Morphology Prediction And Numerical Simulation Of Laser Cladding Nickel-based Alloy Coating On Cr12MoV Steel

Laser cladding technology has the advantages of fast forming speed,excellent microstructure and wide range of materials,which is of great significance to the surface strengthening and remanufacturing of die steel subjected to impact wear for a long time.Nickel-based alloy due to its high strength,high toughness and corrosion resistance of advantage and widely used in laser cladding materials,but in the process of laser cladding is difficult to precisely control the morphology of cladding layer size,and because the laser quenching heat characteristic of easy to produce a great deal of heat stress,and defects such as cracks in the cladding layer,Therefore,it is necessary to study the distribution of temperature field and stress field during laser cladding.In this paper,cold working die steel Cr12 MoV and nickel-based coating were used as research objects to explore the effects of laser current,laser scanning speed and laser pulse width on the height and width of the cladding layer,and establish a multi-parameter coupled regression equation for predicting the morphology and size of the cladding layer.The influence of laser current and laser scanning speed on the temperature field and residual stress of single-channel laser cladding was studied by finite element numerical simulation,and the influence of lap ratio on the temperature field and residual stress of multi-channel laser cladding was analyzed.The research results are as follows:In this paper,25 groups of laser cladding nickel-based alloy coatings were obtained by orthogonal experiment,and the multi-parameter coupling linear regression equation about the cross section width and height of cladding layer was established.The width error of cladding layer of Cr12 MoV die steel laser cladding nickel-based alloy was predicted to be accurate to 0.86%,with an average error of 6%.The height error can be accurate to0.56% and the average error is 10%.As the laser current and pulse width increase,the cladding layer width increases and the cladding layer height decreases.The width of cladding layer is greatly affected by scanning speed,and decreases with the increase of scanning speed,but the height of cladding layer is little affected by scanning speed.The prediction errors of the width and height of the cladding layer and the linear regression equation are 4.82% and 3.6% respectively by using different laser process parameters from the orthogonal test,which proves the accuracy and universality of the mathematical model.Secondly,a single-channel laser cladding model was established by finite element software ANSYS,and the distribution characteristics of comet temperature field with slightly lag temperature and the maximum temperature history of the node under different laser processes were obtained.It was concluded that the maximum temperature of the node increased with the increase of laser current,and decreased with the increase of laser scanning speed.Combined with the solidification theory of metal,the temperature gradient,cooling rate and solidification rate at the top,middle and bottom of the cladding layer were calculated,and the microstructure size of the cladding layer was predicted,which verified the accuracy of temperature field simulation.The residual stress of cladding layer was calculated by ANSYS transient structure analysis module under different paths and different process parameters.The residual stress reached the maximum along the laser scanning direction at the interface between matrix and cladding layer.The residual stress of cladding decreases with the increase of scanning speed and increases with the increase of laser current while other laser parameters remain unchanged.Therefore,the optimal process of laser cladding nickel base alloy coating on Cr12 MoV steel is determined as follows: scanning speed 200 mm/min,laser current 160 A,laser pulse width 6 ms,laser frequency 8 Hz,and the minimum residual stress of cladding layer is 375 MPa under this laser process.At the same time,the models of the three overlapped laser cladding with the overlapped rate of 30%,40% and 50% were established,and the temperature history of the joints in the same position of the multiple channels was analyzed,and the influence law of different overlapped rate on the temperature of each channel was obtained.The microstructure of multi-channel lap zone and non-lap zone is analyzed,and the ratio of cooling speed and G/S in lap zone is smaller than that in non-lap zone by calculation of solidification theory,so smaller microstructure can be obtained.By calculating the residual stress of laser cladding layer with different lap ratio,the minimum residual stress of cladding layer is 155 MPa when the lap ratio is 40%.