Research On Slurry Erosion Resistance And Mechanism Of Ni-based Alloy Sprayed And Fused Coatings

Slurry erosion widely exists in marine engineering,pipelines and water conservancy machinery,and has become one of the important reasons for material damage and equipment failure.It not only brings huge economic losses,but also seriously threatens production safety.The use of surface technology,especially surface coating technology,can effectively improve the slurry erosion resistance of the erosion parts and prolong their service life.Ni-based alloys are widely used due to their good processability,stable structure,and excellent wear resistance,oxidation resistance,and corrosion resistance.Ni-based self-fluxing alloys are the most widely used type of Ni-based alloys,including Ni Cr BSi series,Ni Cr BSi CuMo series,and WC-reinforced Ni Cr BSi and WC-reinforced Ni Cr BSi CuMo.In this thesis,Ni60A,Ni55MoA,Ni60 CuMo,Ni WC35,Ni55 MoA-WC,and Ni60 CuMo-WC Ni-based alloy sprayed and fused coatings were prepared by using oxy-acetylene flame spraying and fusing technology.The XRD and SEM methods were used to analyze the microstructure of the sprayed and fused coatings.Hardness and electrochemical properties of sprayed and fused coatings were tested;the slurry erosion resistance properties and mechanism of 6 spray-sprayed layers in fresh water and 3.5wt.% Na Cl media were studied.The research results show that the addition of a certain amount of Mo can significantly improve the toughness and refine the structure of the sprayed and fused coatings,so that it has good resistance to electrochemical corrosion.Although the addition of WC significantly improves the hardness of the sprayed and fused coatings,however,its ability to resist electrochemical corrosion is reduced.The addition of different elements will have different effects on the slurry erosion resistance of the sprayed and fused coatings.Adding a certain amount of Cu,Mo,and WC on the basis of Ni Cr BSi can improve the slurry erosion resistance of the sprayed and fused coatings in fresh and 3.5wt.% Na Cl medium,and the addition of WC improves the slurry erosion resistance of the sprayed and fused coatings more significantly.The addition of nano-WC improves the slurry erosion resistance of the sprayed and fused coatings better than ordinary micron WC.The research also shows that in fresh water media,the material loss of the sprayed and fused coatings are mainly caused by mechanical action,but in 3.5 wt.%NaCl media,the material loss of the sprayed and fused coatings are includes mechanical shock,electrochemical corrosion,and mechanical shock and the he interaction of electrochemical corrosion.There are obvious differences in the slurry erosion resistance between the six Ni-based alloy sprayed and fused coatings.The sprayed and fused coating Ni60 CuMo-WC has the best slurry erosion resistance in fresh water and 3.5wt.% Na Cl media.The slurry erosion resistance in fresh water and3.5wt.% Na Cl media was improved by approximately 83%,74%,and 78%,64%,respectively,compared to the sprayed and fused coatings Ni60 A and Ni60 CuMo.In fresh water,the slurry erosion of Ni60 A sprayed and fused coating is mainly micro-cutting.The slurry erosion mechanism of Ni60 CuMo sprayed and fused coating is the combination of multiple deformation and micro-cutting.The slurry erosion mechanism of Ni60 CuMo-WC spray coating is mostly multiple deformation,micro-cutting and "shadow protection" of WC.In 3.5 wt.% Na Cl media,the three sprayed and fused coatings of Ni60 A,Ni60CuMo and Ni60 CuMo-WC all caused anodic dissolution due to the formation of galvanic cells between different phases,thereby accelerating the removal of coating materials.The addition increases the number of grain boundaries in the sprayed and fused coating,and the potential difference between the WC and ? phase solid solutions is large.This makes the interaction of sprayed and fused coating Ni60 CuMo-WC more effective than the sprayed and fused coatings Ni60 A and Ni60 CuMo during the slurry erosion test.