Study Of Nickel Based Carbide Coatings On Cutter Ring Material For TBM Hob By Laser Cladding

As the main cutting parts in tunneling,the hob of TBM need to extrusion and friction with the rock during the work,so it need to have a high hardness and wear resistance.This paper aimed at solve the problem of that the hob cutter ring is easy to wear and consume in using.We use laser cladding to prepare the nickel based composite coatings on 40 CrNiMo,which is used on hob cutter.In order to provide the foundation for cutter ring repairing.Through the orthogonal test we studied the effect to the layer in different process. We use optical microscopy,OLYMPUS microscopy, SEM and wear testing machine to research the microstructure,phase composition,microhardness and wear resistance.The results show that:After adding different kinds of tungsten carbide in nickel base alloy,the hardness of the cladding layer increased significantly.The strengthening methods of the cladding layer with nickel coated tungsten carbide and sintered tungsten carbide are mainly based on solid solution strengthening.There’s no tungsten carbide undissolved or emission,and in cladding layer with sintered tungsten,the W elements segregation at grain boundaries.The microstructure from the bottom to the top are planar crystals,columnar dendrites and fine dendrites.In the cladding layer with cast tungsten carbide,The microstructure of cladding layer is more refined and the microhardness is increased gradually with the content increased.When the content is 10%,the tungsten carbide are all melting,the microstructure are similar to the cladding layers which contain nickel coated tungsten carbide;When the content increased to 20%,there have tungsten carbide surplus,and many coarse dendrites are formed around the tungsten carbide particles;When the content increased to 30%,the surplus tungsten carbide increased and distribution more uniform,there are many small particles tungsten carbide and W riched phase appeared near the tungsten carbide,the dendritic structures reduct;When the content increased to 40%,the needle like structure appears and the increase tend of microhardness becomes less obvious. Through the analysis of the organization, we use the composite powder to do the orthogonal experiment which have 30% cast tungsten carbide in it.The optimum process :Laser power was 1 000 W, scanning speed was 4 mm/s, powder feeding rate was 7.28 g/min.By comparing experiments,we choose the lap ratio is 40% to do the multi-channel and multi-layer experiments.The microstructure of the overlap areas are coarse than it in single channel and the microhardness decreased slightly,the growth pattern of organizations in the overlap area along the front layer and channer or growth reverse the heat loss direction.In terms of wear resistance, it increased by 7.7 times than cutter ring,the wear mode mainly is abrasive wear.