High-Pressure Rolling Reduces Grain Size and Distortion, Improves Mechanical Properties and Produces Isotropy in Ti-6Al-4V wire+arc Additively Manufactured Parts

Mechanical properties anisotropy, residual stress and distortion are some of the issues that are limiting the industrial adoption of Ti–6Al–4V components made by additive manufacture. High-pressure, inter-pass rolling of welds is known to address residual stresses and distortion; hence it was applied to Ti– 6Al–4V wire+arc additive manufactured linear components.

The microstructure was changed to an equiaxed one throughout the component, and the size of prior β grains, which would otherwise traverse the height of the component, was reduced to 89 μm. The overall thickness of α phase lamellae decreased by 25%. A substantial increase in hardness, yield strength, ultimate tensile strength and elongation was observed, and mechanical properties isotropy was achieved when rolling at 75 kN.

In terms of geometry, a change was observed: part width increased –and layer height decreased– by as much as 18%. Moreover, layer height standard deviation was greatly reduced, therefore improving the repeatability of the deposition process and favouring its automation. This technique should be applicable to all additive manufacture processes where practicable.