Chromium carbide coatings for high temperature erosion resistance

Escalating operation and maintenance costs and increasing intervals between outages place a heavy burden upon electric power producing components. To meet this demand, component life cycles must be extended with either material upgrades or utilization of surface protection products. This paper will discuss the experiences of the Tennessee Valley Authority in the application of thermal spray coatings and try to relate some of these experiences to component performance in fossil power plants' steam turbine components. The development of high velocity thermal spray processes has given coatings an advantage over the use of high priced material upgrades. Chromium carbide coatings have proven the most economical of the surface protection products for use in high temperature applications where solid particle erosion occurs. These coatings have received extensive laboratory testing where limited field results are now just becoming available. Various thermal spray coatings will be described. The development of newer coatings and laboratory test data will be discussed. Optical microscopy and wear studies will be included in the discussion. Where appropriate and available, comparisons to standard plasma sprayed coatings and uncoated substrata are made.