Effects of chip conditions on the solid state recycling of Ti-6Al-4V machining chips

Five different types of Ti-6Al-4V machining chips were recycled in their solid state using equal channel angular pressing (ECAP). The chips were produced by either turning or milling with or without the application of a coolant. All the as-recycled materials achieved full density but their microstructures, including the prior chip boundary spacing and grain size, are dependent on the starting chip morphologies and dimensions. The differences, however, were largely removed in the subsequent mill-annealing processing consisting of β homogenisation, hot deformation and final annealing, leading to near-identical mill-annealed microstructures for all different types of chips consisting of equiaxed α + β grains with lamellar α, typical following such a treatment. The recycled and mill-annealed materials possess high yield strengths of  >900 MPa and satisfactory tensile ductility of  >11%, comparable or superior to the original commercial mill-annealed Ti-6Al-4V and independent of the initial chip conditions.