Influence of the Duty Cycle on the Characteristics of Al₂O₃Coatings Formed on the Al-1050 by Plasma Electrolytic Oxidation

Abstract

Oxide coatings were prepared on Al-1050 substrates by an environment-friendly plasma electrolytic oxidation (PEO) process using an electrolytic solution of Na 2 SiO 3 (8 g/L) and NaOH (3 g/L). The effects of three different duty cycles (20%, 40%, and 60%) and frequencies (50 Hz, 200 Hz, and 800 Hz) on the structure and micro-hardness of the oxide coatings were investigated. XRD analysis revealed that the oxides were mainly composed of α-Al 2 O 3 , γ-Al 2 O 3 , and mullite. The proportion of each crystalline phase depended on various electrical parameters, such as duty cycle and frequency. SEM images indicated that the oxide coatings formed at a 60% duty cycle exhibited relatively coarser surfaces with larger pore sizes and sintering particles. However, the oxides prepared at a 20% duty cycle showed relatively smooth surfaces. The PEO treatment also resulted in a strong adhesion between the oxide coating and the substrate. The oxide coatings were found to improve the micro-hardness with the increase of duty cycle. The structural and physical properties of the oxide coatings were affected by the duty cycles.

Crystal Structure, Microstructure and Mechanical Properties of NbN Coatings Deposited by Asymmetric Bipolar Pulsed DC Sputtering

“…of the coatings. 9) The studies reported thus far on NbN coatings are primarily on the use of dc sputtering method, most of which involve variations in the amount of flown-in nitrogen, the substrate temperature and the deposition time as coating process variables. [10][11][12] In particular, no study results of quantitative analysis and consideration have been reported for the effects of plasma process variables such as duty cycle and pulse frequency using the asymmetric bipolar pulse sputtering method on crystal structure, surface and cross section microstructure, grain size, etc.…”