The influence of the initial structure of high-strength titanium alloy on surface hardening and roughness after ball burnishing

Correlation dependences between diamond ball burnishing parameters (load and number of passes) and surface characteristics (surface topography, microhardness, roughness, depth and structure of the deformed surface layer) of high-strength VT22 (Ti–5Al–5Mo–5V–1.5Cu–Fe) titanium alloy were investigated. A high-strength titanium alloy with different initial structures (single-phase b- and two-phase (a+b)-lamellar and globular structures) was chosen. It is shown that the load during ball burnishing, regardless of the structural state of the alloy, should not exceed 400 N due to a decrease in surface quality caused by the delamination of the subsurface layers. When the ball burnishing load grows from 100 to 400 N, the surface microhardness of the alloy with the initial two-phase structure increases due to the decrease in the grain size of the a-phase in the near-surface layer. On the other hand, the alloy with the initial single b-structure is less suitable for such treatment. When the number of passes increases, regardless of the initial structural state, in case of a weak sensitivity to the surface hardening, the microrelief of the treated titanium alloy surface decreases.