Gradient microstructure with martensitic transformation for developing a large-size metallic alloy with enhanced mechanical properties

This work presents the development of a large-size metallic alloy rod with low modulus, fast strain hardening and high strength through designing the gradient microstructure with martensitic transformation. The gradient microstructure is revealed in both phases and grain sizes, which consists of amorphous and nano ZrCu phases in the top surface, fine-grained ZrCu, Zr₂Cu and Cu₁₀Zr₇ phases in the subsurface, and coarse-grained Zr₂Cu and Cu₁₀Zr₇ phases in the center. Hardness in the cross section of the metallic alloy rod shows a decreasing tendency from the top surface to center. Compressive mechanical tests illustrate an initial linear elastic deformation to yielding, followed by a fast strain hardening to the final fracture. Strain delocalization process accompanying with martensitic transformation is supposed to take place progressively in the gradient microstructure, which contributes to the performance of low modulus, fast strain hardening and high strength. Shearing fracture model with shear banding, nano wrinkling and micro cracking is revealed, which indicates the mixed mechanical behavior of ductile and brittle models. Gradient microstructure with martensitic transformation is impressive for developing the large-size metallic alloys with low modulus, fast strain hardening and high strength.