Significantly enhanced tensile strength and ductility in nickel aluminium bronze by equal channel angular pressing and subsequent heat treatment

Abstract

Nickel aluminium bronze (NAB) was subjected to equal channel angular pressing (ECAP) at 400 °C for up to 4 passes in routes B_A and C, respectively, followed by isothermal heat treatment with a view to improving the κ phase structures and tensile properties. The lamellar κ_III structure was completely broken after 4 passes in route B_A although route C was less efficient. Spheroidisation and coarsening of the highly deformed κ_III continued during heat treatment especially at ≥600 °C. At 800 °C, both the lamellar structure and the fine κ_IV particles transformed completely into a coarse globular morphology with no distinction between the primary and eutectoid α. Significant increases in strength were achieved by ECAP, reaching a maximum yield strength of 960 MPa with a good ductility of ~14 %. Heat treatment after ECAP was shown to considerably improve tensile ductility to >30 % while keeping the strength high at ~700 MPa, a significant enhancement compared to the as-received NAB.