| Titanium and titanium alloy are widely used in aviation,navigation,automobile andmedical fields because of a series of excellent performance characteristics like low density,high specific strength and good corrosion resistance.However,titanium alloy has low hardness,high friction coefficient,poor wear resistance and other shortcomings,which limits its scope of application.It is found that the laser cladding technology has the characteristics of fast cooling speed,small heat input and less consumables.Therefore,the use of laser cladding technology on titanium alloy surface with high performance coating can effectively improve the surface properties of titanium alloy,has important research value.In this paper,first,the mixed powder is made of Ti,Ni,Al N,Y in different proportions as a cladding material.Then prepare Ti-Ni based composite coating on the titanium alloy surface by selecting the optimal process parameters and cladding method.The phase structure and microstructure of the cladding layer are observed by X-ray diffraction,optical microscopy,scanning electron microscopy and electron probe microscopy.In addition,the hardness and wear resistance of the coating are studied.The 50Ti-40Ni-10 Al N mixed powders are coated with different laser cladding power.The results showed that while Ti,Ni and Al N are melted at high temperature,the Ti Ni,Ti2 Ni,Ti3Al and Ti N is formed.When the laser power is 900 W,the cladding layer has the highest hardness reaches 900 HV,about 3.0 times of the titanium,the wear resistance is the best,about 9.3 times of the matrix.The wear mechanism is sliding contact fatigue wear,accompanied by slight adhesion and abrasive wear.By the selected optimal laser cladding power,the mixed powder of Ti,Ni and Al N with different mass percentage is coated on the surface of titanium alloy.It is found that,within the selected composition range,the influence of the mass percentage of Ti and Ni on the phase composition of the cladding layer is not significant,but it has a great influence on the microstructure.When the mass percentage of Ti,Ni,Al N is 56:34:10,the composite performance is the best,the organization is uniform and there has no crack.The hardness of the cladding layer is 1000 HV,about 3.3 times of the matrix,and the abrasion resistance is about 22.3 times of the base.In order to improve the microstructure of the cladding layer and the defects such as cracks and holes,a rare earth element Y with different mass percentage of Y is added on thebasis of 56Ti-34Ni-10 Al N.It is found that when the Y content reaches 1.5 wt.%,the macroscopic morphology,microhardness and dilution of the cladding layer are in the optimal state,and the surface has no holes,cracks and other defects.The microhardness is 950 HV,about 3.0 times of the matrix,and in the bonding area the hardness is slow down,and it has the best wear resistance,about 60.4 times of the base.After laser cladding with different cladding method,lap rate,two and three channel laser cladding process,it is found that when "long pendulum-turn" approach is used in two channel cladding,the quality of the cladding surface is not good.But when the cladding layer is formed by the "dragon U-turn" cladding method,and the lap ratio is 40%,the surface quality of the cladding layer is good and the wear resistance is the best,which is 121.9 times of the substrate,and the cross section transverse microhardness is the highest,with the average hardness of 840 HV.For the three laser cladding,when the lap rate is 40 %,according to separated laser cladding,the sequential laser cladding has the highest hardness,up to 950 HV,and is more uniform. |
PDF Full Text Request