Cobalt-based amorphous/nanocrystalline composite coatings have been grown by arc ion plating together with a specimen cooling system.With decreasing substrate temperature,the coatings undergo significant structure evolution.The degree of crystallization first decreases and subsequently increases as confirmed by X-ray diffraction.The cluster size first decreases and then remains constant as confirmed by transmission electron microscopy.The effect of substrate temperature on the evolution of the structure has been studied as a result of a competition between nucleation thermodynamics and kinetics of crystalline growth.With decreasing the substrate temperature,the microhardness and the critical load of the composite coatings firstly increased,and then remained almost constant.And the saturation magnetization revealed the opposite trend over the same range.The essence of these phenomena was ascribed to the microstructural variations caused by the decrease of the substrate temperature. Cobalt-based amorphous / nanocrystalline composite coatings have been grown by arc ion plating together with a specimen cooling system. W. decreasing substrate temperature, the coatings undergo significant structural evolution. Degree of crystallization first reduced and subsequently increasing as confirmed by X-ray diffraction The cluster size first decreases and then remains constant as confirmed by transmission electron microscopy. The effect of substrate temperature on the evolution of the structure has been studied as a result of a competition between nucleation thermodynamics and kinetics of crystalline growth. temperature, the microhardness and the critical load of the composite coatings said increased, and then remaining almost constant. And the saturation magnetization revealed the opposite trend over the same range. The essence of these phenomena was ascribed to the microstructural variations caused by the decrease of the substrate temperature.