Influence of micro-rolling on the strength and ductility of plasma-arc additively manufactured Ti–6Al–4V alloys

Abstract

The aim of this study was to reduce the number of defects, refine the grain size, and improve the mechanical properties of Ti–6Al–4V. We investigated the effect of interpass micro-rolling on the microstructures and mechanical properties of Ti–6Al–4V alloys produced via plasma arc additive manufacturing (PAAM). The non-rolled plasma-arc additively manufactured (PAAMed) sample exhibited coarse columnar crystals, basket-weave microstructures, and Widmanstätten structures, while the interpass-micro-rolled PAAMed sample exhibited fine equiaxed crystals and basket-weave microstructures. Interpass micro-rolling could significantly reduce the number density and size of defects during PAAM, and the rolled samples exhibited lower mechanical property anisotropy than the non-rolled samples. Moreover, the rolled sample exhibited a higher yield strength (∼797.66 and 793.45 MPa), tensile strength (∼939.73 and 935.71 MPa), and elongation (∼12.83% and 14.73%) in the X- and Z-directions than the unrolled sample. These enhanced mechanical properties can be attributed to αGB fragmentation, grain boundary strengthening, dislocation strengthening, and a low crack density. The micro-cracks preferentially nucleated around defects in the non-rolled sample, resulting in high crack and defect densities.

Keywords

• Plasma arc additive manufacturing
• Micro-rolling
• Ti–6Al–4V alloy
• Defects
• Basket-weave microstructure
• Strength and ductility