Yonghao Zhao
Nanjing University of Science and Technology, China
Title: A high-entropy alloy with ultrahigh ductility breaks strength-ductility paradox
Biography
Biography: Yonghao Zhao
Abstract
For thousands of years, human being has been searching and preparing both strong and ductile materials. However, strength and ductility of a material are generally mutually exclusive. This is the well-known strength-ductility paradox, which exists for centuries. The underlying mechanism for the strength-ductility paradox of metals and alloys is dislocation-slip dominated plastic deformation, which could be traced back to 1930’s. Here by means of alloying designation, we developed a new face-centered cubic (FCC) high entropy alloy (HEA) NiCoFeVMo with unique {111}<110> slip features including short slip distance, low mobile dislocation exhaustion rate, dynamic nucleation, homogeneous distribution of high-density dislocations and nano-scale planar slip lamella. These unique deformation mechanisms break the strength-ductility paradox by a super combination of an ultra-high tensile ductility of 90% (36% for coarse-grained Ni) and an ultimate tensile strength of 980 MPa (346 MPa for Ni). First principles calculation revealed that the unstable stacking fault energy, i.e. {111}<110> slip potential barrier of the HEA varies continuously from 830 to 1200 mJ/m2, different from the unique value of 977 mJ/m2 for Ni. The variable slip potential barriers results in the above unique HEA slip features. Our work explores a new concept for designing both strong and ductile alloys by actuating new slip features.