SHS powders for thermal spray applications

Self-propagating high temperature synthesis (SHS) is defined as a combustion process in which reagents, when ignited, spontaneously transform, to complete conversion, into products, due to the exothermic heat of reaction. This process has been recently recognised as a very promising technique for materials processing: ceramics, intermetallics and cermets with good physico-chemical properties have been produced at low costs. The use of SHS products for thermal spray applications represents a natural evolution of the technique. Demanded characteristics for thermal spray feedstock powders can be very different, depending on the spraying process, the operating conditions, the desired properties of the final coating, etc. However, technical requirements can also be extremely rigid and detailed. As a consequence, the production process must be reliable and flexible, while remaining possibly inexpensive. SHS is investigated as a promising candidate technique for the production of different powders to be used for thermal spray coatings with different applications: metallic mixtures are considered, as well as ceramic and composite powders. The chemical and morphological features of different SHS powders are described, and their technical characteristics of flowability and sprayability are outlined. Wear performance and hardness tests results for some of the coatings obtained by both air and vacuum plasma spraying of SHS powders are also reported. (C) 1996 Elsevier Science Limited and Techna S.r.l.