Effect Of Niobium On The Microstructure And Property Of Nickel-based Alloy Coating By Laser Cladding

In this paper, Ni60 alloy powder and Nb+Ni60 alloy powder were deposited on 45# steel using a continuous wave IPG fiber laser. Stereomicroscope and optical microscope were used to analysis macro profile and the dilution rate in different laser process, such as the laser power, scanning speed, carrier gas flow rate, overlap rate and quantity of the powder. Scanning electron microscopy(SEM), energy spectrum analysis(EDS) and electron back scattering spectroscopy analysis(EBSD) were used to perform the tissue morphology and phase composition of precipitated phase with different powder. Vickers microhardness of the clad layer was measured by a microhardness tester, and abrasive resistance of the clad layer was measured by a wear testing machine.The result shows that:In single clad layer, the clad width increases with the increase of laser power and amount of powder, decreases with the increase of scanning speed and carrier gas flow rate. The clad height increases with the increase of laser power and amount of power, decreases with the increase of scanning speed and carrier gas flow rate. The depth of fusion increases with the increase of laser power and carrier gas flow rate, decreases with the increase of scanning speed and the amount of powder. The dilution rate of the clad layer increases with the increase of laser power, scanning speed and carrier gas flow rate, decreases with the increase of the amount of power.The Ni60 laser deposited coatings is mainly composed of the γ-Ni solid solution, block polycrystalline orthorhombic CrB, dendritic single crystalline hexagonal Cr7C3, and eutectic composition. With the increases of cladding layer dilution rate, the Fe element of the cladding layer suppresses the formation of the Cr7C3 and CrB. When the dilution rate was 38%, Ni60 cladding layer is mainly composed of γ-Ni solid solution and eutectic organization.Nb + Ni60 laser deposited coatingis mainly composed of the γ-Ni solid solution, dispersed NbC particles, CrB type chromium borides and eutectic. It is found that the microstructural of Nb modified Ni60 laser deposited coatingis fined. In situ NbC particleis found in the microstructural. With the increase of Nb content, the NbC particle size becomes bigger. The precipitation of the NbC particles suppresses the formation of the Cr7C3. When the mass fraction of Nb is less than 8%, the NbC as the nucleation center of the CrB, and the structure of the CrB turned into radial microstructure. When the mass fraction of Nb is 10%, The CrB and NbC nucleation independently, the CrB turned into acicular.The hardness of the cladding layer is higher than the substrate, when the dilution rate of the Ni60 cladding layer is 4%,the fluctuations of the hardness is very big, because the uneven distribution of organization. Lead to the the highest hardness value is about 1 100 HV0.5. With the increase of the dilution rate, the cladding layer hardness value reduced. The hardness of the Nb modified cladding layer is complicated. At first the hardness decrease with the increase of the Nb, then the hardness increase with the increase of the Nb. When added about 6wt%Nb, the hardness is lowest. It is about 530HV0.5.The toughness of the Nb modified cladding layer become better, lead to the improve of the abrasion performance. When added about 6wt%Nb, the cladding layer achieved the best wear resistance. The wear situation of cladding layer are mainly adhesive wear and abrasive wear.