Research On WC/SS316L Composite Coating Prepared By Supersonic Laser Deposition

The deposition of ceramic-metal composite coating onto metal substrate is an advanced material surface strengthening processing.The composite coating is usually characterized with comprehensive properties which combine strength and toughness of metal with high temperature resistance,wear resistance,corrosion resistance and other excellent performance of ceramic phase.The traditional laser cladding,thermal spraying and self-propagating high temperature synthesis technique for the preparation of ceramic-metal composite coatings involve high heat input and the powder is thus prone to oxidation,decomposition,phase change and damage,especially for phase transformation sensitive ceramic phase(such as WC,diamond),so it is difficult to keep the integrity of its morphology and composition in the preparing process.Besides,the existence of residual thermal stress in composite deposition is also easy to induce crack in the coating.Supersonic laser deposition(SLD),which combines cold spraying(CS)with laser heating,is applied to improve the deposition efficiency,coating density and bonding strength of low pressure cold spraying,and then strengthen the coating's property.Supersonic laser deposition technology not only keeps the solid deposition characteristics of cold spraying,but also expands the materials scope of cold spraying.Based on the advantage of supersonic laser deposition technology,this paper employed SLD technology to deposit composite materials of SS316 L and WC which were widely used to fabricate ceramic-metal composite coating with comprehensive performance.Based on the process parameters for depositing SS316 L by SLD,the WC/SS316 L composite coating was prepared with the optimized parameters.The deposition characteristics,microstructure,ceramic particle content,WC/SS316 L particle interaction mechanism and wear performance of the as-deposited composite coatings with different laser irradiation were studied temperature in this paper and compared with laser cladding counterpart.Moreover,this paper also discussed the deposition behavior and failure mechanism of WC/SS316 L composite coating prepared by supersonic laser deposition,and the main conclusions of this paper were listed as follows:1.During the preparation of single SS316 L coating,laser irradiation had a great effect on the deposition efficiency,coating/matrix interfacial bonding,micro hardness and corrosion resistant properties of the coating.Within a certain range of laser irradiation temperature,the peak height,deposition efficiency and micro hardness increased with the laser irradiation temperature.And scanning velocity had significant influence on macro-morphology of the as-deposited coatings2.The content of WC particles in the WC/SS316 L composite coating increased with the laser irradiation temperature.With the laser irradiation temperature of 800 oC,the content of WC particles in SLD coating got to 29.29 % which was very close to the original content(30%)of the powder.3.The friction coefficient of supersonic laser deposition coating was 28 % lower than that of the laser cladding specimen,thus exhibiting better wear-resistant properties.This is due to that supersonic laser deposition coating had higher content of WC,and the WC particles were uniformly distributed.Besides,the reinforcement particles and matrix phase were well bonded.4.The SLD WC/SS316 L coating was densification and retained the internal organization of original particle.The XRD analysis showed that the phase of SLD coating was the same with powder which preserved the solid deposition advantage in cold spraying technology.5.In the process of SLD,matrix produced pitting due to severe impact of particles;at the same time the particles got effective deposition to form the first layer.Subsequent impacting particles continuously impinged onto the matrix to make the further deformation degree of the particles which had deposited and the porosity thus reduced.Because of the laser irradiation effect,the bonding mechanism between WC and SS316 L turned from mechanical interlocking to metallurgical bonding.In the process of electrochemical corrosion,etchant solution expanded into the coating because the bonding between WC and SS316 L was not complete dandified.The potential was different in the bonding part and formed primary cell which aggravates the coating deterioration.