Surface modification of 3 D-printed alloy Ti-6Al-4V by ultrasonic impact treatment

The mechanical characteristics, phase composition, macroscopic residual stresses and surface topography of the Ti-6Al-4V alloy produced by different technologies-selective laser melting (SLM) of powder and traditional hot rolling (VT6) were studied. Ultrasonic impact treatment (UIT) in an inert environment was used to modify the surface of samples of various types. In the initial state, the SLM sample, which consists of the hexagonal alpha-phase, has a slightly higher (1.3 times) microhardness (HV) value than that of the hot-rolled VT6 bar, for which, in addition to the alpha-phase, the presence of the cubic beta-phase (18%) was observed. After UIT, an increase in the value of & Ncy;V 10 0 by 1.6-1.8 times was registered, regardless of the alloy production method. Data obtained by the nanoindentation method satisfactorily agree with this result-the instrumental hardness, H IT , increases by 1.4-1.5 times. Among the reasons for hardening (the hardness increase) recorded for both types of studied alloys, a high level of compressive stresses of the 1st kind plays a decisive role in the case of UIT-treated hot-rolled samples of VT6. The increase in microhardness of the UIT-treated SLM samples occurs largely due to the deformational refinement of the grain/subgrain structure (down to 15 nm) and a significant dislocation density, which causes the lattice microstrain in acicular martensite, which was formed at the SLM process due to the high cooling rate.