High-performance conventional engineering materials (including Al alloys, Mg alloys, Cu alloys, stainless steels, Ni superalloys, etc.) and newly-developed high entropy alloys are all compositionally-complex alloys (CCAs). In these CCA systems, the second-phase particles are generally precipitated in their solid-solution matrix, in which the precipitates are diverse and can result in different strengthening effects. The present work aims at generalizing the precipitation behavior and precipitation strengthening in CCAs comprehensively. First of all, the morphology evolution of second-phase particles and precipitation strengthening mechanisms are introduced. Then, the precipitation behaviors in diverse CCA systems are illustrated, especially the coherent precipitation. The relationship between the particle morphology and strengthening effectiveness is discussed. It is addressed that the challenge in the future is to design the stable coherent microstructure in different solid-solution matrices, which will be the most effective approach for the enhancement of alloy strength.

Glassy Ni-based alloys with high thermal stability and high corrosion resistance were synthesized in Ni-Ta-Ti-Zr(-Co) alloy system. Glassy Ni₆₀Ta_40−x−yTi_xZr_y alloys exhibit supercooled liquid region exceeding 50 K in a wide composition range and the largest supercooled liquid region of 67 K was obtained at Ni₆₀Ta₂₀Ti₁₅Zr₅. Glassy Ni₅₅Ta₂₀Ti₁₀Zr₈Co₇ alloy exhibits the highest thermal stability among the Ni-based glassy alloys reported up to date, which is evidenced by its high T_g and T_x of 899 K and 977 K, respectively, and a larger supercooled liquid region of 78 K. Bulk glassy Ni₅₅Ta₂₀Ti₁₀Zr₈Co₇ alloy in a rod form with a diameter of 1 mm can be prepared by copper mold casting. The glassy Ni-Ta-Ti-Zr(-Co) alloys are spontaneously passivated with low passive current density in 1 N H₂SO₄ and 1 N HCl solutions and their corrosion rate was less than 0.1 μm/year in the above solutions.