Study On The Wear&Corrosion Resistance Of Ni-based And Stainless Steel Coatings Prepared By Laser Cladding

In order to improve the wear and corrosion resistance of the surface of the hydrauliccylinder and drill sleeve,45steel and00Cr18Ni9stainless steel were used as the simulatematerials and on which the Ni/WC and316L/WC coatings were prepared using a fiberlaser equipment with round spot and a semi-conductor laser equipment with rectangularspot respectively. The effects of the parameters and content of WC on the microstructureand properties of the coatings were investigated, the strengthening theories were exploredand the optimized parameter was given in this paper.By using the suitable parameters, the low void rate, non-cracks Ni/WC and316L/WCcoatings which have a good metallurgical bonding with the substrates can be obtained onthe surface of45steel and00Cr18Ni9stainless steel respectively. The coating can bedivided into3zones in the section which are the cladding zone, the dilution zone and theheat-affected zone. The cladding layer mainly consist of the γ phase and someprecipitated phases. Compared to the substrates, the microhardness of the coatings have agreat improvement and the effect of the parameters on the microhardness is that themicrohardness was promoted as the power reduced and (or) the scanning speed increasedwithin limits. The addition of WC particles is good for the improvement of themicrohardness. The reason that the coatings have high microhardness is the fine grainobtained during the quick melting and quick solidification process and the solutionstrengthening and precipitation strengthening exist in the coating.Because of the high microhardness and the fine grain, the wear resistance of thecoatings is much better than the substrates. The addition of the WC particles has a greatdeal in improving the wear resistance of the coatings. Compared with the substrates whichhave a typical characteristic of adhesive wear, the wear mechanism of the coatingspresents an abrasive-major wear. The corrosion resistance of the coatings is much betterthan the substrate’s, and the addition of the WC particles will decrease the corrosionresistance of the coatings.Ni-based coating with very low dilution rate (about7.5%) can be obtained on thesurface of45steel using a semi-conductor laser with rectangular spot and the coating mainly containsγ(Ni),, interdendritic eutectic of CrB, Cr2B with γ(Ni) and Chromiumborides. After treatment in550℃，the coating has a smaller grain size than the unannealedone and exhibits a relatively homogeneous matrix which is like the zebra-stripe. Beforeannealing, there are2directions residual stresses along2directions in the surface of thecoating, the longitudinal stress which has an average of670MPa and the transverse stresswhich has an average of570MPa. The annealing process can diminish both of the stressesin two different directions and eliminate the gap between them. The tearing tendency hasbeen prevented obviously. The annealing process also has a good affect on theimprovement of the microhardness and the wear resistance of the coating.The optimized parameters in the experiment are power2.5kW, scanning speed360mm/min in preparing Ni/WC coatings on the surface of45steel using the fiber laserwith round spot, power2.4kW，scanning speed8mm/s in preparing316L/WC coatings onthe surface of00Cr18Ni9stainless steel using the fiber laser with round spot and power3.3kW, scanning speed10mm/s in preparing the Ni-based coatings using thesemi-conductor laser with rectangular spot.