Study On Microstructure And Properties Of Ni-base Laser Cladding Layer Treated By Ultrasonic Impact

Most of the mechanical parts,engineering components,etc.are damaged from the surface of the material in the actual application.In order to effectively improve the wear resistance and corrosion resistance of the material,laser cladding technology is used to prepare high-quality coatings on the surface without damaging the shape and inherent properties of the matrix material,which has significant economic benefits.However,the forming quality and accuracy of laser cladding usually can not meet the requirements.In order to solve the surface defects of laser cladding parts and meet the high requirements of dimensional accuracy and surface quality,it is necessary to reprocess the laser cladding layer.Therefore,the laser cladding + ultrasonic impact composite treatment technology is selected to prepare wear-resistant and corrosionresistant coatings,which provides theoretical guidance for practical engineering application.In this paper,Ni35,Ni45 and Ni55 laser cladding layers were prepared on Q235 steel plate with three kinds of Ni based powders by laser cladding equipment.The matrix phases of the three cladding layers are all γ-(Fe,Ni)solid solution.There are a lot of lamellar eutectic structure in Ni35 cladding layer,and carbides such as W2 C and M23C6 are formed in Ni45 cladding layer due to the dissolution of WC.The phase structure of Ni55 cladding layer is complex,and there are many collapsing WC particles in the cladding layer,which are interwoven with γ-(Fe,Ni)solid solution,M23C6 and Cr3C2.Among the three cladding layers,Ni45 and Ni55 cladding layers have better wear resistance,while Ni35 cladding layer has weaker wear resistance due to its lower hardness.The wear mechanism of Ni35 cladding layer is mainly abrasive wear;Ni45 cladding layer is mainly abrasive wear with a little fatigue wear;Ni55 cladding layer is mainly fatigue wear.The self corrosion current density of Ni35,Ni45 and Ni55 cladding layers are 0.6028 μA/cm2、0.8565μA/cm2、3.541 μA/cm2,respectively.The corrosion resistance of Ni35 is the best,followed by Ni45 and Ni55.The continuous eutectic structure on the surface of Ni35 cladding layer was broken by ultrasonic impact treatment,and the strong plastic deformation was induced.The broken eutectic particles were dispersed in the cladding layer.A 130 μm deep plastic deformation layer and about 2 μm thick Nanolayer were formed on the surface of Ni35 cladding layer.The results show that the segregation of elements on the surface of cladding layer is also improved.The microstructure of Ni45 cladding layer is compact,and only about 5 μm deep plastic deformation layer is produced on the surface under the action of ultrasonic impact;the effect of ultrasonic impact is weakened by massive carbides in Ni55 cladding layer,while the "weak zone" around carbides appears obvious "collapse".The "peak clipping and valley filling" effect of ultrasonic impact surface strengthening technology can greatly reduce the surface roughness of three kinds of cladding layers.Compared with the sample without ultrasonic impact treatment,the surface roughness of Ni35 cladding layer decreased by 90.0%,Ni45 cladding layer decreased by 79.7%,Ni55 cladding layer decreased by 18.8%.Moreover,the surface hardness of the three kinds of cladding layers are improved to a certain extent,by 26.2%,9.7% and 2.3% respectively,and the depth of the hardened layer is about 600 μm,200 μm and 100 μm respectively.After ultrasonic impact treatment,the friction and wear coefficient of the cladding layer decreases and the weight loss decreases significantly.The abrasive wear in Ni45 cladding layer disappears.It is certain that ultrasonic impact can significantly improve the friction and wear properties of Ni based cladding layer.After ultrasonic impact treatment,the polarization curves of three kinds of Ni based cladding layers all move to the left and upward,the positive displacement of potential ΔE is 159.53 m V,131.43 m V and 127.37 m V respectively,and the self corrosion current density decreases by 82.80%,60.99% and 83.54% respectively,which indicates that ultrasonic impact treatment can improve the corrosion resistance of the materials.