A research team led by Professor Jian Lu of City University of Hong Kong, in collaboration with the China Academy of Engineering Physics and Dalian University of Technology, has used laser powder bed fusion (LPBF) additive manufacturing to in-situ construct chemical medium-range order (CMRO) structures in a BCC-structured multi-principal element alloy (Al₂Ti₇Zr₂Nb₅). The ultra-fast cooling rate of LPBF (10³–10⁸ K/s) “freezes” the high-temperature chemical fluctuation state, resulting in a uniform distribution of B2-type CMRO clusters with an average size of ~1.6 nm, a volume fraction of ~20%, and full coherency with the matrix. Compared to as-cast alloys without CMRO (elongation of only ~1%), the LPBF-processed alloy achieves an excellent synergy of yield strength 1023 MPa, uniform elongation ~20%, and total elongation ~32%. Even at 873 K, its yield strength remains as high as 700 MPa. The conditional fracture toughness (KJQ) reaches 158 MPa·m^1/2, far exceeding typical BCC refractory high-entropy alloys. This study is the first to systematically reveal that LPBF can “lock in” thermodynamically metastable CMRO structures via rapid cooling, providing a new pathway for achieving high strength and toughness in BCC alloys at room temperature.