Study On Microstructure And Properties Of Gradient Ni-Base/Ceramic Composite Layer Of Laser Cladding On 45 Steel

Laser cladding has the advantages of concentration of energy density,close metallurgical bonding and wide selection of materials.The use of laser cladding technology to prepare Ni-base/ceramic coating on the surface of 45 steel can significantly improve the surface properties of the material and greatly extend the service life of the mud pump cylinder liner.The test selected Ni35 as the self-fluxing alloy powder,selected Sialon(Si3N4,Al2O3,AlN)and WC as the strengthening phase powder,optimized the alloy powder ratio and cladding process parameters,and designed the gradient cladding process.The forming characteristics,microstructure and properties of two alloy ceramic powders were compared and analyzed.The optimal ratio of Sialon ceramic powder was determined as:56%Si3N4+34%Al2O3+10%AlN.Gradient cladding process is set:gradient cladding Sialon alloy(first layer:6%Sialon + 94%Ni35,second layer:20%Sialon + 80%Ni35);gradient cladding WC alloy system(first layer:40%WC+60%Ni35 second layer:60%WC+40%Ni35).The alloy cladding layer was prepared using different cladding process parameters.The microstructure of the Sialon alloy graded cladding layer and the WC alloy cladding layer was analyzed.Sialon alloy gradient cladding layer and the parent material interface region is a wavy curve,the average dilution rate is about 1/8;WC alloy cladding layer and the parent material interface area is relatively straight,the dilution rate is low.The average dilution rate at the gradient interface of both cladding layers is large.There is a strip of bright zone at the junction of the cladding layer and the base metal,which is a flat crystal zone.It is proved that a good chemical and metallurgical bond is formed between the base and the cladding layer.In the cladding layer,when the strengthening ratio is relatively small,the columnar crystal structure is easily formed under the action of the temperature gradient.When the strengthening ratio is relatively high,the solid solution and dispersion strengthening play a major role,and the structure becomes a cell-like crystal morphology.The WC alloy-based cladding layer contains a large amount of unmelted WC particles,while the Sialon alloy system melts sufficiently.Through EDS and XRD analysis,the element distribution and content of the cladding layer were determined.The main component of the cladding layer was Ni,and the strengthening phase was network,like distributed around it.Ni-Cr-Fe,Al1.1Ni0.9 and AlxFe3Si1-x precipitated in the Sialon alloy gradient cladding.The strengthening phases such as Cr23C6,Cr7C3,and Ni3Fe precipitated in the WC alloy cladding layer.Analysis of the defects of Sialon alloy gradient cladding layer and WC alloy cladding layer.In the solidification process,the integrity of the material cannot be freely contracted,leading to the presence of penetration cracks in the cladding layer.During the cladding process,Si3N4 and WC decompose at high temperature to form pore defects.With the increase of laser power,both the porosity and the porosity of the pores become larger.The microcracks in the Sialon alloy cladding layer are mostly concentrated at the interface,which is mainly caused by the stress concentration caused by the large temperature gradients and subcooling at the interfacial joints;the microcracks in the cladding layer of the WC alloy are mostly concentrated in the reticulated reinforcing phase.The main reason is that the unmelted WC particles seriously affect the fluidity of the melt,and the volume shrinkage during melt solidification cannot be compensated in time,resulting in a large amount of stress concentration.The Ni melting point is relatively low in the relative strengthening phase,and is finally solidified in the solidification process.Due to the volume shrinkage,the pits are not compensated and the density of the cladding layer is reduced.Sialon alloy gradient cladding layer,under the same laser power,the slower the cladding speed,the higher the microhardness of the cladding layer,the better the wear resistance;the higher the laser power is at the same cladding speed.The higher the microhardness of the cladding layer,the better the wear resistance.WC alloy gradient cladding layer,with the increase of WC content,the loss weight of the cladding layer is gradually reduced,and the wear resistance is correspondingly improved.