Research On The Nitride Films On The Gun Barrel Material By Magnetron Sputtering Technology

Since the working conditions are high-temperature and high-pressure powder gas,severe friction and wear between rotating band and bore,and salt air corrosion in the marine climate during gun launching process,the important indicators to measure the gun bore performance are anti-high-temperature oxidation,wear and salt air corrosion resistance.The traditional eletrodeposited chromium coating has not been meeting the working condition demand of the gun bore due to the higher energy gun propellant applied to the gun system with the requirement of the shooting long range.In order to improve the performance of the gun barrel,alternative film technologies and materials need to be developed.The CrAlN film was firstly deposited on the gun barrel material PCrNi₃ Mo steel surface by means of magnetron sputtering technology,and the rare metal V was added to the film to further improve the film overall property based on comprehensive analysis of the technologies of prolonging the gun barrel life at home and abroad to start from film preparation to improve the gun bore performance.The film deposition process was comprehensively optimized by testing and analyzing the hardness and elasticity modulus,friction and wear,anti-hightemperature oxidation and corrosion resistance of the film,which can provide the theoretical reference for the prolonging life technology of gun barrel.The achieved research results are as follows:?1?The process parameters influence on the magnetron sputtered films: The film structure was loose and appeared obvious spot flaws without substrate negative bias during sputtering.When the substrate negative bias was 50-100 V,the sputtering particle energy increased and the film surface was even and compact.When the substrate negative bias was 150 V,the particle bombing energy increased and caused the film surface damage.When the substrate negative bias was 200 V and 300 V,the surface damage became severer and caused the film surface quality reduce,and thereinto,the film with 100 V negative bias has the best surface quality.When the sputtering electric current changed in the range of 0.1-0.2A,the sputtering rate increased with the increase of the sputtering electric current,and at the same time,the film was even and compact,and its mechanical property increased due to the sputtering particle energy increase.When the sputtering electric current changed in the range of 0.2-0.4A,the exorbitant particle energy bombing made the surface damage,and meanwhile,the exorbitant sputtering electric current made the Cr particle energy and quantity increase and the unnitrided Cr as simple substance was in the film,which caused the mechanical property of the film reduce,and thereinto,the film with 0.2 A sputtering electric current has the best surface quality and mechanical property.The hardness and elasticity modulus of the film increased with the N₂ flow increase due to the partly unnitrided Cr atoms when N₂/Ar<3/4.The Cr atom was completely nitrided,and the hardness and elasticity modulus of the film attained maximum value when N₂ flow increased to N₂/Ar=1.The hardness and elasticity modulus of the film began to reduce a little when continuing to increase the ratio of N₂/Ar.To sum up,the CrN film has the best quality,and its hardness and elasticity modulus are 21.38 GPa and 272.71 GPa,respectively,when the negative bias is 100 V,the sputtering electric current 0.2 A and N₂/Ar 1.?2?The preparation and mechanical property of the CrAlN and CrAlVN: The CrAlN films with the different Al compositions were prepared by controlling Al target power?50-200W?and their surface are cauliflower-like and the cross-section fracture displays typical columnar crystal structure.The addition of Al makes the grains finer and has solution strengthening effect in certain scope.The Cr0.34Al0.66 N has the highest hardness and elasticity modulus?23.91 GPa and 316.2GPa?and its friction coefficient is 0.293.The CrAlVN films with the different V compositions were prepared by controlling V target electric current?0.03-0.09A?.The addition of the rare metal V makes the grains finer,which makes the surface more smooth and compact,and the distance between the columnar crystals reduce,and moreover,the V solution in the CrAlN causes lattice distortion and gives rise to solution strengthening.The Cr0.31Al0.62V0.07 N film has the highest hardness and elasticity modulus?24.98 GPa and 336.02GPa?and its friction coefficient is 0.186.?3?Anti-oxidation performance of gun steel substrate,CrAlN and CrAlVN films: The two oxides,Fe₃O₄ and Fe₂O₃,formed on the gun steel surface at 500? after 10 h in air and The three oxides,FeO,Fe₃O₄ and Fe₂O₃,formed on the gun steel surface at 600? and 700? after 10 h in air.The oxide films appeared delaminating and spalling at 700?.The main oxide film Al₂O₃ formed on the CrAlN film surface at 750? and 850? after 20 h in air.The film was mainly composed of fcc-CrN except a little wurtzite AlN at 750? whilst it consisted of CrN,Cr₂ N and Cr at 850? after 20 h in air.the oxidation film,mainly including Fe₃O₄ and Fe₂O₃,formed at the film surface at 950? after 20 h in air.The main oxidation film Al₂O₃ formed and the transformation of AlVO4?V3O7?VO2 took place with the temperature increasing on the CrAlVN film surface at 750?,850? and 950? after 20 h in air,and at the same time,the film phase maintained fcc-CrN structure.The V addition restrains the columnar crystal growth and makes the fine grain size about 7 nm,which increases the antihigh-temperature performance of the film,prolongs the Fe diffusion from the substrate to the film and stabilizes the film phase structure.The hardness and elasticity modulus of the CrAlN film decreases rapidly whilst those of the CrAlVN film only decreases a little.The hardness and elasticity modulus of the CrAlVN film was 20.82 GPa and 314.6GPa respectively at 950? after 20 h in air,16.7% and 6.4% reduction in contrast to the as-deposited film.?4?Corrosion resistance of gun steel substrate,CrAlN and CrAlVN films: the active dissolution took place on the PCrNi₃ Mo steel and the corroded production on the surface had no protection effect in 3.5% NaCl solution.Both the CrAlN and the CrAlVN films have passive films,and therefore increase the corrosion resistance performance,and moreover,they restrain the cathodic reactions of the PCrNi₃ Mo steel.The CrAlVN film exhibits better protective effect due to the uniform and compact microstructure.