Research On Application Foundation Of Multi-Layer Laser Cladding On Steels

In the article, The Nano-structure Feedstock （NF） WC/Co-Ni base and Fe basecomposite tungsten carbide coatings were fabricated by wide-band CO2laser claddingtechnique on45steel. Based on the single layer laser cladding, the （NF） WC/Co-Ni basecomposite tungsten carbide coatings were fabricated by wide-band CO2multi-layer lasercladding technique on45steel. The weight fractions of the adding （NF） WC/Co rang is0%～10%～20%～30%of each layer in the multi-layer cladding is changing in gradient.SEM, EDAX ray energy dispersive spectrometer, X’ Pert PRO X-ray diffractionfunction, optical microscopy and atomic force microscopy were used to observe andanalysis the microstructure, composition distribution, phase composition, surface structureand wear surface morphology of the clad layer. Use the HX-1000microhardness tester totest the microhardness of the clad layer. Prepare the Vickers indentation in clad layer byusing HV-50Vickers hardness tester, and then determine the fracture toughness of cladlayer by EVANS method. Test the wear coefficient and wear resistance of the lasercladding by using HT-600high temperature friction and wear tester.The results of the single layer laser cladding experiments indicate that: The （NF）WC/Co-Ni base and Fe base composite tungsten carbide coatings, which has the featuresof a fine grain, homogeneous structure, no pores and cracks, and a good metallurgicalbonding with the substrate. Under the microscope, the mainly phase of the Ni-basedcladding layer the white phase Cr₂Fe₁₄C, Cr-Ni-Fe-C and WC are mainly distribute on thematrix which are black （Fe, Ni）, B₂Fe3Ni₃and Fe₃Ni₂. The mainly phase of the Fe-basedcladding layer the white carbide phase Cr-Ni-Fe-C, W2Cand Fe3W3C are mainly distributeon the matrix which are black （Fe, Ni） and B2Fe3Ni3. Under the same load, the averagefracture toughness of （NF） WC/Co-Ni composite coatings prepared by the traditional spraymethod is9MN m^-3/2. While under the Vickers hardness tester in the current maximumload, the （NF）WC/Co composite coatings prepared by laser cladding there is no cracks, the results show that the of the latter than the former has significantly improved, whichdemonstrates that nanometer phases can serve the anti-cracking function. Under thecondition of the same process parameters, Ni-based clad layer hardness is the hardness ofthe substrate2.5times. Fe-based clad layer hardness is the hardness of the substrate1.9times. The microhardness of the Ni-based clad layer is higher than the Fe-based clad layerby138.7HV.The results of the multi-layer laser cladding experiments indicate that: The single cladlayer, two clad layers, three clad layers and four clad layers were fabricated by wide-bandCO2laser cladding technique on45steel. They are smooth surface and free of pores andcracks, and a good metallurgical bonding with the substrate. The phases of the four kindmulti-layers are mainly the eutectic mixture of Fe and Ni, Cr-Ni-Fe-C, Cr₂Fe₁₄C and othercomplex carbide phase distribute on them. With the weight fractions of （NF） WC/Coincreased gradually, there are W2C, Ni17W3, WC and the presence of element W in the cladlayer. There is no significantly difference of the different structure of the clad multi-layersunder the low magnification scanning electron microscope; the density level of clad layersis increased with the weight fractions of the （NF） WC/Co gradual increased under the highmagnification scanning electron microscope. The morphology and distribution of thecarbide reinforcement of the clad multi-layers are mainly divided into cellular distributionand fine granular dendrite carbide phase. The microhardness of the clad multi-layer fromthe substrate to the layer surface is gradient increased, and the hardness of clad layers isincreased with the weight fractions of granulated （NF） WC/Co increased. The clad layershardness is the hardness of the substrate2.0～2.5times. The friction coefficient of the cladmulti-layer has been enhanced than that of the substrate, but the wear quality is decreased.When the weight fractions of （NF） WC/Co reach to30%, the average friction coefficient is0.511, Wear scar width is the smallest, the wear resistance is the best, the wear quality isonly0.05%of the substrate. Under the same load, the average fracture toughness of （NF）WC/Co-Ni composite coatings prepared by the traditional spray method is9MN m^-3/2.While under the Vickers hardness tester in the current maximum load, the （NF）WC/Cocomposite coatings prepared by multi-layer laser cladding there is no cracks, the resultsshow that the of the latter than the former has significantly improved, which demonstratesthat nanometer phases also can serve the anti-cracking function in the clad multi-layer.