Wear-resistant thin films of MRI-230D-Mg alloy using plasma-driven electrolytic oxidation

TL;DR

This study develops and compares plasma-driven electrolytic oxidation coatings on MRI-230D-Mg alloy, revealing that PEO coatings offer better wear resistance than hybrid coatings, with microstructural analysis and tribological testing under dry sliding conditions.

Contribution

It introduces hybrid coatings combining PEO and laser surface alloying on Mg alloy and evaluates their microstructure and wear behavior, providing insights into their durability and failure mechanisms.

Findings

PEO coatings have a lower friction coefficient (~0.8) than hybrid coatings (~0.5).

PEO coatings withstand 2 N load without failure, but fail at 5 N; hybrid coatings are worn off at 5 N.

PEO coatings exhibit superior wear resistance compared to hybrid coatings.

Abstract

Wear resistant coatings were produced on a permanent mould cast MRI 230D Mg alloy by (a) PEO in silicate based electrolyte, (b) PEO in phosphate based electrolyte, (c) hybrid coatings of silicate PEO followed by laser surface alloying (LSA) with Al and Al2O3, and (d) hybrid coatings of phosphate PEO followed by LSA with Al and Al2O3. Microstructural characterization of the coatings was carried out by scanning electron microscopy (SEM) and X(ray diffraction. The tribological behavior of the coatings was investigated under dry sliding condition using linearly reciprocating ball-on-flat wear test. Both the PEO coatings exhibited a friction coefficient of about 0.8 and hybrid coatings exhibited a value of about 0.5 against the AISI 52100 steel ball as the friction partner, which were slightly reduced with the increase in applied load. The PEO coatings sustained the test without failure at 2 N load but failed at 5 N load due to micro-fracture caused by high contact stresses. The hybrid coatings did not get completely worn off at 2 N load but were completely removed exposing the substrate at 5 N load. The PEO coatings exhibited better wear resistance than the hybrid coatings and silicate PEO coatings exhibited better wear resistance than the phosphate PEO coatings. Both the PEO coatings melted/decomposed on laser irradiation and all the hybrid coatings exhibited similar microstructure and wear behavior irrespective of the nature of the primary PEO coating or laser energies. SEM examination of worn surfaces indicated abrasive wear combined with adhesive wear for all the specimens. The surface of the ball exhibited a discontinuous transfer layer after the wear test.