis,the microstructure of the cladding samples was observed under microscope and the existence of graphite phase in cladding layer,bonding region and heat affected zone was analyzed.Based on the thermal interaction analysis,the thermodynamic conditions and dynamic conditions that the transformation of graphite phase needed were analyzed.And in order to explore the diffusion behavior of the carbon in the graphite phase,the distribution of the elements in cladding layer was researched by means of electron probe.On the basis of the above research,the micro-components and structure transformation characteristics were studied,thus the transformation laws of the graphite phase during the laser cladding was nailed down.The main controllable parameters of the graphite morphology are extracted based on the analysis of thermal response characteristics of laser cladding and graphite phase behavior mechanism,then the presentation methods of graphite morphology were constructed.Laser cladding experiments were carried out with the design variables of laser parameters and element composition.The relationship between process parameters and graphite morphology parameters in laser cladding process is analyzed.Try to investigate the influence of laser parameters,powder composition and other parameters on the graphite morphology parameters by experiment.