Characterization of dry-sliding wear of HVOF coatings made of Fe3Al powders reinforced with sub-micrometer TiC particles produced by combustion synthesis

Alloys used to fabricate water turbines for power generation are subjected to cavitation wear in an environment propitious to corrosion. Refurbishing by build-up welding of such gigantic infrastructures is time consuming and costly. Therefore, efforts are being deployed to develop coatings that would extend the time span between water turbine overhauls. In that sense, Fe3Al-TiC coatings are being studied in collaboration with the largest hydroelectricity producer in the World to determine if they could eventually be utilized as a coating material for their water turbines. Fe3Al-TiC coatings containing various volume fractions of reinforcing TiC particles were deposited on a mild steel substrate using the high-velocity oxy-fuel (HVOF) technique. The feedstock powders were produced by combustion synthesis. Fe3Al coatings, containing different volume fractions of sub-micrometer TiC particles (30 mol%, 50 mol%, and 70 mol%), were prepared. Dry-sliding wear resistance (pin-on-disk) of the coatings was characterized using a Al2O3 counterface having a diameter of 6.33 mm. Al the sliding wear tests were conducted at room temperature with sliding speeds ranging from 0.04 m/s to 0.8 m/s. It was found that an increase in the TiC content from 30 mol% to 50 mol% increases wear resistance by 11% and 75% for sliding speeds of 0.1 m/s and 0.8 m/s, respectively. Moreover, further increase in TiC content to 70 mol% provided coatings with wear rates one order of magnitude lower than those measured for Fe3Al-50 mol% TiC coatings. It was also found that for Fe3Al-30 mol% TiC coatings, the wear rate increases with increasing sliding speed up to 0.3 m/s. Further augmentation of the sliding speed to 0.8 m/s resulted in an abrupt reduction of the wear rate. The maximum wear rate of each series of coatings shifted to lower speeds with increasing TiC content. For the Fe3Al-50 mol% TiC and Fe3Al-70 mol% TiC series, the principal wear mechanism changed from adhesive wear to abrasive wear with increasing sliding speed. For the Fe3Al-30 mol% TiC series, the main wear mechanisms was abrasive wear and its occurrence was independent of the sliding speed. Results showed that, when using feedstock powders produced by combustion synthesis, HVOF coatings exhibited about 1.5 to 20 times higher wear resistance compared to the feedstock with identical composition produced by high-energy ball milling.