Characterization of the microstructure and texture of functionally graded nickel-Al2O3 nano composite coating produced by pulse deposition

The main goal of this research was the characterization of the microstructure and texture of functionally graded nickel-Al2O3 nano composite coating. This coating was produced by changing the duty cycle under ultrasonic agitation during pulse deposition process. All of the electrodeposited layers were prepared at 20 A.dm(-2) peak current density and constant frequency of 10 Hz, and the duty cycle has been changed from 90% at the first layer to 10% at the fifth layer. According to SEM images and EBSD results, all layers except the last one showed a truncated pyramidal structure which is a typical morphology for Ni deposited coatings with [100] preferred texture. The last layer which was prepared at duty cycle of 10% exhibited a cauliflower (or colony) structure with small grains that probably resulted in random texture in this layer. EDS results showed more alumina particles can be incorporated at lower duty cycles. Foreign ions incorporation during the deposition process could be the reason for a change of [100] fiber texture to almost random orientation of grains. This rather high incorporation is due to either lower current density or higher OFF-Time duration at low duty cycles in pulse plating process. (C) 2013 Elsevier B.V. All rights reserved.