Study On The Laser Cladding Process Of Nickel Based Alloy And The Properties Of The Cladding Layer

As an economical and suitable surface modification technology,laser cladding has played an important role in the modern material processing and manufacturing industry.It is a kind of economical and practical repair technology,because the laser cladding with feeding wire technology has a cheaper cost than the powder laser cladding,and better properties than TIG cladding.In this paper,the feasibility and rationality of the application of laser cladding technology instead of TIG cladding in nuclear power industry is analyzed from the process of cladding and the structure and properties of the cladding layer.In this paper,matrix materials is 304 stainless steel which is also use at the end of the nuclear power equipment,the cladding material is FM-52M nickel base alloy which is used to sealing and cladding nuclear power equipment.Through the exploration of the laser surfacing process,and the study on the microstructure and properties of the cladding layer,and find the laser cladding process which suitable for pressure vessel safety end seal cladding.The main conclusions of this paper are as follows:（1）The influence of laser power,scanning speed,wire feeding speed and defocus amount on the morphology of the cladding is determined by the control variable method and the orthogonal test method.The test results show that the laser power,the scanning speed and the wire feeding speed have a great influence on the forming of the weld bead,and change of defocus in a small range has little effect on the forming of the cladding weld,and the optimum laser cladding process is P=4000W,Vs=20mm/s,Vw=2.5m/min and L=+17mm.The lap test confirms that the flatness of the welding surface is the best when the lap rate is about 37.5%,and it`s undulating degree is below 100um.The single layer welding height of the cladding layer is about 1mm.（2）The macroscopic quality,microstructure,composition,hardness,plasticity,high temperature mechanical properties and DDC crack sensitivity of FM-52M Ni-based alloy cladding layer were analyzed.It is concluded that the cladding layer is well combined with the base material,and there is no significant defect.The hardness of the surfacing layer is increasing gradually from the surface to the matrix.The bonding of each layer of the surfacing layer is close,and no peeling and crack appear.The grain size of the cladding layer is refined,the grain boundary is distorted and the composition is evenly distributed,and the main phases in the microstructure areγ-Ni,MC and M₂₃C₆.（3）Comparing the high temperature tensile tests of TIG surfacing,it is found that the tensile strength,yield strength and elongation of the mechanical properties of the laser cladding layer in the state of normal and high temperature are better than the TIG cladding layer.The fracture mode of the laser cladding layer at the high temperature stage is gradually changed from the quasi cleavage fracture to the intergranular fracture.The grain boundary of the laser cladding layer tends to be straight with the increase of temperature,and the M₂₃C₆carbide dissolves and the plasticity of the material is restored.Comparing the DDC crack sensitivity curves of the laser cladding layer and the TIG cladding layer,it is found that laser cladding layer has better anti DDC crack resistance.The DDC cracks in the laser cladding layer usually occur on the triangle crystal boundary and the grain boundary with larger positive stress.The distortion of the grain boundary of the laser cladding layer can effectively prevent the DDC cracks caused by the slip.The grain size in the microstructure of the laser cladding layer is small and has better deformation coordination ability,which can effectively impede the expansion of DDC cracks.There is less precipitation of M₂₃C₆ carbide at the grain boundary of the laser surfacing layer,which makes the laser cladding layer have better DDC crack resistance.