Microstructure and mechanical properties of an MP159 alloy processed by torsional deformation and subsequent annealing

MP159 alloy is a NiCoCr-based material, with a single-phase face centered cubic structure in the solid solution state. In this paper, the evolutions of the microstructure and mechanical properties of the MP159 alloy after torsional deformation and subsequently annealing treatment were systematically investigated. Detailed microstructural characterization and mechanical properties testing indicate that the torsional deformation introduces gradient structure and gradient hardness distribution along the radial direction in the alloy, leading to the increase of the strength while retaining a decent amount of the ductility. The formed gradient structure includes gradient grain size, gradient dislocation substructures and density. Subsequently annealing treatment only leads to the annihilation of part dislocations and does not change the gradient structure significantly, but introduces nano-sized γ′ phase inside the matrix. The combination of the gradient structure and nano-sized γ′ phase leads to the further increment of the strength.