| Titanium alloys are very important material and have been utilized widely in aerospace industries due to their excellent inherent properties,such as superior strength-to-weight ratio and excellent corrosion resistance.Nevertheless,it can't be used as key tribological moving components because of its relatively lower hardness and wear resistance.The Ti3Si C2 has good performance in both metal and ceramics,and laser cladding in-situ synthesized can directly generate Ti3Si C2 self-lubricating phase from surface of the substrate,and the in-situ synthesized Ti3Si C2 phase grows from the nucleation in the matrix,has a good interface with the matrix,and the size of ceramic phase is small,and evenly distributed in the coating,and the mechanical properties of the surface of the material can be significantly improved.The Ti3Si C2 metal-ceramic composite coatings were prepared at the surface ofTi6Al4V titanium alloys by laser cladding in-situ synthesized with different precursor powders,and characterized the microstructure of those coatings,test the microhardness and the friction and wear behavior of coatings are detected at room temperature.The components of different precursor powders are Mechanical Alloying Ti3Si C2,Ni25 alloy powder(Ni25/Ti3Si C2),Ni25 alloy powder,pure Ti and Si powder,and graphite powder(Ni25/Ti/Si/C);Ni25 alloy powder,pure Ti,Si C powder,and graphite powder(Ni25/Ti/Si C/C);Ni25 alloy powder,Fe Ti powder,Si C powder,and graphite powder(Ni25/Fe Ti/Si C/C),respectively.It has been found through experiments that the laser cladding composite coating with a Ni25 content of 50%has good forming quality and the coating exhibits excellent performance.The results of laser cladding Ni25/Ti3Si C2 composite coatings indicate that:The laser cladding Ti3Si C2 coating has a large dilution rate,and the surface of the coating is recessed toward the substrate.The dilution ratio of the laser cladding Ni25/Ti3Si C2coating is good,but the coating surface has spherical particles with different sizes and with some holes inside of the coating.The average microhardness of coatings is 791.7 HV0.2(Ti3Si C2)and 984.4 HV0.2(Ni25/Ti3Si C2),respectively,which indicated that adding Ni-based alloy powders can significantly improve the hardness of the coating.The average friction coefficient and wear rate of different composite coatings were 0.3963 and13.5×10-5 mm3/N·m,respectively.This indicated that laser cladding Ti3Si C2and Ni25/Ti3Si C2 composite coatings have exhibited favourable tribological properties,but it have poor surface quality of the coatings.The Ni25/Ti/Si/C were used as materials to laser cladding in-situ synthesized Ti3Si C2 composite coatings because of the poor surface quality of the laser cladding Ti3Si C2 composite coatings,and the results show that:the main phase compositions of the coatings were the reinforcing phase Ti C,lubricating phase Ti3Si C2 and Ti5Si3,matrix?-Ti,?-Ni solid solution and Ti Nix intermetallic compound.The average microhardness of coatings is 850.6HV0.2,is about 2.36 times that of the substrate.The average friction coefficient and wear rate of composite coatings were 0.4172 and 13.5×10-5 mm3/N·m,respectively.The reason for the increase in the friction coefficient is due to the high temperature of the molten pool during the cladding process,which causes some of the Si elements to volatilize.Replace Si powder with Si C powder to prevent the evaporation of Si element during cladding,The results of Ni25/Ti/Si C/C laser cladding in-situ synthesized composite coatings indicate that:the addition of Si C has a significant effect on the microstructure of the coating.The coating is metallurgically bonded to the substrate and the microstructure of the cladding layer changes significantly.The black and gray blocky structure(mixture of Ti3Si C2 and TixNi)of the coating has increased.The average microhardness of coatings is1064.6 HV0.2,is about 2.96 times that of the substrate.The average friction coefficient and wear rate of composite coatings were 0.4302 and 18×10-5 mm3/N·m,respectively.The friction coefficient of Ni25/Ti/Si C/C laser cladding composite coatings is similar to the substrate,it shows that less self-lubricating phase Ti3Si C2 is synthesized in the coating.However,the wear rate of composite coatings is much lower than the substrate,which indicates that the composite coating shows good wear resistance.The addition of Fe element can possible to promote the formation of the ternary phase Ti3Si C2,the gray block structure Ti3Si C2 in the coating is obviously increased in Ni25/Fe Ti/Si C/C laser cladding composite coatings,and the grains are finer more.The main phase compositions of the coatings were?-Ti and?-Ni solid solution,the phase of Ti C,Ti3Si C2,Ti5Si3 and phase of FexC.The average microhardness of coatings is 1003.2HV0.2,and the average friction coefficient and wear rate of composite coatings were 0.3824and 12.5×10-5 mm3/N·m,respectively,which shows the excellent tribological properties. |
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