Large current ion beam polishing and characterization of mechanically finished titanium alloy (Ti6Al4V) surface

Ti6Al4V samples with a surface roughness of about 0.2 mu m were polished by a high fluence ion beam source, and influences of the ion current, energy and incident angle on the surface roughness of Ti6Al4V were studied. The as-polished surfaces were characterized by laser scanning confocal microscopy (LSCM), atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS). The LSCM images revealed that the density of pits in the original surface decreased greatly after the ion polishing process. In addition, the surface roughness calculated from these images proved that the mean value reduced to 53 nm with an ion energy, current and incident angle of 600 eV, 130 mA and 75 degrees, respectively. The smoothing effect was also confirmed by the power spectral density (PSD) functions calculated from the AFM data. GIXRD patterns indicated that the Ti6Al4V samples mainly contain the hexagonal close packed (HCP) alpha-Ti, no recognizable peaks corresponding to the body centered cubic (BCC) beta-Ti were observed. Furthermore, after the ion beam polishing process, the phase of all the as-polished samples kept steady. The XPS results revealed that C, O, Ti, Al and V were present in both the original as well as the polished samples. In addition, due to the highly reactive characteristics of Ti, Al and V elements, a higher signal for oxygen can also be observed on the outermost surface of the ion beam polished samples. The polishing process of Ti6Al4V surface bombarded by Ar ion beam is also simulated by binary collision approximation (BCA) code SDTrimSP, the effects of ion beam energy and incident angle on the sputtering yield were investigated. The results showed that the sputtering yield of Ti, Al and V atoms increased almost linearly with the ion energy. However, as for the influence of ion incident angle, the sputtering yield first increased gradually from 0 degrees and peaked at about 65 degrees, then decreased rapidly because the incident angle is too large for Ar ion to penetrate into the surface of Ti6Al4V sample.