Investigation On Microstructure And Properties Of Co-based Alloy Coatings Cladded By Laser On H13 Steel

Laser cladding is a multidisciplinary technology with laser heating and melting,mass exchange in the melted pool and rapid solidification,which is mainly used in surface modification and remanufacturing.On the basis of the original experiment,the new Co-based alloy coatings were prepared by pulsed laser with different laser power.The main research contents include the influence of laser power on the microstructure,phase and dilution of Co-based alloy coatings,analysis of the amorphous forming ability of Co-based material,calculates the temperature field of the coatings with the simulation software,thermodynamics and dynamics of its microstructure formation mechanism for a summary analysis,finally,the effects of laser power on the physical properties of Co-based alloy coatings are analyzed.The microstructure characteristics of the cross section of the coating were analyzed.At the upper and middle region of the cross section of Co-based alloy coatings,amorphous phase accounted for the majority.At the bottom,the dendrite accounts for the majority.The laser power of the cladding layer of 467 W was the shortest,which was 10?m.It can be found that Co-based alloy coating was a composite of amorphous and crystalline phases through the XRD and TEM analysis.The amorphous content of amorphous coating of 467 W was the largest.The amorphous peak could be seen near 44 degree.Main crystalline phases existed were Fe Ni3 phase??-Co phase and Cr2Ni3 phase.With the increase of laser power,the dilution rate of coating is increasing.The Inoue three principles and Yan parameter method were used to analyze the microstructure formation mechanism of new alloy cladding,verifying the amorphous forming ability of Co-based powder under the laser cladding preparation process.The cladding was prepared as a pure amorphous alloy by a strip technique,and its critical cooling rate,reduced temperature and supercooling liquid zone(?T_x)were calculated,indicating that the coating had strong amorphous forming ability and high thermal stability.The temperature field of coatings with different power was simulated by Marc finite element simulation software,the cooling rate of the coating was calculated to be greater than the critical cooling rate.Based on the analysis of the thermodynamics and kinetic theory,it was found that the formation reason of the coatings mixed with the amorphous phase and crystalline phase were mainly high cooling rate,melt flow,solute diffusion,and heterogeneous nucleation of Fe element aggregation.The effects of different laser power on the hardness of Co-based alloy coatings were studied.When the laser power was 467 W,the hardness of the coating reached 1192.5HV0.2.The hardness of the upper and middle areas of the cladding were fluctuates from above to normal because the hardness of the amorphous phase was different from that of the crystalline phase.As the distance from the surface of the cladding becomes larger,the hardness of the cladding decrease.The corrosion resistance and abrasion resistance of coating with different laser power and substrate were analyzed.In the 3.5wt.%Na Cl solution and 1mol/L HCl solution,there were the following conclusions: The corrosion potential of the coating that laser power was 350 W was the highest,corrosion current of the coating that laser power was 467 W was least,there were many passivation phenomena in the HCl solution,particularly the coating of laser power being 467 W was first.In the impedance experiment,the impedance radius of the coating with laser power of 467 W was the largest,which indicates that the corrosion resistance was the strongest in these two corrosive environments.At room temperature,the friction coefficient of the coating was almost 0.15,the wear loss of coating with laser power of 467 W was the smallest,wear depth was the smallest,indicating the maximum wear resistance.The wear mechanism of the cladding was mainly abrasive wear,and a small amount of adhesive wear,and the wear mechanism of the substrate were a lot of adhesive wear and abrasive wear.