Comparison of Corrosion Resistance and Cytocompatibility of MgO and ZrO2 Coatings on AZ31 Magnesium Alloy Formed via Plasma Electrolytic Oxidation

In this work, one coating is comprised of ZrO2 and the other consists of MgO as main phase composition was produced on AZ31 magnesium alloy using one-step plasma electrolytic oxidation (PEO). The purpose of this work was to study the corrosion resistance and cytocompatibility of the above-coated AZ31 magnesium alloys in order to provide a basis for AZ31 Mg alloy’s clinical applications of biomedical use. The morphology and phase composition of the coatings were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion properties were examined using electrochemical testing, hydrogen evolution measurements, and immersion tests in a simulated body fluid (SBF). Compared with bare magnesium and the MgO coating, the ZrO2-containing coating exhibited an improved corrosion resistance. Cell proliferation assays and cell morphology observations showed that the ZrO2-containing coating was not toxic to the L-929 cells. The ZrO2 coating was much denser and more homogeneous than the MgO coating, hence the corrosion resistance of the ZrO2-coated AZ31 Mg alloy was superior and more stable than the MgO-coated AZ31 Mg alloy, and ZrO2/AZ31 did not induce a cytotoxic reaction to L-929 cells and promote cell growth.

Mechanical and tribological performance of a hybrid MMC coating deposited on Al-17Si piston alloy by laser composite surfacing technique

Laser composite surfacing (LCS) is a photon driven manufacturing technology that can be utilized for depositing hybrid metal matrix composite coatings (HMMC) on softer Ti/Al/Mg alloys to enhance their tribo-mechanical properties. LCS offers the advantages of higher directionality, localized microstructural refinement and higher metallurgical bonding between coating and substrate. The current research presents the tribo-mechanical evaluation and characterization of solid lubricant based Ni–WC coatings deposited by LCS on Al–Si piston alloy by varying the concentration of graphite between 5-to-15-weight percentage. The tribological behavior of LCS samples was investigated using a ball-on-plate tribometer. Results indicate that the surface hardness, wear rate and friction coefficient of the Al–Si hypereutectic piston alloy were improved after LCS of graphite based HMMC coatings. The maximum surface hardness of 781H_v was acquired for the Ni–WC coating containing 5 wt% graphite. The friction coefficient of Al–Si under dry sliding conditions was reduced from 0.47 to 0.21. The reduction in the friction coefficient was attributed to the formation of a shearable transfer layer, which prevented delamination and reduced adhesion, abrasion and fatigue cracking.

The addition of graphite as solid lubricant has significantly reduced the friction coefficient and wear of a Ni–WC composite coating.

Introducing a composite coating containing CNTs with good corrosion properties: characterization and simulation

A duplex composite coating containing carbon nanotubes (CNTs) was successfully deposited on a Mg–Zn–Ca alloy by an atmospheric plasma spraying (APS) technique.