Basalt, an abundant and inexpensive natural raw material, is a glass-ceramic with good abrasion-wear resistance and chemical stability. Traditionally cast-shaped into flag stones, pipe linings and even fibrous composites, basalt can be processed by thermal spraying, potentially yielding highly dense coatings with few defects. Such overlays can seal base materials for wear applications in corrosive environments. Basalt coatings are produced by a number of common thermal spray techniques, including water-stabilized plasma spraying (WSP), high-velocity oxy-fuel (HVOF) and conventional air plasma spraying (APS). In-flight particle temperature and velocities are monitored with a particle diagnostic system (DPV 2000). Using different feedstock size cuts, the attainable ranges of particle states are delineated. Spray parameters are selected for each of the processes, based on deposition efficiency and porosity criteria. For typical conditions, particle velocities vary from 100 m/sec for WSP to 800 m/sec with HVOF. The microstructure and composition of the coatings are evaluated by scanning electron microscopy (SEM) and EDS-SEM. Crystal phase analysis is performed by X-ray diffraction (XRD). Abrasion resistance (ASTM G-65) and hardness (Vickers) of the as-sprayed coatings are compared. The microstructures and tribological properties are related to the particle size, temperature and velocity distributions, which are distinctly different for each process.

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