  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.
