Behavior of Thermally Sprayed Wear Protective Coatings Exposed to Different Abrasive Wear Conditions in Comparison to Hard Chromium Platings

Abstract

For deposition of protective coatings different coating techniques are available. Usually, detailed evaluation of various deposit types and materials is necessary for selection of the best suited coating for specific application fields and demands. Subject of this work are thermally sprayed functional coatings applied as wear (and corrosion) protective layers. Examination of different optimized thermal spray coatings, i.e. HVOF sprayed WC/Co(Cr) and Cr3C2/NiCr coatings, conventional flame sprayed and fused self fluxing alloy coatings reinforced by hardmetal and APS sprayed oxide Al2O3/TiO2 and Cr2O3 coatings, is done in comparison to thick hard chromium platings. Two abrasive wear tests featuring wear by lose abrasive particles are carried out. These impart dry wear conditions according to ASTM G65 (Rubber Wheel test) and wear by abrasive suspensions according to ASTM G75 (Miller test). The work also contains evaluation of newly developed HVOF torch components permitting increased combustion gas, and therefore also particle, velocities concerning the benefit in terms of coating properties. Exemplary evaluation of the new components influence on velocity and temperature of spray particles is carried out by comparative SprayWatch analyses. Both the influence on the coatings microstructure and the wear performance are studied. Coating microstructure is evaluated qualitatively by optical and scanning electron microscopy and the micro hardness HV0.3 is measured. Worn surfaces are studied by SEM in order to deduce wear mechanisms.

Manufacturing of nickel based cermet coatings by the HVOF process

“…In previous works, a conic expansion nozzle was found to provide optimum particle acceleration. 26,27 The spray torch was machine mounted onto a robotic arm, and a consistent spray pattern was implemented. The transverse speed of the torch range was between 50 and 100 mm s − 1 , and the raster path across the substrate overlapped by at least one-half of the spray footprint diameter.…”

“…[22][23][24] Process optimisation can be implemented by measurement of the inflight particle state, 25 such as surface temperature, velocity and diameter; and relating these parameters to the coating process parameters and properties. Previous research ha identified the interactions of process parameters, such as spray tance (standoff distance), oxygen/fuel ratio and the gun technology 23,24,26 in relation to DE and coating properties.…”

Thermal Spraying of Wear and Corrosion Resistant Surfaces

“…If the wear loss of different materials shall be compared, the volumetric material removal has to be calculated or measured (compare chapter "Optical 3D surface analysis"). For some thermal spray coating types, volumetric wear losses according to the ASTM G 65 wear test are given in Table 2 [30].…”

“…The parameters of the test -grinding pressure, type and size of the abrasive material, corrosive medium, counter body material and test temperaturecan easily be adapted to specific demands. Although variations of the test design are not part of the standardization, this offers a wide range of real working conditions to be modelled [30]. DIN EN 1071-3 "Scratch Test".…”