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In this work, plasma electrolytic oxidation (PEO) ceramic coatings were prepared on magnesium AZ31B alloy. Various electrolyte solutions including phosphate, aluminate and silicate as additives and NaOH Na2SiF6 as constant agent were used to prepare the coatings. Influence of the additives on chemical composition and structure of the PEO coatings were examined by means of scanning electron microscope (SEM) and XRD. From structural analysis it was found that coatings prepared in the aluminate-based electrolyte have the best structural features. Microhardness and tribological characteristics of the PEO coatings were investigated using Vickers hardness test and pin-on-disc test. Microhardness for aluminate-based coating was found to be 1169.63HV while those for silicate-and phosphate-based coatings were 1093.42HV and 285.91HV, respectively. Wear rate of the aluminate-based coating was found to be lowest than all other coatings having a value of mg/Nm. [ABSTRACT FROM AUTHOR]

The composite coatings were fabricated by laser cladding Al/TiN pre-placed powders on Ti–6Al–4V substrate for enhancing wear resistance and hardness of the substrate. The composite coatings were analyzed by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The sliding wear tests were performed by MM200 wear test machine. The hardness of the coatings was tested by HV-1000 hardness tester. After laser cladding, it was found that there was a good metallurgical bond between the coating and the substrate. The composite coatings were mainly composed of the matrix of β-Ti (Al) and the reinforcements of titanium nitride (TiN), Ti3Al, TiAl and Al3Ti. The hardness and wear resistance of the coatings on four samples were greatly improved, among which sample 4 exhibited the highest hardness and best wear resistance. The hardness of the coating on sample 4 was approximately 2.5 times of the Ti–6Al–4V substrate. And the wear resistance of sample 4 was four times of the substrate. [ABSTRACT FROM AUTHOR]