Multimodal powders: A new class of feedstock material for thermal sprayingof hard coatings

We are developing a new class of High Velocity Oxy-Fuel (HVOF) thermal spra y feedstock powders, which consist of aggregates of hard ceramic particles that are either mixed or coated with a more readily fusible nanophase binde r. Thus, during thermal spraying, the nanostructured material undergoes rap id melting while the aggregated material is heated but not necessarily melt ed. A dense coating is formed when the molten nano-material fills the avail able pore spaces between the heated and softened aggregates, providing a st rong and tough matrix for the spray deposited material. Such multimodal coa tings combine moderate hardness with exceptional abrasive wear resistance. Characteristics of the multimodal feed powders, along with the structure an d properties of the resulting coatings, are described in this paper. (C) 20 01 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reser ved.