*Article* **Designing High Entropy Bulk Metallic Glass (HE-BMG) by Similar Element Substitution/Addition**

**Hongyu Ding 1,2,\*, Hengwei Luan 2, Hengtong Bu 2, Hongjie Xu <sup>2</sup> and Kefu Yao 2,\***


**Abstract:** In this paper, we report that two newly designed high entropy bulk metallic glasses (HE-BMGs), Ti20Hf20Cu20Ni20Be20 with a critical diameter of 2 mm, and Ti16.7Zr16.7Nb16.7Cu16.7 Ni16.7Be16.7 with a critical diameter of 1.5 mm, can be fabricated by copper mold casting method. These newly developed HE-BMGs exhibited a high fracture strength over 2300 MPa. The glass forming ability and atomic size distribution characteristics of the HE-BMGs are discussed in detail. Moreover, a parameter *δ* was proposed to evaluate the atomic size distribution characteristics in different HEAs. It showed that this new parameter is closely related to the degree of lattice distortion and phase selection of high-entropy alloys. Adjusting the value of *δ* parameter by similar element substitution/addition would be beneficial for designing high entropy bulk metallic glasses.

**Keywords:** high entropy alloy; bulk metallic glass; similar element substitution/addition; glass forming ability; lattice distortion
