Ductility enhancement in B2-Type Zr-Co-Ni alloys with martensitic transformation

The relationship between the microstructures and mechanical properties in the ternary Zr-Co-Ni alloys has been investigated. X-ray diffraction measurements at room temperature show that Zr₅₀Co₅₀Ni alloys undergo martensitic transformation from the B2 to B33 structures by the substitution amounts of Ni above 14% for Co. The tensile strength and elongation increase remarkably by substituting Ni up to 13%. Especially, the Zr ₅₀oCo₃₉Ni₁₁ alloy has the extremely high total elongation of 23%. There are many (021 )_b33 deformation twins in addition to the dislocations with the (lOO)-type Burgers vector just near the fractured area. These twins are considered to be an internal defect of the deformation induced martensite which has high hardness about 430 Hv. Therefore, it is concluded that the remarkable enhancement of the ductility of Zr-Co-Ni alloys is due to the transformation induced plasticity.