Surface nanocrystallisation on Ti-6Al-4V component with a robotic controlled shot peening process

Author:  Yijun Liu1, David Wimpenny1, Ben Mcgrory2, Colin Mcgrory2 1. Manufacturing Technology Centre, Pilot Way, Coventry, CV7 9JU, UK, 2. Sandwell UK Ltd., 2 Foundry Place, Towcester, Northamptonshire, NN12 6FP, UK,
Source:  ICSP14 Milan
Doc ID:  2022055
Year of Publication:  2022
Abstract:  
The present study experimentally investigated the influence of shot peening processing on surface nanocrystallisation in terms of the impact kinetic energy as a function of shot peening coverages. The impact kinetic energy of a single shot peening media varied from 1.8J to 77J, while the shot peening coverage changed from 200% to 1600%. In general, nanocrystallization at Ti6Al4V surface has taken place with all shot peening conditions but with different level of surface damages. Shot peening at lower kinetic energy is beneficial to generate nanocrystalline microstructure to a layer thickness of 5-7 μm, without causing harmful damage on Ti6Al4V surface. However, high impact kinetic energies, especially at higher coverage can cause considerable surface damages in the form of delamination parallel to the surface. Delamination was an accumulating result of micro-voids nucleation, growth and their coalescence to form microcracks in the subsurface region where shear localization and severe plastic deformation took place, as evidenced by superimposed high compressive residual stress level and increased microhardness. Shot peening at a low temperature of -21oC also resulted in nanocrystallisation, however, further investigation of the beneficial effects expected from the cooling process is still needed.