
Plasma transferred wire arc thermal spraying

Plasma transferred wire arc (PTWA) thermal spraying is a thermal spraying process that deposits a coating on the internal surface of a cylindrical surface, or external surface of any geometry. It is predominantly known for its use in coating the cylinder bores of an engine, enabling the use of aluminum engine blocks without the need for heavy cast iron sleeves. A single conductive wire is used as "feedstock" for the system. A supersonic plasma jet melts the wire, atomizes it and propels it onto the substrate. The plasma jet is formed by a transferred arc between a non-consumable cathode and the wire. After atomization, forced gas transports the stream of molten droplets onto the bore wall. The particles flatten when they impinge on the surface of the substrate, due to their high kinetic energy. The particles rapidly solidify upon contact and can form both crystalline and amorphous phases. There is also the possibility to produce multi-layer coatings. The stacked particles make up a highly wear-resistant coating. All conductive wires up to and including 0.0625" (1.6mm) can be used as feedstock material, including "cored" wires. PTWA can be used to apply a coating to the wear surface of engine or transmission components to replace a bushing or bearing. For example, using PTWA to coat the bearing surface of a connecting rod offers a number of benefits including reductions in weight, cost, friction potential, and stress in the connecting rod.
The inventors of PTWA received the 2009 IPO National Inventor of the Year award. This technology was initially patented and developed by inventors by Flame-Spray Industries, Inc. The technology was subsequently improved upon by Ford and Flame-Spray Industries. PTWA is currently in use by BMW for its high performance B58 and S58 engines (the B58 is also found in the 2020 Toyota Supra), Nissan in the Nissan GTR, Ford is implementing it in the new Mustang GT500 Shelby, Caterpillar and other manufacturers are using it for re-manufacturing. 
Other applications for this process include the spraying of internal diameters of pipes. Any conductive wire can be used as the feedstock material, including "cored" wire. Refractory metals as well as low melt materials are easily deposited.
The recent use of PTWA by Nissan and Ford has been to apply a wear resistant coating on the internal surface of engine block cylinder bores. For hypoeutectic aluminum silicon alloy blocks, PTWA provides a great alternative to cast iron liners which are a higher cost and heavier. PTWA also delivers increased displacement in the same size engine package and a potential for better heat transfer.
PTWA coatings are also applied directly to cast iron engine blocks for re-manufacturing. PTWA coated test engines have been run for over 3 million combined miles of trouble free on-the-road performance. The technology is currently in use at a number of major production facilities around the world. It is also being used to coat worn parts, to make them like-new in re-manufacturing facilities.