Research On The Influential Factors And Process Optimization Of Microcrack In Bonding Zone In Laser Cladding With Cast Iron

Cast iron is widely used in large equipment as its high performance.With processed by laser cladding,the usage performance of cast iron can be improved effectively.However,as for bad working condition,it is easy to generate microcracks and propagate macroscopic cracks in bonding zone.Graphite phase,a significant part of cast iron,is not investigated efficiently during laser cladding.Graphite morphology and accumulating way have great influence on bonding strength and microcracks initiation.The research work in this dissertation aims at analyzing stress characteristic of graphite phase and obtaining the optimal process parameter during laser cladding on cast iron.With exploring the influential factor of graphite stress and initiation mechanism of microcracks,the optimal process parameter would be determined in the end.The main research contents are as follows.Based on laser cladding experiment on cast iron with Fe-based alloy powder,the compatibility feature between substrate and cladding layer is investigated.The organizational characteristics of bonding zone,graphite morphology and microcrack phenomenon on graphite tips are analyzed.The average bonding strength is calculated by shear test device.It is helpful to clear and definite the influential mechanism between microstructure around graphite,microcracks and cladding quality.With improved laser heat source and birth-death element technology,laser cladding thermal-mechanical coupling model is established to clarify laser cladding thermal response rules.Based on orthogonal experiment,the maximum residual stress influential factor of bonding zone is clear.It can be used to guide the parameter determination and provides data support on graphite micro model.As for microcrack initiation mechanism on graphite tips,graphite-ambient phase micro model is established on the basis of laser cladding experiment and thermal-mechanical coupling model.It reveals that graphite morphology parameter and accumulating way have great influence on the stress of tips.It also provides an effective way to analyze the graphite phase stress quantitatively.According to laser cladding thermal-mechanical coupling model and graphite-ambient model,the microcrack initiation mechanism is determined with orthogonal experiment.The optimal laser process parameter is obtained from the perspective of residual stress and stress on graphite tips.It contributes to reduce stress and crack initiation,and improves cladding quality further.