| Among the various techniques used to manufacture coatings, thermal spray processes form an important class. These are overlay coatings applied via the route of melt deposition (and in some cases, solid state or semi-solid state). The wide varieties of sub-processes within this group, coupled with a very large choice of materials that can be processed through these methods lend tremendous versatility to the technology.; Physical phenomena that occur during thermal spray processing are inherently complex, involving a large number of interrelated variables from among the hot zone, feedstock characteristics and substrate condition. As a consequence of this, the nature of coatings thus formed is also quite complex.; The traditional approach to study and design coatings involves controlling the hardware-related variables to effect changes in deposits. This method is limited in its utility and does not provide any insight into the mechanisms involved in the development of deposit microstructures.; The methodology and procedure outlined in this dissertation are aimed at exploring the intricacies of this process with respect to the variation of particle state, dependence of coating properties on particle state, level of stresses induced in the coating and the systematic variation of properties & microstructures. The concept of a 'process map' has been utilized to represent the various links in this technique. Tools and techniques have been developed to monitor key aspects of the process---in real time and post processing. Key aspects such as the in flight particle state have been defined, modeled and validated. The efficacy of this method of investigation has been demonstrated through the application to a few model systems---a nickel-aluminum alloy, molybdenum, partially stabilized zirconia and alumina. |
