Microstructure and mechanical behaviors of Co-Ni magneto-shape-memory alloys

Optical microscope, XRD analysis and tensile test were performed to study the influence of Ni element on the microstructure and mechanical behaviors of the magneto-shape-memory alloys Co-Ni. The experimental results show that the martensitic microstructure presents regular plates after homogenizing annealing, and the microstructure shows the lens-like morphology after hot rolling. The crystal structure of thermal martensite is determined to be hcp, with the lattice parameters being a=0.251 nm, c=0.407 nm. The crystal structure of the parent phase is determined to be fcc, with the lattice parameter being a = 0.355 nm. After the elastic deformation stage, the experimental alloys show continuous work hardening and have no obvious yield point elongation. σ_0.2, E decreases and δ increases with the increase of the Ni content. The high deformation strengthening exponent of the parent phase proves that it has low stacking fault energy.