Research On Friction And Wear Mechanism Of Self-lubricating Coating Deposited On Gun Steel

Artillery is an important military weapon in the army at present.With the improvement of its power and continuous firing ability,the friction and wear in gun barrel become more and more serious.Nickel is a kind of metal with high temperature resistance,corrosion resistance and high hardness.As a coating used in barrel bore,the effect of ablation on barrel can be effectively reduced.However,the friction coefficient of nickel is higher and the adhesion is serious in dry friction environment.In order to improve the friction and wear properties of nickel when grease lubrication is not available for gun barrel,Ni-MoS₂and Ni-MoS₂-C composites were prepared by plasma sintering with nickel as matrix,adding MoS₂and graphite solid lubricant.Ni-MoS₂self-lubricating composite coating and Ni-MoS₂-C self-lubricating composite coating were deposited on the surface of gun steel（CrNi3MoVA steel）using composite material as electrode by spark deposition technology.The microstructure and phase composition of the coating were analyzed by SEM,EDS and XRD.The mechanical properties and friction and wear properties of the coating were tested by nano indentation and friction and wear tester.The results show that the surface of Ni-MoS₂composite coating is smooth,and the surface of Ni-MoS₂-C composite coating is cauliflower like,forming a good metallurgical bonding with the substrate.The Ni-MoS₂composite coating is mainly composed of MoS₂,γ-Ni,Mo O₂and Ni_xS.The Ni-MoS₂-C composite coating is mainly composed of MoS₂,γ-Ni,Mo O₂.Ni_xS,Mo C and graphite.The hardness and elastic modulus of Ni-MoS₂composite coating are 5.15 GPa and 141.5 GPa,the friction coefficient is 0.17～0.20,and the wear rate is 1.79×10^-4mm³N^-1m^-1,respectively.Due to the composite effect of graphite and MoS₂in Ni-MoS₂-C coating,the friction and wear properties of Ni-MoS₂-C coating are further improved compared with that of Ni-MoS₂composite coating.The hardness and elastic modulus of Ni-MoS₂-C coating are 6.23GPa and 139.7 GPa,respectively.The stable friction coefficient of Ni-MoS₂-C coating is 0.14～0.16,and the wear rate is 2.89×10^-5mm³N^-1m^-1.It has the best mechanical properties and friction and wear properties.The friction and wear properties of CrNi3MoVA steel,Ni-MoS₂and Ni-MoS₂-C self-lubricating composite coatings were tested under different loads and different matching pairs.The results show that the friction and wear properties of Ni-MoS₂coating are good in some cases,and it is easy to fail under heavy load and high hardness.The Ni-MoS₂-C coating has the best friction and wear properties under all conditions except for very low load.