Research Of Titanium Carbide Enhanced Coating Prepared By Diode Laser Cladding And Sol-Gel Compound Technique

Precision,quality and service life of tool and mold are very important for industrial production.Metal mold is characterized by large amount and consumption,high technical requirements.High performance coating technology has increasingly been adopted around the world,and has become a key technology of cost saving,productivity increasing,energy conservation,industrial transformation and upgrading.TiC ceramic reinforced metal matrix coating has excellent performances of high hardness and wear resistance which are just needed for tool and mold.TiC reinforced metal matrix coating is generally used on the surface of tool and mold to significantly improve the surface performances and prolong the service life.Laser cladding is an advanced technology of preparing reinforced coating on material surface.With its rapid heating and cooling characteristics,a uniform coating with fine grains can be obtained.Laser cladding technique combined with situ reaction is reactant cladding.Clean hard particles can be generated in the melting pool,which integrate well with the substrate.The stress between the hard particles and coating is small,so the combination is strong.Powder prepared by sol-gel technology is fully mixed and fine,so that the reactants have large contact area.Therefore,the reaction needs less energy,and the in situ formation of fine particles is easy to be achieved.Laser composite sol-gel technology combines the advantages of the two techniques.In this paper,the preparation of TiC reinforced composite coating by continuous diode laser cladding and sol-gel compound process was researched.First,TiO₂ and C mixed powder was prepared from dry gel by sol-gel process;then the preset layer was made using a special pre-prepared method.45 steel was choosed as the base material;with the use of a diode laser,TiC enhanced coating was prepared.The pulse Nd:YAG laser was used in the base of previous studies to prepare TiC reinforced coatings as a comparation.The optical microscopy,scanning electron microscopy?SEM?,X-ray diffraction?XRD?were used to analyze the microstructure and the phase composition of the cladding layer.The micro-hardness tester and friction and wear testing machine were used to test the hardness and wear resistance properties of the cladding layer.Finally,the formation mechanism of TiC reinforced coating was investigated.The results show that the excellent TiC reinforced coating can be prepared through diode laser cladding and sol-gel compound process.When the laser power is600 W and the scanning speed is 3 mm/s,without gas flow rate,the coating with most abundant small TiC particles can be got.The TiC particles are polygonal or irregular with the diameter of 1³?m.In addition,small amount of agglomerated TiC particles with diameter of 40¹00?m can be found in the laser cladding coating.When the scanning speed and air flow rate are constant,as the laser power increases,the coating hardness declines firstly and then rises.When the laser power and the gas flow rate are certain,the coating hardness decreases with the increasing of scanning speed;when the laser power and the scanning speed are certain,with the increase of gas flow rate,the coating hardness firstly decreases and then increases.When the diode laser power is 1000 W,the scanning speed is 1 mm/s and the gas flow rate is 30 L/min,the hardness value of the coating reaches the peak.The average hardness value is 900 HV_0.2.2 and the maximum hardness value is 1151 HV_0.2.The wear resistance of the diode laser cladding coating is up to 13.9 times that of45 steel because of the extremely high hardness resulting from a small amount of TiC particles existing in the coating and much Ti element dissolving in the coating to form high carbon,high alloy and fine martensite.The high magnification morphology shows the presence of punctate pits,which indicates fatigue wear mechanism.The wear resistance of pulsed Nd:YAG laser cladding coating in which the particles are very small is up to 10 times that of 45 steel,and the wear mechanism of the coating is coexistence of abrasive wear and adhesive wear.After thermodynamic analysis of the mechanism of in situ synthesized TiC,it was concluded that solid-solid reaction mechanism is viable.And the dissolving mechanism of Ti C reinforing particles in the melting pool was analyzed.In conclusion,the TiC particles can be dissolved in the molten pool;when the ratio X_Ti/(X_Fe+X_Ti)<0.15(X_Ti is the atom percentage of Ti in the molten pool,X_Fe is the atomic percentage of Fe in the molten pool),TiC can be completely dissolved in the matrix to form solid solution FCC?Fe?or BCC?Fe?containing Ti,C.