Study On Surface Modifications Of TA2 Pure Titanium And TC2 Titanium Alloy By Laser Cladding

Laser cladding has been developed intensively for surface modifications of materials in recent years. In the present work, a pure Ti（TA2） and a Ti alloy（TC2） were selected to be treated by laser cladding to investigate the effect of the treatments on their microstructure, phase component, hardness and corrosion resistance by using scanning electron microscope（SEM）, energy spectrometer（EDX）, X-ray diffraction（XRD）,hardness tester and the electrochemical workstation. The main conclusions are as follows:In the present work, a TiN reinforced coating was produced onto the TA2 pure titanium by laser cladding with TiN/Ti powders. Laser scanning speed is set at 4, 6 and 8mm/s, and scanning power is 3000 W. The surface microhardness was measured. After laser cladding, increased hardness was achieved in the laser clad surface layer, which was about 3-4 times of that of the substrate（²50 HV）. The corrosion property of matrix material and treated samples were both measured in NaCl（3.5 wt%） aqueous solution.From the results we can see that the laser cladding specimens’ corrosion property is clearly becoming better than the substrate. The polarization curves for matrix and laser cladding specimens in the Hank’s simulated body fluids revealed that the corrosion current density of the modified layer（1.2×10-5mA/cm2） decreased to about one-thousand of the substrate.A composite coating was prepared on TA2 pure titanium substrate by laser cladding with TiB2/Ni. Laser scanning speed is 4 mm/s, 6 mm/s and 8 mm/s, and scanning power is3000 W. The cladding layer is consisted of Ti, TiB₂ and NiTi2. Ti phase exists in dendrite form in the cladding layer while TiB₂ phase present in black strips. Ni Ti2 reinforced phase exists in the form of white cellular in the cladding layer. Surface hardness of laser cladding layer has a maximum value of 840 HV, about 4 times of that of the base material. The corrosion performances of the untreated and laser cladding samples are measured in 3.5wt% NaCl aqueous solution. The corrosion current density decreased from 1.3×10-5A/cm2 to 6.6×10-8A /cm2. The results showed that the corrosion resistance of the TA2 pure Ti canbe significantly improved after laser cladding.A TiC/TiB₂ reinforced composite coating was produced onto a TC2 Ti alloy by laser cladding with Ti/TiC/TiB₂ powders. The cladding layer is consisted of Ti, TiC and TiB2.And the surface microhardness was measured. After laser cladding, a maximum hardness of 1100 HV was achieved in the laser cladding surface layer, which is more three times higher than that of the TC2 substrate（³00 HV）. Corrosion tests reveal that the corrosion property of the laser cladding specimen is clearly better than that of the substrate. Besides,the corrosion potential was increased from-0.303 V to 0.756 V, and the corrosion current density declined from 1.75×10-2 A/cm2 to 1.37×10-4mA/cm2.