Spinodal decomposition-mediated multi-architectured α precipitates making a metastable β-Ti alloy ultra-strong and ductile

•A novel metastable β-Ti alloy has been designed based on two semi-empirical methods: the d-electron theory and the e/a electron concentration.•The spinodal decomposition structure boundaries play an important role in plastic deformation.•The multi-architectured structure is responsible for large back stress and achieves a combination of ultra-strong and ductile in the aged alloy.•The spinodal decomposition structure plays important roles in creating multi-architecture α precipitates owing to its chemical composition and lattice strain inhomogeneity.