Control of an HVOF Thermal Spray Process

Abstract

In this chapter, we focus on the industrially-important high velocity oxygen-fuel (HVOF) thermal spray process and show how the concept of accounting for the effect of powder size distribution in the formulation and solution of the control problem can be used to achieve effective feedback control. The HVOF thermal spray technology is widely used to deposit a large variety of metal and ceramic coatings that modify the surface properties of a base material. Using the thermal energy produced by the combustion of fuel with oxygen to heat and propel the spray particles, it provides a highly efficient way to modify the surface properties of the substrate to extend product life, increase performance and reduce maintenance costs. Recently, there is an increasing interest in the HVOF thermal spray processing of nanostructured coatings, whose grain size is less than about 100 nm (Lau et al., 1998b). This interest has been motivated by several factors, including: (1) the cost-effective production of high-quality nanosize powders; (2) the superior qualities of coatings made with the HVOF process (Cheng et al., 2001a); and (3) the discovery that nanostructured coatings exhibit superior qualities over traditional counterparts (made of materials with micro-sized grains) in several aspects including hardness, strength, ductility and diffusivity (Tellkamp et al., 1997; Lau et al., 1998a; Lau et al., 1999).