Gradient Microstructure Induced by Surface Mechanical Attrition Treatment in Grade 2 Titanium Studied Using Positron Annihilation Spectroscopy and Complementary Methods

Abstract

Microstructural changes in grade 2 titanium generated by surface mechanical attrition treatment (SMAT) were studied using positron annihilation lifetime spectroscopy and complementary methods. A significant increase in the mean positron lifetime indicated many lattice defects introduced by SMAT. Two positron lifetime components were resolved in the positron lifetime spectra measured. The longer lifetime revealed the presence of vacancy clusters containing about 3 or 4 vacancies, while the shorter one was attributed to the annihilation of positrons trapped at dislocations. The changes of the positron lifetime indicated a decreasing dislocation density and the presence of a deeper layer with a higher concentration of vacancy clusters at the distance from the treated surface for which the microhardness approached the value for the strain-free matrix. Electrochemical impedance spectroscopy showed the positive effect of SMAT on the corrosion resistance of the titanium studied in a saline environment also after removal of the original oxide layer that was formed during the SMAT.

Comparison of SP, SMAT, SMRT, LSP, and UNSM Based on Treatment Effects on the Fatigue Properties of Metals in the HCF and VHCF Regimes

“…He et al [26] investigated changes in the microstructure of four batches of welded SMA490BW steel specimens treated with different ultrasonic impact treatment parameters, and the gradient microstructure became more obvious as the thickness of the plastic deformation zone increased. Although not as common as in workpieces treated with SMRT and UNSM, some researchers also observed a clear gradient microstructure on other selected titanium and steel workpieces after treatment with the appropriate SP, SMAT, and LSP methods [40][41][42][43]. Nevertheless, these studies did not investigate the effects of SP, SMAT, and LSP-induced gradient microstructure on the very-high-cycle fatigue properties of the selected metals; therefore, these may still be potential areas for future studies.…”

Enhanced Corrosion Resistance and Local Therapy from Nano-Engineered Titanium Dental Implants

“…Huang et al reported that the passive film resistance (R p ) of SMAT-Ti was considerably higher than that of non-treated Ti counterparts in both physiological saline (PS) and simulated body fluid (SBF) solutions [ 79 ]. Moreover, compared with smooth Ti, the grain sizes and boundaries were changed more significantly on roughened Ti after SMAT; hence, SMAT was more effective in enhancing the corrosion resistance of roughened Ti implants [ 80 ]. It is also indicated that remodeling the grain size could thicken the superficial TiO 2 layer on Ti implants by SMAT, establishing a more stable protective layer against chemical corrosion [ 80 ].…”

“…Moreover, compared with smooth Ti, the grain sizes and boundaries were changed more significantly on roughened Ti after SMAT; hence, SMAT was more effective in enhancing the corrosion resistance of roughened Ti implants [ 80 ]. It is also indicated that remodeling the grain size could thicken the superficial TiO 2 layer on Ti implants by SMAT, establishing a more stable protective layer against chemical corrosion [ 80 ].…”