Repair of Titanium Tubing and Pressure Assemblies Using High Pressure Cold Spray

Cold Spray is a solid-state powder deposition technology that operates at lower temperatures than other thermal spray processes. The unique advantage of cold spray is that it can add structural strength to a component without a strength deficit to the substrate because it does not create a heat-affected zone. In the cold spray process, micron-sized metal particles are accelerated in a carrier gas through a supersonic nozzle towards a substrate, where collision results in mechanical interlocking and metallurgical bonding. During the process, the metal particles never reach melting temperatures but are fused through high velocity impact and the resulting shock, deformation, and adiabatic shearing processes. Therefore, substrate heating is minimized, dimensional stability is maintained, and unwanted thermal effects such as oxidation, dissolution, and element vaporization are avoided, making cold spray ideal for repair applications. In this study, we examine the properties, microstructure, and mechanical performance of cold spray depositions of commercially pure titanium powders onto Ti-3Al2.5V tubing, most commonly used for hydraulic systems. The process was approved in 2018 after a Change Evaluation Team (CET) study was conducted by the Air Force. The process is currently only approved for chaffing prevention and life extension on undamaged tubes, however, evidence of its viability for complete repair of chaffed tubing and assemblies in the future, and its potential for application in commercial aviation, will be presented and discussed.