Effect of alumina content on surface morphology and hardness of Ni-P-Al2O3(α) electroless composite coatings

In this research, alumina particles with various contents of 5, 10, 15, 20 and 25 g/l in bath were co-deposited within Ni–P deposits on AISI 1045 steel discs by electroless process. The composite coatings were heat treated at 200, 400 and 600 °C for 1 h and structural changes were evaluated by X-ray diffraction (XRD) analysis. Surface and cross-section morphology of composite deposits have been investigated by scanning electron microscopy (SEM) and volumetric percent of co-deposited particles have been determined by using an image analysis system. The results showed that some parameters such as deposition rate, co-deposited particles percent, roughness and hardness of Ni–P–Al2O3 coatings have been influenced by concentration of alumina in bath whereas average roughness and hardness increased as particles content increased. Also, surface morphology of deposits has been changed from smooth state to nodular appearance. It has been found that heat treated composite deposits in approximately 400 °C have the greatest hardness values.