Microstructure and mechanical behavior of an as-drawn MP35N alloy wire

The deformation response of low Ti (<0.1%), MP35N alloy (35% Co-35% Ni-20% Cr-10% Mo, all in wt%) wire with a ~100 µm diameter was assessed in monotonic and cyclic loading modes. The as-drawn wire exhibited a strong 〈111〉 fiber texture and consisted of a hierarchically twinned microstructure with twins spanning the micrometer to nanometer scale; when deformed in this condition in uniaxial tension at room temperature, high strengths up to 2 GPa, limited tensile ductility of 3% and strain rate sensitivity in the quasi-static regime were noted. The deformed microstructure revealed evidence for slip, twinning and de-twinning, and in the necked region, in the vicinity where fracture had occurred, the fine twins appeared broken down into nanograins. The cyclic response of the as-drawn wire, evaluated using rotary beam bending (R=−1) and in tension-tension fatigue (R=0.3), appeared to be initiation-controlled and sensitive to the presence of extraneous second phase inclusions identified as Al2O3 particles. Cyclically-deformed as-drawn wire samples displayed extensive de-twinning and multiple twin variants formation.