Plasma Polishing as a New Polishing Option to Reduce the Surface Roughness of Porous Titanium Alloy for 3D Printing

Since the internal pulse of porous structures cannot be polished by conventional mechanical pollution, an alternative method needs to be found. Plasma pollution is an environmentally friendly processing method that is especially effective for mental work pieces with complex shapes. To begin, place the separated titanium alloy workpieces in the titanium basket without the different workpieces touching each other.

Put the titanium basket into the heat treatment furnace at room temperature and close the furnace door. Open the gas valve to remove the air and maintain the appropriate degree of vacuum. To set the heat treatment process first, heat the furnace to 800 degrees Celsius for 1.5 hours, and then maintain the temperature for two hours before cooling.

After the heat treatment, cool the furnace to room temperature and fill the furnace with air. Once the furnace returns to atmospheric pressure as seen on the panel, take out the porous titanium alloy workpiece. To image the surfaces of the workpiece using a confocal microscope, place the workpiece on the storage platform horizontally.

Measure the surface arithmetic average roughness or RA parameter. Select 2.5x magnification and choose wide for live mode. To observe the overall situation click auto intensity and go to 5x magnification.

Click Auto Intensity and set the live mode to Comp. Select the area of interest, click set first at the lowest point and set last at the highest point, and set the acquisition to normal. After about five minutes, import the results into a new document in the ConfoMap ST8 software.

The RA is easy to obtain in the parameters table in ConfoMap ST.Observe the overall condition of the workpiece with a five-fold mirror. Then, switch to a high power mirror and focus the field of vision on a trabecular. Quantify the plasma polishing effect by the RA of the workpiece before plasma polishing.

For plasma polishing, use 4%ammonium sulfate solution with pH between 5.7 to 6.1 as the electrolyte. Place the surface of the porous titanium alloy workpiece to be polished horizontally and fix it on the fixture. Then, put the fixture into the plasma polishing machine.

Set the polishing current to 59 amp pairs, the voltage to 313 volts and the polishing electrolyte temperature to 101.6 degrees Celsius, and conduct plasma polishing according to these parameters. After conducting plasma polishing for 90 seconds, take the fixture out of the plasma polishing machine. Then, slightly change the position of the clamping point where the workpiece is fixed to the fixture.

No electrochemical reaction occurred there as it was not in contact with the polishing solution. Conduct plasma polishing again for 90 seconds, and take the fixture out of the plasma polishing machine. Remove the workpiece from the fixture and put it into the ultrasonic cleaning machine with deionized water.

Set the water temperature at 30 degrees Celsius and clean the workpiece for two minutes. After two minutes, take out the workpiece and blow out the residual liquid with high pressure air. After the completion of plasma polishing, image the surfaces using scanning electron microscopy and confocal microscopy in the same way as demonstrated before.

The scanning electron microscopy images revealed the difference in the surface morphologies of the porous titanium alloy workpiece before and after plasma polishing. At 30x and 100x magnification, the surface before plasma polishing appeared rougher. When magnified to 500x, the semi-molten powders and ablative oxide layers observed on the alloy surface before plasma polishing were mostly found to be absent after the polishing.

Interestingly, the porous size and trabecular diameters were consistent with the design even after polishing. The whole and part of the porous titanium alloy workpiece were imaged using the fast rotary confocal microscope. The surface roughness in both cases was high before plasma polishing.

The surface roughness of porous structures as revealed by the RA, significantly reduced after polishing. This technology has explained that porous titanium alloy workpieces can reduce surface roughness through plasma pollution technology. Further studies can be conducted to determine the optimal parameters.