Study On Technology And Tribological Properties Of Laser Cladding Ni Matrix Composite Coating On 45 Steel

This thesis studies the piston pump used for petroleum production,An excellent wear resistance is necessary for the surface of the piston pump,due to the inevitable abrasion caused by the reciprocating friction movement,In this project,wear-resistant composite coatings prepared by laser cladding technology using NiCrAl/WC,NiCrAl/20%WC/Mo S₂and NiCrAl/20%WC/CNTs composite powders as The results show that:1.Using the lower scanning speed,a high dilution rate and a coarse tissue was obtained;When applied the higher scanning speed,the cladding powder were melted incompletely.The wear resistance of the cladding layer was poor when the scanning speed was too high or too low.When the laser power was low,the melting of cladding powder was incomplete and the composition distribution was not uniform.When the laser power was too high,the microstructure was coarse,the dilution rate was high,and the macroscopic cracks and other defects appeared.The wear resistance of the coating was poor.when the laser power was too high or too low.The comprehensive experiment results showed that the best process parameters are obtained when the laser power was1.2k W and the scanning speed was 600mm/min.2.NiCrAl/WC coatings with different contents of WC were prepared on the surface of 45 steel substrate basing on the optimization of process parameters.With the increase of WC content,the hardness and wear volume gradually increased.Compared with 45 steel matrix,the wear resistance of cladding layer decreased when the WC content was 30%and 40%.When the WC content was 20%,the wear resistance of the cladding layer increased by 16%.When the WC content was 20%,the wear resistance of cladding layer was the best,so 20%was the best WC content.3.On the basis of the above experiments,the effects of different contents of Mo S₂and CNTs on the microstructure and properties of cladding layer were studied:（1）NiCrAl/20%WC/Mo S₂coatings with different Mo S₂contents were prepared on the surface of 45 steel.It is found that Mo element has the effect of refining grain,and the microstructure became fine and compact with the increase of Mo S₂addition.The hardness increased gradually,the friction coefficient decreased first and then increased,and the wear volume decreased first and then increased.When the Mo S₂content was5%,the friction coefficient and wear volume were the minimum.Compared with 45steel matrix,the friction coefficient and wear volume were reduced by 55%and 79%,respectively.（2）NiCrAl/20%WC/CNTs coatings with different content of carbon nanotubes were prepared on the surface of 45 steel.It was found that carbon nanotubes had the effect of grain refinement.With the increase of the amount of carbon nanotubes,the microstructure changed from coarse to fine and then to coarse.With the increase of the amount of carbon nanotubes,the hardness first increased and then decreased,the friction coefficient first decreased and then increased,and the wear volume first decreased and then increased.The friction coefficient and wear volume of the coating reached the minimum when the carbon nanotubes content was 3%.Compared with 45steel,the friction coefficient and wear volume of the coating decreased by 53%and91.1%.There are 56 figures,7 tables and 93 references.