Study On Ni-based Ceramic Gradient Coatings On The Drilling Pump Liner By Laser Cladding

As the core of the drilling system,the drilling pump is related to the whole drilling process.The cylinder liner is the most easily damaged part of the drilling pump.Hard particles which are located in the gaps between the piston and cylinder liner will scratch the lining of the cylinder liner.The worn mechanism is the grinding abrasion.Metal alloy materials possess good toughness and Ceramic materials have abrasive resistance and high temperature stability.The laser cladding can form the high-quality coatings which contain these advantages.But there are lots of differences between the Ni-based alloy and the WC particles,which leads to the stress concentration in the laser cladding layers.This stress concentration results in cracks.Gradient coatings ease the stress concentration resulting from the difference between the Ni-based alloy and WC particles.In this paper,the Ni-based WC coatings are prepared by means of laser cladding.Optimizing processing parameters during laser cladding and adopting CaF2/Ni35 transition layer to solve the crack problem.Using experimental facilities observes the microstructures of cladding layers and tests the mechanical properties,in order to get the high-quality coatings.The results show that with the WC increasing,the crack ratio rises,then declines.When the WC content is 30%,the crack ratio reaches its maximum.To ensure formabilities and abrasive resistance,we choose the SD-Ni45 as the based cladding material.The best processing parameters are: laser power 3500 W,scanning speed 100mm/min.By analyzing the microstructures and phases,the superhard coating contains WC?carbonization and ?-Ni.Because of the high content WC,the microhardness of the superhard coating reaches2000HV0.1.Add 5% CaF2 in superhard coating can improve the formabilities of the coating.With low density,CaF2 moves to the surface of the coating and stirs the molten pool to disperse the WC.Although the microhardness is only 1500HV0.1,the coating gets higher abrasive resistance.The Ni35 transition layer is introduced to ease the stress concentration.And the Ni35 transition layer controls the sharp drop phenomenon in microhardness.Finally,we get high-quality laser cladding layer.