1. Introduction

Materials have been developed for exceptional functional performance in specific applications, such as a number of specialty steels or super alloys; however, the increasing demands for combined functional requirements such as high temperatures and corrosive atmospheres in addition to abrasive wear, and the difficulty in machining some of the specialty alloys to the final form, as well as the costs of having an entire part made of such a material has led to the ever increasing demand for coatings. First the difference between thin and thick films is discussed to introduce the thermal spray concept with a short description of the different processes used. A brief history of these processes introduces the different thermal spray applications and shows that these processes are complementary and not competitive.