Abstract

In the context of global warming, the life-cycle and reliability of machine parts supporting
hydroelectric turbine structures cannot be overlooked. The advent of surface engineering provides
useful venues for engineers to ensure a safe and long-lasting supply of green energy. In this work,
thermal spraying was proposed as a method to develop coatings with high tribological
performance and corrosion protection for key components in hydroelectric power stations.
The work is structured in three main sections. The first concerns the development of Sn-alloy
coatings, used in large thrust bearings. It was shown that high-density sprayed coatings can be
produced if proper control of particle size and velocities are used.
In the second section, chemical leaching is proposed as a method to create porous coatings to
bond a high-performance polymer to an underlying bearing pad. A metallic pore former is mixed
and sprayed along with stainless steel particles. An optimal combination of matrix and pore former
particles allowed the successful infiltration of a self-lubricating polymer in pore openings as narrow
as 10 μm.
The final section of the work concerns the behavior of sprayed stainless steel coatings in Cl-ion
rich aqueous solution. It was demonstrated that the substantial drop in the corrosion resistance
of the coatings compared to wrought materials is mostly due to the high density of coating defects,
including pores and oxides. The changes in the electrochemical behavior during the first week of
immersion was attributed to surface chemistry changes including enrichment in Cr-oxides and the
dissolution of active phases.