Plasma Species and Coating Compositions in Aluminum Treated by PEO Using Shot Square Pulse

• Published in: Materials research (São Carlos, São Paulo, Brazil) Vol. 23; no. 3; p. 1
• Main Authors: Lima, Richelly N. de, Vitoriano, Jussier de O., Ferreira Jr, Marcos, Alves Junior, Clodomiro
• Format: Journal Article
• Language: English; Portuguese
• Published: Sao Carlos Universidade Federal do Sao Carlos, Departamento de Engenharia de Materiais 01.01.2020; ABM, ABC, ABPol; Associação Brasileira de Metalurgia e Materiais (ABM); Associação Brasileira de Cerâmica (ABC); Associação Brasileira de Polímeros (ABPol)
• Subjects: Al2O3; Aluminum; Aluminum oxide; CCD cameras; coatings; Cracks; Direct current; ENGINEERING, CHEMICAL; Evolution; Extremely low frequencies; MATERIALS SCIENCE, MULTIDISCIPLINARY; METALLURGY & METALLURGICAL ENGINEERING; Optical emission spectroscopy; Oxidation; PEO; Phases; Porosity; Pulse duration; pulsed plasma; Silicon; Sodium silicates; Transitional aluminas; pulsed plasma; coatings; PEO; aluminum; Al2O3
• ISSN: 1516-1439; 1980-5373; 1980-5373
• DOI: 10.1590/1980-5373-mr-2019-0444

Up to now, plasma electrolytic oxidation (PEO) has been either produced direct current or ultra-low frequency (< 1 kHz) pulsed discharge using high concentration alkaline-silicate electrolytic (Na2SiO3 > 8 g.L-1 with presence of KOH). In order to contribute to these studies, the effect of current pulse width and time duration was investigated using diluted silicate electrolytic (Na2SiO3 2 g.L-1) and high pulse frequencies (> 1 kHz). The PEO process was performed on pure aluminum to try to explain how the phases composing the coatings are formed and distributed over the treatment time. For this, was made in situ monitoring using optical emission spectroscopy (OES) coupled with CCD camera. The crystalline phases evolution in the sample surface was investigated using grazing incidence X-ray diffraction (GIXRD). Regarding the evolution of ceramic phases, it is possible to verify that, internally, the predominant phase is rhombohedral α-Al2O3 but, superficially, the predominant phase is cubic γ-Al2O3. It was verified the presence of Si on the borders of the pores or in proximity to cracks, especially in the treatments with higher pulse width. SEM analysis shows a reduction of the superficial porosity and an increase in coating thickness with pulse width and treatment time.