Microstructure of Nanometer-sized Al2O3 Composite Coating Prepared by Electroless Plating.

Nanometer-sized Al₂O₃ particle-reinforced nickel phosphorus matrix composite (Ni P-Al₂O₃) coatings were prepared by electroless deposition. Particles are found to distribute homogeneously in Ni-P-Al₂O₃ coatings by field emission scanning electron microscopy and transmission electron microscopy. It is found that the crystallization temperature of the composite coating decreases from the results of X-ray diffractometry and differential scanning calorimetry. The activation energy and Avrami exponent of crystallization are lowered due to the co-deposited particles in composite coatings. Nickel phosphide precipitates after heat treatment at 230°C for 24 h in Ni-P-Al₂O₃ coatings, while Ni-P coatings keep amorphous under such condition. Because of the existence of nanometer-sized particles, the microhardness of the composite coatings increases greatly. With heat treatment, the microhardness values of composite coatings can reach as high as HV₅₀ 1 150. [ABSTRACT FROM AUTHOR]