High-strength and ductile (Ti-Ni)-(Cu-Zr) crystalline/amorphous composite materials with superelasticity and TRIP effect

Composition modification of (Ti-Ni)-(Cu-Zr) alloys with addition of Y, Co, Nb, Al and B was performed with the purpose of production of high-strength crystal-glassy phase composites. The structure of these samples with an amorphous phase was examined by X-ray diffraction, scanning and transmission electron microscopy. It was found that the addition of Y does not lead to increase in the glass forming ability of the Ni-Ti-Cu-Zr system alloys. Dual-phase structure allows developing the composite materials, which combine high strength of glassy alloys and good plasticity of crystalline alloys. Sixteen different alloy compositions were prepared and investigated. Mechanical characteristics of the alloys were determined using universal testing machines. For example, Ti₄₀Ni_39.5Cu₈Zr₁₀Co₂Y_0.5 alloy showed the compressive strength about 2600 MPa and total strain about 25%. Transformation-induced plasticity and superelasticity effects were found to exist. Large amount of Y (more than 0.5 at%) induces precipitation of the NiTi₂ phase which is harmful for mechanical properties. The addition of Nb, Al and B leads to increase in yield strength, but Al and B suspend martensitic transformation and as a result these alloys have lower overall plasticity. The specimens demonstrate a good combination of strength and plasticity owing to both the composite effect of a dual-phase structure and the dynamic martensitic transformation that develops during deformation.