Study On Laser Welding Process And Mechanism Of TiC-Ni Cermet And SPHC

As a kind of composite material with excellent properties,TiC-Ni cermets have a good application prospect in industry.However,its inherent brittleness,poor impact resistance,high rigidity and other shortcomings seriously limit its development in the industrial field.In order to expand the application range of TiC-Ni cermets,it is necessary to make the connection with steel.In this paper,TiC-Ni cermets and SPHC are selected as welding samples,and fiber laser welding is used to study the laser welding process and mechanism of "TiC-Ni cermets on SPHC" lap form.The effects of laser power(P),welding speed(v)and defocusing distance(f)on weld formation,microstructure,interface structure and mechanical property of SPHC/TiC-Ni cermet laser lap welding were studied.According to the experimental results,When the laser power is 900 W,the welding speed is 0.04m/s,and the defocusing distance is +2mm,a good weld with beautiful surface shape,good interface structure,no cracks,no fusion and other welding defects can be obtained.Martensite structure is formed inside the weld,and Fe and Ni elements are diffused to form(Fe,Ni)at the weld/TiC-Ni cermet interface.The TiC in reticular form appeared a little at the interface.Increasing the laser power,decreasing the welding speed and decreasing the defocusing distance all lead to the increase of the TiC-Ni Cermet side melting depth,melting width and the number of TiC in reticular form,while the diffusion phenomenon of interface elements is different due to the influence of TiC particle morphology.At the same time,TiC in reticular form and TiC small particles are formed by dissolutions-reprecipitation.The difference is that the TiC in reticular form precipitates at the austenite grain boundary,while TiC small particles become the grain nucleation core and dispersion in the weld.The mutual diffusion of dispersed TiC with Fe and Ni has the effect of diffusion strengthening and solid solution strengthening respectively on the weld,and a small amount of TiC in reticular form can also enhance the weld to a certain extent.When the laser power is900 W,the welding speed is 0.04m/s,and the defocusing distance is +2mm,the TiC-Ni cermet/SPHC joint reaches the maximum tensile shear strength of169.5N/mm.Under these condition,the fracture occurs in the HAZ of TiC-Ni cermet side,showed a ductile fracture mode.The effects of magnetic field assisted TiC-Ni cermet/SPHC laser lap welding on the microstructure,interface structure and mechanical property of the joint were studied.When the laser power is 900 W,the welding speed is 0.04m/s,and the defocus distance is +2mm,the side melting depth and width of TiC-Ni cermet with magnetic field are increased compared with those without magnetic field.The dispersion degree of TiC particless on the weld side is increased,and the element diffusion on the weld/TiC-Ni cermet interface is enhanced.Compared with B=0m T,when B=30m T,the weld grain is refined,grain orientation is diversified,elastic modulus decreases,and hardness increases.With the increase of magnetic field strength,the range of TiC-Ni cermet side molten pool is further expanded,the diffusion of Ni element is significantly improved,The TiC in reticular form is also produced in a large number of weld,weld hardness continues to increase,but under the influence of magnetic field,weld hardness becomes uniform.In addition,when B=30m T,the tensile shear strength of the joint reaches the maximum of 199.7N/mm,which is about 15.1% higher than that without magnetic field under the same welding parameters.The jiont fracture occurred in TiC-Ni cermet,showed a ductile fracture mode.