Development of Novel Cooling and Temperature Monitoring for High Velocity Oxygen Fuel (HVOF) Coating Applications

Temperature control has been a major concern during High Velocity Oxygen Fuel (HVOF) processing since it was originally utilized in the aerospace industry. Typically, temperature must not exceed 300oF to prevent heat damage/ tempering of the substrates on steel alloys, and even lower temperature requirements for aluminum and titanium alloys. These problems have prevented USAF depots from usage of HVOF coatings in many cases on aluminum and titanium components not only due to application temperature concerns, but for cost concerns as well. Shop air cooling has traditionally been the most widely utilized temperature control cooling medium when applying HVOF coatings to aircraft components such as airframe, engine/propeller, and landing gear components, because it is readily available in the shop environment. However, in many cases shop air has proven to be inadequate for controlling substrate temperatures during HVOF application. As a result, longer off-part dwell times to allow for component cooling has become a common practice – an exercise that results in significant powder and gas consumptions – both of which cost money. Additionally, the traditional temperature measuring control has been a continuous reading single point infrared gun aimed at a single location on the component being sprayed. Even though this is a widely accepted method in the HVOF community, it’s only good for measuring localized areas. Consequently, inaccuracies will results as component temperature will vary along the length of the component, particularly for parts with complex geometries. This compounds the temperature issues and makes optimization of temperature control even more difficult. In Phase I of this effort, Engineering & Software System Solutions, Inc. (ES3) conducted a feasibility study to develop/evaluate alternate coolants/delivery systems, liquid/gas nitrogen and liquid/gas carbon dioxide, and advanced temperature monitoring systems to optimize temperature control. Results identified that both liquid nitrogen and carbon dioxide coolant delivery and temperature monitoring system combinations will significantly reduce off-part dwell time and material (powder & gas) consumption; thereby increasing HVOF production throughput. Phase II will conduct a demonstration/validation of a coolant and temperature monitoring system on a typical 4340 low strength steel alloy component coated with HVOF WC-Co-Cr at Robins AFB; and testing will investigate the coolants’ affect on fatigue and coating integrity of HVOF WC-Co-Cr coated coupons to ensure the coolant process does not affect USAF 200626772 performance requirements for usage with the HVOF coated aircraft component applications. Optional testing will be made available for validation and qualification for usage at DoD repair depots covering typical HVOF coatings and substrates. BENEFIT: ES3 anticipates the results of Phase II work will qualify and validate the usage of the Alternate Coolant System & Temperature Monitoring System for typical low strength, low alloy steel components qualified for HVOF WC-Co-Cr application. ES3 anticipates the following benefits from Phase II testing: • A novel cooling process for HVOF coating applications • Specifications for a Multi-location Temperature Monitoring System • Eliminate extended off-part dwell time for cooling • Reduce process time • Reduce powder and fuel costs • Environmentally friendly process