Microstructure Evolution And Properties Of Laser Cladding Cobalt-Based Alloy

Laser cladding is a cladding layer that uses high-energy density laser beams to melt the matrix material and cladding materials added to the surface of the matrix by different methods,so that the cladding materials and the matrix material form metallurgical bonding.It is widely used for surface modification of parts due to its excellent machining accuracy,wide material selection and good metallurgical bonding interface.Cobalt-based superalloys have good comprehensive mechanical properties such as high temperature strength,corrosion resistance and wear resistance,and are widely used in aerospace,marine and nuclear industries.The changes of microstructure and mechanical properties of cobalt-based cladding layer are closely related to the irradiation parameters of high-energy laser beam and the addition of other trace elements,so it is of great significance to study the microstructure and mechanical properties of laser cladding cobalt-based cladding layer.This paper first explores the macro-morphology,dilution ratio and hardness difference of cobalt-based cladding layer under different positive and negative defocusing amounts.It is found that the microstructure and properties of the cladding layer are more uniform and the dilution ratio is smaller under negative defocusing amount.Secondly,the differences of macro-optical morphology,microstructure,hardness and element distribution of cladding layer under different power and laser scanning speed are explored.It is concluded that in this experiment,with the increase of laser power,the dilution rate gradually increases,the microstructure of the cladding layer is coarse,and the hardness tends to decrease.With the increase of scanning speed,the microstructure in the middle part of the cladding layer is refined and there is no obvious difference in hardness.There are more trace S elements in the intergranular elements than in the crystal grains,and the contents of Cr and Fe elements decrease while the contents of other elements increase slightly.Then,the change of coating properties after adding La2O3 to cobalt-based alloy powder was investigated.It is concluded that when La₂O₃ content is 3%,the microstructure of the cladding layer is fine and compact.After rare earth elements are added,the content of Cr and Ni in the cladding layer increases.The variation of friction coefficient with La2O3 content is 3%<1%<5%<0%<10%<7%;In this experiment,when La₂O₃ is added to the alloy powder in an amount exceeding 3%,the properties of the cladding layer will deteriorate.This shows that the addition of rare earth elements has the best range.Finally,the influence of cooling and heat dissipation on the microstructure and properties of the cladding layer is investigated when the cladding substrate is thin.The powder/gas mixed preheating laser cladding is put forward and realized,the laser energy is recycled,and the deformation amount of the laser cladding thin plate is reduced,thus providing an attempted method for recycling the laser cladding energy.The average heat flux under different media conditions is obtained through temperature measurement,and the deformation results are compared.It is shown that the fundamental factor of laser cladding deformation of thin plates is to control the heat flux during laser cladding.There are obvious differences in deformation under different media conditions,but there is little difference in microstructure and microhardness.